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Thursday, July 27, 2023

LGBT parenting

From Wikipedia, the free encyclopedia
Lesbian couple with children

LGBT parenting (also known as rainbow families) refers to lesbian, gay, bisexual, and transgender (LGBT) people raising one or more children as parents or foster care parents. This includes: children raised by same-sex couples (same-sex parenting), children raised by single LGBT parents, and children raised by an opposite-sex couple where at least one partner is LGBT.

Opponents of LGBT parenting have argued that it adversely affects children. However, scientific research consistently shows that gay and lesbian parents are as fit and capable as heterosexual parents, and their children are as psychologically healthy and well-adjusted as those reared by heterosexual parents. Major associations of mental health professionals in the U.S., Canada, and Australia have not identified credible empirical research that suggests otherwise.

Forms

A same-sex couple with their children at San Francisco Pride, 2008.

LGBT people can become parents through various means including current or former relationships, coparenting, adoption, foster care, donor insemination, reciprocal IVF, and surrogacy. A gay man, a lesbian, or a transgender person who transitions later in life may have children within an opposite-sex relationship, such as a mixed-orientation marriage, for various reasons.

Some children do not know they have an LGBT parent; coming out issues vary and some parents may never reveal to their children that they identify as LGBT. Accordingly, how children respond to their LGBT parent(s) coming out has little to do with their sexual orientation or gender identification, but rather with how either parent responds to acts of coming out; i.e. whether there is dissolution of parental partnerships or rather if parents maintain a healthy, open, and communicative relationship after coming out or during transition in the case of trans parents.

Many lesbian, gay, bisexual, and transgender people are parents. In the 2000 U.S. Census, for example, 33 percent of female same-sex couple households and 22 percent of male same-sex couple households reported at least one child under the age of 18 living in the home. As of 2005, an estimated 270,313 children in the United States live in households headed by same-sex couples.

Adoption

Legal status of adoption by same-sex couples around the world:
  Joint adoption allowed
  No laws allowing adoption by same-sex couples and no same-sex marriage
  Same-sex marriage but adoption by married same-sex couples not allowed

Joint adoption by same-sex couples is legal in 27 countries and in some sub-national territories. Furthermore, 5 countries have legalized some form of step-child adoption. Institutional heterosexism can be observed in adoption policies in many parts of the world: some countries or states explicitly prohibit adoption by openly lesbian, gay or bisexual people. Other jurisdictions make decisions about whether LGBTQ people may adopt on a case-by-case basis, with great variability between agencies depending upon the focus of the agency (special needs children, infants, etc.), the religious affiliation of the agency if any, and the disposition of area supervisors and placement workers. There are also legal barriers to international adoptions, since currently no countries which are actively involved in international adoption (e.g. China, Guatemala) permit adoption by openly identified lesbian and gay people. Bisexual, transgender and transsexual people are not typically explicitly named, but are presumably included in these prohibitions.

Judgements

In 1968, California man Bill Jones became one of the first gay men to adopt a child. He later participated in the gay rights movement with Glide Memorial Church.

Sandy Schuster and Madeleine Isaacson, who met at their Pentecostal church, won America's first custody battle in favor of a lesbian couple in 1978.

In January 2008, the European Court of Human Rights ruled that an otherwise legally qualified and suitable candidate must not be excluded from adopting based on their sexual orientation.

In 2010 a Florida court declared that "reports and studies find that there are no differences in the parenting of homosexuals or the adjustment of their children", therefore the Court is satisfied that the issue is so far beyond dispute that it would be irrational to hold otherwise.

Fulton v. City of Philadelphia

Fulton v. City of Philadelphia is a Supreme Court case between Catholic Social Services (CSS) and the city of Philadelphia that took place from November 4, 2020, to June 17, 2021. The city's contracts with adoption agencies prohibit discrimination of LGBTQ couples by law. The city of Philadelphia ended its contract with CSS because the agency refused to consider LGBTQ couples when screening for foster care parents, stating that their actions were due to the religious belief that marriage is between a man and a woman. CSS operates other types of foster care services, like group homes, and received millions of dollars from Philadelphia regardless of the dismissal of their contract. In the court case, CSS claimed that the dismissal of their contract with the city was impeding on their First Amendment right. The lawyer for Philadelphia, Neal Katyal, argued that, "You can't on Monday sign a contract that says we won't discriminate and on Tuesday go ahead and discriminate." The case also aimed to overturn a prior Supreme Court case, Employment Division v. Smith (1990), which concluded that the government's neutral enforcement of a general law is legitimate even if it negatively impacts a religious party. The court ruled that Philadelphia's decision to dismiss the contract violated the rights granted by the Free Exercise Clause of the First Amendment. Despite siding with CSS in Fulton vs. City of Philadelphia, the court did not overturn the 1990 case ruling.

Surrogacy

Some gay couples decide to have a surrogate pregnancy. A surrogate is a woman (possibly a parent) carrying an egg fertilized by sperm, given by a donor or given by a partner. Some people become surrogates for money, others for humanitarian reasons or both. Parents who use surrogacy services can be stigmatized.

Schematic illustration of an AI procedure

Insemination

Insemination is a method used mostly by lesbian couples. It is when a partner is fertilised with donor sperm injected through a syringe. Some people who produce sperm donate it for humanitarian reasons, others for money or both. In some countries, the donor can choose to be anonymous (for example in Spain) and in others, they cannot have their identity withheld (United Kingdom).

Reciprocal IVF

Reciprocal IVF is used by couples who both possess female reproductive organs. Using in vitro fertilization, eggs are removed from one partner to be used to make embryos that the other partner will hopefully carry in a successful pregnancy.

Developing methods

Currently scientists conduct research on alternative types of human parenthood which can aid same-sex couples to have children. One of the possibilities is obtaining sperm from skin stem cells.

Statistics

Public acceptance of legal adoption by trans people (Ipsos, 2017)

According to U.S. Census Snapshot published in December 2007, same-sex couples with children have significantly fewer economic resources and significantly lower rates of homeownership than heterosexual married couples. A literature review of LGBTQ families' economic well being in the US states that there is also greater food insecurity and less ability to access resources to relieve the effects of poverty among LGBTQ families because of the fear of discrimination. One suggested reason for this is that the majority of LGBTQ couples belong to more than one marginalized group which have lower overall incomes than people in non-marginalized communities.

Data from a survey called the American Community Survey carried out from 2014 to 2016 estimated that the number of LGBTQ parents raising children in the United States was 114,000. Out of all of the LGBTQ couples in the US, the survey approximated that 24% of female same-sex couples were raising children in comparison to 8% of male same-sex couples. Additionally about 21% of same-sex partners had an adopted child.

A 2014 literature review of 51 surveys of Transgender people in the US found that between one quarter and one half reported being parents with more Trans women being parents than Trans men. In comparison, a 2015 survey of about 27,700 Transgender and Gender Non-conforming people found that 18% reported being a parent to a child.  Estimates of gay and lesbian parents in the United States have been reported to range between 2 and 8 million , while estimates of children of lesbian and gay parents range from 4 to 14 million.

An LGBTQ Family Building Survey compiled by an LGBTQ rights coalition called Family Equality found that, in the US, in 2019:

63% of LGBTQ Millennials (aged 18-35) are considering expanding their families, either becoming parents for the first time, or by having more children

48% of LGBTQ Millennials are actively planning to grow their families, compared to 55% of non-LGBTQ Millennials, a gap that has narrowed significantly in comparison to older generations

63% of LGBTQ people planning families expect to use assisted reproductive technology, foster care, or adoption to become parents, a significant shift away from older generations of LGBTQ parents for whom the majority of children were conceived through intercourse. 

A study on the empowerment of LGBTQ couples in Finland found there were 4 factors that contributed to higher feelings of support:

1) Parents' willingness to create socially recognized families, 2) Parenthood support, 3) Respectful partnership with all parents, and 4) Accessible services.

According to a 2013–14 survey conducted in Poland by the Institute of Psychology of the Polish Academy of Sciences (IP PAN) on 3000 LGBT people in same-sex relationships living in the country, 9% (11.7% of women and 4.6% of men) of coupled LGBT people were parents. The 2011 Canadian Census had similar conclusions to these of the Polish study: 9.4% of Canadian gay couples were bringing up children.

