Performa/LC 630 Dos Compatible - Dos Card CPU Upgrade

[alxlab]

The Performa/LC 630 Dos Compatible is probably my favorite 68K machine right now. It's pretty easy to upgrade to 128MB of RAM, uses inexpensive IDE hard drives and if your lucky can come with a DOS card. The DOS card in my Performa 630 came with a Cyrix CX486DX2-66 which is pretty good for old DOS gaming. Here's the DOS card and all it's glory:

It's a bit of a strange beast since it uses both the orginal 68LC040 socket and the PDS slot. The 486 CPU is socketed though so the obvious question to ask is can we upgrade it with something better? The answer is yes! The original CPU is 5V with a 33 Mhz bus speed so any upgrade will require a 5V to ~3.3V adapter. Any 33 Mhz bus CPU like the Intel DX4-100 or AMD 5x86 133 Mhz should work. I happened to have a Gainberry Cyrix 5x86-100GP chip which fits the bill:

Here's a bechmark of the old DX-2 66Mhz and the new 5x86 100 Mhz:

It's right on the money. I also tried an AMD-X5-133. Here's a benchmark of the AMD:

Unfortunately with the AMD 133 Mhz CPU Windows 95 crashes on boot. Tried all the jumper setting on the processor but no luck. Maybe a Cyrix 5x86 133Mhz CPU wouldn't have this issue but I don't have one to test with, but I will update this post if I ever find one.

 

[Garth Beagle]

I'd love to upgrade one of my DOS cards with a DX4/100 or similar.

 

[François]

Will this 486 DX4 100 work with the DOS card?

 

[alxlab]

You'll need an 486/5x86 interposer to covert the SPU voltage from 5V to the 3V of a Intel 486 DX4 and set the proper multiplier.

There's actually a couple of github projects if your up to making your own interposer:

486SocketBlaster
486VRM

 

[François]

Is there any CPU upgrade that won’t need an interposer? (I want to keep it simple!)

 

[alxlab]

Is there any CPU upgrade that won’t need an interposer? (I want to keep it simple!)

There are a few.

There's the Intel Overdrive DX4ODPR100 which is an Intel 486 DX4 100MHz with a built in voltage regular.

There's also the 5x86 upgrade processors that include the interposer like this Gainberry Cyrix 5x86-100GP and AM5x85-P75:

I think it's important to note that after trying different CPUs on LC 630 DOS card, the only CPU upgrade that didn't cause Windows 95 to crash is the Cyrix 5x86-100GP. The AM5x85-P75 and Intel Overdrive PODP5V83 only work in DOS. I guess this sort of makes sense since the original CPU is a Cyrix 486 DX2 66MHz. I've never tried upgrading the CPU on the Houdini I-II PDS DOS cards, so I'm not really sure if they have the same problem with Windows 95.

 

[François]

Thanks for the detailed answer! I took a look on eBay, those are quite expensive upgrades!