Category Archives: PC history

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

First Dual-Channel IDE?

The OS/2 Museum recently came into possession of what may be the first adapter with support for two IDE channels… sort of: The adapter was made by Plus Development Corporation, a subsidiary of the disk maker Quantum. This particular specimen … Continue reading

Posted in IDE, PC hardware, PC history, Quantum | 29 Comments

The Secret History of ATAPI

The other day I asked myself a seemingly trivial question: What was the first ATAPI CD-ROM drive and when was it available? Given that ATAPI was a major technology which instantly obsoleted all proprietary CD-ROM interfaces and made SCSI much … Continue reading

Posted in CD-ROM, PC history, Standards, Undocumented | 55 Comments

Looking for High Sierra

Some time ago, I thought it would be useful to understand exactly what is the difference between CD-ROMs recorded in the old High Sierra format versus the ISO 9660 standard. This was in part spurred by the fact that I … Continue reading

Posted in CD-ROM, Documentation, PC history | 23 Comments

Deeper Into ATA History

While looking for something completely unrelated (namely the Rock Ridge extensions to ISO 9660), I came across a cache of old X3T9 committee documents from 1990. In retrospect I’m a little surprised that I hadn’t found these earlier, since the … Continue reading

Posted in IDE, PC history, Standards | 17 Comments

Weird Tales

While researching various aspects of the history of computing, sometimes I come across what can best be described as “weird tales” — unsourced claims that sound interesting but are either provably wrong or there’s no evidence to support them. In … Continue reading

Posted in IBM, Microsoft, PC history, PC press | 22 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 | 21 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