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Sunday, July 23, 2023

LGBT reproduction

From Wikipedia, the free encyclopedia
Diagram of the proposed method of lesbian egg fusion

LGBT reproduction refers to lesbian, gay, bisexual, and transgender (LGBT) people having biological children by means of assisted reproductive technology. It is distinct from LGBT parenting, which is a broader cultural phenomenon including LGBT adoption. In recent decades, developmental biologists have been researching and developing techniques to facilitate same-sex reproduction.

The obvious approaches, subject to a growing amount of activity, are female sperm and male eggs. In 2004, by altering the function of a few genes involved with imprinting, other Japanese scientists combined two mouse eggs to produce daughter mice and in 2018 Chinese scientists created 29 female mice from two female mice mothers but were unable to produce viable offspring from two father mice. One of the possibilities is obtaining sperm and eggs from skin stem cells.

Lack of access to assisted reproductive technologies has been seen as a form of healthcare inequality that faces LGBT people.

Gay men

Some gay couples decide to have a surrogate pregnancy. A surrogate is a woman carrying an egg fertilized by sperm of one of the men. Some women become surrogates for money, others for humanitarian reasons or both. This allows one of the men to be the biological father while the other will be an adopted father.

Gay men who have become fathers using surrogacy have reported similar experiences to those as other couples who have used surrogacy, including their relationships both their child and their surrogate have.

There is theoretical work being done on creating a zygote from two men which would enable both men to be biological fathers, but it is yet to be practically implemented.

Barrie and Tony Drewitt-Barlow from the United Kingdom became the first gay men in the country to father twins born through surrogacy in 1999.

Lesbians

Partner-assisted reproduction, or co-IVF is a method of family building that is used by couples who both possess female reproductive organs. The method uses in vitro fertilization (IVF), a method that means eggs are removed from the ovaries, fertilized in a laboratory, and then one or more of the resulting embryos are placed in the uterus to hopefully create a pregnancy. Reciprocal IVF differs from standard IVF in that two women are involved: the eggs are taken from one partner, and the other partner carries the pregnancy. In this way, the process is mechanically identical to IVF with egg donation. Using this process ensures that each partner is a biological mother of the child according to advocates, but in the strictest sense only one mother is the biological mother from a genetic standpoint and the other is a surrogate mother. However the practice has a symbolic weight greater than LGBT adoption, and may create a stronger bond between mother and child than adoption.

In a 2019 study, quality of infant-parent relationships was examined among egg donor families in comparison to in vitro fertilization families. Infants were between the ages of 6–18 months. Through use of the Parent Development Interview (PDI) and observational assessment, the study found few differences between family types on the representational level, yet significant differences between family types on the observational level. Egg donation mothers were less sensitive and structuring than IVF mothers, and egg donation infants were less emotionally responsive, and involving than IVF infants.

There is theoretical work being done on creating a zygote from two women which would enable both women to be biological mothers, but it is yet to be practically implemented. Creating a sperm from an egg and using it to fertilize another egg may offer a solution to this issue, as could a process analogous to somatic cell nuclear transfer involving two eggs being fused together.

In 2004 and 2018 scientists were able to create mice with two mothers via egg fusion. Modification of genomic imprinting was necessary to create healthy bimaternal mice, while live bipaternal mice were created but were unhealthy likely due to genomic imprinting.

If created, a "female sperm" cell could fertilize an egg cell, a procedure that, among other potential applications, might enable female same-sex couples to produce a child who would be the biological offspring of their two mothers. It is also claimed that production of female sperm may stimulate a woman to be both the mother and father (similar to asexual reproduction) of an offspring produced by her own sperm. Many queries, both ethical and moral, arise over these arguments.

Transgender women

Many trans women want to have children. Some may seek to have children by using their own sperm and an egg donor or biological female partner. Fertility can be impeded in a variety of ways due to feminizing hormone therapy.

Trans women may have lower sperm quality before HRT, which may pose an issue for creating viable sperm samples to freeze.

Estrogens suppress testosterone levels and at high doses can markedly disrupt sex drive and function and fertility on their own. Moreover, disruption of gonadal function and fertility by estrogens may be permanent after extended exposure.

Nonsteroidal antiandrogens like bicalutamide may be an option for transgender women who wish to preserve sex drive, sexual function, and/or fertility, relative to antiandrogens that suppress testosterone levels and can greatly disrupt these functions such as cyproterone acetate and GnRH modulators. However, estrogens suppress testosterone levels and at high doses can markedly disrupt sex drive and function and fertility on their own. Moreover, disruption of gonadal function and fertility by estrogens may be permanent after extended exposure.

Some trans women want to carry their own children through transgender pregnancy, which has its own set of issues to be overcome, because transgender women do not naturally have the anatomy needed for embryonic and fetal development. As of 2008, there were no successful cases of uterus transplantation concerning a transgender woman.

Uterine transplantation, or UTx, is currently in its infancy and is not yet publicly available. As of 2019, in cisgender women, more than 42 UTx procedures had been performed, with 12 live births resulting from the transplanted uteruses as of publication. The International Society of Uterine Transplantation (ISUTx) was established internationally in 2016, with 70 clinical doctors and scientists, and currently has 140 intercontinental delegates. Its goal is to, "through scientific innovations, advance medical care in the field of uterus transplantation."

In 2012, McGill University published the "Montreal Criteria for the Ethical Feasibility of Uterine Transplantation", a proposed set of criteria for carrying out uterine transplants, in Transplant International. Under these criteria, only a cisgender woman could ethically be considered a transplant recipient. The exclusion of trans women from candidacy may lack justification.

In addition, if trans women wish to conceive with a biological male partner, they face the same issues that cisgender gay couples have in creating a zygote.

Only 3% of transgender people take efforts to preserve their fertility in transition 51% of trans women express regrets for not preserving their fertility, and 97% of transgender adults believe it should be discussed before transition.

Transfeminine lactation

Lactation in trans women is an understudied area. A survey of trans healthcare providers found 34% met trans women who expressed interest in inducing lactation. The first documented instance of a trans woman attempting to breastfeed was in 2018 using domperidone to induce lactation. In 2021 lactation was successfully induced in a trans woman.

To induce lactation, domperidone is used at a dosage of 10 to 20 mg 3 or 4 times per day by mouth. Effects may be seen within 24 hours or may not be seen for 3 or 4 days. The maximum effect occurs after 2 or 3 weeks of treatment, and the treatment period generally lasts for 3 to 8 weeks.

Transgender men

Transgender men have a unique situation when it comes to LGBT reproduction as they are one of the only groups that has a risk of unintended pregnancy in a same-gender relationship (cisgender lesbians in relationships with fertile trans women being another example). Pregnancy is possible for transgender men who retain a functioning vagina, ovaries, and a uterus.

Testosterone therapy affects fertility, but many trans men who have become pregnant were able to do so within six months of stopping testosterone.  Another study conducted in 2019 found that transgender male patients seeking oocyte retrieval for either oocyte cryopreservation, embryo cryopreservation, or IVF were able to undergo treatment 4 months after stopping testosterone treatment, on average. All patients experienced menses and normal AMH, FSH, and E2 levels and antral follicle counts after coming off testosterone which allowed for successful oocyte retrieval. Although the long-term effects of androgen treatment on fertility is still widely unknown, oocyte retrieval does not appear to be affected. Future pregnancies can be achieved by oophyte banking, but the process may increase gender dysphoria or may not be accessible due to lack of insurance coverage. Testosterone therapy is not a sufficient method of contraception, and trans men may experience unintended pregnancy, especially if they miss doses.

Many gay transgender men choose to freeze their eggs before transitioning, and choose to have a female surrogate carry their child while when the time comes, using their eggs and their cis male partner's sperm. This allows them to avoid the potentially dysphoria inducing experience of pregnancy, or cessation of HRT for collecting eggs at an older age.

Some studies report a higher incidence of PCOS among transgender men prior to taking testosterone, the disease causes infertility and can make it harder for trans men to freeze eggs, though not all have not found the same association of trans men and PCOS. People with PCOS in general are also reportedly more likely to see themselves as "sexually undifferentiated" or "androgynous" and "less likely to identify with a female gender scheme."

In popular culture

Male pregnancy is commonly explored in slash (homosexual) fan fiction, usually based upon fantasy series such as Supernatural or Harry Potter.

In the Omegaverse themes of LGBT reproduction are common. Alpha females are able to impregnate both males and females, and Omega males are able to be impregnated by both males and females.

Between Alphas and Betas, only females can carry on a pregnancy, but male Omegas are often envisaged as being able to become pregnant via an uterus connected to the rectum, and Alphas can impregnate regardless of their main gender. To make penetration and impregnation easier, male Omegas often have self-lubricating anuses.

