Author Archives: Michal Necasek

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 | 59 Comments

Any Readers in Central Italy?

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

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 | 14 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 | 36 Comments

Making The Simpsons Sing

The talk is, in case it wasn’t clear, about the Kurzweil VGM MIDI synthesizer board. The two larger synthesizer chips are named Homer and Marge, and the three smaller ROM chips are Bart, Lisa, and Maggie. The VGM looks a lot … Continue reading

Posted in E-mu, Kurzweil, MIDI, Sound | 2 Comments

Pascal Out Of Memory

Suppose you want to run the original 1981 vintage IBM Pascal 1.0 (supplied by Microsoft) on a PC that is less than 30 years old. Upon execution, PAS1.EXE may well fail with the following error: Error: Compiler Out Of Memory … Continue reading

Posted in Bugs, Corrections, IBM, Microsoft, PC history | 40 Comments

Frequently Given Misleading Answers

The other day I came across this FGA item describing how to detect virtualized environments. It includes interesting comments which make Microsoft, Intel, and AMD sound stupid, but perhaps only reflect on the author being either deliberately misleading, or trying … Continue reading

Posted in Corrections, Documentation, Virtualization | 9 Comments

Dumping Ensoniq Soundscape ROMs

Let us posit that one has a need to obtain an image of the instrument ROM of an Ensoniq Soundscape S-2000, Elite, or OPUS sound card. There are two basic approaches: A) Desolder or cut off the ROM chip, plug … Continue reading

Posted in Ensoniq, Software Hacks, Sound Blaster | 5 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


For several years now I’ve been trying to continue the DOS history series and write (or rather finish) a DOS 5 page. While tracing the history of DOS 1.0 or 2.0 is quite difficult and the amount of source material … Continue reading

Posted in DOS, PC history, Random Thoughts | 12 Comments