Category Archives: Development

Reconstructing the EGA BIOS

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 | 26 Comments

XMVM Surgery

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

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 | 23 Comments

DOS 2.11 From Scratch

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 | 26 Comments

PC DOS 1.1 From Scratch

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 | 18 Comments

Learn Something Old Every Day, Part III

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

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 | 11 Comments

MS LAN Manager NDDK Anyone?

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 | 9 Comments

Complications, Complications

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

How Old Is OMF?

The Object Module Format (OMF), used by most DOS development tools, and eventually displaced by COFF/ELF in the 32-bit world, is quite old. It is a somewhat strange format because of its age, and it is quite complex, both because … Continue reading

Posted in Development, Intel, Microsoft, PC history, x86 | 8 Comments