Kleshas (Buddhism)

From Wikipedia, the free encyclopedia

Kleshas (Sanskrit: क्लेश, romanizedkleśa; Pali: किलेस kilesa; Standard Tibetan: ཉོན་མོངས། nyon mongs), in Buddhism, are mental states that cloud the mind and manifest in unwholesome actions. Kleshas include states of mind such as anxiety, fear, anger, jealousy, desire, depression, etc. Contemporary translators use a variety of English words to translate the term kleshas, such as: afflictions, defilements, destructive emotions, disturbing emotions, negative emotions, mind poisons, and neuroses.

In the contemporary Mahayana and Theravada Buddhist traditions, the three kleshas of ignorance, attachment, and aversion are identified as the root or source of all other kleshas. These are referred to as the three poisons in the Mahayana tradition, or as the three unwholesome roots in the Theravada tradition.

While the early Buddhist texts of the Pali canon do not specifically enumerate the three root kleshas, over time the three poisons (and the kleshas generally) came to be seen as the very roots of samsaric existence.

Pali literature

In the Pali Canon's discourses (sutta), kilesa is often associated with the various passions that defile bodily and mental states. In the Pali Canon's Abhidhamma and post-canonical Pali literature, ten defilements are identified, the first three of which – greed, hate, delusion – are considered to be the "roots" of suffering.

Sutta Piṭaka: mental hindrances

In the Pali Canon's Sutta Piṭaka, kilesa and its correlate upakkilesa are affective obstacles to the pursuit of direct knowledge (abhijñā) and wisdom (pañña).

For instance, the Samyutta Nikaya includes a collection of ten discourses (SN 27, Kilesa-sayutta) that state that any association of "desire-passion" (chanda-rāgo) with the body or mind is a "defilement of mind" (cittasse'so upakkileso):

"Monks, any desire-passion with regard to the eye is a defilement of the mind. Any desire-passion with regard to the ear... the nose... the tongue... the body... the intellect is a defilement of the mind. When, with regard to these six bases, the defilements of awareness are abandoned, then the mind is inclined to renunciation. The mind fostered by renunciation feels malleable for the direct knowing of those qualities worth realizing."

More broadly, the five hindrances – sensual desire (kāmacchanda), anger (byāpāda), sloth-torpor (thīna-middha), restlessness-worry (uddhacca-kukkucca), and doubt (vicikicchā) – are frequently associated with kilesa in the following (or a similar) manner:

[A]ll those Blessed Ones had first abandoned the five hindrances,
defilements of the mind that weaken wisdom ...
  sabbe te bhagavanto pañcanīvarae pahāya
cetaso upakkilese paññāya dubbalīkarae ... .

Additionally, in the Khuddaka Nikaya's Niddesa, kilesa is identified as a component of or synonymous with craving (taṇhā) and lust (rāga).

Abhidhamma: ten defilements and unwholesome roots

While the Sutta Pitaka does not offer a list of kilesa, the Abhidhamma Pitaka's Dhammasangani (Dhs. 1229ff.) and Vibhanga (Vbh. XII) as well as in the post-canonical Visuddhimagga (Vsm. XXII 49, 65) enumerate ten defilements (dasa kilesa-vatthūni) as follows:

  1. greed (lobha)
  2. hate (dosa)
  3. delusion (moha)
  4. conceit (māna)
  5. wrong views (micchāditthi)
  6. doubt (vicikicchā)
  7. torpor (thīna)
  8. restlessness (uddhacca)
  9. shamelessness (ahirika)
  10. recklessness (anottappa)[7]

The Vibhanga also includes an eightfold list (aṭṭha kilesa-vatthūni) composed of the first eight of the above ten.

Throughout Pali literature, the first three kilesa in the above tenfold Abhidhamma list (lobha dosa moha) are known as the "unwholesome roots" (akusala-mūla or the root of akusala); and, their opposites (alobha adosa amoha) are the three "wholesome roots" (kusala-mūla or the root of kusala). The presence of such a wholesome or unwholesome root during a mental, verbal or bodily action conditions future states of consciousness and associated mental factors (see Karma).

Visuddhimagga: round of defilements




12 Factors   3 Rounds
aging-death   aspects of
vipāka
(results)
 
birth  
 
becoming   kamma
 
clinging   kilesa
 
craving  
 
feeling   vipāka
(results)
 
contact  
 
sense bases  
 
name-form  
 
consciousness  
 
formations   kamma
 
ignorance   kilesa
Figure: The "three rounds" of
Dependent Origination (Vsm. XVII, 298).

In the 5th-century CE commentarial Visuddhimagga, in its discussion of "Dependent Origination" (Pali: paticca-samuppada) (Vsm. XVII), it presents different expository methods for understanding this teaching's twelve factors (nidana). One method (Vsm. XVII, 298) divides the twelve factors into three "rounds" (vaṭṭa):

  • the "round of defilements" (kilesa-vaṭṭa)
  • the "round of kamma" (kamma-vaṭṭa)
  • the "round of results" (vipāka-vaṭṭa).[12][13]

In this framework (see Figure to the right, starting from the bottom of the Figure), kilesa ("ignorance") conditions kamma ("formations") which conditions results ("consciousness" through "feelings") which in turn condition kilesa ("craving" and "clinging") which condition kamma ("becoming") and so on. Buddhaghosa (Vsm. XVII, 298) concludes:

So this Wheel of Becoming, having a triple round with these three rounds, should be understood to spin, revolving again and again, forever; for the conditions are not cut off as long as the round of defilements is not cut off.

As can be seen, in this framework, the round of defilements consists of:

Elsewhere in the Visuddhimagga (Vsm. XXII, 88), in the context of the four noble persons (ariya-puggala, see Four stages of enlightenment), the text refers to a precursor to the attainment of nibbana as being the complete eradication of "the defilements that are the root of the round" (vaṭṭa-mūla-kilesā).

Sanskrit Sravaka and Mahayana literature

Three poisons

The three kleshas of ignorance, attachment and aversion are referred to as the three poisons (Skt. triviṣa) in the Mahayana tradition and as the three unwholesome roots (Pāli, akusala-mūla; Skt. akuśala-mūla ) in the Therevada tradition. These three poisons (or unwholesome roots) are considered to be the root of all the other kleshas.

Five poisons

In the Mahayana tradition, the five main kleshas are referred to as the five poisons (Sanskrit: pañca kleśaviṣa; Tibetan-Wylie: dug lnga).

The five poisons consist of the three poisons with two additional poisons: pride and jealousy. The five poisons are:

Poison/Klesha Sanskrit Pali Tibetan Description Alternate translations
Ignorance moha
avidya
moha
avijja
gti mug
ma rig pa
Lack of discernment; not understanding the way of things Confusion, bewilderment, delusion
Attachment rāga lobha 'dod chags Attachment or desire for what we like Desire, passion
Aversion dvesha dosa zhe sdang Aversion for what we don't like, or for what prevents us from getting what we like Anger, hatred
Pride māna māna nga rgyal Having an inflated opinion of oneself and a disrespectful attitude toward others Arrogance, Conceit
Envy irshya issā phrag dog Being unable to bear the accomplishments or good fortune of others Jealousy

Six root kleshas of the Abhidharma

The Abhidharma-kośa identifies six root kleshas (mūlakleśa):

In the context of the Yogācāra school of Buddhism, Muller (2004: p. 207) states that the Six Klesha arise due to the "...reification of an 'imagined self' (Sanskrit: satkāya-dṛṣṭi)".

Mahaparinirvana Sutra

The Mahayana Mahaparinirvana Sutra lists approximately 50 kleshas, including those of attachment, aversion, stupidity, jealousy, pride, heedlessness, haughtiness, ill-will, quarrelsomeness, wrong livelihood, deceit, consorting with immoral friends, attachment to pleasure, to sleep, to eating, and to yawning; delighting in excessive talking and uttering lies, as well as thoughts of harm.

Two obscurations

Mahayana literature often features an enumeration of "two obscurations" (Wylie: sgrib gnyis), the "obscuration of conflicting emotions" (Sanskrit: kleśa-avaraṇa, Wylie: nyon-mongs-pa'i sgrib-ma) and the "obscuration concerning the knowable" (Sanskrit: jñeya-avaraṇa, Wylie: shes-bya'i sgrib-ma).

Contemporary glosses

Contemporary translators have used many different English words to translate the term kleshas, such as: afflictions, passions, destructive emotions, disturbing emotions, etc.