Research

Scientific research consistently shows that gay and lesbian parents are as fit and capable as heterosexual parents, and their children are as psychologically healthy and well-adjusted as those reared by heterosexual parents. Major associations of mental health professionals in the U.S., Canada, and Australia have not identified credible empirical research that suggests otherwise.

In the United States, studies on the effect of gay and lesbian parenting on children were first conducted in the 1970s, and expanded through the 1980s in the context of increasing numbers of gay and lesbian parents seeking legal custody of their biological children.

Children and young adults with LGBTQ parents are uniquely defined by the fact that they typically identify as heterosexual, but as a function of their membership in an LGBTQ-parent family, they are exposed to minority stress and experience the effects of adulthood. Thus, a central question in this study is, How do young adults with LGBTQ parents explain their sense of connection to or disconnection from the LGBTQ community, both as children (while growing up with LGBTQ parents) and as young adults?

Regarding the transmission of gender roles, LGBTQ parents are caught between two contrasting images: "they are portrayed as either inherently different from, or essentially the same as, heterosexual families". Lesbians are either seen as a threat to heternormativity because they are militant, anti-male feminists, or as especially safe caregivers because they are two loving, nurturing women, who are unlikely to be sexually abusive. Gay men are also caught between these two contrasting images. On one hand they do not have women’s ability to breastfeed children, are perceived as sexually (over)active and potentially predatory and, like lesbians, too political; on the other hand they are more maternal and more feminine than heterosexual men.

The underlying assumption is that gay men and lesbians are different in some essential way from heterosexual people, and this difference implicates their aberrant gender expression. Therefore, they are unable to model appropriate gender behavior to their children, for example, the assumption that gay fathers are unable to bathe their daughters or discuss puberty and menstruation.

Methodology

Studies of LGBT parenting have sometimes suffered from small and/or non-random samples and inability to implement all possible controls, due to the small LGBT parenting population and to cultural and social obstacles to identifying as an LGBT parent.

A 1993 review published in the Journal of Divorce & Remarriage identified fourteen studies addressing the effects of LGBT parenting on children. The review concluded that all of the studies lacked external validity and that therefore: "The conclusion that there are no significant differences in children reared by lesbian mothers versus heterosexual mothers is not supported by the published research database."

Fitzgerald's 1999 analysis explained some methodological difficulties:

Many of these studies suffer from similar limitations and weaknesses, with the main obstacle being the difficulty in acquiring representative, random samples on a virtually invisible population. Many lesbian and gay parents are not open about their sexual orientation due to real fears of discrimination, homophobia, and threats of losing custody of their children. Those who do participate in this type of research are usually relatively open about their homosexuality and, therefore, may bias the research towards a particular group of gay and lesbian parents.

Because of the inevitable use of convenience samples, sample sizes are usually very small and the majority of the research participants end up looking quite homogeneous—e.g. white, middle-class, urban, and well-educated. Another pattern is the wide discrepancy between the number of studies conducted with children of gay fathers and those with lesbian mothers...

Another potential factor of importance is the possibility of social desirability bias when research subjects respond in ways that present themselves and their families in the most desirable light possible. Such a phenomenon does seem possible due to the desire of this population to offset and reverse negative images and discrimination. Consequently, the findings of these studies may be patterned by self-presentation bias.

According to a 2001 review of 21 studies by Stacey and Biblarz published in American Sociological Review: "[R]esearchers lack reliable data on the number and location of lesbigay parents with children in the general population, there are no studies of child development based on random, representative samples of such families. Most studies rely on small-scale, snowball and convenience samples were drawn primarily from personal and community networks or agencies. Most research to date has been conducted on white lesbian mothers who are comparatively educated, mature, and reside in relatively progressive urban centers, most often in California or the Northeastern states."

In more recent studies, many of these issues have been resolved due to factors such as the changing social climate for LGBT people.

Herek's 2006 paper in American Psychologist stated:

The overall methodological sophistication and quality of studies in this domain have increased over the years, as would be expected for any new area of empirical inquiry. More recent research has reported data from probability and community-based convenience samples, has used more rigorous assessment techniques, and has been published in highly respected and widely cited developmental psychology journals, including Child Development and Developmental Psychology. Data are increasingly available from prospective studies. In addition, whereas early study samples consisted mainly of children originally born into heterosexual relationships that subsequently dissolved when one parent came out as gay or lesbian, recent samples are more likely to include children conceived within a same-sex relationship or adopted in infancy by a same-sex couple. Thus, they are less likely to confound the effects of having a sexual minority parent with the consequences of divorce.

A 2002 review of the literature identified 20 studies examining outcomes among children raised by gay or lesbian parents and found that these children did not systematically differ from those raised by heterosexual parents on any of the studied outcomes.

In a 2009 affidavit filed in the case Gill v. Office of Personnel Management, Michael Lamb, a professor of psychology and head of Department of Social and Developmental Psychology at Cambridge University, stated:

The methodologies used in the major studies of same-sex parenting meet the standards for research in the field of developmental psychology and psychology generally. The studies specific to same-sex parenting were published in leading journals in the field of child and adolescent development, such as Child Development, published by the Society for Research in Child Development, Developmental Psychology, published by the American Psychological Association, and The Journal of Child Psychology and Psychiatry, the flagship peer-review journals in the field of child development. Most of the studies appeared in these (or similar) rigorously peer-reviewed and highly selective journals, whose standards represent expert consensus on generally accepted social scientific standards for research on child and adolescent development. Prior to publication in these journals, these studies were required to go through a rigorous peer-review process, and as a result, they constitute the type of research that members of the respective professions consider reliable. The body of research on same-sex families is consistent with standards in the relevant fields and produces reliable conclusions."

Gartrell and Bos's 25-year longitudinal study, published 2010, was limited to mothers who sought donor insemination and who may have been more motivated than mothers in other circumstances. Gartrell and Bos note that the study's limitations included utilizing a non-random sample, and the lesbian group and control group were not matched for race or area of residence.

Michael J. Rosenfeld, associate professor of sociology at Stanford University, wrote in a 2010 study published in Demography that "[A] critique of the literature—that the sample sizes of the studies are too small to allow for statistically powerful tests—continues to be relevant." Rosenfeld's study, "the first to use large-sample nationally representative data," found that children of same-sex couples demonstrated normal outcomes in school. "The core finding here," reports the study," offers a measure of validation for the prior, and much-debated, small-sample studies."

According to a 2005 brief by the American Psychological Association:

In summary, research on diversity among families with lesbian and gay parents and on the potential effects of such diversity on children is still sparse (Martin, 1993, 1998; Patterson, 1995b, 2000, 2001, 2004; Perrin, 2002; Stacey & Biblarz, 2001; Tasker, 1999). Data on children of parents who identify as bisexual are still not available, and information about children of non-White lesbian or gay parents is hard to find (but see Wainright et al., 2004, for a racially diverse sample)... However, the existing data are still limited, and any conclusions must be seen as tentative... It should be acknowledged that research on lesbian and gay parents and their children, though no longer new, is still limited in extent. Although studies of gay fathers and their children have been conducted (Patterson, 2004), less is known about children of gay fathers than about children of lesbian mothers. Although studies of adolescent and young adult offspring of lesbian and gay parents are available (e.g., Gershon et al., 1999; Tasker & Golombok, 1997; Wainright et al., 2004), relatively few studies have focused on the offspring of lesbian or gay parents during adolescence or adulthood.

In 2010 American Psychological Association, The California Psychological Association, The American Psychiatric Association, and the American Association for Marriage and Family Therapy stated:

Relatively few studies have directly examined gay fathers, but those that exist find that gay men are similarly fit and able parents, as compared to heterosexual men. Available empirical data do not provide a basis for assuming gay men are unsuited for parenthood. If gay parents were inherently unfit, even small studies with convenience samples would readily detect it. This has not been the case. Being raised by a single father does not appear to inherently disadvantage children's psychological wellbeing more than being raised by a single mother. Homosexuality does not constitute a pathology or deficit, and there is no theoretical reason to expect gay fathers to cause harm to their children. Thus, although more research is needed, available data place the burden of empirical proof on those who argue that having a gay father is harmful.

