Category Archives: Development

The Strange Case of GetEnvironmentStringsA

Posted on May 22, 2022 by Michal Necasek

It was recently pointed out to me that a simple “hello world” style application built with Open Watcom C/C++ 1.9 does not run on Win32s version 1.30, even though the same executable runs just fine on Windows NT 3.51, Windows … Continue reading →

Posted in Development, NT, Watcom | 21 Comments

Reconstructing the EGA BIOS

Posted on March 19, 2022 by Michal Necasek

A few weeks ago I had a sudden need to understand certain finer points of the operation of EGA/VGA BIOS. I found common reference materials to be inadequate—they tend to do a good job of documenting the data structures the … Continue reading →

Posted in BIOS, Development, Documentation, Graphics, IBM, PC history | 32 Comments

XMVM Surgery

Posted on February 11, 2022 by Michal Necasek

Last week I was prompted to take a look at the Intel Code Builder compiler from 1991, a 32-bit compiler targeting 386 extended DOS and shipping with its own DOS extender. It is what one might call an extremely obscure … Continue reading →

Posted in 386, Development, Intel, PC history, Software Hacks | 10 Comments

Unidentified PC DOS 1.1 Boot Sector Junk Identified

Posted on January 7, 2022 by Michal Necasek

Anyone trying to disassemble the PC DOS 1.1 boot sector soon notices that at offsets 1A3h through 1BEh there is a byte sequence that just does not belong. It appears to be a fragment of code, but it has no … Continue reading →

Posted in Development, DOS, PC history | 24 Comments

DOS 2.11 From Scratch

Posted on September 21, 2021 by Michal Necasek

Warning: Long post! After having good luck with rebuilding core PC DOS 1.1 from source code, I thought I’d do the same with the DOS 2.11 source code released by the CHM. What follows is largely a collection of notes … Continue reading →

Posted in Development, DOS, Microsoft, PC history | 42 Comments

PC DOS 1.1 From Scratch

Posted on September 10, 2021 by Michal Necasek

A number of years ago, the Computer History Museum together with Microsoft released the source code for MS-DOS 1.25 (very close to PC DOS 1.1) and MS-DOS 2.11. I never did anything with it beyond glancing at the code, in … Continue reading →

Posted in Development, DOS, Microsoft, PC history | 24 Comments

Learn Something Old Every Day, Part III

Posted on September 8, 2021 by Michal Necasek

As part of a hobby project, I set out to reconstruct assembly source code that should be built with an old version of MASM and exactly match an existing old binary. In the process I learned how old MASM versions … Continue reading →

Posted in Assembler, Development, Microsoft, PC history | 11 Comments

PC-86-DOS

Posted on September 3, 2021 by Michal Necasek

A number of years ago, an 8″ disk containing Seattle Computer Products (SCP) 86-DOS 1.0 was successfully imaged. The newest files on the disk are dated April 30, 1981, making the disk the oldest complete release of what was soon … Continue reading →

Posted in Development, DOS, IBM, PC history | 18 Comments

MS LAN Manager NDDK Anyone?

Posted on April 2, 2021 by Michal Necasek

For R&D purposes, I would very much like to get my hands on the circa 1991 Microsoft LAN Manager Network Device Driver Kit which was meant to support the development of NDIS 2.0 drivers. While it is obvious that some … Continue reading →

Posted in Development, DOS, Microsoft, Networking, OS/2 | 10 Comments

Complications, Complications

Posted on February 19, 2021 by Michal Necasek

The other day someone asked how hard it would be to modify the Open Watcom linker, wlink, to properly support exports from IOPL segments in OS/2 LX modules. Not terribly hard it turned out, all it needed was to emit … Continue reading →

Posted in Development, OS/2, Watcom | 2 Comments