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First post, by Yuuker

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Couldn't find an answer so i thought i'd double check.

Is there any harm or performance degradation with using a Intel DX4 with write-back cache on a motherboard that doesn't support it? Found out i have one of those models, although it doesn't seem like my DataExpert EXP4044 has any option for toggling write-back cache, neither in the bios or jumpers (only jumpers for L2 write back/through toggling).

Reply 2 of 12, by Anonymous Coward

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If you use configure a DX4 for writeback in a system that doesn't support it, the system will simply crash.
Thankfully most CPUs that support writeback are set to writet hrough by default.

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Reply 4 of 12, by jheronimus

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Anonymous Coward wrote:

Thankfully most CPUs that support writeback are set to writet hrough by default.

The CPU itself has a setting for writeback/writethrough? How do you change that setting? I thought it's only a motherboard/BIOS thing.

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Reply 6 of 12, by jheronimus

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gerwin wrote:

In this pinout table pin B13 works as a WT/WB selector.

Yes, but the only way to interact with that pin is by changing motherboard jumpers/BIOS settings, no? It's not like, say, changing Cyrix 5x86 options through software.

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Reply 7 of 12, by gerwin

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Jumpers/BIOS, yes I think so, don't know about any related CPU registers on the intel 486.
Note that Write-Back did not entirely cooperate with my only 486 VLB system. Not yet at least. So I never benchmarked the supposed benefit.

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Reply 8 of 12, by Yuuker

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Sorry to bump but i didn't figure this quick related follow up question warranted its own thread.

I got the DX4, set the junpers. No boot. Got the lights on the keyboard, but no video.
Re seated it a couple times and even tried swapping back to my DX2 and its jumper configuration (which worked)

I'm theorizing my motherboard doesn't support write-back, but i might be wrong.

Statson doesn't seem to list any jumper for write-back, nor does the bios have anything.
http://stason.org/TULARC/pc/motherboards/D/DA … 86-EXP4044.html

Maybe i'm missing something 😒 Hopefully the chip itself isn't dead.

Reply 10 of 12, by Yuuker

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jheronimus wrote:

JP34 seems to set L2 cache to writeback according to the stason link you’ve posted

Would that do anything for the cpu though? Unless the board is looking for both L1 and L2 states to match.

Reply 11 of 12, by jheronimus

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Yuuker wrote:
jheronimus wrote:

JP34 seems to set L2 cache to writeback according to the stason link you’ve posted

Would that do anything for the cpu though? Unless the board is looking for both L1 and L2 states to match.

I don't think I've ever seen a board that has separate jumpers for L1 and L2 cache. Then again, both my VLB boards (AOpen VI15G QDI Opti 895) have both cache jumpers and a cache setting in BIOS

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Reply 12 of 12, by Yuuker

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jheronimus wrote:
Yuuker wrote:
jheronimus wrote:

JP34 seems to set L2 cache to writeback according to the stason link you’ve posted

Would that do anything for the cpu though? Unless the board is looking for both L1 and L2 states to match.

I don't think I've ever seen a board that has separate jumpers for L1 and L2 cache. Then again, both my VLB boards (AOpen VI15G QDI Opti 895) have both cache jumpers Cand a cache setting in BIOS

Nope, no dice. Changing that jumper made no diffrence. I even tried disabling internal cpu cache via the bios to see if maybe that would bypass any board trouble but to no luck.

Very unsure weather the cpu is dead or not, i have a board with proper L1-writeback support on the way but it won't be here for some time 😒
Either that, or my VLB Video card isn't play nice with a dx4.