Taking an ISA Graphics Card to the Max! ISA Bus Overclocking #isadoom25fps

The 16-bit ISA bus was becoming a very serious bottleneck for PC graphics in the early to mid nineties. 3D games like Doom really didn’t run well unless a VESA Local Bus or PCI graphics card was used. There were some ways to get some extra performance though – by overclocking the ISA bus! Today I’ll be pushing the ISA bus to the max to see just how quick games like Doom can run.

#isadoom25fps

Doom realtic to frames per second conversion (applicable for demo3 only):
FPS = 74690 / ticks

CPU Galaxy’s YouTube Channel:
https://www.youtube.com/@CPUGalaxy

CPU Galaxy’s Website:
https://www.cpu-galaxy.at/

Phil’s DOS Benchmark Pack:
https://www.philscomputerlab.com/dos-benchmark-pack.html

Twitter: https://twitter.com/vswitchzero
Mastodon: https://bitbang.social/@vswitchzero
My Blog: https://vswitchzero.com/

00:00 Introduction
01:03 A Bit of History
02:39 The Doom 25FPS Challenge
04:27 Strategy
05:38 Hardware Setup
08:29 BIOS Woes
11:17 ISA Bus Overclocking
12:28 System Tuning
13:04 Taking the ISA Bus to the Max!
14:58 Result Summary
16:12 Pure ISA Testing
18:26 Other ISA Cards at 25MHz
19:30 Conclusion

A big thanks to @chaslinux and Lee from Nova Scotia for donating parts used in this video today. Much appreciated!