Understanding cache on a 386 \ VOGONS

Understanding cache on a 386

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First post, by Gahhhrrrlic

Posted on 2018-06-04, 02:29

Gahhhrrrlic Offline

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My 386 board has 64k of cache that I was hoping to upgrade to 128 but I haven't yet been able to find that sort of configuration, the next step up seemingly being 256kb. OK. I assume as long as I update the tag chip, that will work alright. The next thing I noticed is that my current cache (Cxk5465p-25) exists as 8 modules which appear to be DIP24 packages, even though they seem to be too small for the socket. I guess this isn't a problem because the computer works just fine but I found it odd that they appeared too small for the socket.

Now I found some cache on ebay that I thought might be worth a look: https://www.ebay.ca/itm/9X-UM61256AK-15-Cache … dMAAOSwZ~hbCsN-

Here you can see that we have 256kb of ram in 8 chips + a tag chip. They are DIP28 packages so while they should fit in my sockets, I am not certain that this means they are in fact compatible. The next thing is that they are faster (15nS vs 25nS), which is good... if it works. Basically I just don't know the rules when it comes to cache so while it seems like I could buy these and they might work, I wouldn't be at all surprised if someone said that they wouldn't. They have more pins, are faster and 256kb is a big upgrade from 64kb so I don't know how the system will handle it. Also my chips are apparently 16k x 4 bit, whatever that means and I have no idea how to interpret this from a compatibility standpoint or if the ones in the ebay ad will work.

Are there any guidelines when selecting cache that would help clarify the selection process for me? Thank you.

https://hubpages.com/technology/How-to-Maximi … -Retro-Computer

Reply 1 of 4, by Anonymous Coward

Posted on 2018-06-04, 03:08

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A picture of your board might help, especially if you know the model number.
If your board has 25ns cache chips, chances are it's an older model which makes it less likely that an upgrade to 256kb will work. Does the board take more than 8MB of RAM? IF not, 64k is more than enough.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 2 of 4, by Gahhhrrrlic

Posted on 2018-06-04, 03:23

Gahhhrrrlic Offline

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I know that this is the board:

MB1333C-40CH
http://www.elhvb.com/mobokive/archive/Biostar … b1333c-40ch.JPG

However all attempts to find any sort of documentation have been unsuccessful so I really cannot say whether it will handle more than 8MB (what it has now) or what sort of cache options I have. I can say that it's been a hero of a board so far if that counts for anything.

P.S. Fitting that Chips should help me regarding a Chips MB 😁

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Reply 3 of 4, by Anonymous Coward

Posted on 2018-06-04, 08:18

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I own a very similar board. Mine is the Abit FU430. It uses the same chipset, and can't work reliably with more than 16MB RAM or more than 64kb cache. I suspect somehow the chipset is flawed, so I advise not trying to upgrade the cache in your system if it's already 64kb. I believe Feipoa has the same board that you do, and he had similar issues.

It's pretty interesting your board uses 16kx4 chips. So even though you have 8 chips, it's not dual banked cache. The extra pins on the socket are probably for the SRAM that is 8-bit wide.

This actually gives me an idea. I suspect that this board may support 256kb cache but only when using 64kx4 SRAMs.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 4 of 4, by Gahhhrrrlic

Posted on 2018-06-04, 15:05

Gahhhrrrlic Offline

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Anonymous Coward wrote:
I own a very similar board. Mine is the Abit FU430. It uses the same chipset, and can't work reliably with more than 16MB RAM or more than 64kb cache. I suspect somehow the chipset is flawed, so I advise not trying to upgrade the cache in your system if it's already 64kb. I believe Feipoa has the same board that you do, and he had similar issues.

It's pretty interesting your board uses 16kx4 chips. So even though you have 8 chips, it's not dual banked cache. The extra pins on the socket are probably for the SRAM that is 8-bit wide.

This actually gives me an idea. I suspect that this board may support 256kb cache but only when using 64kx4 SRAMs.

But if what you're saying is true (and it makes sense to me), then why would it have to be 64 x 4 if the extra socket pins are for 8 bit chips? I guess I don't get the concept fully. Are you saying that I could use 4 modules instead of 8? Sorry, I find the topic a bit confusing still. For example, while 16k x 4bit seems to work out mathematically to the 64k total cache size I have now, how is that split up into 8 pieces? Would it be 2k x 4 bit per module? Will the computer work with only half the sockets populated?

Maybe this would work?

https://www.ebay.com/p/Motorola-MCM6206DP20-3 … 5.c100005.m1851

https://hubpages.com/technology/How-to-Maximi … -Retro-Computer

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