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You are here: MacNN Forums > Enthusiast Zone > Classic Macs and Mac OS > Using 128 MB DIMMs in 7600

Using 128 MB DIMMs in 7600
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Nov 2, 2001, 11:27 PM
 
With 128 MB DIMMs selling at $20 each, I couldn't resist getting them for my 7600, even though Apple only supports 64 MB DIMMs. I got 8 of them, for a total of 1 GB of RAM. The good news is, both OS 9.1 and 10.1 sees all of the memory.

The bad news is, my machine becomes moderately unstable. Moderate because some apps now hard locks my machine, while others works fine. At first I suspect that my DIMMs are faulty, but TechTools reported no problems with them. Playing around a bit more, I found that by creating a 256 MB RAM disk (perhaps smaller sizes will work as well, haven't tried yet) in 9.1, the instability goes away.

Unfortunately, there isn't a point-and-click way of creating a RAM disk under OS 10.1 as far as I know.
Forgive my crosspost from MacFixIt Forum...

What used to be rock solid (I've never had 10.1 hard lock on me before) kernel panics randomly now. Various apps seems to quit unexpectedly more often as well (though this may just be my biased perception, since this happens before the upgrade).

I conjecture that perhaps the 7600 have problems addressing more than 1 GB of memory at the same time. To prove this I need a way to make OS X use less RAM than installed (I'd rather not pull out the DIMMs physically). Any method in doing that?

Also, if anyone else is 128 MB DIMMs with the 7600, please tell me your experiences.

Any other comments are also welcome.

Thanks.

----

I've played around the RAM disk size in OS 9.1, and it seems that the machine will be stable as long as the "Memory too large for VM" warning doesn't show up. In this case, a 36 MB RAM disk will do.

I'm still looking for a solution under OS X though.
When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute--and itís longer than any hour. Thatís relativity.
-- Albert Einstein
     
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Nov 3, 2001, 01:37 AM
 
It still could be bad ram, i got a 512 for my G4 that was bad, and it worked fine and passed all ram tests in calssic, but it made X constantly crash... i sent it back and they replaced it and it solved the problem, so start pulling your sticks one by one and see which one is bad.... i hope you don't have two bad ones... that will make things much more difficult
     
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Nov 3, 2001, 10:29 AM
 
Madoka,

Unfortunately OS X is more sensitive to RAM issues - and not all RAM is the same. What were the specs? EDO 5 v., FPM 4k? And WHERE?

There are some very expensive DIMMs 128MB.
www.macgurus.com has a lot of info on RAM upgrades and so does www.xlr8yourmac.com (where there is another forum - search on the topic of 128MB DIMMs in pre-beige g3).

I'll assume that since you are running X.1 that you have cpu upgrade (G4? G3?) that also pushes the limits when it comes to RAM and reliability. 60 ns OR FASTER (there are some 50 ns DIMMs) can make the difference.

With 'restocking" and shipping fees you could end up OWING if you return them!!! (just kidding, sortof).
     
madoka  (op)
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Nov 3, 2001, 10:46 AM
 
The DIMMs are 60ns EDOs. I thought about testing the DIMMs one by one, but my computer is stored in a hard to reach place, so that's going to be a real pain. And since under OS 9.1 creating a 36 MB RAM disk solves the problem, even if one of the DIMMs is defective, I'll let it slide...

However, I'm still having trouble under OS X. I found some info on using mount_mfs, but so far no luck yet. I know in Linux you can specify how much physical memory the machine should use, regardless of how much is actually installed using a boot parameter "mem=XX"; anything like that in OS X?

The good news (?) is, I can reliably kernel panic OS X now by running the iTunes 2 installer. That should take out some variables with my experimentation.
When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute--and itís longer than any hour. Thatís relativity.
-- Albert Einstein
     
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Nov 3, 2001, 10:56 AM
 
Originally posted by madoka:
<STRONG>With 128 MB DIMMs selling at $20 each, I couldn't resist getting them for my 7600, even though Apple only supports 64 MB DIMMs. I got 8 of them, for a total of 1 GB of RAM. The good news is, both OS 9.1 and 10.1 sees all of the memory.

