Author Archives: Michal Necasek

Troubled Time

Posted on May 30, 2018 by Michal Necasek

This is not an article about current affairs Over the last few weeks, I had several interesting run-ins with time, specifically how time is represented and processed by computers. Deep down it’s really all about a clash of human culture … Continue reading →

Posted in Bugs, PC history, Random Thoughts | 19 Comments

A Word on the CALL 5 Spell

Posted on May 26, 2018 by Michal Necasek

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

ICEBP Finally Documented

Posted on May 25, 2018 by Michal Necasek

After more than 30 years, Intel finally documented the INT1 instruction, also known as ICEBP (opcode F1h), in the latest (May 2018, -067) edition of the SDM. This was probably forced by security concerns, because from a security standpoint, having … Continue reading →

Posted in 386, Documentation, Intel, Undocumented | 14 Comments

SpaceMaker Update

Posted on May 17, 2018 by Michal Necasek

Jeff Parsons has been able to locate an executable compressed with Realia SpaceMaker which significantly pre-dates all hitherto known SpaceMaker or EXEPACK survivors. It’s an editor called DVED.COM version 6.02, found on disk 191 of the PC-SIG Library 8th Edition … Continue reading →

Posted in PC history | 10 Comments

Realia SpaceMaker

Posted on April 30, 2018 by Michal Necasek

A recent exploration of Microsoft’s EXEPACK posed the question whether EXEPACK was the first executable compressor, at least in the world of PCs. It wasn’t. That distinction almost certainly belongs to Realia SpaceMaker, which was probably released sometime in late … Continue reading →

Posted in Compression, Development, PC history | 13 Comments

Undocumented RDTSC

Posted on April 27, 2018 by Michal Necasek

The other day I wrote a simple DOS program which used the RDTSC instruction in order to obtain precise time measurements (of how long it takes a PS/2 keyboard to send data; more about that some other time). The 16-bit … Continue reading →

Posted in Documentation, Intel, Pentium | 15 Comments

The A20-Gate Fallout

Posted on April 13, 2018 by Michal Necasek

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

Any Readers in Central Italy?

Posted on April 6, 2018 by Michal Necasek

This is a very long shot, but maybe someone can help me. I’d very much like to buy a piece of used electronics for sale in Italy (L’Aquila province). Unfortunately the seller requires a local pick-up. I don’t live exactly … Continue reading →

Posted in Random Thoughts | 3 Comments

EXEPACK and the A20-Gate

Posted on March 23, 2018 by Michal Necasek

In 1991, DOS 5.0 brought about what’s perhaps the most common manifestation of A20 control trouble… Packed file is corrupt Microsoft published a KB article about this infamous error, but its author clearly did not understand the true cause of the … Continue reading →

Posted in Bugs, Microsoft, PC history | 19 Comments

The A20-Gate: It Wasn’t WordStar

Posted on March 16, 2018 by Michal Necasek

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