The following table provides brief descriptions of the term kleshas given by various contemporary Buddhist teachers and scholars:

English/Sanskrit term used Description Source
Afflictive emotions ... those mind states that cause suffering, such as depression, fear, hatred, anger, jealousy and so on – it's a long list! Joseph Goldstein. The Emerging Western Buddhism: An Interview with Joseph Goldstein.
Afflictive emotions In general, any defilement or emotion which obscures the mind. They are often summarized as three: ignorance, attachment and aversion. All other negative predispositions are produced on the basis of these three. Khenchen Konchog Gyaltshen (2009). A Complete Guide to the Buddhist Path. p. 451 (from the glossary)
Afflictions Mental factors that produce states of mental torment both immediately and in the long term. The five principal kleshas, which are sometimes called poisons, are attachment, aversion, ignorance, pride, and jealousy. Longchen Yeshe Dorje (Kangyur Rinpoche) (2010). Treasury of Precious Qualities. p. 492 (from the glossary)
Conditioning Factors or Mental Afflictions The processes that not only describe what we perceive, but also determine our responses. Yongey Mingyur Rinpoche (2008). The Joy of Living. p. 115
Mental afflictions In Tibetan a mental affliction is defined as a mental process that has the function of disrupting the equilibrium of the mind. They all have that in common, whether or not there is a strong emotional component to it. Goleman, Daniel (2008). Destructive Emotions: A Scientific Dialogue with the Dalai Lama. Kindle Locations 2553–2555.
Destructive emotions Fundamentally, a destructive emotion—which is also referred to as an ‘obscuring’ or ‘afflictive’ mental factor—is something that prevents the mind from ascertaining reality as it is. With a destructive emotion, there will always be a gap between the way things appear and the ways things are. Goleman, Daniel (2008). Destructive Emotions: A Scientific Dialogue with the Dalai Lama. Kindle Locations 1779–1781.
Defilements These are unskilful factors such as greed, hate, delusion, opinionatedness and lack of moral concern. Whereas the term ‘hindrance’ refers to five sticking points, ‘defilement’ is often used without any definite list, but to refer to any function of the mind which is led by unskilful factors. Ajahn Sucitto (2011). Meditation, A Way of Awakening. Amaravati Publications. p. 263. (from the glossary)
Kleshas Kleshas are the strong conflicting emotions that spin off and heighten when we get caught by aversion and attraction. Pema Chodron. Signs of Spiritual Progress. Shambhala Sun.
Kleshas Kleshas are properties that dull the mind and are the basis for all unwholesome actions. The three main kleshas are passion, aggression, and ignorance. Chögyam Trungpa. The Truth of Suffering and the Path of Liberation. Edited by Judy L. Lief. Shambhala. p. 134 (from the glossary)
Kleshas The basic idea is that certain powerful reactions have the capacity to take hold of us and drive our behavior. We believe in these reactions more than we believe in anything else, and they become the means by which we both hide from ourselves and attempt to cope with a world of ceaseless change and unpredictability. The three poisons of greed, hatred, and ignorance are the classic Buddhist examples, but others include conceit, skeptical doubt, and so-called "speculative" views ... Mark Epstein. Going on Being: Buddhism and the Way of Change, a Positive Psychology for the West. http://www.quietspaces.com/kleshas.html
Kleshas The emotional obscurations (in contrast to intellectual obscurations), usually translated as "poisons" or "defilements." The three main klesas are ignorance, hatred, and desire. The five klesas include these three along with pride and envy.

Thrangu Rinpoche (1993). The Practice of Tranquility & Insight: A Guide to Tibetan Buddhist Mediation (p. 152). Snow Lion. Kindle Edition. p. 152 (from the glossary)

Overcoming the kleshas

All Buddhist schools teach that through Tranquility (Samatha) meditation the kilesas are pacified, though not eradicated, and through Insight (Vipassana) the true nature of the kilesas and the mind itself is understood. When the empty nature of the Self and the Mind is fully understood, there is no longer a root for the disturbing emotions to be attached to, and the disturbing emotions lose their power to distract the mind.

Alternative translations

The term kleshas has been translated into English as:

  • Afflictions
  • Mental afflictions
  • Mental disturbances
  • Afflictive emotions
  • Conditioning factors
  • Destructive emotions
  • Defiled emotions
  • Defilements
  • Dissonant emotions
  • Disturbing emotions
  • Disturbing emotions and attitudes
  • Negative emotions
  • Dissonant mental states
  • Kleshas
  • Passions
  • Poisons
  • Mind poisons
  • Worldly desires

Illusion of control

From Wikipedia, the free encyclopedia

The illusion of control is the tendency for people to overestimate their ability to control events. It was named by U.S. psychologist Ellen Langer and is thought to influence gambling behavior and belief in the paranormal. Along with illusory superiority and optimism bias, the illusion of control is one of the positive illusions.

Definition

The illusion of control is the tendency for people to overestimate their ability to control events, for example, when someone feels a sense of control over outcomes that they demonstrably do not influence.

The illusion might arise because a person lacks direct introspective insight into whether they are in control of events. This has been called the introspection illusion. Instead, they may judge their degree of control by a process which is often unreliable. As a result, they see themselves as responsible for events to which there is little or no causal link. For example, in one study, college students were in a virtual reality setting to treat a fear of heights using an elevator. Those who were told that they had control, yet had none, felt as though they had as much control as those who actually did have control over the elevator. Those who were led to believe they did not have control said they felt as though they had little control.

History

Psychological theorists have consistently emphasized the importance of perceptions of control over life events. One of the earliest instances was when Alfred Adler argued that people strive for proficiency in their lives. Heider later proposed that humans have a strong motive to control their environment and Wyatt Mann hypothesized a basic competence motive that people satisfy by exerting control. Wiener, an attribution theorist, modified his original theory of achievement motivation to include a controllability dimension. Kelley then argued that people's failure to detect noncontingencies may result in their attributing uncontrollable outcomes to personal causes. Nearer to the present, Taylor and Brown argued that positive illusions, including the illusion of control, foster mental health.

The effect was named by U.S. psychologist Ellen Langer and has been replicated in many different contexts.

Occurrence

The illusion is more common in familiar situations, and in situations where the person knows the desired outcome. Feedback that emphasizes success rather than failure can increase the effect, while feedback that emphasizes failure can decrease or reverse the effect. The illusion is weaker for depressed individuals and is stronger when individuals have an emotional need to control the outcome. The illusion is strengthened by stressful and competitive situations, including financial trading. Although people are likely to overestimate their control when the situations are heavily chance-determined, they also tend to underestimate their control when they actually have it, which runs contrary to some theories of the illusion and its adaptiveness. People also showed a higher illusion of control when they were allowed to become familiar with a task through practice trials, make their choice before the event happens like with throwing dice, and when they can make their choice rather than have it made for them with the same odds. People are more likely to show control when they have more answers right at the beginning than at the end, even when the people had the same number of correct answers.

Being in a position of power enhances the illusion of control, which may lead to overreach in risk taking.

By proxy

At times, people attempt to gain control by transferring responsibility to more capable or “luckier” others to act for them. By forfeiting direct control, it is perceived to be a valid way of maximizing outcomes. This illusion of control by proxy is a significant theoretical extension of the traditional illusion of control model. People will of course give up control if another person is thought to have more knowledge or skill in areas such as medicine where actual skill and knowledge are involved. In cases like these it is entirely rational to give up responsibility to people such as doctors. However, when it comes to events of pure chance, allowing another to make decisions (or gamble) on one's behalf, because they are seen as luckier is not rational and would go against people's well-documented desire for control in uncontrollable situations. However, it does seem plausible since people generally believe that they can possess luck and employ it to advantage in games of chance, and it is not a far leap that others may also be seen as lucky and able to control uncontrollable events. In a study conducted in Singapore, the perception of control, luck, and skill when gambling led to an increase in gambling behavior.

In one instance, a lottery pool at a company decides who picks the numbers and buys the tickets based on the wins and losses of each member. The member with the best record becomes the representative until they accumulate a certain number of losses and then a new representative is picked based on wins and losses. Even though no member is truly better than the other and it is all by chance, they still would rather have someone with seemingly more luck to have control over them.

In another real-world example, in the 2002 Olympics men's and women's hockey finals, Team Canada beat Team USA. Prior to the match, a Canadian coin was secretly placed under the ice before the game, an action which the players and officials believed would bring them luck. The members of Team Canada were the only people who knew the coin had been placed there. The coin was later put in the Hockey Hall of Fame where there was an opening so people could touch it. People believed they could transfer luck from the coin to themselves by touching it, and thereby change their own luck..

Demonstration

The illusion of control is demonstrated by three converging lines of evidence: 1) laboratory experiments, 2) observed behavior in familiar games of chance such as lotteries, and 3) self-reports of real-world behavior.

