Author Archives: Michal Necasek

How to Void Your Valuable Warranty

Posted on January 12, 2018 by Michal Necasek

Try installing Quick Pascal 1.0 on DR DOS 3.40: What is going on there? It’s a long story… In 1988, Microsoft became increasingly worried by a new upstart OS from an old rival, DR DOS. Over the years, Digital Research … Continue reading →

Posted in Digital Research, DOS, Microsoft | 47 Comments

There’s Another Possibility

Posted on January 2, 2018 by Michal Necasek

Four years ago we pondered why on Earth a DOS floppy boot sector might start with 69h, supposedly a “direct jump” opcode. Which is the IMUL instruction on 80186 and later, and not documented on 8086. In the meantime, it … Continue reading →

Posted in DOS, Floppies | 57 Comments

AMD64 APM Archive Online

Posted on December 29, 2017 by Michal Necasek

Thanks to Konstantin Belousov, the OS/2 Museum AMD64 APM (Architecture Programmer’s Manual) is now available online. Big thanks to blog readers who recently supplied several missing revisions of the documents. This is a nearly complete archive of all published AMD64 … Continue reading →

Posted in AMD, AMD64, Documentation | 2 Comments

Undocumented 8086 Opcodes, Part I

Posted on December 27, 2017 by Michal Necasek

This is a guest post by Raúl Gutiérrez Sanz This multi-part document is about undocumented 8086 processor opcodes and their behavior. Most of the document will likely apply to the 8088 processor as well, but this has not been verified. … Continue reading →

Posted in 8086/8088, Intel, Undocumented | 13 Comments

How Fast Again?

Posted on December 27, 2017 by Michal Necasek

Or, Yet Another Wikipedia Mystery Looking for something on the Wikipedia USB page, a detail caught my eye. In the version history section, both the table and the text claim that the original 1996 USB 1.0 specification defined 1.5 Mbps … Continue reading →

Posted in Documentation, USB | 38 Comments

AMD64 Manual Vol. 3 Rev. 3.24 Anyone?

Posted on December 24, 2017 by Michal Necasek

AMD tricked me. After not updating anything for months, they updated the AMD64 documentation and not only that, they updated Volume 3 (instruction reference) twice within a few weeks. First to revision 3.24 in November, then 3.25 in December. I … Continue reading →

Posted in AMD, Documentation | 3 Comments

How Apple Created Hackintosh, Part II

Posted on December 20, 2017 by Michal Necasek

There is every indication that throughout the early 2000s, Apple internally built and ran all of OS X on x86 PCs (it’s also something Steve Jobs himself mentioned in 2005). Otherwise why would Apple have x86 drivers for AC’97 audio … Continue reading →

Posted in Apple, Intel, OS X, PC history, Pre-release | 11 Comments

HTT Means Hyper-Threading, Right?

Posted on December 11, 2017 by Michal Necasek

In a logical, ordered world, the HTT bit in CPUID would indicate a processor with Hyper-Threading Technology enabled. But of course the world with Intel inside is anything but logical. The actual meaning of the HTT bit changed several times … Continue reading →

Posted in Documentation, Intel, Pentium 4 | 13 Comments

How Apple Created Hackintosh, Part I

Posted on November 29, 2017 by Michal Necasek

At a developer conference in June 2005, Apple announced that OS X will transition from PowerPC to Intel processors. The first Intel Macs (sometimes nicknamed “Mactels”) were introduced several months later, in January 2006. The announcement generated significant interest in … Continue reading →

Posted in Apple, Intel, PC history, Pre-release | 10 Comments

MS KB Articles

Posted on October 17, 2017 by Michal Necasek

A recent blog post over at pcjs.org explores some of the mysteries surrounding information that at one point or another was published as a Microsoft KnowledgeBase article (or a KB article for short). It’s not entirely clear where the KB … Continue reading →

Posted in Documentation, Microsoft, PC history | 17 Comments