Why only 3GB?

"I'm really put off by the 3GB RAM maximum"

Even if it was a 4GB RAM maximum, how do you like the price of those 2GB modules?

Its just a programming error in activity monitor (because in system profiler it says 4) for iMac intel core 2 duo so when the next version of the Mac os 10.5 or then next iMac model, it should be fixed and able to handel 4gigs.

It's not a programming error. Apple purposely limited the iMac to 3GB. My guess is because they want to push users to the mac pro if then need more memory. Remember, the iMac is a consumer level computer. If you need to do processor/memory intensive task, then the pro series is the way to go.


Glor

It has to do with the motherboard limitations of a laptop/iMac. iMacs actually have relatively faster RAM than Mac Pros when you look at the CPU clockspeed vs. the system bus. 3 gigs of RAM is not an artificial ceiling for RAM - there are real engineering reasons for that limit. Going to (or exceeding) 4 gigs of RAM involved some rather dicey tradeoffs on the Mac Pros. Notice they need big heatsinks for each of those special RAM modules in the Mac Pro, and that the system overhead/bandwidth overhead of those modules is a lot worse?

How do you get that? The system bus on the mac pro is 1033 mhz, nearly twice that of the iMac. You can physically put 2 2GB sodimms in the iMac and it will work with no concerns with heat generation, but the OS limits it to accessing only 3GB or the 4GB installed.

Glor

The memory controller on the new iMacs is only 32 bit enabled. So (like a Windows XP machine) it can only address (see) 3 gigs of RAM. Both the Mac Pros and the larger iMac models have 667 DDR 2 system bus (so 2x667=1,333 FSB) motherboards which can have 256 bit wide memory bandwidth if you install the DIMMs in pairs. The Mac Pro has true 64 bit addressing so it can address far more than 3 gigs of RAM, but the special FB ECC DIMMs it requires have far more overhead and wasted bandwidth than do the iMacs (and require those big heat sinks which obviously would never be a good thing in an iMac). It was an engineering tradeoff.

Surely 32 bit machines can see up to 4GB of RAM?

http://en.wikipedia.org/wiki/32_bit

The new iMac Core 2 Duos are actualy 64 bit based just like the Mac Pro. So with the appropriate controller the limit would be higher but that is not going to happen in the consumer market.

http://www.intel.com/products/processor/core2duo/index.htm

http://www.intel.com/technology/intel64/index.htm

The limit is probably by design so people don't use iMacs to cross in to Pro market.

"The limit is probably by design so people don't use iMacs to cross in to Pro market."

I agree. Apple has gone to a lot of trouble to continually cool these iMacs down since the first generation of the iMac G5, and I doubt they want to return to those days:)) Without having them side by side, the average person can't tell the difference, so this particular market is definitely consumer driven.

It's not limited to it's potential. It's potential is a consumer level mac, if you need more then go to the mac pro.

Glor

I don't agree with you. The iMac duo core is supposed to be a fully 64 bit architecture. Also, the mac pro support support 256 bit wide memory bandwidth if you install them in matched 4's, the iMac is only 128 bit when matched in pairs. Each dimm is only 64 bit. The band width on the mac pro far exceeds the iMac.

Here is the effect of using ecc ram: Speed is one of the memory benefits that will need to be sacrificed slightly when using ECC RAM. Because it spends a small portion of its clock cycles double-checking data, ECC RAM is one or two percent slower than standard RAM. With ECC RAM, however, the increased stability makes up for the lost speed.

But since the mac pro has double the bandwidth of the iMac, even with the minor lose due to ecc error checking, it should be much faster.


Glor

Well, it seems the mystery is solved. Apple has stated that the intel chipset being used in the core2duo imacs and macbook pros limit the memory address space to 3GB. If this is so, then the current iMacs and macbook pros will never be able to access more than 3 GB of memory.



Glor

Yes, the limiter is the memory controller chipset Intel provided and Apple used. It will only address 3 gigs of RAM, and since it is built into the motherboard is not upgradable.

There was another report on macfixit that intel specs show the chipset being used can address up to 4GB of memory, so who knows.

Glor