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Help! memory expansion for Quadra 650

Classicman

Well-known member
Hi dear friends!
Please can you help me with the memory expansion for my Quadra 650?
On ebay and other web marketplace I have found various offers for simms 72 pin and for “EDO” simms… This last type is compatible with my Quadra?
60ns, 70ns, 80ns??
I am quite confused… I ask to the experts for clarification.
Thank you all in advance!
 

Phipli

Well-known member
Hi dear friends!
Please can you help me with the memory expansion for my Quadra 650?
On ebay and other web marketplace I have found various offers for simms 72 pin and for “EDO” simms… This last type is compatible with my Quadra?
60ns, 70ns, 80ns??
I am quite confused… I ask to the experts for clarification.
Thank you all in advance!
Some machines are compatible with EDO, but others aren't, some EDO works when you wouldn't expect it to. I try to find FPM memory for my 650. FPM is what it was spec'd for.

If I was you I'd not buy EDO for my 650 because it is a gamble and you might end up having to try to return it and be charged a restocking fee.

Is this of interest? :
 

Phipli

Well-known member
This should work in the 650... and be insanely over the top if you got four :


If you do get them, don't bother getting 4 because the memory test takes about two minutes before the machine starts booting.

Even 32MB is plenty of RAM.
 

Classicman

Well-known member
Thank you all!!! All precious informations!
Now I have clear ideas regarding the memory expansion of my Q650! :giggle:
 

Juror22

Well-known member
Ok - I'm still a little unclear on the supported RAM size for the 650. Everywhere I look a maximum RAM size is said to be 32 MB SIMMs.
Is anyone running 64MB SIMMs (like what Phipli suggested)?
 

jessenator

Well-known member
According to bbraun: http://www.synack.net/~bbraun/djmemcrom.html
The djMEMC memory controller is used in the 68k Macintosh models Centris and Quadra 610, 650, and 800. These machines, by default, can only use 32MB RAM SIMMs, although some 128MB SIMMs are recognized as 64MB.
This is interesting. Something I hadn't looked into originally. However...
the djMEMC memory controller is capable of using 64MB per bank, with larger SIMMs using 2 contiguous banks per slot.
So if I understand this correctly, even if you used a larger-sized module (which might or might not be recognized), the sum total of memory available remains the same. Without a ROM modification, that means 136 MB is the max (128 + 8 [max on-board]), regardless of the modules installed.
 

Phipli

Well-known member
According to bbraun: http://www.synack.net/~bbraun/djmemcrom.html

This is interesting. Something I hadn't looked into originally. However...

So if I understand this correctly, even if you used a larger-sized module (which might or might not be recognized), the sum total of memory available remains the same. Without a ROM modification, that means 136 MB is the max (128 + 8 [max on-board]), regardless of the modules installed.
Not quite, if you use SIMMs that are recognised as two banks, you can get 64MB per physical RAM slot. Ignore that it says Quadra 800, it is a Centris 650 and I'd just changed the jumpers on the board (they have a common board). Also ignore how much memory the system is using, no battery, so it booted in 24bit mode.

IMG_20211005_175717.jpg
This photo is 4x 128MB SIMMs (each SIMM is effectively two 64MB banks). If you could find some 64MB SIMMs wired as two 32MB banks you'd get the same with no waste.
 

ArmorAlley

Well-known member
This should work in the 650... and be insanely over the top if you got four :


If you do get them, don't bother getting 4 because the memory test takes about two minutes before the machine starts booting.

Even 32MB is plenty of RAM.
I agree with Philpi: 32MB is plenty.
If you do have more though, you can create a RAM disk. You can even boot from it if it is big enough.
 

jessenator

Well-known member
it is a Centris 650 and I'd just changed the jumpers on the board (they have a common board).
Yup :)

if you use SIMMs that are recognised as two banks, you can get 64MB per physical RAM slot
Interesting. I assumed it was similar to the problem with the LPX-40/Tanzania boards where I've used physical 128MB modules and only get 64 out of them, being that the banks are limited in and of themselves. Thanks for demonstrating!
 

Phipli

Well-known member
Interesting. I assumed it was similar to the problem with the LPX-40/Tanzania boards where I've used physical 128MB modules and only get 64 out of them, being that the banks are limited in and of themselves. Thanks for demonstrating!
The banks are limited to 32MB by the ROM, but there are two banks per slot.
 

beachycove

Well-known member
Maximizing your RAM would open up interesting possibilities for booting and working from a RAM DISK, via Maxima or the like. Combined with memory compression software like RAM Doubler, it would then be possible to have a really large RAM disk in the Q650, allowing you to work from more or less instantaneous storage. For instance, a RAM disk could be as big as ~500mb in the machine above (twice the RAM).

You keep your hard drive, but spin it down, or boot from it if you like/as needed. If running from a Maxima RAM disk, the machine automatically backs the RAM drive up to the hard drive on shutdown, and automatically loads on boot from that archive into the RAM disk. Maxima works really well. You get silence, more or less, and the speed increase is very noticeable…. I think a RAM disk is better than any accelerator in a Quadra, and given that the RAM today is so much cheaper than an accelerator (and is arguably better), why not go for it? It’s like having an SSD in the thing.

If I were the OP, I’d go for the maximum RAM myself for this reason alone. Otherwise, 32 or better, 64mb of RAM chips installed is plenty in any 68k machine.
 

Juror22

Well-known member
Thanks for the additional discussion - I'm definitely glad that I was able to get my hands on a Quadra 650, since along with the others in its lineup (the Q800 and the Centris 650) these are real beasts (comparably), even before some of the more extreme upgrades that are available. This has been a terrific and informative discussion.
 

tecneeq

Well-known member
I think going for max memory makes sense if you want to run alternative operating systems to MacOS in the future.
Using A/UX and particularly NetBSD with the full amount of ram is worth the wait at boot time i think.
 

pizzigri

Well-known member
I know this thread is ooooold, but I just purchased some single sided 72 pin SIMMs that have a capacity of 64MB...
and my 650 detects them as 32MB. So, I think Phipli is absolutely right on the money.... the chips on them are Hyundai HY51V65404 60ns x8 EDO, the PCB has also 4 pads for parity chips per side which are not there. The other side has all the pads for a double sided, double bank 128MB simm....
 

eharmon

Well-known member
Since we're resurrecting it, I'll ask a related question: how can you tell if a SIMM is dual-banked? Is double-sided always a clear indicator?

264MB in a Quadra is totally useless but I'm amused by the prospect. Then again, I could probably boot to X in Linux without any trouble...tempting.
 

pizzigri

Well-known member
Well, in my very limited experience in regards to 72 pin simms, the vast majority of double sided sticks are double banked. At least, all the ones I have double sided, are double bank. there will be exceptions...
 
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