Category Archives: DOS

Learn Something Old Every Day, Part XVI: DOS 4.0 SELECT Is Too Clever

Posted on July 2, 2025 by Michal Necasek

A while ago I discovered an antique pirated copy of IBM DOS 4.00 on 5.25″ media, which was something that was missing in my archive. And by antique I mean from August 1988, when DOS 4.0 was practically brand new. … Continue reading →

Posted in Archiving, DOS, IBM, PC history | Leave a comment

Where Did CP852 Come From Again?

Posted on June 27, 2025 by Michal Necasek

An earlier article explored the history of codepage 852 (Latin-2 PC codepage) in released and pre-release versions of DOS and OS/2. At the time of this writing (June 2025), the earliest OS/2 build with some form of CP852 support including … Continue reading →

Posted in DOS, I18N, IBM, PC history | 24 Comments

Learn Something Old Every Day, Part XV: KEYB Is Half of Keyboard BIOS

Posted on June 16, 2025 by Michal Necasek

Recently I had an opportunity to reacquaint myself with the DOS KEYB utility. KEYB is interesting in that it is designed primarily for international users, but one can also run KEYB US to load KEYB with standard US layout. It … Continue reading →

Posted in BIOS, DOS, IBM, Keyboard | 10 Comments

1989 Networking: 3+Open LAN Manager 1.1

Posted on June 4, 2025 by Michal Necasek

The previously mentioned warez dump on archive.org contains a lot of little gems that would have been otherwise lost. One of those might be 3Com’s networking package from 1989, the 3+Open LAN Manager version 1.1. The software was released in … Continue reading →

Posted in 386MAX, 3Com, DOS, LAN Manager, Microsoft, Networking, OS/2 | 15 Comments

Compaq EXTDISK.SYS

Posted on April 16, 2025 by Michal Necasek

This is a follow-up to a previous post about the curious driver in Microsoft OS/2 1.21. After initially writing the article, additional information came to light, explaining why the code was there. In summer 1988, Compaq released the Deskpro 386/25, … Continue reading →

Posted in Bugs, Compaq, DOS, PC history, Storage | 32 Comments

Learn Something Old Every Day, Part XIII: InDOS Is Not Enough

Posted on February 12, 2025 by Michal Necasek

The other day I spent a while trying to understand the purpose of a rather strange looking piece of code inside Borland’s THELP.COM utility shipped with Turbo Pascal 6.0 (THELP.COM was misbehaving under emulated DOS). The THELP utility performs the … Continue reading →

Posted in DOS, PC history, Undocumented | 14 Comments

The Other Three

Posted on January 2, 2025 by Michal Necasek

A previous blog post explored the semi-mysterious yet sometimes highly useful DOS APPEND command. Now it’s time to look at its relatives: ASSIGN, JOIN, and SUBST. ASSIGN ASSIGN is the oldest of the bunch. It was written by IBM and … Continue reading →

Posted in DOS, IBM, PC history | 13 Comments

DOS APPEND

Posted on December 20, 2024 by Michal Necasek

For a long time, I couldn’t quite grasp what the DOS APPEND command could possibly be good for. Until I came across a situation which APPEND was made for. When I worked on organizing and building the DOS 2.11 source … Continue reading →

Posted in DOS, IBM | 46 Comments

Who Knew What When

Posted on June 28, 2024 by Michal Necasek

When Microsoft released the unique early beta build of Multitasking DOS 4, I quickly found out that it does not run in VirtualBox: This was a bit of a surprise, because the more-or-less released versions of Multitasking DOS 4 from … Continue reading →

Posted in 286, DOS, IBM, Microsoft, PC architecture, PC history, VirtualBox | 31 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