Author Archives: Michal Necasek

Learn Something Old Every Day, Part XXI: VGA Memory Access Is Complicated

Posted on May 8, 2026 by Michal Necasek

Last week I had another run-in with VGA emulation, and like last time, the cause was very likely the generally woefully inadequate VGA documentation. The VGA is not, all things considered, a particularly complicated piece of hardware. It has no … Continue reading →

Posted in Documentation, LSOED, VGA | 11 Comments

ICAT and Watcom

Posted on May 7, 2026 by Michal Necasek

Some time ago I embarked on a minor retro development project related to this post. For convenience, I decided to do the development on a Windows host machine and (obviously) test in a VM. For C code compiling, and linking, … Continue reading →

Posted in Debugging, Development, IBM, OS/2, Watcom | 16 Comments

When Networking Doesn’t Work

Posted on May 4, 2026 by Michal Necasek

Last week I spent far too much time trying to get my Windows 11 machine to talk to an antique Tyan SMDC (Server Management Daughter Card) IPMI module over the network. At first, I tried Tyan’s own old TSO (Tyan … Continue reading →

Posted in Bugs, Intel, IPMI, Networking, PC hardware, TCP/IP | 2 Comments

Learn Something Old Every Day, Part XX: 8087 Emulation on 8086 Systems

Posted on April 24, 2026 by Michal Necasek

Not too long ago I had a need and an opportunity to re-acquaint myself with the mechanism used for software emulation of the 8087 FPU on 8086/8088 machines. As mentioned elsewhere, the 8086 CPU (1978) had a generic co-processor interface … Continue reading →

Posted in 8086/8088, Development, Intel, LSOED, Microsoft, x87 | 20 Comments

Learn Something Old Every Day, Part XIX: Athlon XP May Be Athlon MP

Posted on April 20, 2026 by Michal Necasek

Quite a while ago, I acquired a dual-socket (Socket 462 aka Socket A) board for the Athlon MP, AMD’s first entry into the multi-processor/multi-socket market. Over the course of several years, I spent quite some time searching for the board … Continue reading →

Posted in AMD, K7, LSOED, PC hardware, PC history | 8 Comments

Mystery CPUID Bit

Posted on April 17, 2026 by Michal Necasek

Yesterday I had the opportunity to test a recently acquired Athlon 1200 CPU (Thunderbird core, ceramic PGA package). I dreaded the first boot-up attempt because I have had rather bad experience with slightly newer Palomino and Thoroughbred OPGA processors—a surprisingly … Continue reading →

Posted in AMD, K7, PC hardware, Undocumented | 20 Comments

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, LSOED, x86, x87 | 39 Comments

Bitfield Pitfalls

Posted on March 20, 2026 by Michal Necasek

Some time ago I ran into a bug that had been dormant for some time. The problem involved expressions where one of the operands is a bit-field. To demonstrate the problem, I will present a reduced example: #include <stdio.h> #include … Continue reading →

Posted in C, Development, Standards | 4 Comments

DOS Memory Management

Posted on February 27, 2026 by Michal Necasek

The memory management in DOS is simple, but that simplicity may be deceptive. There are several rather interesting pitfalls that programming documentation often does not mention. DOS 1.x (1981) had no explicit memory management support. It was designed to run … Continue reading →

Posted in Development, DOS, Microsoft, PC history | 25 Comments

Cracking DXP and SXD

Posted on January 16, 2026 by Michal Necasek

There are situations where software is available only in the form of a floppy image. This goes especially for historic hardware drivers and patches, which were often distributed only in the form of floppy images. This method was quite popular … Continue reading →

Posted in Archiving, Development, Floppy Images | 4 Comments