AMD 5x86 CPU question

[Amigaz]

Have a spare Asus stason.org VL/I-486SV2G rev 1.4 m otherboard I plan to use with an AMD 5x86 after my VL/I-486SV2GX4 sadly died

The SV2G motherboard doesn't support to 5x86 CPU fully..even after using the latest BIOS..it just sees it as an "enhanced AMD486DX4-S" CPU

I set the FSB to 40mhz so now the CPU runs at 120mhz which it seem to boot happily with

Since the CPU is rated at 133mhz I thought this was a way to take more advantage of it
I don't have so much experience with these VLB motherboards so I'm not sure if this is healthy for the CPU since the CPU is now running at a higher FSB than it's suppose to?

 

[Anonymous Coward]

I doubt it would be much of a problem. It's widely known that 0.35 micron core that AMD used in the am5x86 was capable of more than 133MHz, and that 150 and 160MHz parts were dropped at the last minute. Overclocking to those speeds using the 40 and 50MHz bus was pretty common, and had a very high success rate. I've run my ADW (lower heat rating than ADZ) at both 150MHz and 160MHz for a long time without any problems at all. I would say that running your 5x86 at 120MHz is probably being pretty conservative...perhaps it's even officially supported in the AMD white papers, maybe you should have a look. The only thing you'd have to watch out for is VLB cards that don't like 40MHz, which was a pretty common problem.

 

[Amigaz]

I doubt it would be much of a problem. It's widely known that 0.35 micron core that AMD used in the am5x86 was capable of more than 133MHz, and that 150 and 160MHz parts were dropped at the last minute. Overclocking to those speeds using the 40 and 50MHz bus was pretty common, and had a very high success rate. I've run my ADW (lower heat rating than ADZ) at both 150MHz and 160MHz for a long time without any problems at all. I would say that running your 5x86 at 120MHz is probably being pretty conservative...perhaps it's even officially supported in the AMD white papers, maybe you should have a look. The only thing you'd have to watch out for is VLB cards that don't like 40MHz, which was a pretty common problem.

ahh..thanks for the info's

I actually got it booting at 3x50 (150mhz) too by mistake, had set the FSB multiplier jumpers wrong, hehe

Not sure if I will take advantage of all the 5x86 featurex though since the CPU isn't properly recognized.

mmm...I guess I'll have VLB timing issues, have a pile of VLB gfx cards and I/O controllers to test though...one of each should work....I hope

 

[Anonymous Coward]

The am5x86 doesn't really have much in the way of "features" like the cx5x86. am5x86 is just a regular 486 with smaller die size and 4x multiplier. The only feature you can really control is the caching policy. Using writeback caching will give you about a 10% cpu performance boost, but not all motherboards support it. Additionally, there is some kind of problem related to am5x86 in that it will not cooperate with VLB SCSI controllers that use DMA while writeback cache is enabled. Setting the CPU to write-through will fix the problem though.