Category Archives: Documentation

USB 0.9

Posted on June 2, 2018 by Michal Necasek

A couple of months ago I lamented the fact that historic USB documentation appears to have vanished from the face of the Earth. Today I finally found one such document, the USB 0.9 specification from April 13, 1995, published almost … Continue reading →

Posted in Documentation, PC history, USB | 30 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

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

Frequently Given Misleading Answers

Posted on February 21, 2018 by Michal Necasek

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

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

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 | 36 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

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

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

SGDT/SIDT Fiction and Reality

Posted on May 4, 2017 by Michal Necasek

PSA: Actual hardware behavior takes precedence over vendor documentation. Or, as they say… trust but verify. A reader recently complained how Intel and AMD do not implement the SGDT and SIDT instructions the same way. AMD documentation states that these … Continue reading →

Posted in 286, 386, AMD, Documentation, Intel | 39 Comments