Author Archives: Michal Necasek

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 | 32 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

8×19 Text Mode Font Origins

Posted on August 15, 2025 by Michal Necasek

I was recently made aware of something that I had noticed before, but never paid much attention to. Consider this screenshot of a BIOS POST screen: VGA text modes usually use 720×400 resolution and 8×16 fonts (expanded to 9×16). The … Continue reading →

Posted in BIOS, Computing History, Intel | 39 Comments

More than Two Hard Disks in DOS

Posted on July 22, 2025 by Michal Necasek

Investigating the rather odd behavior of the Microsoft OS/2 1.21 disk driver led me to Compaq and their EXTDISK.SYS driver. While experimenting with various setups, I realized that DOS versions older than 5.0 do not support more than two hard … Continue reading →

Posted in Bugs, Compaq, DOS, Microsoft, PC history | 84 Comments

Learn Something Old Every Day, Part XVII: DHCP and ARP Don’t Mix in WSA SMP

Posted on July 19, 2025 by Michal Necasek

I just spent an inordinate amount of time debugging a VM running OS/2 Warp Server Advanced SMP (WSA SMP). The VM was working fine (except for sometimes hanging very early during boot, a known issue with the SMP kernel), but … Continue reading →

Posted in Bugs, IBM, LSOED, Networking, OS/2, TCP/IP | 3 Comments