Easy noob question - Can iMac 8,1 use DDR2 PC2-4200 instead of PC2-6400?

fredleysir

macrumors newbie
Original poster
Mar 1, 2008
19
0
I know Apple calls for DDR2 PC2-6400 officially, but I have some PC2-4200 not being used - I was wondering if it would work? I can never remember the rules on RAM backwards compatibility. Any help is appreciated, Thank you!
 

puchelaar

macrumors newbie
Apr 12, 2010
8
0
As far as I know, the lowest speed of one of the components (in this case the memory that you still have lying around) will become the speed at which all the memory operates. Lowering this speed will probably have some negative effect, but probably this will be 'overridden' by the positive effect of having more memory.

Since the lower speed doesn't 'hurt' the other components in any way, it is safe to try it out and see for yourself.
 

rkaufmann87

macrumors 68000
Dec 17, 2009
1,760
38
Folsom, CA
I know Apple calls for DDR2 PC2-6400 officially, but I have some PC2-4200 not being used - I was wondering if it would work? I can never remember the rules on RAM backwards compatibility. Any help is appreciated, Thank you!

No it cannot. Only install what is specified for your system.
 

fredleysir

macrumors newbie
Original poster
Mar 1, 2008
19
0
No it cannot. Only install what is specified for your system.
Can you tell me why not? I was thinking the same thing the poster above you mentioned - that RAM was backwards compatible (as long as it's DDR2-DDR2, etc) but it would just run at the slower speed, obviously. I just didn't know if Apple had any restrictions on slower speeds or anything


Edit: Let me clarify: the iMac currently has no RAM. If I install this PC2-4200 stick, will it work? (I would just try it but don't have the iMac in my hands yet)
 

pubjoe

macrumors 6502
Aug 14, 2007
266
6
I have no idea why he said that. I reckon it'll work, and if it doesn't it certainly won't do any harm - other than taking slightly longer over ram operations.

I'm currently running memtest on a 2009 imac in which I have installed faster than recommended ram. It's completed 8 loops over about 4 hours, no troubles so far.

I'd probably want to go for faster ram if possible though - and might sell/replace the slower modules that you have. But that's irrelevant to your question. Put it in and try. It can't do any harm.
 

rkaufmann87

macrumors 68000
Dec 17, 2009
1,760
38
Folsom, CA
Can you tell me why not? I was thinking the same thing the poster above you mentioned - that RAM was backwards compatible (as long as it's DDR2-DDR2, etc) but it would just run at the slower speed, obviously. I just didn't know if Apple had any restrictions on slower speeds or anything


Edit: Let me clarify: the iMac currently has no RAM. If I install this PC2-4200 stick, will it work? (I would just try it but don't have the iMac in my hands yet)
Sorry I'm not an engineer so I can't tell you why. What I can tell you is that installing incorrect RAM in iMacs is a frequent cause of Kernel Panics which can damage your OS and data. Therefore if you want to try and risk it to save a few bucks do so at your own risk. It might work but my time and data is definetely more valuable than $50 or so, the cost of the correct RAM.
 

pubjoe

macrumors 6502
Aug 14, 2007
266
6
Install the ram and then run memtest for about 10 loops. If there's a memory problem, memtest will find it.
 

JBennett

macrumors newbie
Dec 24, 2012
4
0
Please Help, Doing upgrade as a gift!

Please help me, my parents have a 8.1 iMac which is only running on 1gb and I'm upgrading their computer as a gift. I decided to go with 4gb from Cosair but when I ordered it online I did not realize that it was a single stick, not a kit.

Should I return the memory and get the 2x2gb instead? If not, should I remove the other stick in there when I install the 4gb? It looks like it is running 1 1gb of ram now as opposed .5x.5.

Any help appreciated. Would rather get it right after the holidays then mess it up now. Thank!
 

Intell

macrumors P6
Jan 24, 2010
18,883
372
Inside
You can put the single 4GB stick into the iMac and it'll see a total of 5GB. Nothing wrong with doing it that way.