Interchangeable BIOS chip?

[Beton]

Hi guys!
This might be a stupid question but nevertheless I would like to know the answer.
Recently I bought a bunch of spare or repair motherboards.
One of them misses the BIOS chip. The chip is the MX25L4005A. Every voltage rails are fine on the motherboard but obviously it won't post without the BIOS. And even with the BIOS chip it's not guaranteed to boot up, somebody removed the ic for a reason.
So I have another one motherboard which has a somewhat similar BIOS chip, the MX25L8005. The only difference is that the former is a 4mbit while the latter is 8mbit chip but everything else is the same according to the datasheets, voltages, sector size, currents, etc.

So can I put the 8mbit chip onto the 4mbit board and expect it to work?
My guess is yes but maybe somebody did this kind of "repair" before me and knows the answer because I don't want to waste the time with this in case it's a failed attempt from the beginning because 4 of the 8 pads are missing so I also have repair those. I could order the chip from aliexpress (5 pieces / 1.5USD) but it would arrive in March next year...

Thank you in advance for the answer.

[foshland]

Re: Interchangeable BIOS chip?

If the boards are the same, maybe the size of the bios chip doenst matter, while the info inside is the same. Maybe the 8mb one is half unused and filled with FFF or 000

[piernov]

Re: Interchangeable BIOS chip?

Must use same size. Using larger size can work on older platforms but will still cause problems such as not being able to update the BIOS with vendor tools.

https://logi.wiki/index.php/User:Pie...part_number.3F

[Beton]

Re: Interchangeable BIOS chip?

Thanks. These two MBs are fairly old (<2009) and they use BIOS and not UEFI. UEFItools doesn't show the descriptor region where the VSCC table would be.
Later on updating the BIOS can be an issue yes although in my mind this is like replacing a a 1MB disk with a 2MB disk consisting the same 1MB program. I might try it later.

[DynaxSC]

Re: Interchangeable BIOS chip?

Hi, in my opinion it will work. You only need to program the first half on the bios chip. Put the latest BIOS available on the vendor site, so you never need to update any more as this is an old mobo without any support. Some vendors personalize the bios chips, eg. ASUS, eg. with serial no and network MAC address for the network module. There are tools to transfer such information into the BIOS file (the bios from the vendor site will not be personalized), eg. UEFI Tool, but I'm not sure if UEFI tool handles also old non UEFI bioses, probably not. But there should exist some older tools. But usually the mobo's work also with unpersonalized bioses, but the MAC is then all zeros or FF's. Might theoretically give some network problems.