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What is the Maximum RAM on a Mac II Series Mac?

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Has anyone figured out, done or otherwise documented the maximum amount of maximum RAM on a Mac II Series Mac and with what type of RAM?


I know of one case - MacClassic and his SE/30 having 69Megs using EDO RAM. This is his post:



In theory he could have 128MB of RAM on the SE/30 but did not have enough resources to get it done. Personally I would like to know what is obtainable in theory and what was done in the past by the members.

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The SE/30 can accommodate 128 megabytes of memory, and the IIx, IIcx, IIci, and IIfx can also do 128MB. The IIvi/vx/P600 are said to accomodate 68 megs of memory and the IIsi, 65 megs.


I had either 33 or 65 megs in my IIsi back when I had and was using it. I had a Performa 600 (IIvx) as well, but never really put a whole bunch of memory in that system. Maybe 16-20 megs or there-abouts.


At about the same time, I also had an 840 and it never made sense for me to try to hot-rod a II series system beyond what my 840 was able to do, because this was well before RAM had that much bearing on how fast a computer worked (in the way that just adding more RAM to a new Mac today will help the whole system run faster because the system will fill it with disk cache, etc.)


I used my IIsi's unusually high amount of RAM (it came to me that way) and an FPU that had been installed to run A/UX, which was probably the only thing it ever did that my 840 couldn't or didn't do better, even if the 840 didn't have as much memory. (I think I had 40 or 48 megs in my first 840 though.)

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You would have to be a really demanding power user to actually need 128mb in a Mac that old. Upgrading it that high just because you can when you have no use for it is a questionable use of your vintage computing funds when you could be using that money for acquiring something else for your collection. Unless you have an unlimited budget and don't have to worry about things like rent, food, and utilities. :D

Edited by Quadraman
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128MB on a Mac II Series is only using 16MB SIMMs on 8 slots. 16MB SIMM, though not cheap, can be found at low cost on sites like Ebay. Compared to 128MB PC100/133 DIMMs? It's about the same if not a bit more. All one has to do is search for it.


Though I doubt I would be pushing a Mac to that extreme, more memory is always better. I do deal with multi-media files and no matter the system used, the files take up a lot of RAM to process.

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The last time I bought 16 meg 30 pin SIMMs, they were less than $10 apiece. That's still not dirt cheap, but it's not bad, especially since you'll never need to replace them. I think it cost $60 for all eight.


Mac OS doesn't need that much memory, but aside from the memory test, it certainly doesn't hurt. If you prefer to not reboot often, it's all the better that applications can open with the full amount of memory they want and memory fragmentation isn't an issue.


I'm in the market for sixteen 16 meg 30 pin SIMMs for the Amiga version of the SE/30 - the original Amiga 3000. It has a FastLane Z3 which can take up to 256 megs. Do I need it? No. Do I want to max it out just so it's maxed out? Yes. I doubt I'll be trying to build gcc on it any time soon, which so far is the only thing that absolutely won't work with less than 256 megs. It might be an interesting experiment to see how many weeks it'd take, though...

Edited by johnklos
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i would like to add.


LC-III - 36 megs is the best i could get.

LC-475-605 - 128megs

pretty sure the 

LC-575 is 64 megs of ram.


the Power Mac 6100, will accept (2) 128 meg simms… 256 megs of ram!


and bbraun was able, with a ROM hack get his quadra 650 i believe to 512 megs of ram…. 

Pretty sure the Quadra 800 is also capable of 512 megs or ram with the rom hack.


also desoldering the onboard ram with the lc-475 / q605      gets you some better performance


and you can desolder the ram from the IIsi…  and solder on the ram chips form any of the 4mb onboard,  mac boards, and solder it onto the IIsi to take you from 1mb to 4mb onboard.

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I'm pretty sure that the LC475 has 4MB RAM soldered onto the motherboard, so 132MB is the limit.

I have that and it is an impressive sight. I got my 128MB SIMM from a Sun Cobalt server. They get hot too.

They are big fellows and the block the heatsink on the CPU, if you've managed to beef up the processor to 68030 33MHz or beyond.

My plan is to boot to a system with a massive RAM disk (say 64MB) use an AppleScript to copy the System Folder across to the RAM disk and reboot from the RAM disk.

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On the topic of why you'd even want so much RAM: I think the biggest reasons would be to run A/UX, which is probably the one situation on an old Mac where just having more RAM will help, because UNIX operating system. The other situation would be if you were running 7.6.1 or 8.1 (with WishIWere or whatever) on such an '030 system.


The 900/950 can use 256 megs of RAM, and the main reason for that is almost certainly its purpose as a content creation and UNIX workstation. (The official was originally listed at 64, I wonder when that changed, it's likely just a result of bigger SIMMS becoming available.)


512MB in a 650/800 (same system, different case) would be neat, but I question what you'd really be doing with it that wouldn't be better done with something that has a beefier CPU and storage for the era. That won't stop people from doing it though, and it would be a sight to behold for sure.


Otherwise, In the actual '80s and early '90s if you needed 128 (or 256/512) megs of RAM for something you probably also needed a little bit more CPU horsepower than the 68030, and better software than Mac System 6 or 7.


In re ram temperatures: I would classify it as "abnormal" for memory in Macs to get really warm. Anybody else who has 64/128MB simms, do those get very warm? It may be worth finding cooler RAM for an LC series machine, ArmorAlley -- I personally believe that (especially if the RAM gets hot too) that hot-rodding LC-series machines with >100MB RAM and 10k SCSI disks will eventually cause problems, because those systems don't really have that much in the way of cooling.

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i bet we could run that by the guy who created the aztechmonster? maybe he wants to whip one up and sell it?


so the presto plus, one could desolder the cpu and install a faster cpu and re-clock it with the oscillator?

does yours have a LC or full 040 on there?   Zack sent me his presto plus, with his LC, and i poped his 16 meg simm out

and installed a 32 meg one.  it worked just fine in his LC I,  he was screaming along, lol with 42 megs of ram... Running Mac OS 8.1!!!!

pretty sweet.

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What about the use of SIMM Tree (or stacker or saver) that lets one plugs 2 or 4 matching SIMMs into one existing slot?  At one time I had a pair (left and right low profile, there was high profile for system that had 4 slots as the high profile could fit over low profile) for my Centris way back when memory was at a heart attack inducing $50 per MB and I was able to get a few 4MB sticks dirt cheap.  A few years later I sold those 4MB and the tree and got a 32MB SIMM for something like $30 new.


Dang I am old.  Today I could get 2 high performance 32GB (2x16) RAM for modern PC for that same $200 a single 4MB stick went new back in '93, and that's not factoring inflation.

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Speaking of memory, I've been pondering just how much memory should I put in a recently acquired Macintosh IIsi (it currently has 3MB, which is really unacceptable). 

My basic goal is to run System 7.5.5 or Mac OS 7.6.1 at an acceptable speed, and maybe play some games on it (nothing really serious). I've been thinking of running A/UX on this baby, but I guess I'd need to find a coprocessor PDS board before (any suggestion?). 
I googled a bit and I was oriented towards putting 16MB on it, would it be enough? Should I look directly for a more substantial 64MB upgrade?

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For that IIsi, I have seen many networking cards come with a with an empty socket for an FPU. 


For memory, max out what you can afford. I think somebody was selling some ram here or $30. But in the very least one might want to over clock the cpu to 25MHz. If you want AUX for it, it will need the RAM and Hard drive as much as possible.

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