Laboratory experiments

One kind of laboratory demonstration involves two lights marked "Score" and "No Score". Subjects have to try to control which one lights up. In one version of this experiment, subjects could press either of two buttons. Another version had one button, which subjects decided on each trial to press or not. Subjects had a variable degree of control over the lights, or none at all, depending on how the buttons were connected. The experimenters made clear that there might be no relation between the subjects' actions and the lights. Subjects estimated how much control they had over the lights. These estimates bore no relation to how much control they actually had, but was related to how often the "Score" light lit up. Even when their choices made no difference at all, subjects confidently reported exerting some control over the lights.

Observed behavior in games

Ellen Langer's research demonstrated that people were more likely to behave as if they could exercise control in a chance situation where "skill cues" were present. By skill cues, Langer meant properties of the situation more normally associated with the exercise of skill, in particular the exercise of choice, competition, familiarity with the stimulus and involvement in decisions. One simple form of this effect is found in casinos: when rolling dice in a craps game people tend to throw harder when they need high numbers and softer for low numbers.

In another experiment, subjects had to predict the outcome of thirty coin tosses. The feedback was rigged so that each subject was right exactly half the time, but the groups differed in where their "hits" occurred. Some were told that their early guesses were accurate. Others were told that their successes were distributed evenly through the thirty trials. Afterwards, they were surveyed about their performance. Subjects with early "hits" overestimated their total successes and had higher expectations of how they would perform on future guessing games. This result resembles the irrational primacy effect in which people give greater weight to information that occurs earlier in a series. Forty percent of the subjects believed their performance on this chance task would improve with practice, and twenty-five percent said that distraction would impair their performance.

Another of Langer's experiments replicated by other researchers involves a lottery. Subjects are either given tickets at random or allowed to choose their own. They can then trade their tickets for others with a higher chance of paying out. Subjects who had chosen their own ticket were more reluctant to part with it. Tickets bearing familiar symbols were less likely to be exchanged than others with unfamiliar symbols. Although these lotteries were random, subjects behaved as though their choice of ticket affected the outcome. Participants who chose their own numbers were less likely to trade their ticket even for one in a game with better odds.

Self reported behavior

Yet another way to investigate perceptions of control is to ask people about hypothetical situations, for example their likelihood of being involved in a motor vehicle accident. On average, drivers regard accidents as much less likely in "high-control" situations, such as when they are driving, than in "low-control" situations, such as when they are in the passenger seat. They also rate a high-control accident, such as driving into the car in front, as much less likely than a low-control accident such as being hit from behind by another driver.

Explanations

Ellen Langer, who first demonstrated the illusion of control, explained her findings in terms of a confusion between skill and chance situations. She proposed that people base their judgments of control on "skill cues". These are features of a situation that are usually associated with games of skill, such as competitiveness, familiarity and individual choice. When more of these skill cues are present, the illusion is stronger.

In 1998, Suzanne Thompson and colleagues argued that Langer's explanation was inadequate to explain all the variations in the effect. As an alternative, they proposed that judgments about control are based on a procedure that they called the "control heuristic". This theory proposes that judgments of control depend on two conditions; an intention to create the outcome, and a relationship between the action and outcome. In games of chance, these two conditions frequently go together. As well as an intention to win, there is an action, such as throwing a die or pulling a lever on a slot machine, which is immediately followed by an outcome. Even though the outcome is selected randomly, the control heuristic would result in the player feeling a degree of control over the outcome.

Self-regulation theory offers another explanation. To the extent that people are driven by internal goals concerned with the exercise of control over their environment, they will seek to reassert control in conditions of chaos, uncertainty or stress. One way of coping with a lack of real control is to falsely attribute oneself control of the situation.

The core self-evaluations (CSE) trait is a stable personality trait composed of locus of control, neuroticism, self-efficacy, and self-esteem. While those with high core self-evaluations are likely to believe that they control their own environment (i.e., internal locus of control), very high levels of CSE may lead to the illusion of control.

Benefits and costs to the individual

In 1988 Taylor and Brown have argued that positive illusions, including the illusion of control, are adaptive as they motivate people to persist at tasks when they might otherwise give up. This position is supported by Albert Bandura's claim in 1989 that "optimistic self-appraisals of capability, that are not unduly disparate from what is possible, can be advantageous, whereas veridical judgements can be self-limiting". His argument is essentially concerned with the adaptive effect of optimistic beliefs about control and performance in circumstances where control is possible, rather than perceived control in circumstances where outcomes do not depend on an individual's behavior.

In 1997 Bandura also suggested that:

"In activities where the margins of error are narrow and missteps can produce costly or injurious consequences, personal well-being is best served by highly accurate efficacy appraisal."

Taylor and Brown argue that positive illusions are adaptive, since there is evidence that they are more common in normally mentally healthy individuals than in depressed individuals. However, in 1998 Pacini, Muir and Epstein showed that this may be because depressed people overcompensate for a tendency toward maladaptive intuitive processing by exercising excessive rational control in trivial situations, and note that the difference with non-depressed people disappears in more consequential circumstances.

There is also empirical evidence that high self-efficacy can be maladaptive in some circumstances. In a scenario-based study, Whyte et al. showed in 1997 that participants in whom they had induced high self-efficacy were significantly more likely to escalate commitment to a failing course of action. In 1998 Knee and Zuckerman challenged the definition of mental health used by Taylor and Brown and argue that lack of illusions is associated with a non-defensive personality oriented towards growth and learning and with low ego involvement in outcomes. They present evidence that self-determined individuals are less prone to these illusions.

In the late 1970s, Abramson and Alloy demonstrated that depressed individuals held a more accurate view than their non-depressed counterparts in a test which measured illusion of control. This finding held true even when the depression was manipulated experimentally. However, when replicating the findings Msetfi et al. (2005, 2007) found that the overestimation of control in nondepressed people only showed up when the interval was long enough, implying that this is because they take more aspects of a situation into account than their depressed counterparts. Also, Dykman et al. (1989) showed that depressed people believe they have no control in situations where they actually do, so their perception is not more accurate overall. Allan et al. (2007) has proposed that the pessimistic bias of depressives resulted in "depressive realism" when asked about estimation of control, because depressed individuals are more likely to say no even if they have control.

A number of studies have found a link between a sense of control and health, especially in older people. This link for older people having improved health because of a sense of control was discussed in a study conducted in a nursing home. As the residents at the nursing home were encouraged to make more choices for themselves, there was more sense of control over their daily lives. This increase in control increased their overall happiness and health compared to those not making as many decisions for themselves. It was even speculated that with results so promising could slow down or reverse cognitive decline that may occur with aging. 

Fenton-O'Creevy et al. argue, as do Gollwittzer and Kinney in 1998, that while illusory beliefs about control may promote goal striving, they are not conducive to sound decision-making. Illusions of control may cause insensitivity to feedback, impede learning and predispose toward greater objective risk taking (since subjective risk will be reduced by illusion of control).

Applications

Psychologist Daniel Wegner argues that an illusion of control over external events underlies belief in psychokinesis, a supposed paranormal ability to move objects directly using the mind. As evidence, Wegner cites a series of experiments on magical thinking in which subjects were induced to think they had influenced external events. In one experiment, subjects watched a basketball player taking a series of free throws. When they were instructed to visualise him making his shots, they felt that they had contributed to his success.

A study published in 2003 examined traders working in the City of London's investment banks. They each watched a graph being plotted on a computer screen, similar to a real-time graph of a stock price or index. Using three computer keys, they had to raise the value as high as possible. They were warned that the value showed random variations, but that the keys might have some effect. In fact, the fluctuations were not affected by the keys. The traders' ratings of their success measured their susceptibility to the illusion of control. This score was then compared with each trader's performance. Those who were more prone to the illusion scored significantly lower on analysis, risk management and contribution to profits. They also earned significantly less.

Kernel (operating system)

From Wikipedia, the free encyclopedia
An oversimplification of how a kernel connects application software to the hardware of a computer

The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. It is the portion of the operating system code that is always resident in memory and facilitates interactions between hardware and software components. A full kernel controls all hardware resources (e.g. I/O, memory, cryptography) via device drivers, arbitrates conflicts between processes concerning such resources, and optimizes the utilization of common resources e.g. CPU & cache usage, file systems, and network sockets. On most systems, the kernel is one of the first programs loaded on startup (after the bootloader). It handles the rest of startup as well as memory, peripherals, and input/output (I/O) requests from software, translating them into data-processing instructions for the central processing unit.

The critical code of the kernel is usually loaded into a separate area of memory, which is protected from access by application software or other less critical parts of the operating system. The kernel performs its tasks, such as running processes, managing hardware devices such as the hard disk, and handling interrupts, in this protected kernel space. In contrast, application programs such as browsers, word processors, or audio or video players use a separate area of memory, user space. This separation prevents user data and kernel data from interfering with each other and causing instability and slowness, as well as preventing malfunctioning applications from affecting other applications or crashing the entire operating system. Even in systems where the kernel is included in application address spaces, memory protection is used to prevent unauthorized applications from modifying the kernel.