The bad news is, my machine becomes moderately unstable. Moderate because some apps now hard locks my machine, while others works fine. At first I suspect that my DIMMs are faulty, but TechTools reported no problems with them. ...</STRONG>
madoka,

you should compare the form factors of your old RAM modules and the new ones. In a 7600, there is only limited room between the motherboard and the part of the computer that contains the power supply, unlike the more ample space in a tower-style enclosure like 8500 or 9600. I have once tried to put another DIMM (a "good name" brand one, not a cheap no name) into a free RAM socket that was just a little bit wider that the original RAM bars. The result was instability in otherwise rock-stable applications like BBEdit and Eudora. Obviously, the motherboard got some pressure via this RAM module from the power supply carrier when the case was closed. I threw out the RAM module again - and the problems were gone.

And just to be sure: You did not mix up FPM and EDO type RAMs, I understand.

Regards,

Walter.
     
madoka  (op)
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Nov 3, 2001, 11:18 PM
 
Since I had nothing better to do, I decided to test the DIMMs individually (which took me the whole afternoon and in the process I busted an IDE cable...), using iTunes 2 installer as the tester. And I was able to nail down the 2 DIMMs that seems to be causing the problem.

BUT! When I put my machine back together with what I thought was the good DIMMs, OS X kernel paniced upon boot. I rebooted twice after than to make sure it's not a fluke, and the same KP poped up. Frustrated, I rearranged the DIMMs and voila! So far everything works.

So the bottom line is, I still don't know if it's the problem with the DIMMs or with my 7600...but I guess 768MB is still a lot.

Mr. Ferstl,

I got 8 identical 60ns EDO RAM, and they are shorter than some of the original DIMMs I pulled out, so I don't think the power supply is exerting any pressure on them.
When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute--and itís longer than any hour. Thatís relativity.
-- Albert Einstein
     
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Nov 7, 2001, 04:11 AM
 
If you're using a G3 or G4 upgrade for that computer, I think you're seeing a problem that pops up a lot. When your RAM is interleaved with certain upgrades, it tends to make your computer unstable. If you take a look now at how your RAM sticks are set up, you will probably notice that they're not interleaved. (If they are, disregard this.) If they're not interleaved, set them to be interleaved and test it again. You'll probably find that the computer crashes a lot. A fix for this usually involves removing your motherboard cache (with a G3 upgrade, it really doesn't do much anyways, since it moves at the same speed as the bus - the bottleneck for the upgrade), or de-interleaving the RAM. You could probably leave seven of the sticks in, since your RAM wouldn't be interleaved. ... Maybe stick a 64MB stick in the empty slot?

Hope this helps.
     
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Nov 7, 2001, 06:19 AM
 
Madoka,

iNub could be on to something. I know the 7600 supports interleaving and I think I read somthing about interleaving and instability with G3 upgrades over at xlr8yourmac.com. Don't quite me, but it sounds like it might be something worth trying.

Actually, I think the interleaving is supported in pairs, but don't hold me to that.

Where did you find 128MB DIMMs for $20?
A lie can go halfway around the world before the truth even gets its boots on. - Mark Twain
     
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Nov 7, 2001, 08:23 AM
 
I have an 8500 that I took to work.
It has a G3-400 running on a 56.8 MHz bus at 454 /227 MHz.
It has 4 - 60ns EDO 128MB's and 2 64 MB of the same variety. Interleaved and stable, no MoBo L2 cache.
Might be an issue with your bus speed, if you upped to a G3, can you set DIP switches to change that?
It only runs OS 9.1 tho, not X; 10 is still slow feeling on my G4, no interest in trying it on something less than half as fast.
     
madoka  (op)
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Nov 7, 2001, 11:00 PM
 
Thanks to everyone who's responded to my question.

I've always installed memory in pairs of the same size and specification, so that they stay interleaved. I've not experienced instability before, and I've upgraded my processor card twice. The motherboard L2 cache has been removed since I installed my first processor upgrade.

So far, I'm running on 768 MB of memory (128 MB x 6), and both OS 9 (without the RAM disk trick), and OS X seems to be back to normal. Hasn't had a kernel panic since.

Maybe there's some issues with my bus speed being set too high, but then I didn't know that's related to hou much memory one has installed. The bottom line for me, it's working right now, and I hate to break it by messing around. Maybe for another day...
When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute--and itís longer than any hour. Thatís relativity.
-- Albert Einstein
     
   
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