Mostek MK4027N-2 for Apple-1.

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Last seen: 7 months 3 weeks ago
Joined: Jan 30 2021 - 11:55
Posts: 50
Mostek MK4027N-2 for Apple-1.

Hello everyone. 

I have found locally some Mostek MK4027N-2 dram ic's. My question is. Are this rams a good choice for my Apple-1 replica. In case that I am not in hurry to get them as my replica it's not ready to boot, should  wait for other speed type or get the before disappear?


Thank you!

Last seen: 1 week 1 day ago
Joined: Apr 1 2020 - 16:46
Posts: 636
All 16-pin 2nd generation 1kx4 DRAMs work in the Apple-1 ...

... as long as they follow the industry standard pinout and signaling. I've sucessfully used Motorola MCM4027, Mostek MK4027, and Intel D2104.


Note that I gave no suffixes to the type numbers as these just encode package type, temperature range, and speed grade: any exisiting combination of them work with the Apple-1. People always worry about speed but you can ignore it, as all 2nd generation DRAM were made with a silicon gate process technology and hence it's impossible to get a slow one that would be slower than the fastest 1st generation DRAMs which had metal gates. The timing oneshot in the Apple-1 must be set right, of course, to 480ns (as seen in the manual).


This freedom of choice opens up a tremendously large source of parts. There are still some 10,000 of each type available at chip brokers - per broker !

Mostek is particularly abundant, but expect tarnished leads (high silver content). 


As for your question if these MK4027 you have seen are "good", I can't answer it. Beware of socket pulls ! One vendor tried to sell me those and when I requested a sample tube, there were half a dozen duds in them which my diagnostics PROM immediately identified. So no deal here ! The dirty little secret is that back in the day these DRAMs were expensive and so OEMs producing memory boards would pull bad ones out of the sockets and put them back into tubes to resell to surplus places catering hobbyists. This is how you may end up with another guy's rejects.


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