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Search Results for: "call 5"
A Word on the CALL 5 Spell
After years of searching for some reasonably widespread DOS application which used the CP/M-style CALL 5 interface and coming up with absolutely nothing, Jeff Parsons of pcjs.org found one: None other than Microsoft Word, specifically the spell checker in the … Continue reading
Posted in DOS, Microsoft, PC history
10 Comments
The A20-Gate Fallout
A recent post explored the motivation (i.e. backwards compatibility) to implement the A20 gate in the IBM PC/AT. To recap, the problem IBM solved was the fact that 1MB address wrap-around was an inherent feature of the Intel 8086/8088 CPU, … Continue reading
Posted in IBM, Microsoft, PC architecture, PC history
93 Comments
The A20-Gate: It Wasn’t WordStar
Although WordStar was long suspected to be the reason (or at least one of the major reasons) for implementing the A20 gate hardware on the PC/AT and all the associated problems later on, it is now all but certain that … Continue reading
Posted in 286, IBM, Microsoft, PC history, WordStar
37 Comments
WordStar Again
While trying to work on my DOS 5.0 article, I looked at DOS 5.0 build 224 from June 1990, which is the oldest surviving beta of DOS 5.0. And the README contains the following intriguing text, which reminded me of … Continue reading
Posted in DOS, PC history, WordStar
74 Comments
86-DOS Was an Original
In case it wasn’t sufficiently obvious already: A forensic expert now confirmed that 86-DOS, née QDOS, and (by extension) MS-DOS were not copies of CP/M, either on source or binary level. This comes hardly as a surprise, despite years (nay, … Continue reading
Posted in DOS, Microsoft, PC history
6 Comments
Another witness against WordStar
Previous posts examined the question why IBM implemented the A20 hardware in the PC/AT, causing endless headaches to future PC hardware and software developers. WordStar emerged as a possible culprit, but no one would quite point the finger at it. … Continue reading
Posted in DOS, PC history, WordStar
17 Comments
WordStar needs address wraparound?
The CP/M compatible interface in DOS was initially documented, later forgotten, and then re-discovered every once in a while. In 1989, John Switzer described parts of the CALL 5 system call interface mechanism in a slightly hysterical article as a “back … Continue reading
Posted in DOS, PC architecture, WordStar
11 Comments
Who needs the address wraparound, anyway?
The infamous A20 gate is well known and documented in hair-raising detail. What’s much less well documented is the real purpose of the A20 gate, that is, who actually needs the 8086 address wrap-around to be emulated in the first … Continue reading
Posted in DOS, PC architecture
4 Comments