Category Archives: 286

Learn Something Old Every Day, Part XVIII: How Does FPU Detection Work?

Posted on March 28, 2026 by Michal Necasek

This post ended up being much longer than originally intended because halfway into writing it, I found that 286 and later CPUs don’t behave the way I had assumed they would… While investigating a bug related to a program using … Continue reading →

Posted in 286, 8086/8088, x86, x87 | 34 Comments

Missing XENIX Disks

Posted on July 22, 2024 by Michal Necasek

The previously mentioned warez mega dump contains disk images of SCO 286 XENIX 2.1.0. The release appears to be from February 1986. It is the oldest SCO 286 XENIX release that I know of. But there’s a hitch. The warez … Continue reading →

Posted in 286, Archiving, SCO, Xenix | 34 Comments

Who Knew What When

Posted on June 28, 2024 by Michal Necasek

When Microsoft released the unique early beta build of Multitasking DOS 4, I quickly found out that it does not run in VirtualBox: This was a bit of a surprise, because the more-or-less released versions of Multitasking DOS 4 from … Continue reading →

Posted in 286, DOS, IBM, Microsoft, PC architecture, PC history, VirtualBox | 31 Comments

Xenix 2.2 vs. VGA

Posted on April 15, 2022 by Michal Necasek

The other day I started wondering why certain old versions of 286 and 386 XENIX look a bit weird in emulation: The characters are cut off, because XENIX sets up an EGA text mode with 8×14 character matrix but uses … Continue reading →

Posted in 286, 386, PC architecture, PC history, VGA, Xenix | 14 Comments

1987 Networking: ELS NetWare 286 Level I 2.0a

Posted on January 24, 2020 by Michal Necasek

A rare find recently turned up: NetWare from 1987, specifically the low-end ELS variant of NetWare 286 version 2.0a (ELS may be claimed to mean Entry Level System or maybe Entry Level Server, but at least originally it stood for … Continue reading →

Posted in 286, 3Com, Kryoflux, NetWare, Networking | 29 Comments

Another Strange 286 Board

Posted on January 20, 2020 by Michal Necasek

The OS/2 Museum sometimes seems to have a knack for acquiring hardware so obscure that it cannot be even identified. One of the more recent arrivals was a seemingly typical Baby AT 286 board with an 8 MHz CPU. The … Continue reading →

Posted in 286, PC hardware, PC history | 28 Comments

FasterModeSwitch: Is It Really?

Posted on October 31, 2018 by Michal Necasek

Short answer: Yes. Before launching into the long answer, let’s recap what it even is. FasterModeSwitch is a SYSTEM.INI setting in Windows 3.1 which applies only to Standard (286) mode and can therefore be found in the [standard] section of … Continue reading →

Posted in 286, BIOS, Microsoft, Windows | 14 Comments

The A20-Gate: It Wasn’t WordStar

Posted on March 16, 2018 by Michal Necasek

Although WordStar was long suspected to be the reason (or at least one of the major reasons) for implementing the A20 gate hardware on the PC/AT and all the associated problems later on, it is now all but certain that … Continue reading →

Posted in 286, IBM, Microsoft, PC history, WordStar | 37 Comments

SGDT/SIDT Fiction and Reality

Posted on May 4, 2017 by Michal Necasek

PSA: Actual hardware behavior takes precedence over vendor documentation. Or, as they say… trust but verify. A reader recently complained how Intel and AMD do not implement the SGDT and SIDT instructions the same way. AMD documentation states that these … Continue reading →

Posted in 286, 386, AMD, Documentation, Intel | 39 Comments

There’s More to the 286 XENIX Story

Posted on March 22, 2017 by Michal Necasek

It turns out that there is a rather interesting story behind the 286 XENIX incompatibility with 386 and later processors. Here’s roughly what happened in chronological order. In 1982, Intel released the iAPX 286 processor, later known as the 80286 or simply 286. This … Continue reading →

Posted in 286, 386, Intel, Microsoft | 43 Comments