Author Archives: Michal Necasek

Minor 387 Documentation Mystery

Posted on January 10, 2025 by Michal Necasek

So here I am, writing a bit of test code to figure out the behavior of x87 FPUs with regard to saving and loading the FPU state (FSTENV/FLDENV and FSAVE/FRSTOR instructions in different modes and formats). The original real-mode only … Continue reading →

Posted in Documentation, Intel, x87 | 6 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

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

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 | 44 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 | 12 Comments

OS/2 TCPBEUI Name Resolution

Posted on October 8, 2024 by Michal Necasek

Sometimes I have the following problem to deal with: An OS/2 system uses NetBIOS over TCP/IP (aka TCPBEUI) and should communicate with a SMB server (likewise using TCPBEUI) on a different subnet. This does not work on OS/2 out of … Continue reading →

Posted in IBM, Networking, OS/2, TCP/IP | 49 Comments

IBM PC 5150 Model Numbers

Posted on September 24, 2024 by Michal Necasek

Recently I came across a minor mystery—the model numbers of the original IBM PC. For such a pivotal product, there is remarkably little detailed original information from the early days. When IBM started selling the PC, it used two methods … Continue reading →

Posted in IBM, PC hardware, PC history | 25 Comments

OS/2 2.0 Commitments

Posted on September 23, 2024 by Michal Necasek

Last week the OS/2 Museum received a rather interesting donation: a thick spiral bound document titled Third party commitment to IBM’s OS/2 Version 2.0, and labeled IBM COMDEX/SPRING ’92. The binder is a collection of about 250 press releases that … Continue reading →

Posted in IBM, Marketing, OS/2, PC history | 8 Comments

OS/2 2.11 SMP Woes

Posted on September 8, 2024 by Michal Necasek

IBM OS/2 V2.11 for Symmetric Multiprocessing (OS/2 2.11 SMP) was released in mid-1994 in response to Windows NT and its SMP support. The package was nothing more (and nothing less) than OS/2 V2.11 with support for SMP hardware. It was … Continue reading →

Posted in IBM, OS/2, PC history, SMP | 31 Comments