Higher Refresh Rate in DOS Games

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I decided to stay in my parent’s house for a weekend and although almost all my computer equipment is somewhere else for a long time, under a thick layer of dust I’ve found my old Compaq DeskPro SFF box and a 17-inch CRT that my father bought new in 1998. Surprisingly, the system still works and its hard drive is loaded with many DOS and early 3D-accelerated games… Great time to play all episodes of Blood (a game based on the Duke Nukem 3D engine).

I like playing old games on CRTs but I hate low refresh rates used in DOS games (60-70Hz). If you have as sensitive eyes as I have, there is a solution called UniRefresh. It can modify default refresh rates for each supported resolution and it works well with most games that use VESA. That allowed me to play the game in 640×400@120Hz. Yay!

UniRefresh needs a graphics card supporting VBE 3.0 (VESA BIOS Extensions). Use the latest DOS version of SciTech Display Doctor to emulate VBE 3.0 support on older cards.

Mobile CPU Upgrades

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Siemens-Nixdorf PCD-4ND is a 486-based laptop from 1993-1995. It was quite popular in Germany and you could have seen a few of them still in use even ten years ago (mostly connected to expensive industrial devices using a serial port).

I like how easy it was to upgrade the CPU in this particular laptop. It took about 20 seconds to remove a small plastic cover and replace the CPU board. There were probably four options during the lifecycle of the machine – 25-MHz 486SX, 50-MHz 486DX2 and 75-MHz/100-MHz 486DX4 (Intel called it ‘Intel DX4’).

Note the WDC graphics chip below the CPU board slot. It shared the bus with the CPU as it was connected using VLB (= VESA Local Bus) instead of the older ISA/AT bus. This allowed to use fast 32-bit transfers on a frequency equal to the CPU external clock (25/33-MHz) without a sophisticated bus controller (EISA, PCI). This chip was used in many laptops of this era and it was surprisingly powerful. It allowed up to 1024×768 with 256 colors and 640×480 with 65k colors and it could accelerate bit-block transfers as well as graphics primitives.