RAM Question - DDR2 667 to DDR2 800 ??

Yes. It will. The relevant factors are the data-rate (DDR versus DDR2 versus DDR3), the form-factor (all are the same size SO-DIMM) and the speed rating (MHz).

When it comes to speed ratings for RAM, the higher MHz number simply means that the RAM is qualified to run up to that speed with a certain reliability and lifespan. You can use 800MHz RAM on a machine that uses 667MHz RAM without any problem whatsoever. In fact, some manufacturers will test 800MHz RAM and sell it as 667MHz RAM if it fails the 800MHz quality control tests but passes the 667MHz test.

Using "faster" RAM doesn't buy you anything, however, if the machine you are putting it into operates at the slower speed. Installing 800MHz modules in a machine that can only go up to 667MHz means that the modules will operate at 667MHz Generally, the 667MHz RAM would be cheaper.

I have a white Intel Core 2 Duo iMac ca. 2006 that I recently upgraded to 3GB of RAM using 800MHz modules (the old ones were 667MHz, which is the speed that the machine uses). I only used the 800MHz modules because I got them at a ridiculously low price.

Also, you can mix the slower and faster modules in the same computer as long as the slowest module is rated at the max speed usable by the computer. For example, you can put a 667MHz and 800MHz module in the same computer if that computer uses 667MHz memory. However, you can't put a 667MHz and 800MHz module in the same machine if it uses 800MHz memory.

Hi bigdazzler,

it is always best to upgrade using RAM-modules which have the same specifications as the one replaced.
Although 800MHz RAM modules should be compatible in 667MHz slots, there are reports that when using two 800MHz modules in a 667MHz Mac, the Mac won't run.
But with one 800MHz ist runs.

So I would propose to get 2x1GB 667MHZ RAM modules for that Mac.

Regards

Stefan

The short answer is no it is not compatible. Your friend needs to use the memory specified in her manual. If she cannot locate it she can download it from Apple at:

http://support.apple.com/manuals/#imac

Simply type in the serial number of the machine and off it will locate the correct manual.

Regards,

Roger

Now I am really confused as I am constantly reading conflicting data. One individual says "you can" run 2x2MB 800MHZ, DDR2 chips, another says"no you can't". While the 'yes you can' has always been my understanding, when I try to install them into my computer, it will not turn on (discussed in many strings in this forum).

So JD (or any others), since you have managed to get higher MHz chips to run in your computer, any suggestions on how to get my computer to recognize the 4 GB? All chips are good but any time I put in the 2-2GB 800 MHz chips in, you can hear it turn on, the fans run, but the screen is blank and there is no starting beep. OK problem solvers, put your heads together and solve this one, PLEASE! Oh, and btw, the PRAM thing doesn't fix this problem.

Some modules may be designed to run at the lower speed. Others may not be. That's why the experience varies. The only way to know for sure that it will work is to buy the proper ones that match the specifications. With faster RAM, even if it seems to be working, you never know if it is working 100% or not. There is absolutely no advantage to using faster RAM (the iMac will not run faster).

People should refer to the OWC web site. If you start here

http://eshop.macsales.com/shop/apple/memory/iMac

it's pretty hard to order the wrong RAM. Even if you don't buy from OWC, the item description will provide the exact specifications for the module(s) you need to buy.

In my Macbook originally came with two 1GB 667MHz modules, after I changed them for two 2GB 800MHz modules my Macbook does not starts but one 667 and one 800 work, however I'm getting a lot of application and system crashes. After I put back the original two 667 modules everything it's fine

Hi JD
I also have the late 2006 iMac(2.16MHz 24") and am waiting for 2x2GB sticks of 800MHz to turn up, having first read it would be backwards compatible, I ordered it, then found conflicting reports as to whether it would even start up!
Just wondering if you could tell me the details of your set up as you are the only person I can find with the same machine and the higher speed ram.
Regards
Duncan

As a footnote gents........I put the 800MHz Ram (2x2GB) into my 24"iMac 2.16 GHz (Late 2006) and it is all working as it should.