The kernel's interface is a low-level abstraction layer. When a process requests a service from the kernel, it must invoke a system call, usually through a wrapper function.

There are different kernel architecture designs. Monolithic kernels run entirely in a single address space with the CPU executing in supervisor mode, mainly for speed. Microkernels run most but not all of their services in user space, like user processes do, mainly for resilience and modularity. MINIX 3 is a notable example of microkernel design. Instead, the Linux kernel is monolithic, although it is also modular, for it can insert and remove loadable kernel modules at runtime.

This central component of a computer system is responsible for executing programs. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors.

Random-access memory

Random-access memory (RAM) is used to store both program instructions and data. Typically, both need to be present in memory in order for a program to execute. Often multiple programs will want access to memory, frequently demanding more memory than the computer has available. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough memory is available.

Input/output devices

I/O devices include peripherals such as keyboards, mice, disk drives, printers, USB devices, network adapters, and display devices. The kernel provides convenient methods for applications to use these devices which are typically abstracted by the kernel so that applications do not need to know their implementation details.

Resource management

Key aspects necessary in resource management are defining the execution domain (address space) and the protection mechanism used to mediate access to the resources within a domain. Kernels also provide methods for synchronization and inter-process communication (IPC). These implementations may be located within the kernel itself or the kernel can also rely on other processes it is running. Although the kernel must provide IPC in order to provide access to the facilities provided by each other, kernels must also provide running programs with a method to make requests to access these facilities. The kernel is also responsible for context switching between processes or threads.

Memory management

The kernel has full access to the system's memory and must allow processes to safely access this memory as they require it. Often the first step in doing this is virtual addressing, usually achieved by paging and/or segmentation. Virtual addressing allows the kernel to make a given physical address appear to be another address, the virtual address. Virtual address spaces may be different for different processes; the memory that one process accesses at a particular (virtual) address may be different memory from what another process accesses at the same address. This allows every program to behave as if it is the only one (apart from the kernel) running and thus prevents applications from crashing each other.

On many systems, a program's virtual address may refer to data which is not currently in memory. The layer of indirection provided by virtual addressing allows the operating system to use other data stores, like a hard drive, to store what would otherwise have to remain in main memory (RAM). As a result, operating systems can allow programs to use more memory than the system has physically available. When a program needs data which is not currently in RAM, the CPU signals to the kernel that this has happened, and the kernel responds by writing the contents of an inactive memory block to disk (if necessary) and replacing it with the data requested by the program. The program can then be resumed from the point where it was stopped. This scheme is generally known as demand paging.

Virtual addressing also allows creation of virtual partitions of memory in two disjointed areas, one being reserved for the kernel (kernel space) and the other for the applications (user space). The applications are not permitted by the processor to address kernel memory, thus preventing an application from damaging the running kernel. This fundamental partition of memory space has contributed much to the current designs of actual general-purpose kernels and is almost universal in such systems, although some research kernels (e.g., Singularity) take other approaches.

Device management

To perform useful functions, processes need access to the peripherals connected to the computer, which are controlled by the kernel through device drivers. A device driver is a computer program encapsulating, monitoring and controlling a hardware device (via its Hardware/Software Interface (HSI)) on behalf of the OS. It provides the operating system with an API, procedures and information about how to control and communicate with a certain piece of hardware. Device drivers are an important and vital dependency for all OS and their applications. The design goal of a driver is abstraction; the function of the driver is to translate the OS-mandated abstract function calls (programming calls) into device-specific calls. In theory, a device should work correctly with a suitable driver. Device drivers are used for e.g. video cards, sound cards, printers, scanners, modems, and Network cards.

At the hardware level, common abstractions of device drivers include:

  • Interfacing directly
  • Using a high-level interface (Video BIOS)
  • Using a lower-level device driver (file drivers using disk drivers)
  • Simulating work with hardware, while doing something entirely different

And at the software level, device driver abstractions include:

  • Allowing the operating system direct access to hardware resources
  • Only implementing primitives
  • Implementing an interface for non-driver software such as TWAIN
  • Implementing a language (often a high-level language such as PostScript)

For example, to show the user something on the screen, an application would make a request to the kernel, which would forward the request to its display driver, which is then responsible for actually plotting the character/pixel.

A kernel must maintain a list of available devices. This list may be known in advance (e.g., on an embedded system where the kernel will be rewritten if the available hardware changes), configured by the user (typical on older PCs and on systems that are not designed for personal use) or detected by the operating system at run time (normally called plug and play). In plug-and-play systems, a device manager first performs a scan on different peripheral buses, such as Peripheral Component Interconnect (PCI) or Universal Serial Bus (USB), to detect installed devices, then searches for the appropriate drivers.

As device management is a very OS-specific topic, these drivers are handled differently by each kind of kernel design, but in every case, the kernel has to provide the I/O to allow drivers to physically access their devices through some port or memory location. Important decisions have to be made when designing the device management system, as in some designs accesses may involve context switches, making the operation very CPU-intensive and easily causing a significant performance overhead.

System calls

In computing, a system call is how a process requests a service from an operating system's kernel that it does not normally have permission to run. System calls provide the interface between a process and the operating system. Most operations interacting with the system require permissions not available to a user-level process, e.g., I/O performed with a device present on the system, or any form of communication with other processes requires the use of system calls.

A system call is a mechanism that is used by the application program to request a service from the operating system. They use a machine-code instruction that causes the processor to change mode. An example would be from supervisor mode to protected mode. This is where the operating system performs actions like accessing hardware devices or the memory management unit. Generally the operating system provides a library that sits between the operating system and normal user programs. Usually it is a C library such as Glibc or Windows API. The library handles the low-level details of passing information to the kernel and switching to supervisor mode. System calls include close, open, read, wait and write.

To actually perform useful work, a process must be able to access the services provided by the kernel. This is implemented differently by each kernel, but most provide a C library or an API, which in turn invokes the related kernel functions.

The method of invoking the kernel function varies from kernel to kernel. If memory isolation is in use, it is impossible for a user process to call the kernel directly, because that would be a violation of the processor's access control rules. A few possibilities are:

  • Using a software-simulated interrupt. This method is available on most hardware, and is therefore very common.
  • Using a call gate. A call gate is a special address stored by the kernel in a list in kernel memory at a location known to the processor. When the processor detects a call to that address, it instead redirects to the target location without causing an access violation. This requires hardware support, but the hardware for it is quite common.
  • Using a special system call instruction. This technique requires special hardware support, which common architectures (notably, x86) may lack. System call instructions have been added to recent models of x86 processors, however, and some operating systems for PCs make use of them when available.
  • Using a memory-based queue. An application that makes large numbers of requests but does not need to wait for the result of each may add details of requests to an area of memory that the kernel periodically scans to find requests.

Kernel design decisions

Protection

An important consideration in the design of a kernel is the support it provides for protection from faults (fault tolerance) and from malicious behaviours (security). These two aspects are usually not clearly distinguished, and the adoption of this distinction in the kernel design leads to the rejection of a hierarchical structure for protection.

The mechanisms or policies provided by the kernel can be classified according to several criteria, including: static (enforced at compile time) or dynamic (enforced at run time); pre-emptive or post-detection; according to the protection principles they satisfy (e.g., Denning); whether they are hardware supported or language based; whether they are more an open mechanism or a binding policy; and many more.

Support for hierarchical protection domains is typically implemented using CPU modes.

Many kernels provide implementation of "capabilities", i.e., objects that are provided to user code which allow limited access to an underlying object managed by the kernel. A common example is file handling: a file is a representation of information stored on a permanent storage device. The kernel may be able to perform many different operations, including read, write, delete or execute, but a user-level application may only be permitted to perform some of these operations (e.g., it may only be allowed to read the file). A common implementation of this is for the kernel to provide an object to the application (typically so called a "file handle") which the application may then invoke operations on, the validity of which the kernel checks at the time the operation is requested. Such a system may be extended to cover all objects that the kernel manages, and indeed to objects provided by other user applications.

An efficient and simple way to provide hardware support of capabilities is to delegate to the memory management unit (MMU) the responsibility of checking access-rights for every memory access, a mechanism called capability-based addressing. Most commercial computer architectures lack such MMU support for capabilities.

An alternative approach is to simulate capabilities using commonly supported hierarchical domains. In this approach, each protected object must reside in an address space that the application does not have access to; the kernel also maintains a list of capabilities in such memory. When an application needs to access an object protected by a capability, it performs a system call and the kernel then checks whether the application's capability grants it permission to perform the requested action, and if it is permitted performs the access for it (either directly, or by delegating the request to another user-level process). The performance cost of address space switching limits the practicality of this approach in systems with complex interactions between objects, but it is used in current operating systems for objects that are not accessed frequently or which are not expected to perform quickly.

