[baparry]

I have just taken delivery of a new white Macbook and I upgraded HD to WD Scorpio Blue 500 GB HD and memory to Corsair VSA4GSKIT667C4 Mac Memory 4GB 2 X 2GB PC2-5300 667MHz200 -Pin SODIMM for apple laptops.

It would not work even after correctly reinstalling the new memory a number of times

I decided to put back the original memory but by mistake I installed 1 old dimm and one new dimm and the computer then installed Mac OS X on the new HD and works OK.
Info shows 3GB of Memory = 1 x 2 GB and 1 x 1GB.

Why will it not accept 4 GB?

[Simon]

Have you swapped the new DIMMs? Maybe the one you took out was simply a lemon?

[raynman]

Hi baparry.

I have a similar problem, but not identical, so I would be interested if you found resolution for your situation. Or if anyone else has ideas...

I just purchased two sticks Patriot brand PS22G8002S (each is 2gb PC2-6400 800mhz CL-5) on sale for what I hoped to be an upgrade to 4gb on my Macbook 4,1 C2D 2.1ghz.

I had been led to believe from reading the RAM sticky on this forum, that higher speed ram (800mhz) would simply "downclock" to the requisite 667mhz and be recognized as 667mhz by my macbook.

I first installed both sticks, and the macbook would not boot (some startup noises, then white sleep-light, no boot), so I replaced the old sticks (1gb ea for 2gb total) and it booted fine, so no logic board damage when installing the new sticks (phew!).

Then I tried one old stick and one NEW stick, and it booted fine (!) and recognized 3gb ram. ALL POSSIBLE COMBINATIONS of old/new sticks and two different ram slots, as long as 2+1 were installed it booted fine, so all ram sticks are apparently good! so.... Why does my macbook, which SHOULD support 4gb ram (albeit 667mhz!) NOT recognize 4GB of 800mhz ram? Does it need one "slow stick" in to "downclock" to the accepted mhz ram speed? (that would be my best guess for now!)

...at any rate, I am preparing a return request to send back the 2x2gb 800mhz sticks, and will follow the rules and order my 667mhz 2x2gb and see if that works (I cannot imagine that it would not).

and in response to baparry again -- check under "about this mac" "more information" to see what the "bus speed" is on the computer. the 667mhz bus speed support only 3gb, even with 4gb installed (so I understand from what I've read) I do not know if that might be your situation. I thought that even with 2x2gb sticks, the C2D 667mhz bus speed macbook would boot fine and just recognize a total of 3gb ram.

thanks all,
Ray
(raynman)

[Simon]

Originally Posted by raynman 

I thought that even with 2x2gb sticks, the C2D 667mhz bus speed macbook would boot fine and just recognize a total of 3gb ram.

It does.

I think the mistake you made is that you went for 800 MHz PC2-6400 SO-DIMMs instead of 667 MHz PC2-5300 SO-DIMMs. In principle faster RAM should work, but it's known that some of those don't play nice with Macs. The MacBook RAM sticky points it out.

There are also reports of PC2-6400 incompatibilities with Penryn MacBooks which presumably also means that there would be incompatibilities with October 2008 MacBook Whites.