A significant increase in methodological rigor was achieved in a 2020 study by Deni Mazrekaj at University of Oxford, Kristof De Witte and Sofie Cabus at KU Leuven published in the American Sociological Review. The authors used administrative longitudinal data on the entire population of children born between 1998 and 2007 in the Netherlands, which was the first country to legalize same-sex marriage. They followed the educational performance of 2,971 children with same-sex parents and over a million children with different-sex parents from birth. This was the first study to address how children who were actually raised by same-sex parents from birth (instead of happening to live with a same-sex couple at some point in time) perform in school while retaining a large representative sample. The authors found that children raised by same-sex parents from birth perform better than children raised by different-sex parents in both primary and secondary education. According to the authors, a major factor explaining these results was parental socioeconomic status. Same-sex couples often have to use expensive fertility treatments and adoption procedures to have a child, meaning they tend to be wealthier, older and more educated than the typical different-sex couple. However, the study concluded that the positive effects of being raised by same-sex parents still remained after controlling for socioeconomic status, though they did lessen. The authors hypothesize that homophobic discrimination could cause same-sex parents to compensate by investing more time and energy into their children.

Consensus

Scientific research that has directly compared outcomes for children with gay and lesbian parents with outcomes for children with heterosexual parents has found that children raised by same-sex couples are as physically or psychologically healthy, capable, and successful as those raised by opposite-sex couples, despite the reality that considerable legal discrimination and inequity remain significant challenges for these families. Major associations of mental health professionals in the U.S., Canada, and Australia, have not identified credible empirical research that suggests otherwise. Sociologist Wendy Manning echoes their conclusion that "[The] studies reveal that children raised in same-sex parent families fare just as well as children raised in different-sex parent families across a wide spectrum of child well-being measures: academic performance, cognitive development, social development, psychological health, early sexual activity, and substance abuse." The range of these studies allows for conclusions to be drawn beyond any narrow spectrum of a child's well-being, and the literature further indicates that parents' financial, psychological and physical well-being is enhanced by marriage and that children benefit from being raised by two parents within a legally recognized union. There is evidence that nuclear families with homosexual parents are more egalitarian in their distribution of home and childcare activities, and thus less likely to embrace traditional gender roles. Nonetheless, the American Academy of Pediatrics reports that there are no differences in the interests and hobbies between children with homosexual versus heterosexual parents.

Since the 1970s, it has become increasingly clear that it is family processes (such as the quality of parenting, the psychosocial well-being of parents, the quality of and satisfaction with relationships within the family, and the level of co-operation and harmony between parents) that contribute to determining children's well-being and outcomes rather than family structures, per se, such as the number, gender, sexuality and cohabitation status of parents.  Since the end of the 1980s, as a result, it has been well established that children and adolescents can be as well-adjusted in nontraditional settings as in traditional settings. Furthermore, whereas factors such as the number and cohabitation status of parents can and do influence relationship quality in aggregate, the same has not been demonstrated for sexuality. According to sociologist Judith Stacey of New York University, "Rarely is there as much consensus in any area of social science as in the case of gay parenting, which is why the American Academy of Pediatrics and all of the major professional organizations with expertise in child welfare have issued reports and resolutions in support of gay and lesbian parental rights". These organizations include the American Academy of Pediatrics, the American Academy of Child and Adolescent Psychiatry, the American Psychiatric Association, the American Psychological Association, the American Association for Marriage and Family Therapy, the American Psychoanalytic Association, the National Association of Social Workers, the Child Welfare League of America, the North American Council on Adoptable Children, and Canadian Psychological Association. In 2006, Gregory M. Herek stated in American Psychologist: "If gay, lesbian, or bisexual parents were inherently less capable than otherwise comparable heterosexual parents, their children would evidence problems regardless of the type of sample. This pattern clearly has not been observed. Given the consistent failures in this research literature to disprove the null hypothesis, the burden of empirical proof is on those who argue that the children of sexual minority parents fare worse than the children of heterosexual parents."

Studies and analyses include Bridget Fitzgerald's 1999 analysis of the research on gay and lesbian parenting, published in Marriage & Family Review, which found that the available studies generally concluded that "the sexual orientation of parents is not an effective or important predictor of successful childhood development" and Gregory M. Herek's 2006 analysis in American Psychologist, which said: "Despite considerable variation in the quality of their samples, research design, measurement methods, and data analysis techniques, the findings to date have been remarkably consistent. Empirical studies comparing children raised by sexual minority parents with those raised by otherwise comparable heterosexual parents have not found reliable disparities in mental health or social adjustment. Differences have not been found in parenting ability between lesbian mothers and heterosexual mothers. Studies examining gay fathers are fewer in number but do not show that gay men are any less fit or able as parents than heterosexual men." Additionally, some fear that children will inherit their parent's gender dysphoria or alternate mental health issues in the case of trans parent, yet there is research that suggests "an absence of evidence that children raised by transgendered [sic] parents have a greater chance of experiencing […] development issues than raised by non-transgender parents" and further clinical research shows that "children of gender-variant parents do not develop gender dysphoria or mental diseases" due to their parents' diagnosis with gender identity disorder.  A 1996 meta-analysis found "no differences on any measures between the heterosexual and homosexual parents regarding parenting styles, emotional adjustment, and sexual orientation of the child(ren)"; and a 2008 meta-analysis reached similar conclusions.

In June 2010, the results of a 25-year ongoing longitudinal study by Nanette Gartrell of the University of California and Henny Bos of the University of Amsterdam were released. Gartrell and Bos studied 78 children conceived through donor insemination and raised by lesbian mothers. Mothers were interviewed and given clinical questionnaires during pregnancy and when their children were 2, 5, 10, and 17 years of age. In the abstract of the report, the authors stated: "According to their mothers' reports, the 17-year-old daughters and sons of lesbian mothers were rated significantly higher in social, school/academic, and total competence and significantly lower in social problems, rule-breaking, aggressive, and externalizing problem behavior than their age-matched counterparts in Achenbach's normative sample of American youth."

Analysis of extensive social science literature into the question of children's psychological outcomes of being raised by same-sex parents by the Australian Institute of Family Studies in 2013 concluded that "there is now strong evidence that same-sex parented families constitute supportive environments in which to raise children" and that with regard to lesbian parenting "...clear benefits appear to exist with regard to: the quality of parenting children experience in comparison to their peers parented in heterosexual couple families; children's and young adults' greater tolerance of sexual and gender diversity; and gender flexibility displayed by children, particularly sons."

Sexual orientation and gender role

Reviews of data from studies thus far suggest that children reared by non-heterosexual parents have outcomes similar to those of children reared by heterosexual parents with respect to sexual orientation. According to the U.S. Census, 80% of the children being raised by same-sex couples in the United States are their biological children. Regarding biological children of non-heterosexuals, a 2016 review lead by J. Michael Bailey states "We would expect, for example, that homosexual parents should be more likely than heterosexual parents to have homosexual children on the basis of genetics alone", since there is some genetic contribution to sexual orientation, and parents and children share 50 percent of their genes.

Important observations from research on twins separated at birth and large adoption studies, is that parents tend to have little to no environmental effects on their children's behavioural traits, which are instead correlated with genes shared between parent and child and the non-shared environment (environment which is unique to the child, such as random developmental noise and events, as opposed to rearing). The 2016 Bailey et al. review concludes that there "is good evidence for both genetic and nonsocial environmental influences on sexual orientation" including prenatal developmental events, but that there is better evidence for biological mechanisms relating to male sexual orientation, which appears unresponsive to socialization, saying "we would be surprised if differences in social environment contributed to differences in male sexual orientation at all." In contrast, they say that female sexual orientation may be somewhat responsive to social environment, saying "it would also be less surprising to us to discover that social environment affects female sexual orientation and related behavior, that possibility must be scientifically supported rather than assumed."

A 2013 statement from the American Academy of Child and Adolescent Psychiatry states that children of LGBT parents do not have any differences in their gender role behaviors in comparison to those observed in heterosexual family structures.

