Upgrade memory to 8GB

"From my experience going to 6Gig is workable on this system. Going to 8 is very risky.

So far I've found the slower clocked CPU based systems work better than the higher clocked CPU's of this model line when pushing the limit to 8gigs. I suspect the controller logic runs into trouble with the higher lines it has to read on faster CPU based systems. In any case its not worth the hassle so I stop at 6gig when upgrading any of this model line

Referring to the following pages you'll see Apple doesn't support more than 4gig and many third parties likewise stop there as well.

Apple has updated their spec sheets before when newer memory chips or firmware updates allowed more memory to be supported. Then again, timing is everything. As this is such an old system Apple may have decided not to update the spec sheet (remember they need to do a lot of testing before they bless more memory per a given system). So these sheets could be very dated and Apple never took the time to do the testing hence the sheets show the limit is still 4gigs yet 6gigs work and 8gigs is going too far due to hardware limits (memory controller on faster CPU based systems).

Apple:

iMac (Mid 2007): Memory Specifications

iMac (Early 2008): Memory specifications

Crucial: search for: 4GB kit (2GBx2) DDR2 PC2-6400 Unbuffered NON-ECC 1.8V

Just to be clear the Intel Support logic can only address 6 GB of RAM (limit of address lines) So you can use either 6 GB of RAM or you can use in some systems 8 GB of RAM but only the base 6 GB will be used."

"Yes this machine will run 2 - 4GB chips for a Max RAM of 8GB.

Update: but only 6GB can be accessed.

If this Answer is helpful please remember to return and mark it Accepted."

"Hi,

I installed a Hynix DDR2 800mhz 2X4Gb ... The Mac reads it a 8gb installed. No Issues. I am doing a memtest and it access all the ram up to 7.98 GB which so far shows OK results and i am still waiting for the check to completely finish. The only thing is that when i open Youtube videos.. the imac slows down to the state of hanging. But it is a flash problem which i will address by following the procedures in other forums. It is a html5 problem and maybe can be corrected in due time. However, other apps run swiftly.

So i guess it is not an issue. Lets wait and see what the test says.

Shiva

Update (08/09/2015)

Hi Guys, Sorry for the late reply. I only got the email from this forum site today.

CONFIRMED that only 6GB of RAM works perfectly. 8 GB sends the system to an unknown abyss of darkness! LOL ...

@atroys - Hynix from Hong Kong

@bobhdeleon - Answered above"

"I have a mid-2007 iMac 24 2.4Ghz with El Capitan. I previously had 3Gbs installed then I went to use 6 (4+2), it worked well... Now I'm 8Gbs(2x4) and it works well either. The difference I have with (2+4) and (4+4) is that in (4+4) you use only 6Gbs but you have dual channel enabled!!! No issue noticed so far...

Cheers..."

"Hey Folks,

Just wanted to share my experience. Seen a lot of messages online saying that it works for other people. Just tried this on mine (Early 2008 20-inch, A1224), and it craps out with 8GB. (More specifically, it boots extremely slowly – on the order of 10 minutes – and I can't get past the login screen.)

FYI, the RAM I used was Komputerbay RAM purchased off Amazon, 800MHz unbuffered non-ecc per Apple's memory specification page.

6GB works fine."

"My Current Config:

SSD

6 GB of RAM

it runs smooth no problem.

if I move to 8GB, I get spikes of CPU all the times, and system that never idles.

I have tried different versions of OSX, 10.6, 10.7 and 10.8 the behaviour doesn't change"