Category Archives: Development

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 | 12 Comments

Time Trouble

Posted on March 7, 2025 by Michal Necasek

Last Friday I had a moment of panic. While investigating why different run-time libraries might interpret file timestamps differently, I noticed that even Windows doesn’t always agree with itself. When was dos4gw.exe last modified, at 10:14 PM or 9:14 PM? … Continue reading →

Posted in Bugs, Development, Microsoft | 20 Comments

Learn Something Old Every Day, Part XIV: read() Return Value May Surprise

Posted on February 25, 2025 by Michal Necasek

Last week I amused myself by porting some source code from Watcom C to Microsoft C. In general that is not difficult, because Watcom C was intended to achieve a high degree of compatibility with Microsoft’s C dialect. Yet one … Continue reading →

Posted in C, Development | 11 Comments

I Thought I Found a Bug…

Posted on December 25, 2024 by Michal Necasek

So I was working on improving a DOS emulator, when I found that something seemingly trivial wasn’t working right when COMMAND.COM was asked to do the following: echo AB> foo.txtecho CD>> foo.txt Instead of ABCD, foo.txt contained ABBC. I verified … Continue reading →

Posted in Bugs, C, Development, Watcom | 25 Comments

Stack Checking on OS/2

Posted on November 19, 2024 by Michal Necasek

A while ago I was involved in debugging a seemingly simple yet mysterious problem: A piece of code (a fairly simple interface DLL) built with the Open Watcom compiler was failing with a bogus stack overflow error. The mystery was … Continue reading →

Posted in Debugging, Development, OS/2, Watcom | Leave a comment

Programming NetBIOS on OS/2

Posted on October 23, 2024 by Michal Necasek

Recently I spent some time trying to understand a piece of networking code, and it turned out to be far more difficult than it should have been. The code in question is the NetBIOS interface of C-Kermit and was originally … Continue reading →

Posted in Development, Documentation, IBM, Microsoft, Novell, OS/2 | 25 Comments

Learn Something Old Every Day, Part XII: Strange File Resizing on DOS

Posted on June 7, 2024 by Michal Necasek

Someone recently asked an interesting question: Why do Microsoft C and compatible DOS compilers have no truncate() and/or ftruncate() library functions? And how does one resize files on DOS? OK, that’s actually two questions. The first one is easy enough … Continue reading →

Posted in Computing History, CP/M, Development, Documentation, DOS, Microsoft | 29 Comments

Learn Something Old Every Day, Part XI: DOS Directory Searches are Bizarre

Posted on May 7, 2024 by Michal Necasek

A while ago I started playing with EMU2, a piece of software which calls itself “A simple text-mode x86 + DOS emulator”. It is indeed relatively simple, only emulating an 8086 (or maybe 80186, with little bits of 80286 here … Continue reading →

Posted in Development, DOS, Undocumented | 53 Comments

How Not To Release Historic Source Code

Posted on April 26, 2024 by Michal Necasek

This is how to not do it: GitHub Don’t get me wrong, it’s absolutely brilliant that Microsoft was able to release a fairly complete (minus DOSSHELL) source code for MS-DOS 4.00 or 4.01 (see below). As much as it was … Continue reading →

Posted in Development, DOS, Source code | 83 Comments

Tarbell to Cromemco

Posted on January 23, 2024 by Michal Necasek

While playing around with old versions of 86-DOS, I came across a disk image of 86-DOS 1.14. I ran the older 86-DOS versions in the SIMH simulator which can emulate the Cromemco disk controller supported by 86-DOS. Unfortunately the 86-DOS … Continue reading →

Posted in Development, DOS, PC history | 16 Comments