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First post, by Arvid

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I want to upgrade the BIOS on some socket 3 motherboards. What kind of chips does these motherboards usually use and what size is needed? Can you use a larger size than needed or do they need to be exact?
Is it possible to use EEPROM chips so I don´t have to use a UV eraser if I want to erase them?

Reply 1 of 7, by Deksor

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Which motherboard do you use ?
most 486 motherboard use 64KB ROMs which are very often compatible with 27C512 chips, but some socket 3 boards use 128KB chips of another kind (same kind as later pentium boards)

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Reply 3 of 7, by Arvid

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Deksor wrote on 2021-01-13, 16:22:

Which motherboard do you use ?
most 486 motherboard use 64KB ROMs which are very often compatible with 27C512 chips, but some socket 3 boards use 128KB chips of another kind (same kind as later pentium boards)

There are a couple of motherboards, I don´t have access to look at them right now but one I remember the name of is MS4144. It´s a PCI 486 board, and it seems the BIOS file is 128kb.

TheMobRules wrote on 2021-01-13, 16:28:

Yes, 27C512 is the most common one, in that case you can use W27C512 as a replacement which is an EEPROM and doesn't require UV to be erased. Several late 486 boards already come with EEPROMs.

I tried searching for this part number on mouser but it was listed as discontinued. Is there another variant that mouser sells that I can use? Should I just order 128kb variants and use that for BIOS files that are 64kb or should I use the "correct" size for the motherboard?

Thanks for all help in this matter, I´m completely new to ROM chips and burning them. I did recently manage to burn a XTIDE ROM and use it in an old 286 but that is all the experience I have in these matters 😀

Reply 4 of 7, by adalbert

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Arvid wrote on 2021-01-13, 16:46:

I tried searching for this part number on mouser but it was listed as discontinued. Is there another variant that mouser sells that I can use? Should I just order 128kb variants and use that for BIOS files that are 64kb or should I use the "correct" size for the motherboard?

128KB chip may work, but only if you duplicate the BIOS file contents, by doing something like that: copy /b 64kbios.bin + 64kbios.bin 128kbios.bin

Reply 5 of 7, by Arvid

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I have found out that two of the boards I intend to update have 28 pin chips so for those I can use the W27C512 that was suggested.
However for the board that use 32 pin DIP chip that needs 128kb (1 mbit) of space, what chip do I need there? Does someone have a model number so I know what to order?

Reply 7 of 7, by Arvid

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frudi wrote on 2021-01-14, 11:01:

I'm using 29EE010 on my Asus PVI-486SP3. I don't recall if it originally came with this chip or if I replaced it at some point, in any case it works.

Thank you, I will try one of those.