Author Archives: Michal Necasek

OS/2 2.0, Spring ’91 Edition

Posted on July 10, 2018 by Michal Necasek

Thanks to a generous reader, a curiously nondescript box labeled “OS/2 32-Bit Pre-release” recently turned up at the OS/2 Museum. The box looks very much like retail IBM products from the early 1990s, but has no identifying description except for … Continue reading →

Posted in IBM, Microsoft, OS/2, PC history, Pre-release | 35 Comments

ANOMALY: meaningless REX prefix used

Posted on June 20, 2018 by Michal Necasek

While trying to get work done, I was confronted by several disturbing messages printed on the console of a 64-bit Windows 7 system: [0x7FEEFEFAAA0] ANOMALY: meaningless REX prefix used [0x7FEEFEE48C0] ANOMALY: meaningless REX prefix used [0x7FEEFEE54B0] ANOMALY: meaningless REX prefix used This … Continue reading →

Posted in Bugs, Debugging | 9 Comments

A Brief History of Unreal Mode

Posted on June 15, 2018 by Michal Necasek

After a run-in with a particularly crazy manifestation of unreal mode (Flat Assembler, or fasm), I decided to dig deeper into the history of this undocumented yet very widely used feature of 32-bit x86 processors. For the purposes of this … Continue reading →

Posted in 386, Corrections, Microsoft, PC history, Undocumented | 47 Comments

USB 0.9

Posted on June 2, 2018 by Michal Necasek

A couple of months ago I lamented the fact that historic USB documentation appears to have vanished from the face of the Earth. Today I finally found one such document, the USB 0.9 specification from April 13, 1995, published almost … Continue reading →

Posted in Documentation, PC history, USB | 30 Comments

Troubled Time

Posted on May 30, 2018 by Michal Necasek

This is not an article about current affairs Over the last few weeks, I had several interesting run-ins with time, specifically how time is represented and processed by computers. Deep down it’s really all about a clash of human culture … Continue reading →

Posted in Bugs, PC history, Random Thoughts | 18 Comments

A Word on the CALL 5 Spell

Posted on May 26, 2018 by Michal Necasek

After years of searching for some reasonably widespread DOS application which used the CP/M-style CALL 5 interface and coming up with absolutely nothing, Jeff Parsons of pcjs.org found one: None other than Microsoft Word, specifically the spell checker in the … Continue reading →

Posted in DOS, Microsoft, PC history | 10 Comments

ICEBP Finally Documented

Posted on May 25, 2018 by Michal Necasek

After more than 30 years, Intel finally documented the INT1 instruction, also known as ICEBP (opcode F1h), in the latest (May 2018, -067) edition of the SDM. This was probably forced by security concerns, because from a security standpoint, having … Continue reading →

Posted in 386, Documentation, Intel, Undocumented | 14 Comments

SpaceMaker Update

Posted on May 17, 2018 by Michal Necasek

Jeff Parsons has been able to locate an executable compressed with Realia SpaceMaker which significantly pre-dates all hitherto known SpaceMaker or EXEPACK survivors. It’s an editor called DVED.COM version 6.02, found on disk 191 of the PC-SIG Library 8th Edition … Continue reading →

Posted in PC history | 10 Comments

Realia SpaceMaker

Posted on April 30, 2018 by Michal Necasek

A recent exploration of Microsoft’s EXEPACK posed the question whether EXEPACK was the first executable compressor, at least in the world of PCs. It wasn’t. That distinction almost certainly belongs to Realia SpaceMaker, which was probably released sometime in late … Continue reading →

Posted in Compression, Development, PC history | 13 Comments

Undocumented RDTSC

Posted on April 27, 2018 by Michal Necasek

The other day I wrote a simple DOS program which used the RDTSC instruction in order to obtain precise time measurements (of how long it takes a PS/2 keyboard to send data; more about that some other time). The 16-bit … Continue reading →

Posted in Documentation, Intel, Pentium | 15 Comments