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Macintosh IIci RAM configuration

slomacuser

Well-known member
I want to set mine IIci for 20 MB RAM as below on graph the BANK B is 4x 1MB and BANK A is 4x 4MB. But notes contradict the graph with "For best performance with on-board video, put the smaller SIMMs in BANK A. So what is right position now? BANK B 4x 1MB, BANK A 4x 4MB or BANK B 4x 4MB, BANK A 4x 1MB?

IIci_RAM.jpg
 

jessenator

Well-known member
Yes, and the Apple Memory Guide indicates something similar:
FnRscy5h.jpg


I found all sorts of anecdotal evidence while trolling some older sites: some saying the tech info is wrong, others claiming there's a hardware limit to 16MB total...All sorts of things...

What I also found was an Apple technical document. Some interesting things in there.

Having the RBV (RAM-Based Video) chip (Figure 4, #5) on the logic board enables the Macintosh IIci to drive a 640 x 480 screen at up to 8 bits/pixel and a 640 x 870 screen at up to 4 bits/pixel without the need for a video card.
If there is RAM in both bank A and bank B, the Macintosh IIci will operate more efficiently with the larger RAM SIMMs in bank B.
If you are using built-in video, you must 'have SIMMs in
bank A, because the built-in video uses bank A for
video framing. If you are using a video card, then using
bank A is optional.

So what I'm gathering is that you should keep your 4MB SIMMs in Bank B, and the smaller ones in Bank A. However, since the max resolution and color depth is technically 640x480 at 8-bit, there's not much use in putting in more than the minimal amount of RAM into Bank A, for video at least.

So that 17MB configuration would seem to be the most efficient one, on paper anyway. I don't have one to test on, with something like MacBech to do a video suite, to test between the 17MB and a 20MB. My guess would be negligible improvement.


Beyond what you're asking:
My supposition is that the complaints from those users in the late '90s were from using mixed RAM, and/or running larger configs of RAM with built in video which led to their instability; that an external video card would have alleviated the problems.

Since the internal video wasn't designed for anything heftier than 640x480@8-bit, it might just be overwhelmed?

I'd like to know how these limits work in the real world. The IIci I had for s while only had 20 MB as well, so I never tested the upper ranges of memory.
 
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