Watch on YouTube: https://www.youtube.com/watch?v=8oWyogPZ7Bw
PC-SPRINT - Overclocking The First PC With A DIY Open Source Hardware Solution From 1985!
Introduction
Join me as I tell you all about the PC-SPRINT. The plans for this DIY overclocking solution were released for free in 1985, so I decided to build one in 2020 and use it to overclock my 1981 IBM 5150 PC!
This video was created for RetroFair 2020. Unfortunately due to humanity’s impending doom the VCF Pacific Northwest vintage computer show has been cancelled this year. Originally scheduled for the weekend of 21st/22nd of March, @JohnKennedyMSFT over on Twitter suggested that we take the event online instead.
To be honest I wouldn’t have been able to attend the event anyway as it’s a few thousand miles from me, although I’ve been an active user of the VCFed forums for years - in fact, that’s where the original inspiration came from for this project.
The GitHub repo I mentioned in the video is available here: https://github.com/reeshub/pc-sprint
Official RetroFair 2020 Playlist: https://www.youtube.com/playlist?list=PLpKSFwrlcf8bPwLVgDQ5HLFrQHQftpaNs
My other RetroFair 2020 Video about EGA on a CGA monitor: https://youtu.be/pmJoILDevDc
Script
Hey everyone, welcome to my retrofair 2020 video.
I only have 5 minutes, so lets get stuck in.
This is my IBM 5150, the first DOS PC. This PC was so revolutionary that unless you’re watching this on a mobile device or a TV, you’re more than likely watching it on a direct descendant of this machine.
Released in 1981 for around $1500 which is about $4000 in today’s money, the 5150 was famously built to an open standard using off the shelf components, leading to an explosion of clones and the creation and eventual domination of the standard in the home computer market.
The 5150 had an Intel 8088 CPU clocked at 4.77 MHz, and that’s what I want to talk to you about today. Things were moving pretty rapidly in the early 80s and faster machines came along, leaving the 5150 looking obsolete fairly quickly.
As with pretty much every other computer on the market at the time, accelerators and upgrades were available, and the one I’m currently obsessed with is this, the PC-SPRINT. This was released as an early form of “open hardware” back in 1985 by a chap called Doug Severson, who gave away the plans on BBSes and in magazines so people could build their own using less than $10 worth of parts. So that’s what I did.
The 5150 uses a 14.31MHz crystal to generate its timing signals, which are then divided by an Intel 8284A clock oscillator chip to generate the 4.77MHz CPU clock for the 8088. The PC-SPRINT works by adding a second 8284A and crystal to generate a faster clock signal for the CPU. Of course, we also need to replace the 8088 with something faster, so I opted for the NEC V20 which was another popular period upgrade in its own right.
So let’s have a look inside and see how I installed mine.
The PC-SPRINT slots neatly into the 8284A socket. Then two buttons are added - one momentary switch that acts as a hardware reset button and a latching switch which enables and disables the faster clock speed. Of course both of these became standard on PCs in the 80s and 90s.
So just a quick look at the performance improvements. I’ll show the CheckIt benchmarks here but I’ve run a few others and they all show a similar improvement of around 50-55% across the board when running in turbo mode.
There are some games that were unplayable before which are working great now under turbo mode, meaning that I’ll be getting much more use out of this machine. I’m working on a series of videos about upgrading this machine including a longer one about the PC-SPRINT, which should be along in the not too distant future.
There’s also a link to my GitHub repo with the plans and a lot more information down in the description, so feel free to check that out too. I’ve made everything available under an open source license in the same spirit as the original, and I’m also working on a version with some enhancements too!
Thanks for watching, and I hope you enjoy the rest of the retrofair videos. I know I will be!
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