PLCC or DIP?
Lots of eBay results from China but I saw 3 from the US (use the "US only" filter), all the US listings are for PLCC versions though.
One of the US results has no picture but they give the part number as SST27SF010-70-3C-NH, which makes it PLCC.
In case it helps search, the SST datasheet gives these package codes:
NH = PLCC 32pin
WH = TSOP 32pin
PH = DIP 32pin

If this is for a motherboard then you might be able to substitute other parts, such as 29F010 which has a lot more search results. From a quick look at the datasheet the pinout matches except a possible wrinkle if you want to flash the chip in the board. The board might support flashing it and might not.

There's also a 256KB version of your chip with part number 27SF020 which has a couple US results in DIP packaging. The only difference between those is an extra address pin which is "NC" on the smaller version.
For reading purposes, I doubt the motherboard would care about the difference.
Flashing software could be picky about the chip's identification, but I think UniFlash wouldn't care.

If you flash a 256KB chip outside the mobo then double the image first

1copy /b  bios.bin+bios.bin bios256K.bin

and burn the doubled version to the chip. That way the extra address line won't matter.

Thanks for the response!

Yes I’m needing a DIP version for a Zida/Tomato 4DPS 486 board. I mistakenly inserted the original bios backwards and toasted it. So mad at myself for not triple checking orientation.

I went ahead and ordered a TL866II programmer and I found a listing for some
ATMEL AT29C020-15PC EEPROMs on eBay. The pins seem to match up from the data sheet I found. It is a larger 256k chip so I’ll double the image as mentioned. Do you think this would work?

yes it will work just fine!
also a UV eprom 27c010 will work - you just won't be able to do updates on BIOS on the motherboard with awdflash

keropi wrote on 2020-08-06, 09:45:

yes it will work just fine!
also a UV eprom 27c010 will work - you just won't be able to do updates on BIOS on the motherboard with awdflash

Awesome, I’m kind of excited to try this out, thank you!

keropi wrote on 2020-08-06, 09:45:

yes it will work just fine!
also a UV eprom 27c010 will work - you just won't be able to do updates on BIOS on the motherboard with awdflash

Would it be correct to assume that machines that have an ISA Plug n Play BIOS on up are the ones that actually need EEPROM? (Due to the ESCD)

jakethompson1 wrote on 2020-08-07, 00:31:

keropi wrote on 2020-08-06, 09:45:

yes it will work just fine!
also a UV eprom 27c010 will work - you just won't be able to do updates on BIOS on the motherboard with awdflash

Would it be correct to assume that machines that have an ISA Plug n Play BIOS on up are the ones that actually need EEPROM? (Due to the ESCD)

Most (I think nearly all) 32-bit era boards save everything into battery backed RAM. A lot of early boards have the RAM combined with the battery in those NVSRAM chips. After that there's just a simple battery socket, and on those boards I believe the RAM that holds the settings is typically in the southbridge chip. Any of those boards ought to work with a regular EPROM as long as the pinout matches for reading.

The earliest motherboard I've seen that saved some settings into the Flash ROM was a very late AthlonXP board (ABit AN7) which is probably from 2004 or something like that (pretty sure they had Athlon64 boards by the time it came out). The BIOS on that board displayed a warning message when some changes were being saved, and there was an obvious delay while it flashed the chip. That process made me nervous every time, but it never failed on me.

Boards that save settings into the Flash ROM might be more picky about what kind of chip you use. Flash chips that are otherwise similar to each other can have different schemes for programming and sector protection.

EpoX P55-TX2 (around 1997) saves things in the Flash ROM. At first I suspected a corrupted BIOS, since the image inside was different from all the files I had, but then noticed that a section always changes, containing strings such as CPU name (in plain text) among other things. I concluded it must be the ESCD or DMI data, and my guess is that the behaviour is not unique to this board.

So I'd say using Flash instead of an UV-EPROM should be safe; the other way around, not so much.

Just wanted to say thanks again, got my 4DPS 2.1 running! Used an Intel chip that showed up first.