That 16kb shown is from your Cyrix 5x86 CPU.

First thing to do would be to check that any jumpers on the board are set correctly and that the bios is set to enable it.

fsinan wrote on 2024-02-07, 21:15:

This is a new configuration with a new board. It is reported that 256KB cache is installed. Jumper setting is ok.

But look at speedsys...Sudden drop after 16K?? Cache control program in dosbench reported just 16K cache...

Yes, looks like you have a board with fake cache.

The number written on the data chips suggests being a Winbond type, but it does not even look similar than the original.

EDIT: Also the tag ram looks strange. poorly printed writing.

A telltale sign for boards with fake cache is that there is no option to enable/disable L2 cache in the BIOS. This is because the actual L2 cache option is hidden from the setup screen and fixed at disabled. The "256KB cache" message below the system configuration box is just hardcoded plain text.

Obviously the Bios telling there is 256kB of cache, but there is none, is also a very strong hint for fake cache.

CoffeeOne wrote on 2024-02-07, 23:46:

Obviously the Bios telling there is 256kB of cache, but there is none, is also a very strong hint for fake cache.

At bios it is enabled. 256K reported but it seems it is fake. I would like to buy a set of srams but almost all sellers do not offer tag-ram. I couldnt find on ebay.

Maybe at least my tagram is real, how can I check it?

CoffeeOne wrote on 2024-02-07, 23:46:

Obviously the Bios telling there is 256kB of cache, but there is none, is also a very strong hint for fake cache.

There are other possibilities for this behaviour: The BIOS might correctly detect and initialize the L2 cache, and then intentionally disable it when it boots into DOS: For example, some boards implement the turbo/de-turbo feature by disabling L2 cache, so if this board requires the turbo switch pins to be bridged to run in turbo mode, and the turbo switch pins are open, you could observe this behaviour, too.

fsinan wrote on 2024-02-08, 05:47:

At bios it is enabled. 256K reported but it seems it is fake. I would like to buy a set of srams but almost all sellers do not offer tag-ram. I couldnt find on ebay.

The tag ram claims to be a standard fast 32K x 8 SRAM with an access time of 15ns. They usually have model numbers like 61256 or 62256. I found some offers searching for "15ns 32kx8 dip". The results look like they are too narrow, but you get a list of actual model numbers you could research instead.

If your cache is fake (which is likely, because the chips look dodgy), the BIOS knows that "enabling cache" is just for show, and possibly never even tries to actually enable the L2 cache. Replacing the fake chips by real chips might not help unless you patch the BIOS to support real cache. If making or searching the Internet for BIOS patch or re-programming the BIOS of your board is beyond your comfort zone, it likely isn't worth to spend money on real cache chips.

brand new 32K x 8 $4 https://www.digikey.com/en/products/detail/re … SA12TPG/2011023

mkarcher wrote on 2024-02-08, 06:40:

There are other possibilities for this behaviour: The BIOS might correctly detect and initialize the L2 cache, and then intentio […]
Show full quote

CoffeeOne wrote on 2024-02-07, 23:46:

Obviously the Bios telling there is 256kB of cache, but there is none, is also a very strong hint for fake cache.

There are other possibilities for this behaviour: The BIOS might correctly detect and initialize the L2 cache, and then intentionally disable it when it boots into DOS: For example, some boards implement the turbo/de-turbo feature by disabling L2 cache, so if this board requires the turbo switch pins to be bridged to run in turbo mode, and the turbo switch pins are open, you could observe this behaviour, too.

fsinan wrote on 2024-02-08, 05:47:

At bios it is enabled. 256K reported but it seems it is fake. I would like to buy a set of srams but almost all sellers do not offer tag-ram. I couldnt find on ebay.

The tag ram claims to be a standard fast 32K x 8 SRAM with an access time of 15ns. They usually have model numbers like 61256 or 62256. I found some offers searching for "15ns 32kx8 dip". The results look like they are too narrow, but you get a list of actual model numbers you could research instead.

