800 MHz in 667 MHz iMac

You should use the RAM specified for your system. It is possible that faster RAM will operate at the slower speed, but there are no guarantees.

Absolutely. However, the 800MHz it doesn't buy you anything, it's still going to operate at 667MHz in your system.

The speed rating is merely the top speed that RAM is rated for. In fact, you could use 667MHz RAM in a machine using an 800MHz bus. That's called "over-clocking" and it's a pretty risky practice as using slower RAM in a faster generally leads to RAM failure, lockups, etc.

However, using the faster memory in a machine with a slower bus is just fine.

Except that with Macs it does not always work. There have been plenty of folks trying this very issue 800 MHz RAM in a 667 MHz Mac and all they get is a dead Mac with a black screen.

Dah•veed

So far, this has not been my experience. I've only don it on a few dozen, but never had an issue (with PCs either, for that matter).

FWIW, the memory modules themselves are the same. They are first manufactured, then they are sorted into speed during the QC process. Depending on the process and controls, RAM modules from the same batch might be graded 1000MHz, 800MHz, or 667MHz. If you have an issue, it's more often then not a seating issue.

Your biggest concerns, actually are the actual form factor (size and pins), and voltage. If those are within spec, any speed equal to or greater than your bus speed will work.

The only reason I've been using 800MHz memory in our older Macs, actually, has been that I found a source where I could get it at a steep discount that made them much cheaper.

As already mentioned you can but it's not a good idea. Better to upgrade the memory with the memory specified in the manual, deviating from that just causes problems. Memory is pretty cheap these days it should cost less than $80.00 for good quality memory.

+Can I upgrade and replace the 667MHz DD2 SDRAM from the older iMac with the newer 800 MHz DDR2 SDRAM from the new machine?+

Since it will cost you nothing by using the DDR2 Apple RAM removed from the newer iMac, since they physically will fit due to DDR2 RAM being backwards compatible, and since there would be absolutely no possibility of risk to your three-year old iMac, you should definitely try it and see how they work. It's not as if you will be the first one doing this:)) It's been done - other users have done the same thing.

It can take a surprising amount of force to get RAM modules fully seated in the 2006 models, regardless which brand you try, so once you're certain you have the notches oriented accurately don't be hesitant to seat them forcefully. Otherwise you'll just be repeating it - and, the less handling of the RAM modules, the better for them.

Don't forget the older iMac might need a PRAM reset after installing new RAM - to enable recognition. I always do that reset during the first startup after I install a RAM upgrade in any Mac, whether a mini or a Mac Pro.

Message was edited by: myhighway

Roger is right.

http://eshop.macsales.com/item/Other%20World%20Computing/5300DDR2S2GB/

$80 for 4GB.

Lifetime warranty.
And, you get to sleep at night.

Hi BM

As suggested by others, there is no guaranty, you may just get a black screen and the correct PC2-5300 667MHz ram is cheap.

In many cases reported in the forum it only worked with 1 667MHz and 1 800MHz module installed in the earlier systems, installing 2 800MHz modules failed to even boot the iMac.

Check out a few examples:
http://discussions.apple.com/thread.jspa?messageID=8230847&#8230847
http://discussions.apple.com/thread.jspa?messageID=8956193&#8956193
http://discussions.apple.com/thread.jspa?messageID=8467594&#8467594

Dennis

While you are on the right track, you are factually in error when you state that "… the memory modules themselves are the same."

While a lower speed module may use matched individual higher speed chips than the module is rated at, modules may differ according to circuit design, and the programming content of the SPD EEPROM—or Serial Presence Detect Electrically Erasable Programmable Read-Only Memory—device. While it is relatively unusual to see circuit designs which render modules unworkable in applications they were not specifically designed for when they physically mate with a slot, it is quite common to see failures based upon a SPD mismatch.

Apple looks to SPD data to determine module identity, in accordance with the JEDEC standard. Your machine knows not what is physically inserted into a compatible slot without this information. Apple publishes memory module design specification publicly for its machines which are based upon JEDEC standards, and these are used by designers and fabricators to insure compatibility.

A technical note from Micron in portable document format—which explains SPD technology—is available for download here.

Dennis,

There's a big difference between using Apple OEM DDR2 RAM pulled from a working iMac and moving it over to another working DDR2 iMac, and purposely purchasing out-of-spec third party RAM that is not even known to be in working condition.

All three example links you provided above involve the purchase and installation of third party RAM that was not known to be in working condition:

1. "I ordered 800 mhz memory by mistake"
2. "i bought 2x2gb sticks of compatiable ram from crucial.com."
3. "i purchased 4 gigs of ram from amazon"

After first seeing a black screen, the users found a normal screen after inserting working RAM. In fact, in several other threads I've read, some users have stated Crucial has explained to them that they have mistakenly supplied RAM that was wrongly described or wrongly manufactured, and that a refund or exchange could be made for returns.

Until users start pulling OEM DDR2 800MHz RAM from working Macs and finding it won't run DDR2 667MHz specified Macs, I'll have to continue to find this concept a bit on the speculative side, and advise the OP BurntMonkey that he's making an economically and technically wise move.

However, I am glad to now know this problem exists, as I noticed several months ago that the 800MHz modules at Crucial's website were actually priced below their 667MHz module brothers. I assumed that meant Crucial had stepped up their production to a new level, but perhaps they were simply trying to offload the inventory;)

Message was edited by: myhighway

Good point, now I'm a little curious to know if 2 modules of the Apple OEM 800MHz ram work.

Most of the threads I had read were prior to any mention, well at least any admission of bad ram from Crucial.

myhighway, where the heck' have you been???? Don't mind me, it's good to see you around these parts again.

+curious to know if 2 modules of the Apple OEM 800MHz ram work+

Right - based on how the board works: problems draw crowds, success finds something better to do - it might be awhile til we know for sure. And I don't have a single stick of 800MHz around, either:(

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.