Category Archives: Development

A House of Cards

Posted on December 30, 2022 by Michal Necasek

As one step in the development of the Windows 3.x/2.x display driver, I needed to replace a BIOS INT 10h call to set the video mode with a “native” mode set code going directly to the (virtual) hardware registers. One … Continue reading →

Posted in Bugs, Development, Microsoft, Windows | 49 Comments

Win16 Retro Development

Posted on December 20, 2022 by Michal Necasek

Several months ago I had a go at producing a high resolution 256-color driver for Windows 3.1. The effort was successful but is not yet complete. Along the way I re-learned many things I had forgotten, and learned several new … Continue reading →

Posted in Debugging, Development, Microsoft, Windows | 25 Comments

Undefined Isn’t Unpredictable

Posted on November 7, 2022 by Michal Necasek

The other day I discovered that 32-bit FreeBSD 11.2 has strange trouble running in an emulated environment. Utilities like ping or top would just hang when trying to print floating-point numbers through printf(). The dtoa() library routine was getting stuck … Continue reading →

Posted in AMD, Development, Documentation, Intel | 22 Comments

Antique Display Driving

Posted on July 29, 2022 by Michal Necasek

Here’s a preview of something I’ve been slowly working on, bit by bit: That screenshot surely looks a little funny. That’s because it is Windows 1.04 running with a heavily modified 256-color Windows 3.x display driver, using resources from a … Continue reading →

Posted in Development, Microsoft, Windows | 36 Comments

Learn Something Old Every Day, Part VI: Backward Buffer Overwrite

Posted on July 13, 2022 by Michal Necasek

A few days ago I spent far too much time debugging a largish piece of 16-bit Windows code written in assembler. I found a scenario where (fortunately fairly reproducibly) Windows crashed because the internal state of a DLL got corrupted. … Continue reading →

Posted in Bugs, Development, Windows | 24 Comments

Windows 9x Video Minidriver Source Code

Posted on June 24, 2022 by Michal Necasek

As promised, here is the source code for the Windows 9x VirtualBox display minidriver. For discussion of the source code, see the included readdev.txt file. The code was developed on a Windows 10 host system. For extra credit, I attempted … Continue reading →

Posted in Development, Source code, VirtualBox, Watcom, Windows 95 | 18 Comments

Windows 9x Video Minidriver HD+

Posted on June 6, 2022 by Michal Necasek

The OS/2 Museum has made available the first version of a display driver disk for Windows 9x running on VirtualBox. The driver uses a linear framebuffer and supports 8/16/24/32bpp modes with resolutions up to 1920×1200 pixels (see more below). The … Continue reading →

Posted in Development, VirtualBox, Watcom, Windows 95 | 61 Comments

The Strange Case of GetEnvironmentStringsA

Posted on May 22, 2022 by Michal Necasek

It was recently pointed out to me that a simple “hello world” style application built with Open Watcom C/C++ 1.9 does not run on Win32s version 1.30, even though the same executable runs just fine on Windows NT 3.51, Windows … Continue reading →

Posted in Development, NT, Watcom | 21 Comments

Reconstructing the EGA BIOS

Posted on March 19, 2022 by Michal Necasek

A few weeks ago I had a sudden need to understand certain finer points of the operation of EGA/VGA BIOS. I found common reference materials to be inadequate—they tend to do a good job of documenting the data structures the … Continue reading →

Posted in BIOS, Development, Documentation, Graphics, IBM, PC history | 32 Comments

XMVM Surgery

Posted on February 11, 2022 by Michal Necasek

Last week I was prompted to take a look at the Intel Code Builder compiler from 1991, a 32-bit compiler targeting 386 extended DOS and shipping with its own DOS extender. It is what one might call an extremely obscure … Continue reading →

Posted in 386, Development, Intel, PC history, Software Hacks | 10 Comments