If your cache is fake (which is likely, because the chips look dodgy), the BIOS knows that "enabling cache" is just for show, and possibly never even tries to actually enable the L2 cache. Replacing the fake chips by real chips might not help unless you patch the BIOS to support real cache. If making or searching the Internet for BIOS patch or re-programming the BIOS of your board is beyond your comfort zone, it likely isn't worth to spend money on real cache chips.

I can do it, no problems. I need one 28-dip tagram and 4 32-dip modules.

Curious about this possibly fake L2 cache case, I’ve looked at the available BIOSes for this board on TheRetroWeb. The https://theretroweb.com/motherboards/s/u-boar … emicolon-b#bios page lists 2 BIOSes that have the same date.
A 03/20/96-UMC-881/886A-2A4X5U03C-00 and a 03/20/96-UMC-881/886A-2A4X5000C-00 BIOS. The later has the “U0” manufacturer ID for U-Board removed, usually a telltale sign of an illegal BIOS.

These BIOSes are compressed so after decompressing the “original.tmp” main module from both BIN-files, I could compare these BIOSes.
Call me not surprised when I found one extra piece of code in the suspect 2A4X5000 BIOS. This extra code sets the L2 cache value at a fixed 256KB for display on the BIOS summary screen, irrespective of the actual L2 value as detected earlier during POST!
Apart from this extra routine, these BIOSes are identical.

So the 2A4X5U03C BIOS is the correct BIOS for your board, and the (illegal) 2A4X5000C BIOS was fixed to hide fake cache!
@fsinan, this find makes it very likely you have fake cache on your board. What is the BIOS-ID of your BIOS now?

Regards, Jan

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

fsinan wrote on 2024-02-08, 14:33:

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

If the only difference in the "fake cache Bios" is to show always 256kB in the startup screen regardless of the amount of detected cache, I think it is fine, when you keep it.
When you are going to buy real sram chips, then I would suggest to buy 4 times ISSI61C1024-15 from China and one time 32kx8 15ns any brand.
The ISSI chips are mostly also fake (re-labelled), but most of them work, so buy 5 pieces of it. With a bit of luck 4 of it will work.
=> Then you have 512kB of cache, which is maximum for the board.

I would not worry about motherboard cache.
As long as you have 64kb thats fine.
256kb or 512kb of cache will only get you about a 2% performance boost at best.
It’s not worth upgrading. If you really want a performance boost upgrade the CPU to a faster one.

Intel486dx33 wrote on 2024-02-08, 15:38:

I would not worry about motherboard cache. As long as you have 64kb thats fine. 256kb or 512kb of cache will only get you about […]
Show full quote

I would not worry about motherboard cache.
As long as you have 64kb thats fine.
256kb or 512kb of cache will only get you about a 2% performance boost at best.
It’s not worth upgrading. If you really want a performance boost upgrade the CPU to a faster one.

Totally off the topic.

fsinan wrote on 2024-02-08, 14:33:

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

Changing to the official BIOS does not hurt. Of course the message "256KB Cache" during boot will disappear as long as no cache is installed, but the official BIOS is fully prepared to work on a board without any working cache chips. You might get a BIOS complaint like "CACHE MEMORY BAD - DO NOT ENABLE CACHE", but IIRC that's a message on earlier BIOSes, and most likely AMI. If I remember wrong and you get that message with the original BIOS, just disable the L2 cache and you are fine.

mkarcher wrote on 2024-02-08, 17:14:

fsinan wrote on 2024-02-08, 14:33:

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

Changing to the official BIOS does not hurt. Of course the message "256KB Cache" during boot will disappear as long as no cache is installed, but the official BIOS is fully prepared to work on a board without any working cache chips. You might get a BIOS complaint like "CACHE MEMORY BAD - DO NOT ENABLE CACHE", but IIRC that's a message on earlier BIOSes, and most likely AMI. If I remember wrong and you get that message with the original BIOS, just disable the L2 cache and you are fine.

I agree, the official 2A4X5H03C BIOS should work fine and will indicate the actual L2 cache size. With the fake chips it will display “None”. 😉

Because the 2A4X5000C only “fixes” the L2 cache size display to 256KB and doesn’t display any cache warning messages, I believe the 2A4X5H03C BIOS won’t complain about the fake L2 cache either.