If the firmware does not support protection mechanisms, it is possible to simulate protection at a higher level, for example by simulating capabilities by manipulating page tables, but there are performance implications. Lack of hardware support may not be an issue, however, for systems that choose to use language-based protection.

An important kernel design decision is the choice of the abstraction levels where the security mechanisms and policies should be implemented. Kernel security mechanisms play a critical role in supporting security at higher levels.

One approach is to use firmware and kernel support for fault tolerance (see above), and build the security policy for malicious behavior on top of that (adding features such as cryptography mechanisms where necessary), delegating some responsibility to the compiler. Approaches that delegate enforcement of security policy to the compiler and/or the application level are often called language-based security.

The lack of many critical security mechanisms in current mainstream operating systems impedes the implementation of adequate security policies at the application abstraction level. In fact, a common misconception in computer security is that any security policy can be implemented in an application regardless of kernel support.

According to Mars Research Group developers, a lack of isolation is one of the main factors undermining kernel security. They propose their driver isolation framework for protection, primarily in the Linux kernel.

Hardware- or language-based protection

Typical computer systems today use hardware-enforced rules about what programs are allowed to access what data. The processor monitors the execution and stops a program that violates a rule, such as a user process that tries to write to kernel memory. In systems that lack support for capabilities, processes are isolated from each other by using separate address spaces. Calls from user processes into the kernel are regulated by requiring them to use one of the above-described system call methods.

An alternative approach is to use language-based protection. In a language-based protection system, the kernel will only allow code to execute that has been produced by a trusted language compiler. The language may then be designed such that it is impossible for the programmer to instruct it to do something that will violate a security requirement.

Advantages of this approach include:

  • No need for separate address spaces. Switching between address spaces is a slow operation that causes a great deal of overhead, and a lot of optimization work is currently performed in order to prevent unnecessary switches in current operating systems. Switching is completely unnecessary in a language-based protection system, as all code can safely operate in the same address space.
  • Flexibility. Any protection scheme that can be designed to be expressed via a programming language can be implemented using this method. Changes to the protection scheme (e.g. from a hierarchical system to a capability-based one) do not require new hardware.

Disadvantages include:

  • Longer application startup time. Applications must be verified when they are started to ensure they have been compiled by the correct compiler, or may need recompiling either from source code or from bytecode.
  • Inflexible type systems. On traditional systems, applications frequently perform operations that are not type safe. Such operations cannot be permitted in a language-based protection system, which means that applications may need to be rewritten and may, in some cases, lose performance.

Examples of systems with language-based protection include JX and Microsoft's Singularity.

Process cooperation

Edsger Dijkstra proved that from a logical point of view, atomic lock and unlock operations operating on binary semaphores are sufficient primitives to express any functionality of process cooperation. However this approach is generally held to be lacking in terms of safety and efficiency, whereas a message passing approach is more flexible. A number of other approaches (either lower- or higher-level) are available as well, with many modern kernels providing support for systems such as shared memory and remote procedure calls.

I/O device management

The idea of a kernel where I/O devices are handled uniformly with other processes, as parallel co-operating processes, was first proposed and implemented by Brinch Hansen (although similar ideas were suggested in 1967). In Hansen's description of this, the "common" processes are called internal processes, while the I/O devices are called external processes.

Similar to physical memory, allowing applications direct access to controller ports and registers can cause the controller to malfunction, or system to crash. With this, depending on the complexity of the device, some devices can get surprisingly complex to program, and use several different controllers. Because of this, providing a more abstract interface to manage the device is important. This interface is normally done by a device driver or hardware abstraction layer. Frequently, applications will require access to these devices. The kernel must maintain the list of these devices by querying the system for them in some way. This can be done through the BIOS, or through one of the various system buses (such as PCI/PCIE, or USB). Using an example of a video driver, when an application requests an operation on a device, such as displaying a character, the kernel needs to send this request to the current active video driver. The video driver, in turn, needs to carry out this request. This is an example of inter-process communication (IPC).

Kernel-wide design approaches

The above listed tasks and features can be provided in many ways that differ from each other in design and implementation.

The principle of separation of mechanism and policy is the substantial difference between the philosophy of micro and monolithic kernels. Here a mechanism is the support that allows the implementation of many different policies, while a policy is a particular "mode of operation". Example:

  • Mechanism: User login attempts are routed to an authorization server
  • Policy: Authorization server requires a password which is verified against stored passwords in a database

Because the mechanism and policy are separated, the policy can be easily changed to e.g. require the use of a security token.

In minimal microkernel just some very basic policies are included, and its mechanisms allows what is running on top of the kernel (the remaining part of the operating system and the other applications) to decide which policies to adopt (as memory management, high level process scheduling, file system management, etc.). A monolithic kernel instead tends to include many policies, therefore restricting the rest of the system to rely on them.

Per Brinch Hansen presented arguments in favour of separation of mechanism and policy. The failure to properly fulfill this separation is one of the major causes of the lack of substantial innovation in existing operating systems, a problem common in computer architecture. The monolithic design is induced by the "kernel mode"/"user mode" architectural approach to protection (technically called hierarchical protection domains), which is common in conventional commercial systems; in fact, every module needing protection is therefore preferably included into the kernel. This link between monolithic design and "privileged mode" can be reconducted to the key issue of mechanism-policy separation; in fact the "privileged mode" architectural approach melds together the protection mechanism with the security policies, while the major alternative architectural approach, capability-based addressing, clearly distinguishes between the two, leading naturally to a microkernel design (see Separation of protection and security).

While monolithic kernels execute all of their code in the same address space (kernel space), microkernels try to run most of their services in user space, aiming to improve maintainability and modularity of the codebase. Most kernels do not fit exactly into one of these categories, but are rather found in between these two designs. These are called hybrid kernels. More exotic designs such as nanokernels and exokernels are available, but are seldom used for production systems. The Xen hypervisor, for example, is an exokernel.

Monolithic kernels

Diagram of a monolithic kernel

In a monolithic kernel, all OS services run along with the main kernel thread, thus also residing in the same memory area. This approach provides rich and powerful hardware access. UNIX developer Ken Thompson stated that "it is in [his] opinion easier to implement a monolithic kernel". The main disadvantages of monolithic kernels are the dependencies between system components – a bug in a device driver might crash the entire system – and the fact that large kernels can become very difficult to maintain; Thompson also stated that "It is also easier for [a monolithic kernel] to turn into a mess in a hurry as it is modified."

Monolithic kernels, which have traditionally been used by Unix-like operating systems, contain all the operating system core functions and the device drivers. A monolithic kernel is one single program that contains all of the code necessary to perform every kernel-related task. Every part which is to be accessed by most programs which cannot be put in a library is in the kernel space: Device drivers, scheduler, memory handling, file systems, and network stacks. Many system calls are provided to applications, to allow them to access all those services. A monolithic kernel, while initially loaded with subsystems that may not be needed, can be tuned to a point where it is as fast as or faster than the one that was specifically designed for the hardware, although more relevant in a general sense.

Modern monolithic kernels, such as the Linux kernel, the FreeBSD kernel, the AIX kernel, the HP-UX kernel, and the Solaris kernel, all of which fall into the category of Unix-like operating systems, support loadable kernel modules, allowing modules to be loaded into the kernel at runtime, permitting easy extension of the kernel's capabilities as required, while helping to minimize the amount of code running in kernel space.

Most work in the monolithic kernel is done via system calls. These are interfaces, usually kept in a tabular structure, that access some subsystem within the kernel such as disk operations. Essentially calls are made within programs and a checked copy of the request is passed through the system call. Hence, not far to travel at all. The monolithic Linux kernel can be made extremely small not only because of its ability to dynamically load modules but also because of its ease of customization. In fact, there are some versions that are small enough to fit together with a large number of utilities and other programs on a single floppy disk and still provide a fully functional operating system (one of the most popular of which is muLinux). This ability to miniaturize its kernel has also led to a rapid growth in the use of Linux in embedded systems.

These types of kernels consist of the core functions of the operating system and the device drivers with the ability to load modules at runtime. They provide rich and powerful abstractions of the underlying hardware. They provide a small set of simple hardware abstractions and use applications called servers to provide more functionality. This particular approach defines a high-level virtual interface over the hardware, with a set of system calls to implement operating system services such as process management, concurrency and memory management in several modules that run in supervisor mode. This design has several flaws and limitations:

  • Coding in kernel can be challenging, in part because one cannot use common libraries (like a full-featured libc), and because one needs to use a source-level debugger like gdb. Rebooting the computer is often required. This is not just a problem of convenience to the developers. When debugging is harder, and as difficulties become stronger, it becomes more likely that code will be "buggier".
  • Bugs in one part of the kernel have strong side effects; since every function in the kernel has all the privileges, a bug in one function can corrupt data structure of another, totally unrelated part of the kernel, or of any running program.
  • Kernels often become very large and difficult to maintain.
  • Even if the modules servicing these operations are separate from the whole, the code integration is tight and difficult to do correctly.
  • Since the modules run in the same address space, a bug can bring down the entire system.
In the microkernel approach, the kernel itself only provides basic functionality that allows the execution of servers, separate programs that assume former kernel functions, such as device drivers, GUI servers, etc.

