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IIsi RAM Upgrade

CygnusTM

Member
I recently picked up a IIsi. It came with 5MB of RAM (4 1MB SIMMs installed), and I am trying to upgrade to 17MB. I picked up 4 4MB SIMMs on eBay (https://www.ebay.com/itm/224577279767), and the IIsi won't see the SIMMs at all. I've tried reseating it and a PRAM reset. How picky is the IIsi about RAM? My research tells me that the SIMMs I bought should work. I haven't seen anything warning against parity, low profile or 3 chip SIMMs. Thanks.
 

Fizzbinn

Well-known member
Is this an issue with 2 chip 4Mbit SIMMs vs. 8 chip 1Mbit chip SIMMs?

From the Macintosh IIsi Developer Note:

“The Bank B expansion memory can contain either four 256 KB SIMMs (made from 1-Mbit fast page mode parts), four 1 MB SIMMs, four 4 MB SIMMs, or four 16 MB SIMMs.”​
Is the “made from 1-Mbit fast page mode parts” comment really only about 256KB SIMMs?

All the 30-pin SIMMs I have are 8 or 9 chip, 256KB, 1MB, and 4MB.

Anyone using 2 (or 3, supporting parity that the IIsi ignores) chip SIMMs in their IIsi? (or IIci, which has the same memory architecture from my understanding)
 
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bibilit

Well-known member
The IIsi is a bit picky about ram, had an issue recently, strange issue is that the IIsi is able to cope with 2Mb sticks and not other machines.
 

CygnusTM

Member
They should be fine as long as they're 100ns or faster and they need to be installed in a matched bank (four identical simms), though I've not seen anything about parity compatibility so unsure if that would be the issue. This page suggests that it shouldn't be:

Yeah, that was one of the pages I used when I was researching. These are FPM chips with better than 100 ns speed, so I thought they would work.
Is this an issue with 2 chip 4Mbit SIMMs vs. 8 chip 1Mbit chip SIMMs?

From the Macintosh IIsi Developer Note:

“The Bank B expansion memory can contain either four 256 KB SIMMs (made from 1-Mbit fast page mode parts), four 1 MB SIMMs, four 4 MB SIMMs, or four 16 MB SIMMs.”​
Is the “made from 1-Mbit fast page mode parts” comment really only about 256KB SIMMs?

All the 30-pin SIMMs I have are 8 or 9 chip, 256KB, 1MB, and 4MB.

Anyone using 2 (or 3, supporting parity that the IIsi ignores) chip SIMMs in their IIsi? (or IIci, which has the same memory architecture from my understanding)
I did find one page (https://oldcrap.org/2018/11/25/macintosh-iisi/) that seems to show a IIsi with 3-chip SIMMs.
 

CygnusTM

Member
So after examining the SIMMs more closely and searching part numbers on the PCB, I found that these aren't the Samsung parts stated in the listing. They are actually Siemens parts that I can't find much info on. So they are getting returned. I bought another set that specifically says they work in a IIsi, so I should have better luck with those. Thanks for the insights, everyone.
 
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