Note that your BIOS is stored in a D27C010 128KB UV-EPROM chip and can’t be flashed.
Do you have an (E)EPROM programmer to program a new chip? It is usually easier to get a new 27C010 or equivalent (E)EPROM chip to program the official BIOS in, and keep the old BIOS chip as backup. It saves the hassle of erasing the old chip with UV-light first.

Cheers, Jan

Chkcpu wrote on 2024-02-08, 19:09:

I agree, the official 2A4X5H03C BIOS should work fine and will indicate the actual L2 cache size. With the fake chips it will di […]
Show full quote

mkarcher wrote on 2024-02-08, 17:14:

fsinan wrote on 2024-02-08, 14:33:

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

Changing to the official BIOS does not hurt. Of course the message "256KB Cache" during boot will disappear as long as no cache is installed, but the official BIOS is fully prepared to work on a board without any working cache chips. You might get a BIOS complaint like "CACHE MEMORY BAD - DO NOT ENABLE CACHE", but IIRC that's a message on earlier BIOSes, and most likely AMI. If I remember wrong and you get that message with the original BIOS, just disable the L2 cache and you are fine.

I agree, the official 2A4X5H03C BIOS should work fine and will indicate the actual L2 cache size. With the fake chips it will display “None”. 😉

Because the 2A4X5000C only “fixes” the L2 cache size display to 256KB and doesn’t display any cache warning messages, I believe the 2A4X5H03C BIOS won’t complain about the fake L2 cache either.

Note that your BIOS is stored in a D27C010 128KB UV-EPROM chip and can’t be flashed.
Do you have an (E)EPROM programmer to program a new chip? It is usually easier to get a new 27C010 or equivalent (E)EPROM chip to program the official BIOS in, and keep the old BIOS chip as backup. It saves the hassle of erasing the old chip with UV-light first.

Cheers, Jan

No I dont have a programmer and wasnt aware of that. This board gave me so many probems....

Can I change the ROM chip to a flashable one?

by Chkcpu analysis:
>Apart from this extra routine, these BIOSes are identical.
you wont gain anything by flashing official bios

rasz_pl wrote on 2024-02-09, 15:28:

by Chkcpu analysis:
>Apart from this extra routine, these BIOSes are identical.
you wont gain anything by flashing official bios

That's what I wanted to say, too. Complete overkill to get a programmer and buy a new chip in this case.
Changing to the official BIOS does not hurt is true, but only if you have everything at hand.

Chkcpu wrote on 2024-02-08, 19:09:

I agree, the official 2A4X5H03C BIOS should work fine and will indicate the actual L2 cache size. With the fake chips it will di […]
Show full quote

mkarcher wrote on 2024-02-08, 17:14:

fsinan wrote on 2024-02-08, 14:33:

WOW Great find, thank you. Mine is "2A4X5000C"...So it is fake...What happens if I change the bios? Does it boot? Later I'll change the chips.

Changing to the official BIOS does not hurt. Of course the message "256KB Cache" during boot will disappear as long as no cache is installed, but the official BIOS is fully prepared to work on a board without any working cache chips. You might get a BIOS complaint like "CACHE MEMORY BAD - DO NOT ENABLE CACHE", but IIRC that's a message on earlier BIOSes, and most likely AMI. If I remember wrong and you get that message with the original BIOS, just disable the L2 cache and you are fine.

I agree, the official 2A4X5H03C BIOS should work fine and will indicate the actual L2 cache size. With the fake chips it will display “None”. 😉

Because the 2A4X5000C only “fixes” the L2 cache size display to 256KB and doesn’t display any cache warning messages, I believe the 2A4X5H03C BIOS won’t complain about the fake L2 cache either.

Note that your BIOS is stored in a D27C010 128KB UV-EPROM chip and can’t be flashed.
Do you have an (E)EPROM programmer to program a new chip? It is usually easier to get a new 27C010 or equivalent (E)EPROM chip to program the official BIOS in, and keep the old BIOS chip as backup. It saves the hassle of erasing the old chip with UV-light first.

Cheers, Jan

Does the modified bios display the correct amount of cache when real cache is present, ie 64, 128, 256, 512K, or will it always display the fake 256K amount ?