A 2005 review by Charlotte J. Patterson for the American Psychological Association found that the available data did not suggest higher rates of homosexuality among the children of lesbian or gay parents. Herek's 2006 review describes the available data on the point as limited. Stacey and Biblarz and Herek stress that the sexual orientation and gender identification of children is of limited relevance to discussions of parental fitness or policies based on the same. In a 2010 review comparing single-father families with other family types, Stacey and Biblarz state, "We know very little yet about how parents influence the development of their children's sexual identities or how these intersect with gender." When it comes to family socialization processes and "contextual effects," Stacey and Biblarz say that children with such parents are more likely to grow up in relatively more tolerant school, neighborhood, and social contexts.

Social challenges and support systems

Lesbian couple with children

Children may struggle with negative attitudes about their parents from the harassment they may encounter by living in society. There are many risks and challenges that can occur for children of LGBT families and their parents in North America, including those in the individual domain, family domain, and community/school domain. Hegemonic social norms can lead some children to struggle in all or several domains. Social interactions at school, extracurricular activities, and religious organizations can promote negative attitudes towards their parents and themselves based on gender and sexuality. Bias, stereotypes, micro-aggressions, harm, and violence that both students and parents can often encounter are a result of identifying outside of social normative, cis-gender, heterosexual society or having their identity used as a weapon against them.

The forms of harm and violence that LGBT young people can experience include physical harm and harassment, cyber harassment, assault, bullying, micro-aggressions and beyond. Due to the increased risk of harm experienced, children of LGBT parents and LGBT students can also experience increased levels of stress, anxiety, and self-esteem issues. Several legal and social protections support children and parents who experience transphobia and homophobia in the community, school, and family. Practicing and developing supportive networks within schools and working towards resilience skills can assist in creating safe environments for students and parents. Social supports, ally development, and positive school environments are direct ways to challenge homophobia and transphobia directed at these students and their families. Several networks and school clubs can be set up and led by student youth to create positive school environments and community environments for LGBT students and their families. Organizations such as Gay-Straight Alliance Network (GSA), American Civil Liberties Union(ACLU), and Gay, Lesbian & Straight Education Network (GLSEN) can assist in supportive school environments. Community resources for LGBT children and parents such as the Human Rights Campaign (HRC), The Trevor Project, and Parents, Families, and Friends of Lesbians and Gays (PFLAG) can assist in building personal support systems.

Other

Stephen Hicks, a reader in health and social care at the University of Salford questions the value of trying to establish that lesbian or gay parents are defective or suitable. He argues such positions are flawed because they are informed by ideologies that either oppose or support such families. In Hicks' view:

Instead of asking whether gay parenting is bad for kids, I think we should ask how contemporary discourses of sexuality maintain the very idea that lesbian and gay families are essentially different and, indeed, deficient. But, in order to ask this, I think that we need a wider range of research into lesbian and gay parenting... More work of this sort will help us to ask more complex questions about forms of parenting that continue to offer some novel and challenging approaches to family life.

Misrepresentation by opponents

In a 2006 statement, the Canadian Psychological Association released an updated statement on their 2003 and 2005 conclusions, saying, "The CPA recognizes and appreciates that persons and institutions are entitled to their opinions and positions on this issue. However, CPA is concerned that some persons and institutions are misinterpreting the findings of psychological research to support their positions when their positions are more accurately based on other systems of belief or values." Several professional organizations have noted that studies which opponents of LGBT parenting claim as evidence that same-sex couples are unfit parents do not in fact address same-sex parenting, however, and therefore do not permit any conclusions to be drawn about the effects of the sexes or sexual orientations of parents. Rather, these studies, which only sampled heterosexual parents, found that it was better for children to be raised by two parents instead of one, and/or that the divorce or death of a parent had a negative effect on children. In Perry v. Brown, in which Judge Vaughn Walker found that the available studies on stepchildren, which opponents of same-sex marriage cited to support their position that it is best for a child to be raised by its biological mother and father, do not isolate "the genetic relationship between a parent and a child as a variable to be tested" and only compare "children raised by married, biological parents with children raised by single parents, unmarried mothers, step families and cohabiting parents," and thus "compare various family structures and do not emphasize biology." Perry also cited studies showing that "adopted children or children conceived using sperm or egg donors are just as likely to be well-adjusted as children raised by their biological parents."

Gregory M. Herek noted in 2006 that "empirical research can't reconcile disputes about core values, but it is very good at addressing questions of fact. Policy debates will be impoverished if this important source of knowledge is simply dismissed as a 'he said, she said' squabble."

Other aspects

Marriage

Same-sex parenting is often raised as an issue in debates about the recognition of same-sex marriage by law.

Trans parenting

There is little to no visibility or public support through pregnancy and parenting resources directed towards trans parents.

Transgender parents, like cisgender and/or heterosexual parents, can have children in a number of ways, such as biological gestation, adoption, surrogacy, and with biomedical interventions. Trans parents often face different barriers to parenthood than non-trans parents, much of which has to do with the societal expectations of what parents look like.

While "once gay and lesbian parents attain parenthood status[…] they almost never lose it" this is not the case for trans parents, as seen with the cases of Suzanne Daly (1983) and Martha Boyd (2007), two trans women who both had their parental rights, with regard to biological children, terminated on the basis of their diagnosis of gender identity disorder and their trans status. They were perceived to have abandoned their role as "fathers" through their MTF transition, and were perceived to have acted selfishly in putting their own sexual/identity needs before the wellbeing of their children. These cases are amongst many legal custody battles fought by trans parents whereby U.S. courts have completely overlooked defendants' suitability as "parents" as opposed to "mothers" or "fathers," roles that are heavily gendered and come with strict societal understandings of normative parental behaviour. In the case of trans individuals who desire to become parents and to be legally recognized as mothers or fathers of their children, courts often refuse to legally acknowledge such roles because of biological discrimination. An example of this is the X, Y and Z vs. U.K case, whereby X, a trans man who had been in a stable relationship with Y, a biological woman who gave birth to Z through artificial insemination through which X was always present, was denied the right to be listed as Z's father on their birth certificate due to the fact that they did not directly inseminate Y.

Recently, Canada has started acknowledging trans parental rights in terms of custody arrangements and of legal recognition of parental status. In 2001, a trans woman was permitted to retain custody of her daughter after her ex-partner filed for sole custody on the basis of her transition. The courts ruled that "the applicant's transsexuality, in itself, without further evidence, would not constitute a material change in circumstances, nor would it be considered a negative factor in a custody determination", marking a landmark case in family law whereby "a person's transsexuality is irrelevant on its own as a factor in his or her ability to be a good parent". Additionally, a resident trans man from Toronto, Canada "was permitted to identify as [the child's] father on the province of Ontario's Statement of Live Birth Form", marking a decoupling of genetics and bio-sex in relation to parental roles.

Stressors for trans parents

Transgender families can experience unique social pressure. Consequently, transgender parents may experience stressors or barriers relating to their gender transition, which can have an impact on their overall family dynamics and can influence outcomes for transgender people. Many trans individuals cite, since their younger years, not wanting to have children or become pregnant due to the body and gender dysphoria that accompanies childbearing. This relates back toward a large problem for trans individuals even in a non-parenting context, because much of how society views gender does not leave a space for trans individuals. Additionally, a sense of support, especially from family, was found to be an important factor for coping with stressors in a study from 2014. It revealed that 43% of participants stated that they mostly depended on their children for support to help their coping with stress related to their gender transition, while 29% named their partner as their most important support. A 2016 study examined how potential stressors for families, access to resources, and the trans parent's perceptions impact how the family functions. The functioning of the family refers to their ability to handle stress and in turn, their ability to steer clear of crisis situations. The study's findings indicate that experience of stigma surrounding transgender identities, uncertainty of their role or status of acceptance in their families following gender transition, and sense of coherence had the most profound impact on family functioning. Sense of Coherence refers to viewing one's environment as "comprehensible, manageable, and meaningful." Experiencing stigma, as well as uncertainty of their acceptance within their families, were found to contribute to lower satisfaction in family functioning. The study also found that negative effects of stigma can be offset by a strong sense of coherence, while satisfaction in the family's functioning can be strengthened by a strong sense of coherence.

