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256AK vs 257AK Cache

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First post, by feipoa

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Does anyone know what the difference between 486 cache (2 rows of 14 pins) that is marked as *256AK-15 vs. that marked *257AK-15?

I have, for example, cache with markings:
UM61256AK-15

And some as:
W24257AK-15

I am inclined to think that that the *257 contains an extra Kilobit. Any ideas why? Is it for error detection? A parity kilobit? Is the *257 slightly faster and thus intended for use as a the TAG-RAM?

Reply 1 of 3, by Old Thrashbarg

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No, different manufacturers used different part numbers, that's all... the UM61256 is a UMC chip, the W24257 is a Winbond chip, and they're both 32Kx8 SRAM chips.

Reply 2 of 3, by feipoa

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Are you speculating or do you know this from past research or experience? ISSI and Alliance also use *256 notation.

I am puzzled one company would take the oddball part number approach. Winbond's 64K chips read *512, which makes sense, not 513 or 514. I have the spec sheet for the W24257AK-15 chip which does specify 32768 x 8, so I guess they wanted to be different. I see no mention of anything special like error detection.

Reply 3 of 3, by Markk

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It is indeed as Old Thrashbarg says. I had found a table some time ago, that mentions all the different part numbers of each manufacturer, that all correspond to the same type. But unfortunately I can't seem to find it right now.
I also can tell you for sure it is the same, as I happen to have lots of chips of each type (winbond/umc - 257/256) and they work the same way...

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