Opinion Question: Tale of two CPUs

I have a Socket 3 board that works pretty well. It has 128K of cache (can go higher, just need good chips to put in it), and supports up to a DX4-100Mhz.

I've thought about it a bit. It does support a 40MHz and 50MHz bus. So, if you had the choice of either of these two CPUs:

DX4-100Mhz (33MHz bus)
DX-50Mhz (50MHz bus)

Which would you choose? I'm leaning a bit towards the 50MHz chip, but given my disk I/O is a 16-ISA SCSI card, I'm not sure the faster bus speed will actually provide any benefit. Thoughts?

I'd take the DX4. Can you put a P83 Overdrive in there? That would be even better.

>> YMK said:

I'd take the DX4. Can you put a P83 Overdrive in there? That would be even better. Click to expand...

It would support the 83MHz Overdrive...if they weren't at blood diamond money costs on FleaBay now. :/

Depending on what you want to run, they're worth it. Just have a plan for swapping out that tiny heatsink and obnoxious fan.

If the system has VLB slots that you would like to use, then you want to go the DX4 100MHz route. The reason Intel abandoned the DX 50MHz (so I've been told) is that other chips weren't always reliable at a 50MHz bus speed, though shortages of the DX 50MHz may also have contributed to poor adoption. Getting VLB cards to run at 40MHz can be a task and usually requires using 1 wait state. 50MHz may be out of spec for a lot of VLB cards.

If it's a Socket 3 board with PCI, then any bus speed above 33MHz will result in an overclock of the PCI bus, and a 50MHz bus speed is likely to be too extreme of an overclock for 32-bit PCI devices.

If you only plan to use ISA, then by all means go for the DX 50MHz. (I'd try it at that speed, if I had the processor.) You'll probably have to experiment with the ISA clock divider to find a speed all of your cards are stable at. If you're lucky, maybe you'll still be able to pick a divider of 4 or 5 (some ISA cards are happy at 10MHz or 12.5MHz). But you may have to use a divider of 6, which would result in an ISA bus speed of 8.33MHz, and most ISA cards that would feel right in a 486 will be happy at that speed.

>> jdmcs said:

If the system has VLB slots that you would like to use, then you want to go the DX4 100MHz route. The reason Intel abandoned the DX 50MHz (so I've been told) is that other chips weren't always reliable at a 50MHz bus speed, though shortages of the DX 50MHz may also have contributed to poor adoption. Getting VLB cards to run at 40MHz can be a task and usually requires using 1 wait state. 50MHz may be out of spec for a lot of VLB cards. If it's a Socket 3 board with PCI, then any bus speed above 33MHz will result in an overclock of the PCI bus, and a 50MHz bus speed is likely to be too extreme of an overclock for 32-bit PCI devices. If you only plan to use ISA, then by all means go for the DX 50MHz. (I'd try it at that speed, if I had the processor.) You'll probably have to experiment with the ISA clock divider to find a speed all of your cards are stable at. If you're lucky, maybe you'll still be able to pick a divider of 4 or 5 (some ISA cards are happy at 10MHz or 12.5MHz). But you may have to use a divider of 6, which would result in an ISA bus speed of 8.33MHz, and most ISA cards that would feel right in a 486 will be happy at that speed. Click to expand...

So some (very long overdue) updates. I ended up with an AMD 486DX4-100Mhz chip from a different project system/board and a slightly better 486 board with VLB. Aside from some weird graphics issues in Inner Space (possible bad RAM on the Diamond VLB card) it's been running great!

One happy accident is the Adaptec 1542B I'm using with a BlueSCSI V2 works just fine with the 3.5"/5.25" combo floppy drive. I wasn't 100% sure the floppy controller would support these odd-ball combo units but, well here we are. :)