Author Archives: Michal Necasek

A Tale of Two Displays

Posted on November 8, 2014 by Michal Necasek

By sheer coincidence, two new computers arrived in my family at almost the same time, and they couldn’t be more different. At first sight, the most striking difference is the quality of their displays, and it says a lot about … Continue reading →

Posted in Apple, Graphics, PC hardware | 12 Comments

Original CEMM Unearthed

Posted on November 5, 2014 by Michal Necasek

An important fragment of PC history was unearthed a few days ago: An image of a Compaq Deskpro 386 supplemental disk from August 1986, containing among other things CEMM.EXE, Compaq’s original expanded memory emulator shipped with the Deskpro 386. The … Continue reading →

Posted in 386, Compaq, DOS | 28 Comments

Site Update

Posted on November 1, 2014 by Michal Necasek

In the past two weeks or so, I’ve been fighting with the site instead of adding content. The hosting company was complaining of too high resource usage on a shared server… but was unable to provide me with detailed access … Continue reading →

Posted in Site Management | 8 Comments

Book Review: Unauthorized Windows 95

Posted on October 9, 2014 by Michal Necasek

A Few Decades Late Book Reviews Unauthorized Windows 95 Developer’s Resource Kit, by Andrew Schulman IDG Books, November 1994; 593 pages, ISBN 1-56884-305-4; $39.99 A testimony to the incredible level of hype surrounding Microsoft’s “Chicago”, Unauthorized Windows 95 was published nearly a year before … Continue reading →

Posted in Books, DOS Extenders, Windows 95 | 17 Comments

Installing Windows 95 on SCSI in a VM

Posted on September 26, 2014 by Michal Necasek

For the adventurous, it is possible to install Windows 95 in a VM configured with SCSI storage (hard disk, CD-ROM) attached to an emulated BusLogic HBA. This works in VirtualBox, but there’s a catch—the emulated PCI BusLogic HBA must have … Continue reading →

Posted in BusLogic, SCSI, VirtualBox, Windows 95 | 7 Comments

Forward Compatibility, Landmines

Posted on September 20, 2014 by Michal Necasek

Several years ago, after attempting to get a very old 286 version of Xenix running in a VM, I concluded that it was probably incompatible with any 386 and later processor. Recently I revisited this issue and examined the problem … Continue reading →

Posted in 286, Intel, Xenix | 32 Comments

386 Memory Managers and DMA

Posted on September 12, 2014 by Michal Necasek

A while ago I ran into an odd problem: A virtual machine running QEMM 9.0 (aka QEMM 97) would crash more or less every time it tried to read something from a floppy. No such problem was observable in any … Continue reading →

Posted in 386, Bugs, DOS, PC hardware | 7 Comments

Floating-Point Exceptions and DOS Extenders

Posted on September 5, 2014 by Michal Necasek

Recently I had a need to test the behavior of floating-point exceptions (FPEs) in environments where traditional FPE reporting is used. To briefly recap, in the original PC equipped with an 8088/8087 pair, floating-point exceptions, which are generally asynchronous events, were … Continue reading →

Posted in 386, Bugs, DOS, DOS Extenders, PC architecture | Leave a comment

OS/2 Kernel Debugger and MVDM Interrupts

Posted on August 29, 2014 by Michal Necasek

While working on an unrelated problem, I noticed a strange behavior of one of my OS/2 VMs running OS/2 Warp 4.52. To cut a long story short, if an unhandled floating-point exception occurred in a DOS window (VDM, or Virtual … Continue reading →

Posted in Bugs, Debugging, OS/2 | 12 Comments

IBM Blue Lightning: World’s Fastest 386?

Posted on August 22, 2014 by Michal Necasek

One of the OS/2 Museum’s vintage boards is a genuine Made in U.S.A. Alaris Cougar. These boards were produced by IBM for Alaris and are a bit unusual: There’s a small IBM DLC3 processor in plastic package soldered on board, … Continue reading →

Posted in 386, IBM, Intel, PC hardware, PC history | 62 Comments