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IBM released documentation after the PC had been cloned through "clean room" reverse engineering.


Then the cloners moved at warp speed. According to Wikipedia, the PC AT shipped in 1984. For nostalgia, I kept my copy of IBM Personal Computer Hardware Reference Library Technical Reference, Pub #1502494.

"This manual describes the various units of the IBM Personal Computer AT and how they interact. It also has information about the basic input/output system (BIOS) and about programming support.

The information in this publication is for reference, and is intended for hardware and program designers, programmers, engineers, and anyone else who needs to understand the design and operation of the IBM Personal Computer AT."

It includes the source listing of the PC AT BIOS, as well as complete interface pinouts, etc.

The colophon for this manual reads

First Edition (March 1984)

So what is your time line for IBM only publishing this manual after the PC AT was cloned?


I was an early Compaq employee. The documentation produced by the research team was vetted for anything not descriptive of behavior, then forwarded through lawyers, who logged each document, to the engineering team designing Compaq's compatible BIOS from the functional specs. A weird side effect: the process reproduced BIOS-level bugs for complete compatibility.


The first IBM PC was publicly released for sale on August 12, 1981.

The first "100% Compatible" was the Compaq Portable in 1982. It wasn't the first "compatible" to market, but it claimed to be the first that hit the "100%" mark and validated the clone market.


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