Category Archives: x86

Better Late Than Never

Posted on May 30, 2016 by Michal Necasek

Better late than never, although in this instance, it’s really really late—about thirty years late. In the world of computing, that is eternity. The talk is about the new CR4.UMIP control bit documented in the latest (revision 58) Intel SDM, … Continue reading →

Posted in 286, Intel, x86 | 11 Comments

Curious Instructions

Posted on December 13, 2014 by Michal Necasek

Years ago, Geoff Chappell (the author of DOS Internals, among other things) published an article about mysterious instructions that Microsoft’s LINK knows but Intel’s documentation is silent about. The fourteen listed instructions were: LOADALL, CFLSH, WRECR, RDECR, SVDC, RSDC, SVLDT, … Continue reading →

Posted in Documentation, Intel, x86 | 11 Comments

Undocumented 8086 Opcodes

Posted on December 21, 2013 by Michal Necasek

A minor mystery recently surfaced while analyzing DOS boot sectors. DOS uses several criteria when deciding whether a boot sector contains a valid BPB, and one of the criteria is (oddly enough) checking whether the first two bytes of the … Continue reading →

Posted in 8086/8088, Documentation, Intel, x86 | 57 Comments

LOADALL Strikes Again

Posted on October 18, 2013 by Michal Necasek

A minor mystery recently popped up while running IBM’s OS/2 1.1 (1988), the first OS/2 version with the Presentation Manager GUI. While Microsoft’s and IBM’s releases of OS/2 were fully compatible from application perspective, there were differences in the drivers … Continue reading →

Posted in IBM, Intel, Microsoft, OS/2, x86 | 9 Comments

BSD Buglets

Posted on June 15, 2013 by Michal Necasek

Last week I ran into two wholly unrelated problems while researching the history of BSD-derived Unix systems on PCs. Both are classics in their category and merit a closer look. Y2K Strikes Again The first issue is a very typical … Continue reading →

Posted in BSD, UNIX, x86 | 11 Comments

If you ENTER, you might not LEAVE

Posted on June 7, 2013 by Michal Necasek

I’ve recently spent some time debugging curious hangs/aborts in two more or less exotic operating systems, Plan 9 and QNX 4.25. Both turned to be caused by the same innocuous-looking BIOS change, even though the circumstances were somewhat different and … Continue reading →

Posted in Intel, x86 | 9 Comments

Windows NT BSOD Aclock Port

Posted on November 7, 2012 by tenox

Do you remember the famous Windows NT Blue Screen Of Death? For years it was a source of jokes and bad reputation of Windows reliability. There even was a Blue Screen Saver! Today we fortunately see much less of it, but it … Continue reading →

Posted in 386, Development, NT, VGA, Windows, x86 | 10 Comments

Solaris 2.5.1 and 2.6 crashes on modern Intel CPUs

Posted on April 20, 2012 by Michal Necasek

I recently found that Solaris 2.6 and 2.5.1 does not work when run in a VM on a modern Intel CPU (Sandy Bridge generation Core i7), or to be exact fails most of the time (about nine times out of … Continue reading →

Posted in Solaris, VirtualBox, Virtualization, x86 | 20 Comments

64-bit trouble with Solaris 10 U4 and earlier

Posted on March 26, 2012 by Michal Necasek

On many newer systems, Solaris 10 releases up to and including Solaris 10 8/07 (that is Update 4, also known as S10U4) behave in an unhelpful manner. The installer can be launched from CD or DVD and the system can be … Continue reading →

Posted in Solaris, x86 | 12 Comments

AVX support disrupts WoW64 debugging

Posted on February 29, 2012 by Michal Necasek

Sometimes, the old and the new intersect in unexpected ways. After upgrading to a Sandy Bridge based system (Core i7) and Windows 7 SP1 64-bit some time ago, I noticed that debugging exceptions in 32-bit user programs didn’t quite work … Continue reading →

Posted in Windows, x86 | 18 Comments