When stigma is reduced around trans parenting, such as from supportive family, adoption staff, and healthcare professionals, trans people can more easily find satisfaction and a positive family functioning.

Wednesday, July 26, 2023

Memory management

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Memory_management
https://en.wikipedia.org/wiki/Memory_management

Memory management is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. This is critical to any advanced computer system where more than a single process might be underway at any time.

Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have an extensive effect on overall system performance.

In some operating systems, e.g. OS/360 and successors, memory is managed by the operating system. In other operating systems, e.g. Unix-like operating systems, memory is managed at the application level.

Memory management within an address space is generally categorized as either manual memory management or automatic memory management.

Manual memory management

An example of external fragmentation

The task of fulfilling an allocation request consists of locating a block of unused memory of sufficient size. Memory requests are satisfied by allocating portions from a large pool of memory called the heap or free store. At any given time, some parts of the heap are in use, while some are "free" (unused) and thus available for future allocations.

Several issues complicate the implementation, such as external fragmentation, which arises when there are many small gaps between allocated memory blocks, which invalidates their use for an allocation request. The allocator's metadata can also inflate the size of (individually) small allocations. This is often managed by chunking. The memory management system must track outstanding allocations to ensure that they do not overlap and that no memory is ever "lost" (i.e. that there are no "memory leaks").

Efficiency

The specific dynamic memory allocation algorithm implemented can impact performance significantly. A study conducted in 1994 by Digital Equipment Corporation illustrates the overheads involved for a variety of allocators. The lowest average instruction path length required to allocate a single memory slot was 52 (as measured with an instruction level profiler on a variety of software).

Implementations

Since the precise location of the allocation is not known in advance, the memory is accessed indirectly, usually through a pointer reference. The specific algorithm used to organize the memory area and allocate and deallocate chunks is interlinked with the kernel, and may use any of the following methods:

Fixed-size blocks allocation

Fixed-size blocks allocation, also called memory pool allocation, uses a free list of fixed-size blocks of memory (often all of the same size). This works well for simple embedded systems where no large objects need to be allocated, but suffers from fragmentation, especially with long memory addresses. However, due to the significantly reduced overhead this method can substantially improve performance for objects that need frequent allocation / de-allocation and is often used in video games.

Buddy blocks

In this system, memory is allocated into several pools of memory instead of just one, where each pool represents blocks of memory of a certain power of two in size, or blocks of some other convenient size progression. All blocks of a particular size are kept in a sorted linked list or tree and all new blocks that are formed during allocation are added to their respective memory pools for later use. If a smaller size is requested than is available, the smallest available size is selected and split. One of the resulting parts is selected, and the process repeats until the request is complete. When a block is allocated, the allocator will start with the smallest sufficiently large block to avoid needlessly breaking blocks. When a block is freed, it is compared to its buddy. If they are both free, they are combined and placed in the correspondingly larger-sized buddy-block list.

Slab allocation

This memory allocation mechanism preallocates memory chunks suitable to fit objects of a certain type or size. These chunks are called caches and the allocator only has to keep track of a list of free cache slots. Constructing an object will use any one of the free cache slots and destructing an object will add a slot back to the free cache slot list. This technique alleviates memory fragmentation and is efficient as there is no need to search for a suitable portion of memory, as any open slot will suffice.

Stack allocation

Many Unix-like systems as well as Microsoft Windows implement a function called alloca for dynamically allocating stack memory in a way similar to the heap-based malloc. A compiler typically translates it to inlined instructions manipulating the stack pointer. Although there is no need of manually freeing memory allocated this way as it is automatically freed when the function that called alloca returns, there exists a risk of overflow. And since alloca is an ad hoc expansion seen in many systems but never in POSIX or the C standard, its behavior in case of a stack overflow is undefined.

A safer version of alloca called _malloca, which reports errors, exists on Microsoft Windows. It requires the use of _freea. gnulib provides an equivalent interface, albeit instead of throwing an SEH exception on overflow, it delegates to malloc when an overlarge size is detected. A similar feature can be emulated using manual accounting and size-checking, such as in the uses of alloca_account in glibc.

Automatic memory management

In many programming language implementations, the runtime environment for the program automatically allocates memory in the call stack for non-static local variables of a subroutine, called automatic variables, when the subroutine is called, and automatically releases that memory when the subroutine is exited. Special declarations may allow local variables to retain values between invocations of the procedure, or may allow local variables to be accessed by other subroutines. The automatic allocation of local variables makes recursion possible, to a depth limited by available memory.

Garbage collection

Garbage collection is a strategy for automatically detecting memory allocated to objects that are no longer usable in a program, and returning that allocated memory to a pool of free memory locations. This method is in contrast to "manual" memory management where a programmer explicitly codes memory requests and memory releases in the program. While automatic garbage collection has the advantages of reducing programmer workload and preventing certain kinds of memory allocation bugs, garbage collection does require memory resources of its own, and can compete with the application program for processor time.

Systems with virtual memory

Virtual memory is a method of decoupling the memory organization from the physical hardware. The applications operate on memory via virtual addresses. Each attempt by the application to access a particular virtual memory address results in the virtual memory address being translated to an actual physical address. In this way the addition of virtual memory enables granular control over memory systems and methods of access.

In virtual memory systems the operating system limits how a process can access the memory. This feature, called memory protection, can be used to disallow a process to read or write to memory that is not allocated to it, preventing malicious or malfunctioning code in one program from interfering with the operation of another.

Even though the memory allocated for specific processes is normally isolated, processes sometimes need to be able to share information. Shared memory is one of the fastest techniques for inter-process communication.

Memory is usually classified by access rate into primary storage and secondary storage. Memory management systems, among other operations, also handle the moving of information between these two levels of memory.

Memory management in OS/360 and successors

IBM System/360 does not support virtual memory. Memory isolation of jobs is optionally accomplished using protection keys, assigning storage for each job a different key, 0 for the supervisor or 1–15. Memory management in OS/360 is a supervisor function. Storage is requested using the GETMAIN macro and freed using the FREEMAIN macro, which result in a call to the supervisor (SVC) to perform the operation.

In OS/360 the details vary depending on how the system is generated, e.g., for PCP, MFT, MVT.

In OS/360 MVT, suballocation within a job's region or the shared System Queue Area (SQA) is based on subpools, areas a multiple of 2 KB in size—the size of an area protected by a protection key. Subpools are numbered 0–255. Within a region subpools are assigned either the job's storage protection or the supervisor's key, key 0. Subpools 0–127 receive the job's key. Initially only subpool zero is created, and all user storage requests are satisfied from subpool 0, unless another is specified in the memory request. Subpools 250–255 are created by memory requests by the supervisor on behalf of the job. Most of these are assigned key 0, although a few get the key of the job. Subpool numbers are also relevant in MFT, although the details are much simpler. MFT uses fixed partitions redefinable by the operator instead of dynamic regions and PCP has only a single partition.

Each subpool is mapped by a list of control blocks identifying allocated and free memory blocks within the subpool. Memory is allocated by finding a free area of sufficient size, or by allocating additional blocks in the subpool, up to the region size of the job. It is possible to free all or part of an allocated memory area.

The details for OS/VS1 are similar to those for MFT and for MVT; the details for OS/VS2 are similar to those for MVT, except that the page size is 4 KiB. For both OS/VS1 and OS/VS2 the shared System Queue Area (SQA) is nonpageable.

In MVS the address space includes an additional pageable shared area, the Common Storage Area (CSA), and an additional private area, the System Work area (SWA). Also, the storage keys 0-7 are all reserved for use by privileged code.

VM (operating system)

From Wikipedia, the free encyclopedia
The default login screen on VM/370 Release 6.

VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers.