Microkernels

Microkernel (also abbreviated μK or uK) is the term describing an approach to operating system design by which the functionality of the system is moved out of the traditional "kernel", into a set of "servers" that communicate through a "minimal" kernel, leaving as little as possible in "system space" and as much as possible in "user space". A microkernel that is designed for a specific platform or device is only ever going to have what it needs to operate. The microkernel approach consists of defining a simple abstraction over the hardware, with a set of primitives or system calls to implement minimal OS services such as memory management, multitasking, and inter-process communication. Other services, including those normally provided by the kernel, such as networking, are implemented in user-space programs, referred to as servers. Microkernels are easier to maintain than monolithic kernels, but the large number of system calls and context switches might slow down the system because they typically generate more overhead than plain function calls.

Only parts which really require being in a privileged mode are in kernel space: IPC (Inter-Process Communication), basic scheduler, or scheduling primitives, basic memory handling, basic I/O primitives. Many critical parts are now running in user space: The complete scheduler, memory handling, file systems, and network stacks. Micro kernels were invented as a reaction to traditional "monolithic" kernel design, whereby all system functionality was put in a one static program running in a special "system" mode of the processor. In the microkernel, only the most fundamental of tasks are performed such as being able to access some (not necessarily all) of the hardware, manage memory and coordinate message passing between the processes. Some systems that use micro kernels are QNX and the HURD. In the case of QNX and Hurd user sessions can be entire snapshots of the system itself or views as it is referred to. The very essence of the microkernel architecture illustrates some of its advantages:

  • Easier to maintain
  • Patches can be tested in a separate instance, and then swapped in to take over a production instance.
  • Rapid development time and new software can be tested without having to reboot the kernel.
  • More persistence in general, if one instance goes haywire, it is often possible to substitute it with an operational mirror.

Most microkernels use a message passing system to handle requests from one server to another. The message passing system generally operates on a port basis with the microkernel. As an example, if a request for more memory is sent, a port is opened with the microkernel and the request sent through. Once within the microkernel, the steps are similar to system calls. The rationale was that it would bring modularity in the system architecture, which would entail a cleaner system, easier to debug or dynamically modify, customizable to users' needs, and more performing. They are part of the operating systems like GNU Hurd, MINIX, MkLinux, QNX and Redox OS. Although microkernels are very small by themselves, in combination with all their required auxiliary code they are, in fact, often larger than monolithic kernels. Advocates of monolithic kernels also point out that the two-tiered structure of microkernel systems, in which most of the operating system does not interact directly with the hardware, creates a not-insignificant cost in terms of system efficiency. These types of kernels normally provide only the minimal services such as defining memory address spaces, inter-process communication (IPC) and the process management. The other functions such as running the hardware processes are not handled directly by microkernels. Proponents of micro kernels point out those monolithic kernels have the disadvantage that an error in the kernel can cause the entire system to crash. However, with a microkernel, if a kernel process crashes, it is still possible to prevent a crash of the system as a whole by merely restarting the service that caused the error.

Other services provided by the kernel such as networking are implemented in user-space programs referred to as servers. Servers allow the operating system to be modified by simply starting and stopping programs. For a machine without networking support, for instance, the networking server is not started. The task of moving in and out of the kernel to move data between the various applications and servers creates overhead which is detrimental to the efficiency of micro kernels in comparison with monolithic kernels.

Disadvantages in the microkernel exist however. Some are:

  • Larger running memory footprint
  • More software for interfacing is required, there is a potential for performance loss.
  • Messaging bugs can be harder to fix due to the longer trip they have to take versus the one off copy in a monolithic kernel.
  • Process management in general can be very complicated.

The disadvantages for microkernels are extremely context-based. As an example, they work well for small single-purpose (and critical) systems because if not many processes need to run, then the complications of process management are effectively mitigated.

A microkernel allows the implementation of the remaining part of the operating system as a normal application program written in a high-level language, and the use of different operating systems on top of the same unchanged kernel. It is also possible to dynamically switch among operating systems and to have more than one active simultaneously.

Monolithic kernels vs. microkernels

As the computer kernel grows, so grows the size and vulnerability of its trusted computing base; and, besides reducing security, there is the problem of enlarging the memory footprint. This is mitigated to some degree by perfecting the virtual memory system, but not all computer architectures have virtual memory support. To reduce the kernel's footprint, extensive editing has to be performed to carefully remove unneeded code, which can be very difficult with non-obvious interdependencies between parts of a kernel with millions of lines of code.

By the early 1990s, due to the various shortcomings of monolithic kernels versus microkernels, monolithic kernels were considered obsolete by virtually all operating system researchers. As a result, the design of Linux as a monolithic kernel rather than a microkernel was the topic of a famous debate between Linus Torvalds and Andrew Tanenbaum. There is merit on both sides of the argument presented in the Tanenbaum–Torvalds debate.

Performance

Monolithic kernels are designed to have all of their code in the same address space (kernel space), which some developers argue is necessary to increase the performance of the system. Some developers also maintain that monolithic systems are extremely efficient if well written. The monolithic model tends to be more efficient through the use of shared kernel memory, rather than the slower IPC system of microkernel designs, which is typically based on message passing.

The performance of microkernels was poor in both the 1980s and early 1990s. However, studies that empirically measured the performance of these microkernels did not analyze the reasons of such inefficiency. The explanations of this data were left to "folklore", with the assumption that they were due to the increased frequency of switches from "kernel-mode" to "user-mode", to the increased frequency of inter-process communication and to the increased frequency of context switches.

In fact, as guessed in 1995, the reasons for the poor performance of microkernels might as well have been: (1) an actual inefficiency of the whole microkernel approach, (2) the particular concepts implemented in those microkernels, and (3) the particular implementation of those concepts. Therefore it remained to be studied if the solution to build an efficient microkernel was, unlike previous attempts, to apply the correct construction techniques.

On the other end, the hierarchical protection domains architecture that leads to the design of a monolithic kernel has a significant performance drawback each time there's an interaction between different levels of protection (i.e., when a process has to manipulate a data structure both in "user mode" and "supervisor mode"), since this requires message copying by value.

The hybrid kernel approach combines the speed and simpler design of a monolithic kernel with the modularity and execution safety of a microkernel

Hybrid (or modular) kernels

Hybrid kernels are used in most commercial operating systems such as Microsoft Windows NT 3.1, NT 3.5, NT 3.51, NT 4.0, 2000, XP, Vista, 7, 8, 8.1 and 10. Apple's own macOS uses a hybrid kernel called XNU which is based upon code from OSF/1's Mach kernel (OSFMK 7.3) and FreeBSD's monolithic kernel. They are similar to micro kernels, except they include some additional code in kernel-space to increase performance. These kernels represent a compromise that was implemented by some developers to accommodate the major advantages of both monolithic and micro kernels. These types of kernels are extensions of micro kernels with some properties of monolithic kernels. Unlike monolithic kernels, these types of kernels are unable to load modules at runtime on their own. Hybrid kernels are micro kernels that have some "non-essential" code in kernel-space in order for the code to run more quickly than it would were it to be in user-space. Hybrid kernels are a compromise between the monolithic and microkernel designs. This implies running some services (such as the network stack or the filesystem) in kernel space to reduce the performance overhead of a traditional microkernel, but still running kernel code (such as device drivers) as servers in user space.

Many traditionally monolithic kernels are now at least adding (or else using) the module capability. The most well known of these kernels is the Linux kernel. The modular kernel essentially can have parts of it that are built into the core kernel binary or binaries that load into memory on demand. It is important to note that a code tainted module has the potential to destabilize a running kernel. Many people become confused on this point when discussing micro kernels. It is possible to write a driver for a microkernel in a completely separate memory space and test it before "going" live. When a kernel module is loaded, it accesses the monolithic portion's memory space by adding to it what it needs, therefore, opening the doorway to possible pollution. A few advantages to the modular (or) Hybrid kernel are:

  • Faster development time for drivers that can operate from within modules. No reboot required for testing (provided the kernel is not destabilized).
  • On demand capability versus spending time recompiling a whole kernel for things like new drivers or subsystems.
  • Faster integration of third party technology (related to development but pertinent unto itself nonetheless).

