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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.
 

jasa1063

Member
The memory configuration I went with was 4x256KB 60ns SIMMs in Bank A and 4x16MB 60ns SIMMs in Bank B. I then used the IIsi RAM-Muncher INIT extension to allocate all the remaining memory in Bank A for video. On most benchmarks I get over a 20% improvement in performance vs the benchmark running in Bank A. While you can install a NuBus video card, I have found the IIci internal video to be faster. NuBus cards run at 10MHz, while the memory in the IIci is running at 25MHz. Unless the NuBus video card has hardware acceleration, the IIci video should win out.
 

Fizzbinn

Well-known member
The memory configuration I went with was 4x256KB 60ns SIMMs in Bank A and 4x16MB 60ns SIMMs in Bank B. I then used the IIsi RAM-Muncher INIT extension to allocate all the remaining memory in Bank A for video. On most benchmarks I get over a 20% improvement in performance vs the benchmark running in Bank A. While you can install a NuBus video card, I have found the IIci internal video to be faster. NuBus cards run at 10MHz, while the memory in the IIci is running at 25MHz. Unless the NuBus video card has hardware acceleration, the IIci video should win out.
Ditto to this! Although I just up the Disk Cache instead of using RAM-Muncher. If you are only interested in 8-bit 640x480 this has the benefit of fast video and a significant speed bump.
 

slomacuser

Well-known member
We are talking about IIci not IIsi, so the RAM-Muncher does nothing special to it as IIci has no built in DRAM
 

volvo242gt

Well-known member
Except in one case. And that would be, as an example, a IIci 5/80. The IIsi RAM-Muncher INIT works in a IIci when bank A contains 1MB of RAM. Only. Once you have more than 1MB of RAM in bank A, it doesn't really help much at all. The same effect can be achieved by upping the disk cache to 768K on those IIci machines that have 1MB of RAM in bank A.
 

MrFahrenheit

Well-known member
I did some benchmarks on a IIsi whereby o increased disk cache settings until the benefit of increasing it leveled off.

Performance increased about 20% on average by bumping disk cache size to 384kb but leveled off and has no discernible benefit above that.

Not sure why or how that works, but you don’t need to fill the entire 1MB on a IIsi to shift the video over, it can be done with only a small increase in disk cache.

If you have a IIsi and are able to verify my results I’d love to know I’m not alone. I’ll try and find my photo of the results and update here.

Edit: found it

C3E44799-B2E6-4C01-BC84-8A3C00286A2C.jpeg87AAE8ED-7A5C-437E-94E4-09699062B98B.jpeg
 
Last edited:

jasa1063

Member
We are talking about IIci not IIsi, so the RAM-Muncher does nothing special to it as IIci has no built in DRAM
The 1MB memory soldered onto the motherboard on the IIsi is in Bank A which is also where the video memory is. The video memory on the IIci is also in Bank A, so the Isi RAM-Muncher INIT works exactly the same as it does in the IIsi with 1MB of memory installed in Bank A on the IIci.
 
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