The following versions are known:

Virtual Machine Facility/370
VM/370, released in 1972, is a System/370 reimplementation of earlier CP/CMS operating system.
VM/370 Basic System Extensions Program Product
VM/BSE (BSEPP) is an enhancement to VM/370 that adds support for more devices (such as 3370-type fixed-block-architecture DASD drives), improvements to the CMS environment (such as an improved editor), and some stability enhancements to CP.
VM/370 System Extensions Program Product
VM/SE (SEPP) is an enhancement to VM/370 that includes the facilities of VM/BSE, as well as a few additional fixes and features.
Virtual Machine/System Product
VM/SP, a milestone version, replaces VM/370, VM/BSE and VM/SE. Release 1 added EXEC2 and XEDIT System Product Editor; Release 3 added REXX; Release 6 added the shared filesystem.
Virtual Machine/System Product High Performance Option 
VM/SP HPO adds additional device support and functionality to VM/SP, and allows certain S/370 machines that can utilize more than 16 MB of real storage to do so, up to 64 MB. This version was intended for users that would be running multiple S/370 guests at once.
Virtual Machine/Extended Architecture Migration Aid 
VM/XA MA is intended to ease the migration from MVS/370 to MVS/XA by allowing both to run concurrently on the same processor complex.
Virtual Machine/Extended Architecture System Facility 
VM/XA SF is an upgraded VM/XA MA with improved functionality and performance.
Virtual Machine/Extended Architecture System Product 
VM/XA SP is an upgraded VM/XA MA with improved functionality and performance, offered as a replacement for VM/SP HPO on machines supporting S/370-XA. It includes a version of CMS that can run in either S/370 or S/370-XA mode.
Virtual Machine/Enterprise Systems Architecture 
VM/ESA provides the facilities of VM/SP, VM/SP HPO and VM/XA SP. VM/ESA version 1 can run in S/370, ESA/370 or ESA/390 mode; it does not support S/370 XA mode. Version 2 only runs in ESA/390 mode. The S/370-capable versions of VM/ESA were actually their own separate version from the ESA/390 versions of VM/ESA, as the S/370 versions are based on the older VM/SP HPO codebase, and the ESA/390 versions are based on the newer VM/XA codebase.
z/VM, the last version still widely used as one of the main full virtualization solutions for the mainframe market. z/VM 4.4 was the last version that could run in ESA/390 mode; subsequent versions only run in z/Architecture mode.

The CMS in the name refers to the Conversational Monitor System, a component of the product that is a single-user operating system that runs in a virtual machine and provides conversational time-sharing in VM.

Overview

The heart of the VM architecture is the Control Program or hypervisor abbreviated CP, VM-CP and sometimes, ambiguously, VM. It runs on the physical hardware, and creates the virtual machine environment. VM-CP provides full virtualization of the physical machine – including all I/O and other privileged operations. It performs the system's resource-sharing, including device management, dispatching, virtual storage management, and other traditional operating system tasks. Each VM user is provided with a separate virtual machine having its own address space, virtual devices, etc., and which is capable of running any software that could be run on a stand-alone machine. A given VM mainframe typically runs hundreds or thousands of virtual machine instances. VM-CP began life as CP-370, a reimplementation of CP-67, itself a reimplementation of CP-40.

Running within each virtual machine is another operating system, a guest operating system. This might be:

  • CMS (Conversational Monitor System, renamed from the Cambridge Monitor System of CP/CMS). Most virtual machines run CMS, a lightweight, single-user operating system. Its interactive environment is comparable to that of a single-user PC, including a file system, programming services, device access, and command-line processing. (While an earlier version of CMS was uncharitably described as "CP/M on a mainframe", the comparison is an anachronism; the author of CP/M, Gary Kildall, was an experienced CMS user.)
  • GCS (Group Control System), which provides a limited simulation of the MVS API. IBM originally provided GCS in order to run VTAM without a service OS/VS1 virtual machine and VTAM Communications Network Application (VCNA). RSCS V2 also ran under GCS.
  • A mainstream operating system. IBM's mainstream operating systems (e.g., the MVS and DOS/VSE families, OS/VS1, TSS/370, or another layer of VM/370 itself (see below)) can be loaded and run without modification. The VM hypervisor treats guest operating systems as application programs with exceptional privileges – it prevents them from directly using privileged instructions (those which would let applications take over the whole system or significant parts of it), but simulates privileged instructions on their behalf. Most mainframe operating systems terminate a normal application which tries to usurp the operating system's privileges. The VM hypervisor can simulate several types of console terminals for the guest operating system, such as the hardcopy line-mode 3215, the graphical 3270 family, and the integrated console on newer System/390 and System Z machines. Other users can then access running virtual machines using the DIAL command at the logon screen, which will connect their terminal to the first available emulated 3270 device, or the first available 2703 device if the user is DIALing from a typewriter terminal.
  • Another copy of VM. A second level instance of VM can be fully virtualized inside a virtual machine. This is how VM development and testing is done (a second-level VM can potentially implement a different virtualization of the hardware). This technique was used to develop S/370 software before S/370 hardware was available, and it has continued to play a role in new hardware development at IBM. The literature cites practical examples of virtualization five levels deep. Levels of VM below the top are also treated as applications but with exceptional privileges.
  • A copy of the mainframe version of AIX or Linux. In the mainframe environment, these operating systems often run under VM, and are handled like other guest operating systems. (They can also run as 'native' operating systems on the bare hardware.) There was also the short-lived IX/370, as well as S/370 and S/390 versions of AIX (AIX/370 and AIX/ESA).
  • A specialized VM subsystem. Several non-CMS systems run within VM-CP virtual machines, providing services to CMS users such as spooling, interprocess communications, specialized device support, and networking. They operate behind the scenes, extending the services available to CMS without adding to the VM-CP control program. By running in separate virtual machines, they receive the same security and reliability protections as other VM users. Examples include:
    • RSCS (Remote Spooling and Communication Subsystem, aka VNET) – communication and information transfer facilities between virtual machines and other systems
    • RACF (Resource Access Control Facility) — a security system
    • Shared File System (SFS), which organizes shared files in a directory tree (the servers are commonly named "VMSERVx"
    • VTAM (Virtual Telecommunications Access Method) – a facility that provides support for a Systems Network Architecture network
    • PVM (VM/Pass-Through Facility) – a facility that provides remote access to other VM systems
    • TCPIP, SMTP, FTPSERVE, PORTMAP, VMNFS – a set of service machines that provide TCP/IP networking to VM/CMS
    • Db2 Server for VM – a SQL database system, the servers are often named similarly to "SQLMACH" and "SQLMSTR"
    • DIRMAINT – A simplified user directory management system (the directory is a listing of every account on the system, including virtual hardware configuration, user passwords, and minidisks).
    • MUMPS/VM — an implementation of the MUMPS database and programming language which could run as guest on VM/370. MUMPS/VM was introduced in 1987 and discontinued in 1991.
  • A user-written or modified operating system, such as National CSS's CSS or Boston University's VPS/VM.

Hypervisor interface

IBM coined the term hypervisor for the 360/65 and later used it for the DIAG handler of CP-67.

The Diagnose instruction ('83'x—no mnemonic) is a privileged instruction originally intended by IBM to perform "built-in diagnostic functions, or other model-dependent functions." IBM repurposed DIAG for "communication between a virtual machine and CP." The instruction contains two four-bit register numbers, called Rx and Ry, which can "contain operand storage addresses or return codes passed to the DIAGNOSE interface," and a two-byte code "that CP uses to determine what DIAGNOSE function to perform." A few of the available diagnose functions are listed below.

Hexadecimal code Function
0000 Store Extended-Identification Code
0004 Examine Real Storage
0008 Virtual Console Function—Execute a CP command
0018 Standard DASD I/O
0020 General I/O—Execute any valid CCW chain on a tape or disk device
003C Update the VM/370 directory
0058 3270 Virtual Console Interface—perform full-screen I/O on an IBM 3270 terminal
0060 Determine Virtual Machine Storage Size
0068 Virtual Machine Communication Facility (VMCF)

CMS use of DIAGNOSE

At one time, CMS was capable of running on a bare machine, as a true operating system (though such a configuration would be unusual). It now runs only as a guest OS under VM. This is because CMS relies on a hypervisor interface to VM-CP, to perform file system operations and request other VM services. This paravirtualization interface:

  • Provides a fast path to VM-CP, to avoid the overhead of full simulation.
  • Was first developed as a performance improvement for CP/CMS release 2.1, an important early milestone in CP's efficiency.
  • Uses a non-virtualized, model-dependent machine instruction as a signal between CMS and CP: DIAG (diagnose).

