Acorn Archimedes A3020 25MHZ ARM250 Overclock
Following up my little overclocking experiment with the Archimedes A3010 where we managed to push the machine to run at 26MHZ rather than it's original 12MHZ.
Here I do the same with the A3020. Well I settled for 25MHZ on this machine as this seems to be the limits for this particular ARM250 chip. Although both machines share some similarities, such a the ARM250 CPU and the same RISC OS 3.1 operating system. When it comes to the RAM however the A3020 does not have the 2 large expansion slots that the A3010 had, which means we cannot use the IFEL RAM expansion carrier board here.
Before proceeding with the overclock mod, here is the performance of the machine measured in !ArmSI V4. As you can see it is pretty much identical to the 12MHZ A3010 doing just over 7 MIPs.
The A3020 has 2MB of RAM mounted directly on the motherboard with a further 4 expansion sockets that can take old fashioned zip RAM that takes the total RAM to 4MB. To achieve the 25MHZ overclock on this machine we can replace the 2MB of RAM on the motherboard with some faster RAM.
Replacement 28ns RAM
The RAM I have chosen to replace it with has this marking M5416258B-28J and was suggested by munchausen on the forums. Here they are in all their unused glory:
Using a hot air re-work station I removed the original 4 RAM IC's and replaced them with these faster chips. The speed of this RAM is rated at 28ns which equates to about 35MHZ. It's not possible to run the A3020 at that speed but it will happily run along at 25MHZ! Here are the new RAMs nicely soldered in place:
The A3020 motherboard has a space (X100) ready for a new crystal to be soldered straight on without any ghastly hacks. As I usually do, I soldered in an empty socket so I can swap crystals with ease. There is also an empty spot for the resistor too. R10 requires a 220 ohm resistor be fitted to complete the overclock mod.
All Done!
Now, finally, with the new super fast RAM fitted and the machine booted up and all working well, it's time to benchmark it again. The machine is now running at 25MHZ rather than the original 12MHZ so, as you can imagine, with a 100%+ speed increase, its a much nicer machine to use!
Is Overclocking Bad for the CPU?
As I said when overclocking the A3010, there are a lot of arguments out there for and against overclocking. I personally am in favour of overclocking provided steps are taken to ensure the overclocked chips whether it is the CPU or RAM has sufficient cooling. The extra speed makes the machine more usable, not just playing CPU intensive games but also using the RISC OS desktop.
That just about wraps up my overclocking experiments with the ARM250 based Acorn Archimedes machines.
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