Author Archives: Michal Necasek

Undocumented VflatD

Posted on February 23, 2012 by Michal Necasek

The virtual flat framebuffer driver, or VflatD, was introduced in Windows 95 in order to ease development of display drivers. It was surprisingly poorly documented and the sample drivers did not illustrate its use very well. A short backgrounder may … Continue reading →

Posted in Documentation, VGA, Windows | 6 Comments

Kernel Debugging with VirtualBox

Posted on February 21, 2012 by Michal Necasek

Virtualization readily lends itself to debugging of low-level code that is difficult to analyze in conventional environments. It is also convenient for kernel debugging which would otherwise require two separate systems or at least a separate serial terminal. OS/2 Setting … Continue reading →

Posted in Development, OS/2, VirtualBox | 4 Comments

How to please WDCTRL

Posted on February 2, 2012 by Michal Necasek

As any user of 16-bit Windows knows, Microsoft Windows 3.1x in 386 Enhanced mode supported a coveted feature called 32-bit disk access (sometimes also called FastDisk). The “32-bit” designation was slightly misleading as there was no 32-bit data path to … Continue reading →

Posted in BIOS, Windows | 3 Comments

Retro development with aclock

Posted on January 29, 2012 by Michal Necasek

In the past few days, I embarked upon a project to port Antoni Sawicki’s aclock, a small text-based clock program (aclock stands for analog clock), to 16-bit Windows. While aclock itself has been ported to over 150 platforms, it is a … Continue reading →

Posted in Development, PC history, Windows | 14 Comments

What’s in a name… OS/2 or DOS?

Posted on January 27, 2012 by Michal Necasek

There have been many rumors that the name “OS/2” was chosen only shortly before the product was announced. It’s not entirely clear what the name would have been otherwise, but quite likely DOS 5; certainly DOS in some form. There … Continue reading →

Posted in Documentation, DOS, OS/2, PC history | 4 Comments

How to make sure your program doesn’t run on Windows 95

Posted on January 24, 2012 by Michal Necasek

For Christmas, I bought myself the book The Old New Thing by Raymond Chen, a long-time Microsoft programmer. The purchase was spurred by discovering, through Google Books, an excerpt of a riveting description of how various software titles abused the DPMI … Continue reading →

Posted in PC history | 12 Comments

DOS/V graphics text modes and scrolling

Posted on January 22, 2012 by Michal Necasek

I recently ran into an interesting difference in the way various DOS/V versions manage VGA memory. DOS/V of course refers to the Japanese versions of DOS which are capable of running on standard “Western” hardware. Microsoft has a very long … Continue reading →

Posted in DOS, VGA | Leave a comment

Jumpy PS/2 mouse in Enhanced mode Windows 3.x

Posted on December 21, 2011 by Michal Necasek

There’s an interesting (and quite annoying) bug specific to Windows 3.x running in 386 enhanced mode (also known as Windows/386) and using a PS/2 mouse. In some situations, the mouse may jump to the top or the bottom of the … Continue reading →

Posted in Windows | 9 Comments

Simple Windows NT video miniport for VirtualBox

Posted on December 18, 2011 by Michal Necasek

A few months ago, I developed a trivial video miniport for use in Windows NT virtual machines. The primary goal was to improve display speed and get past the 800×600, 16 color display mode which is the maximum Windows NT … Continue reading →

Posted in NT, VirtualBox | 26 Comments

Microsoft OS/2 1.0 user documentation

Posted on December 17, 2011 by Michal Necasek

In late 1987, Microsoft shipped a set of OS/2 1.0 user documentation as part of the OS/2 SDK. The set included the Setup Guide, Beginning User’s Guide (a tutorial style document), and User’s Reference. The manuals were similar in style … Continue reading →

Posted in Documentation, OS/2 | 3 Comments