Minidisks

CMS starting up after the user MAINT (system administrator) has logged in.

CMS and other operating systems often have DASD requirements much smaller than the sizes of actual volumes. For this reason CP allows an installation to define virtual disks of any size up to the capacity of the device. For CKD volumes, a minidisk must be defined in full cylinders. A minidisk has the same attributes as the underlying real disk, except that it is usually smaller and the beginning of each minidisk is mapped to cylinder or block 0. The minidisk may be accessed using the same channel programs as the real disk.

A minidisk that has been initialized with a CMS file system is referred to as a CMS minidisk, although CMS is not the only system that can use them.

It is common practice to define full volume minidisks for use by such guest operating systems as z/OS instead of using DEDICATE to assign the volume to a specific virtual machine. In addition, "full-pack links" are often defined for every DASD on the system, and are owned by the MAINT userid. These are used for backing up the system using the DASD Dump/Restore program, where the entire contents of a DASD are written to tape (or another DASD) exactly.

The CMS editor on VM/370, editing a COBOL program source file.

Shared File System

VM/SP Release 6 introduced the Shared File System  which vastly improved CMS file storage capabilities. The CMS minidisk file system does not support directories (folders) at all, however, the SFS does. SFS also introduces more granular security. With CMS minidisks, the system can be configured to allow or deny users read-only or read-write access to a disk, but single files cannot have the same security. SFS alleviates this, and vastly improves performance.

The SFS is provided by service virtual machines. On a modern VM system, there are usually three that are required: VMSERVR, the "recovery machine" that does not actually serve any files; VMSERVS, the server for the VMSYS filepool; and VMSERVU, the server for the VMSYSU (user) filepool. The file pool server machines own several minidisks, usually including a CMS A-disk (virtual device address 191, containing the file pool configuration files), a control disk, a log disk, and any number of data disks that actually store user files.

Invoking the System/360 COBOL compiler on VM/370 CMS, then loading and running the program.

With modern VM versions, most of the system can be installed to SFS, with the few remaining minidisks being the ones absolutely necessary for the system to start up, and the ones being owned by the filepool server machines.

An example of a non-CMS guest operating system running under VM/370: DOS/VS Release 34. The DOS/VS system is now prompting the operator to enter a supervisor name to continue loading.

If a user account is configured to only use SFS (and does not own any minidisks), the user's A-disk will be FILEPOOL:USERID. and any subsequent directories that the user creates will be FILEPOOL:USERID.DIR1.DIR2.DIR3 where the equivalent UNIX file path is /dir1/dir2/dir3. SFS directories can have much more granular access controls when compared to minidisks (which, as mentioned above, can often only have a read password, a write password, and a multi-write password). SFS directories also solve the issues that may arise when two users write to the same CMS minidisk at the same time, which may cause disk corruption (as the CMS VM performing the writes may be unaware that another CMS instance is also writing to the minidisk).

The file pool server machines also serve a closely related filesystem: the Byte File System. BFS is used to store files on a UNIX-style filesystem. Its primary use is for the VM OpenExtensions POSIX environment for CMS. The CMS user virtual machines themselves communicate with the SFS server virtual machines through the IUCV mechanism.

History

The early history of VM is described in the articles CP/CMS and History of CP/CMS. VM/370 is a reimplementation of CP/CMS, and was made available in 1972 as part of IBM's System/370 Advanced Function announcement (which added virtual memory hardware and operating systems to the System/370 series). Early releases of VM through VM/370 Release 6 continued in open source through 1981, and today are considered to be in the public domain. This policy ended in 1977 with the chargeable VM/SE and VM/BSE upgrades and in 1980 with VM/System Product (VM/SP). However, IBM continued providing updates in source form for existing code for many years, although the upgrades to all but the free base required a license. As with CP-67, privileged instructions in a virtual machine cause a program interrupt, and CP simulated the behavior of the privileged instruction.

OS/VS1 starting under VM/370.

VM remained an important platform within IBM, used for operating system development and time-sharing use; but for customers it remained IBM's "other operating system". The OS and DOS families remained IBM's strategic products, and customers were not encouraged to run VM. Those that did formed close working relationships, continuing the community-support model of early CP/CMS users. In the meantime, the system struggled with political infighting within IBM over what resources should be available to the project, as compared with other IBM efforts. A basic problem with the system was seen at IBM's field sales level: VM/CMS demonstrably reduced the amount of hardware needed to support a given number of time-sharing users. IBM was, after all, in the business of selling computer systems.

Melinda Varian provides this fascinating quote, illustrating VM's unexpected success:

The marketing forecasts for VM/370 predicted that no more than one 168 would ever run VM during the entire life of the product. In fact, the first 168 delivered to a customer ran only CP and CMS. Ten years later, ten percent of the large processors being shipped from Poughkeepsie would be destined to run VM, as would a very substantial portion of the mid-range machines that were built in Endicott. Before fifteen years had passed, there would be more VM licenses than MVS licenses.

Using DASD Dump/Restore (DDR) to back up a VM/370 system.

A PC DOS version that runs CMS on the XT/370 (and later on the AT/370) is called VM/PC. VM/PC 1.1 was based on VM/SP release 3. When IBM introduced the P/370 and P/390 processor cards, a PC could now run full VM systems, including VM/370, VM/SP, VM/XA, and VM/ESA (these cards were fully compatible with S/370 and S/390 mainframes, and could run any S/370 operating system from the 31-bit era, e.g., MVS/ESA, VSE/ESA).

In addition to the base VM/SP releases, IBM also introduced VM/SP HPO (High Performance Option). This add-on (which is installed over the base VM/SP release) improved several key system facilities, including allowing the usage of more than 16 MB of storage (RAM) on supported models (such as the IBM 4381). With VM/SP HPO installed, the new limit was 64 MB; however, a single user (or virtual machine) could not use more than 16 MB. The functions of the spool filesystem were also improved, allowing 9900 spool files to be created per user, rather than 9900 for the whole system. The architecture of the spool filesystem was also enhanced, each spool file now had a unique user ID associated with it, and reader file control blocks were now held in virtual storage. The system could also be configured to deny certain users access to the vector facility (by means of user directory entries).

Releases of VM since VM/SP Release 1 supported multiprocessor systems. System/370 versions of VM (such as VM/SP and VM/SP HPO) supported a maximum of two processors, with the system operating in either UP (uniprocessor) mode, MP (multiprocessor) mode, or AP (attached processor) mode. AP mode is the same as MP mode, except the second processor lacks I/O capability. System/370-XA releases of VM (such as VM/XA) supported more. System/390 releases (such as VM/ESA) almost removed the limit entirely, and some modern z/VM systems can have as many as 80 processors. The per-VM limit for defined processors is 64.

When IBM introduced the System/370 Extended Architecture on the 3081, customers were faced with the need to run a production MVS/370 system while testing MVS/XA on the same machine. IBM's solution was VM/XA Migration Aid, which used the new Start Interpretive Execution (SIE) instruction to run the virtual machine. SIE automatically handled some privileged instructions and returned to CP for cases that it couldn't handle. The Processor Resource/System Manager (PR/SM) of the later 3090 also used SIE. There were several VM/XA products before it was eventually supplanted by VM/ESA and z/VM.

In addition to RSCS networking, IBM also provided users with VTAM networking. ACF/VTAM for VM was fully compatible with ACF/VTAM on MVS and VSE. Like RSCS, VTAM on VM ran under the specialized GCS operating system. However, VM also supported TCP/IP networking. In the late 1980s, IBM produced a TCP/IP stack for VM/SP and VM/XA. The stack supported IPv4 networks, and a variety of network interface systems (such as inter-mainframe channel-to-channel links, or a specialized IBM RT PC that would relay traffic out to a Token Ring or Ethernet network). The stack provided support for Telnet connections, from either simple line-mode terminal emulators or VT100-compatible emulators, or proper IBM 3270 terminal emulators. The stack also provided an FTP server. IBM also produced an optional NFS server for VM; early versions were rather primitive, but modern versions are much more advanced.