Modules, generally, communicate with the kernel using a module interface of some sort. The interface is generalized (although particular to a given operating system) so it is not always possible to use modules. Often the device drivers may need more flexibility than the module interface affords. Essentially, it is two system calls and often the safety checks that only have to be done once in the monolithic kernel now may be done twice. Some of the disadvantages of the modular approach are:

  • With more interfaces to pass through, the possibility of increased bugs exists (which implies more security holes).
  • Maintaining modules can be confusing for some administrators when dealing with problems like symbol differences.

Nanokernels

A nanokernel delegates virtually all services – including even the most basic ones like interrupt controllers or the timer – to device drivers to make the kernel memory requirement even smaller than a traditional microkernel.

Exokernels

Exokernels are a still-experimental approach to operating system design. They differ from other types of kernels in limiting their functionality to the protection and multiplexing of the raw hardware, providing no hardware abstractions on top of which to develop applications. This separation of hardware protection from hardware management enables application developers to determine how to make the most efficient use of the available hardware for each specific program.

Exokernels in themselves are extremely small. However, they are accompanied by library operating systems (see also unikernel), providing application developers with the functionalities of a conventional operating system. This comes down to every user writing their own rest-of-the kernel from near scratch, which is a very-risky, complex and quite a daunting assignment - particularly in a time-constrained production-oriented environment, which is why exokernels have never caught on.[citation needed] A major advantage of exokernel-based systems is that they can incorporate multiple library operating systems, each exporting a different API, for example one for high level UI development and one for real-time control.

Multikernels

A multikernel operating system treats a multi-core machine as a network of independent cores, as if it were a distributed system. It does not assume shared memory but rather implements inter-process communications as message passing. Barrelfish was the first operating system to be described as a multikernel.

History of kernel development

Early operating system kernels

Strictly speaking, an operating system (and thus, a kernel) is not required to run a computer. Programs can be directly loaded and executed on the "bare metal" machine, provided that the authors of those programs are willing to work without any hardware abstraction or operating system support. Most early computers operated this way during the 1950s and early 1960s, which were reset and reloaded between the execution of different programs. Eventually, small ancillary programs such as program loaders and debuggers were left in memory between runs, or loaded from ROM. As these were developed, they formed the basis of what became early operating system kernels. The "bare metal" approach is still used today on some video game consoles and embedded systems, but in general, newer computers use modern operating systems and kernels.

In 1969, the RC 4000 Multiprogramming System introduced the system design philosophy of a small nucleus "upon which operating systems for different purposes could be built in an orderly manner",[46] what would be called the microkernel approach.

Time-sharing operating systems

In the decade preceding Unix, computers had grown enormously in power – to the point where computer operators were looking for new ways to get people to use their spare time on their machines. One of the major developments during this era was time-sharing, whereby a number of users would get small slices of computer time, at a rate at which it appeared they were each connected to their own, slower, machine.

The development of time-sharing systems led to a number of problems. One was that users, particularly at universities where the systems were being developed, seemed to want to hack the system to get more CPU time. For this reason, security and access control became a major focus of the Multics project in 1965.[48] Another ongoing issue was properly handling computing resources: users spent most of their time staring at the terminal and thinking about what to input instead of actually using the resources of the computer, and a time-sharing system should give the CPU time to an active user during these periods. Finally, the systems typically offered a memory hierarchy several layers deep, and partitioning this expensive resource led to major developments in virtual memory systems.

Amiga

The Commodore Amiga was released in 1985, and was among the first – and certainly most successful – home computers to feature an advanced kernel architecture. The AmigaOS kernel's executive component, exec.library, uses a microkernel message-passing design, but there are other kernel components, like graphics.library, that have direct access to the hardware. There is no memory protection, and the kernel is almost always running in user mode. Only special actions are executed in kernel mode, and user-mode applications can ask the operating system to execute their code in kernel mode.

Unix

A diagram of the predecessor/successor family relationship for Unix-like systems

During the design phase of Unix, programmers decided to model every high-level device as a file, because they believed the purpose of computation was data transformation.

For instance, printers were represented as a "file" at a known location – when data was copied to the file, it printed out. Other systems, to provide a similar functionality, tended to virtualize devices at a lower level – that is, both devices and files would be instances of some lower level concept. Virtualizing the system at the file level allowed users to manipulate the entire system using their existing file management utilities and concepts, dramatically simplifying operation. As an extension of the same paradigm, Unix allows programmers to manipulate files using a series of small programs, using the concept of pipes, which allowed users to complete operations in stages, feeding a file through a chain of single-purpose tools. Although the end result was the same, using smaller programs in this way dramatically increased flexibility as well as ease of development and use, allowing the user to modify their workflow by adding or removing a program from the chain.

In the Unix model, the operating system consists of two parts: first, the huge collection of utility programs that drive most operations; second, the kernel that runs the programs. Under Unix, from a programming standpoint, the distinction between the two is fairly thin; the kernel is a program, running in supervisor mode, that acts as a program loader and supervisor for the small utility programs making up the rest of the system, and to provide locking and I/O services for these programs; beyond that, the kernel didn't intervene at all in user space.

Over the years the computing model changed, and Unix's treatment of everything as a file or byte stream no longer was as universally applicable as it was before. Although a terminal could be treated as a file or a byte stream, which is printed to or read from, the same did not seem to be true for a graphical user interface. Networking posed another problem. Even if network communication can be compared to file access, the low-level packet-oriented architecture dealt with discrete chunks of data and not with whole files. As the capability of computers grew, Unix became increasingly cluttered with code. It is also because the modularity of the Unix kernel is extensively scalable. While kernels might have had 100,000 lines of code in the seventies and eighties, kernels like Linux, of modern Unix successors like GNU, have more than 13 million lines.

Modern Unix-derivatives are generally based on module-loading monolithic kernels. Examples of this are the Linux kernel in the many distributions of GNU, IBM AIX, as well as the Berkeley Software Distribution variant kernels such as FreeBSD, DragonFly BSD, OpenBSD, NetBSD, and macOS. Apart from these alternatives, amateur developers maintain an active operating system development community, populated by self-written hobby kernels which mostly end up sharing many features with Linux, FreeBSD, DragonflyBSD, OpenBSD or NetBSD kernels and/or being compatible with them.

Classic Mac OS and macOS

Apple first launched its classic Mac OS in 1984, bundled with its Macintosh personal computer. Apple moved to a nanokernel design in Mac OS 8.6. Against this, the modern macOS (originally named Mac OS X) is based on Darwin, which uses a hybrid kernel called XNU, which was created by combining the 4.3BSD kernel and the Mach kernel.

Microsoft Windows

Microsoft Windows was first released in 1985 as an add-on to MS-DOS. Because of its dependence on another operating system, initial releases of Windows, prior to Windows 95, were considered an operating environment (not to be confused with an operating system). This product line continued to evolve through the 1980s and 1990s, with the Windows 9x series adding 32-bit addressing and pre-emptive multitasking; but ended with the release of Windows Me in 2000.

Microsoft also developed Windows NT, an operating system with a very similar interface, but intended for high-end and business users. This line started with the release of Windows NT 3.1 in 1993, and was introduced to general users with the release of Windows XP in October 2001—replacing Windows 9x with a completely different, much more sophisticated operating system. This is the line that continues with Windows 11.

The architecture of Windows NT's kernel is considered a hybrid kernel because the kernel itself contains tasks such as the Window Manager and the IPC Managers, with a client/server layered subsystem model. It was designed as a modified microkernel, as the Windows NT kernel was influenced by the Mach microkernel but does not meet all of the criteria of a pure microkernel.

IBM Supervisor

Supervisory program or supervisor is a computer program, usually part of an operating system, that controls the execution of other routines and regulates work scheduling, input/output operations, error actions, and similar functions and regulates the flow of work in a data processing system.

Historically, this term was essentially associated with IBM's line of mainframe operating systems starting with OS/360. In other operating systems, the supervisor is generally called the kernel.

In the 1970s, IBM further abstracted the supervisor state from the hardware, resulting in a hypervisor that enabled full virtualization, i.e. the capacity to run multiple operating systems on the same machine totally independently from each other. Hence the first such system was called Virtual Machine or VM.

Development of microkernels

Although Mach, developed by Richard Rashid at Carnegie Mellon University, is the best-known general-purpose microkernel, other microkernels have been developed with more specific aims. The L4 microkernel family (mainly the L3 and the L4 kernel) was created to demonstrate that microkernels are not necessarily slow. Newer implementations such as Fiasco and Pistachio are able to run Linux next to other L4 processes in separate address spaces.

Additionally, QNX is a microkernel which is principally used in embedded systems, and the open-source software MINIX, while originally created for educational purposes, is now focused on being a highly reliable and self-healing microkernel OS.

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