Author Archives: Michal Necasek

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 | 1 Comment

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

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

A 100 Year Old Consul Typewriter?

Posted on January 9, 2026 by Michal Necasek

Spurred by a discussion about Polish keyboard layouts, I tried to find more about the history of Czech keyboard layouts. Unfortunately, finding actual documents turned out to be very difficult. What I did find is that prior to the current … Continue reading →

Posted in Computing History, Keyboard, Typewriter | 33 Comments

NetWare Pure IP on DOS

Posted on December 10, 2025 by Michal Necasek

It is fair to say that Novell struggled with moving from the IPX protocol to TCP/IP. Of course a big part of the problem was that IPX worked extremely well on LANs and IP brought absolutely no advantages for basic … Continue reading →

Posted in DOS, NetWare, Networking | 29 Comments

Wait here. No, wait here!

Posted on November 11, 2025 by Michal Necasek

While working on a hobby project, I set up an OS/2 MCP2 (Convenience Package 2 for OS/2 Warp 4) virtual machine with a debug kernel and an expectation that I’d reboot the VM a lot. I was disturbed to find … Continue reading →

Posted in Bugs, Debugging, OS/2 | 6 Comments

The OS/2 Display Driver Zoo

Posted on October 14, 2025 by Michal Necasek

I have recently explored (again) the possibility of writing a high-res display driver for virtualized OS/2. But I ran (again) into a dizzying array of possible solutions, each with its own advantages and a good deal of drawbacks. OS/2 display … Continue reading →

Posted in Development, Documentation, Graphics, IBM, OS/2 | 31 Comments

Messy Mastering

Posted on September 29, 2025 by Michal Necasek

Large companies like IBM, Microsoft, or Novell typically had a well defined process for releasing software on floppies. More often than not, files were not directly copied onto a physical floppy; instead, a tool was used to create an image … Continue reading →

Posted in Archiving, Floppies, IBM, Kryoflux | 20 Comments