There was also a fourth networking option, known as VM/Pass-Through Facility (or more commonly called, PVM). PVM, like VTAM, allowed for connections to remote VM/CMS systems, as well as other IBM systems. If two VM/CMS nodes were linked together over a channel-to-channel link or bisync link (possibly using a dialup modem or leased line), a user could remotely connect to either system by entering "DIAL PVM" on the VM login screen, then entering the system node name (or choosing it from a list of available nodes). Alternatively, a user running CMS could use the PASSTHRU program that was installed alongside PVM, allowing for quick access to remote systems without having to log out of the user's session. PVM also supported accessing non-VM systems, by utilizing a 3x74 emulation technique. Later releases of PVM also featured a component that could accept connections from a SNA network.

VM was also the cornerstone operating system of BITNET, as the RSCS system available for VM provided a simple network that was easy to implement, and somewhat reliable. VM sites were interlinked by means of an RSCS VM on each VM system communicating with one another, and users could send and receive messages, files, and batch jobs through RSCS. The "NOTE" command used XEDIT to display a dialog to create an email, from which the user could send it. If the user specified an address in the form of user at node, the email file would be delivered to RSCS, which would then deliver it to the target user on the target system. If the site has TCP/IP installed, RSCS could work with the SMTP service machine to deliver notes (emails) to remote systems, as well as receive them. If the user specified user at some.host.name, the NOTE program would deliver the email to the SMTP service machine, which would then route it out to the destination site on the Internet.

VM's role changed within IBM when hardware evolution led to significant changes in processor architecture. Backward compatibility remained a cornerstone of the IBM mainframe family, which still uses the basic instruction set introduced with the original System/360; but the need for efficient use of the 64-bit zSeries made the VM approach much more attractive. VM was also utilized in data centers converting from DOS/VSE to MVS and is useful when running mainframe AIX and Linux, platforms that were to become increasingly important. The current z/VM platform has finally achieved the recognition within IBM that VM users long felt it deserved. Some z/VM sites run thousands of simultaneous virtual machine users on a single system. z/VM was first released in October 2000 and remains in active use and development.

IBM and third parties have offered many applications and tools that run under VM. Examples include RAMIS, FOCUS, SPSS, NOMAD, DB2, REXX, RACF, and OfficeVision. Current VM offerings run the gamut of mainframe applications, including HTTP servers, database managers, analysis tools, engineering packages, and financial systems.

CP commands

As of release 6, the VM/370 Control Program has a number of commands for General Users, concerned with defining and controlling the user's virtual machine. Lower-case portions of the command are optional

Command Description
#CP Allows the user to issue a CP command from a command environment, or any other virtual machine after pressing the break key (defaults to PA1)
ADSTOP Sets an address stop to halt the virtual machine at a specific instruction
ATTN Causes an attention interruption allowing CP to take control in a command environment
Begin Continue or resume execution of the user's virtual machine, optionally at a specified address
CHange Alter attributes of a spool file or files. For example, the output class or the name of the file can be changed, or printer-specific attributes set
Close Closes an open printer, punch, reader, or console file and releases it to the spooling system
COUPLE Connect a virtual channel-to-channel adapter (CTCA) to another. Also used to connect simulated QDIO Ethernet cards to a virtual switch.
CP Execute a CP command in a CMS environment
DEFine Alter the current virtual machine configuration. Add virtual devices or change available storage size
DETach Remove a virtual device or channel from the current configuration
DIAL Connect your terminal at the logon screen to a logged-on multi-access virtual machine's simulated 3270 or typewriter terminals
DISConn Disconnect your terminal while allowing your virtual machine to continue running
Display Display virtual machine storage or (virtual) hardware registers
DUMP Print a snapshot dump of the current virtual machine on the virtual spooled printer
ECHO Set the virtual machine to echo typed lines
EXTernal Cause an external interrupt to the virtual machine
INDicate Display current system load or your resource usage
Ipl IPL (boot) an operating system on your virtual machine
LINK Attach a device from another virtual machine, if that machine's definition allows sharing
LOADVFCB Specify a forms control buffer (FCB) for a virtual printer
LOGoff
LOGout
Terminate execution of the current virtual machine and disconnect from the system
Logon
Login
Sign on to the system
Message
MSG
Send a one-line message to the system operator or another user
NOTReady Cause a virtual device to appear not ready
ORDer Reorder closed spool files by ID or class
PURge Delete closed spool files for a device by class,m ID, or ALL
Query Display status information for your virtual machine, or the message of the day, or number or names of logged-in users
READY Cause a device end interruption for a device
REQuest Cause an interrupt on your virtual console
RESET Clear all pending interrupts for a device
REWind Rewind a real (non virtual) magnetic tape unit
SET Set various attributes for your virtual machine, including messaging or terminal function keys
SLeep Place your virtual machine in a dormant state indefinitely or for a specified period of time
SMsg Send a one-line special message to another virtual machine (usually used to control the operation of the virtual machine; commonly used with RSCS)
SPool Set options for a spooled virtual device (printer, reader, or punch)
STore Alter the contents of registers or storage of your virtual machine
SYStem Reset or restart your virtual machine or clear storage
TAg Set a tag associated with a spooled device or file. The tag is usually used by VM's Remote Spooling Communications Subystem (RSCS) to identify the destination of a file
TERMinal Set characteristics of your terminal
TRace Start or stop tracing of specified virtual machine activities
TRANsfer Transfer a spool file to or from another user
VMDUMP Dump your virtual machine in a format readable by the Interactive Problem Control System (IPCS) program product

OpenEdition Extensions

Starting with VM/ESA Version 2, IBM introduced the chargeable optional feature OpenEdition for VM/ESA Shell and Utilities Feature, which provides POSIX compatibility for CMS. The stand-out feature was a UNIX shell for CMS. The C compiler for this UNIX environment is provided by either C/370 or C for VM/ESA. Neither the CMS filesystem nor the standard VM Shared File System has any support for UNIX-style files and paths; instead, the Byte File System is used. Once a BFS extent is created in an SFS file pool, the user can mount it using the OPENVM MOUNT /../VMBFS:fileservername:filepoolname /path/to/mount/point. The user must also mount the root filesystem, done with OPENVM MOUNT /../VMBFS:VMSYS:ROOT/ /, a shell can then be started with OPENVM SHELL. Unlike the normal SFS, access to BFS filesystems is controlled by POSIX permissions (with chmod and chown).

Starting with z/VM Version 3, IBM integrated OpenEdition into z/VM and renamed it OpenExtensions. OpenEdition and OpenExtensions provide POSIX.2 compliance to CMS. Programs compiled to run under the OpenExtensions shell are stored in the same format as standard CMS executable modules. Visual editors, such as vi are unavailable, as 3270 terminals are not capable. Users can use ed or XEDIT instead of vi.

VM mascot

In the early 1980s, the VM group within SHARE (the IBM user group) sought a mascot or logo for the community to adopt. This was in part a response to IBM's MVS users selecting the turkey as a mascot (chosen, according to legend, by the MVS Performance Group in the early days of MVS, when its performance was a sore topic). In 1983, the teddy bear became VM's de facto mascot at SHARE 60, when teddy bear stickers were attached to the nametags of "cuddlier oldtimers" to flag them for newcomers as "friendly if approached". The bears were a hit and soon appeared widely. Bears were awarded to inductees of the "Order of the Knights of VM", individuals who made "useful contributions" to the community.

Criticism

While VM was relatively light-weight (when compared to its counterparts, such as MVS), VM was somewhat unstable in its early days. It was considered quite a feat to keep a VM/370 system up for more than a week. Users also criticized the CMS file system, noting that other operating systems in the mid-1980s had directories, symbolic links, and other key features; CMS had none of these until 1988 when VM/SP release 6 came out, which introduced the Shared File System and alleviated these issues.

Some users also noted that VM OpenEdition was somewhat "unnecessary."

Inequality (mathematics)

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Inequality...