SRAM speed question

MackAttack

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I need to replace some SRAM (9M and 9K on an Atari Assault PCB; part number: HM62256LP-12
Jameco has a similar Hitachi product but rated at 150ns where my SRAM chips show 120ns.

Will the 30ns difference in speed make any difference?
Recommendations for other vendors are welcome.

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So I've always gotten away with matching or faster (lower number) for speed on RAM, but how is this figured out when it's manufactured? Is it a test and they put the different speeds with different labeling?
 
So I've always gotten away with matching or faster (lower number) for speed on RAM, but how is this figured out when it's manufactured? Is it a test and they put the different speeds with different labeling?

That's exactly what they do. It's called a "bin split" or "binning". You test each device to see how fast it will go. You test it at different speeds and you throw it a bin marked with it's fastest passing speed. If you try to make a 100ns part, most of them will work at 100ns. But some of them will only work at 120ns. Some small number are super slow and only work at 150ns. And a few just suck. Those get tossed in the 200ns bin. And some of them over perform and reach 70 ns. A few of them are ridiculous and acheive 55ns. That's how it works! You make 100 parts and test them all. You get three 200ns parts, seven 150ns parts, fifteen 120ns parts, sixty seven 100ns parts, ten 70ns parts, and two 55 ns parts.
 
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