Intel Inc. (Hrsg.):80286 and 80287 Programmer’s Reference Manual. Intel Literature Sales, Santa Clara, CA (USA) 1987, ISBN 1-55512-055-5 (englisch, bitsavers.org[PDF; 27,3MB; abgerufen am 14.März 2021]).
Fred Hantelmann:LINUX für Durchstarter. 2. Auflage. Springer-Verlag, 1999, ISBN 978-3-540-65215-1, 2. Entwicklung von Unix, S.16, 2.3 PC-Unix-Varianten (eingeschränkte Vorschauin der Google-Buchsuche): „Kurz nach der breiten Verfügbarkeit von Intel 80286 Prozessoren stellte SCO im Jahre 1985 das Xenix-286 System V Release 2.0 vor. Aufgrund starker Inanspruchnahme des Prozessors allein für die Steuerung des Betriebssystems hatte es diese Implementierung jedoch zunächst schwer, mit dem auf demselben Prozessortyp etablierten MS-DOS zu konkurrieren.“
Michal Necasek:Forward Compatibility, Landmines.(Blog)In:OS/2 Museum.20.September 2014,abgerufen am 9.August 2026(englisch):„The descriptor format is very similar on the 286 and 386; the 386 version is an extension of the 286 one. In both cases, 8bytes are reserved for a descriptor, but on the 286, only 6bytes are used … The 286 documentation … clearly states that the last word is ‘reserved for iAPX 386’ and ‘must be zero’. Unfortunately, the CPU did not enforce that, and allowed the Xenix developers to create a wonderful landmine bug …“
Michal Necasek:There’s More to the 286 XENIX Story.(Blog)In:OS/2 Museum.22.März 2017,abgerufen am 9.August 2026(englisch):„In late 1982 or in 1983, Microsoft ported XENIX … to the Intel 286 processor. … Although Intel had the XENIX source code, the porting was done entirely by Microsoft. Developers at Microsoft decided to store bookkeeping information in the ‘reserved’ 16bits of a descriptor table entry not used by the 286. This approach reliably worked on 286 processors. … In late 1983, updated 286 documentation marked the last 16 descriptor bits as ‘reserved for iAPX 386, must be zero’. … Intel discovered that 286 XENIX does not work on the 386 at all. … …the reserved descriptor word [was] ignored by the 286, and the 386 interpreted the data in unexpected ways (which immediately crashed the OS). Since Intel engineers had access to the XENIX source code, they were able to re-code the OS not to use the reserved descriptor word. Microsoft was reluctant to accept the patch… … Microsoft pointed out that if Intel didn’t want programmers to use reserved areas, they shouldn’t have let them use those areas in the first place. … In late 1984, IBM XENIX 1.0 for the PC/AT was released. It contained the original Microsoft implementation which puts data in a reserved descriptor word. Since there were no 386s available yet and IBM XENIX 1.0 was bolted to the specific PC/AT models anyway, that did not pose practical problems to IBM’s customers. … The Pentium design was significantly different from the 386/486; it took the 286 XENIX lesson to heart and actively prevented programmers from setting reserved bits in control registers or page tables.“
Michal Necasek:IBM PC XENIX.(Blog)In:OS/2 Museum.26.Oktober 2012,abgerufen am 9.August 2026(englisch).
Michal Necasek:IBM XENIX: Two Steps Forward.(Blog)In:OS/2 Museum.16.März 2017,abgerufen am 9.August 2026(englisch):„Restrict the RAM size to 4MB. This old Xenix can’t handle much memory, and it probably wasn’t even possible to put more into the original PC/AT.“
