Is it possible to upgrade the processor in the Aluminum iMac models? How are these processors mounted?

Officially, Apple does not intend for the processor in any Intel-based iMac models to be upgraded.

Apple considers the memory in the Aluminum iMac models to be a "customer installable part", and upgrading the memory is quite easy, but all other internal components are not considered to be "upgradable" without professional service. Upgrading components other than RAM in the Aluminum iMac models is particularly difficult and doing so definitely should not be attempted by the inexperienced.

For the processor, specifically -- although most of the attention has been focused on upgrading the processor in the Intel-based polycarbonate Mac mini systems -- Intel-based Aluminum iMac models also can be decent upgrade candidates for the highly skilled.

Processor Mounting - 20" & 24" Aluminum iMac Models

Kodawarisan -- whom for quite some time one could expect to tear apart just about any new Mac design within days of its release -- disassembled the original Aluminum iMac and found that the processor is mounted on a ZIF socket, just like the earlier "White" Intel iMac models. The "Early 2008/Penryn" models use the same design and the processors are mounted in the same way.

iFixit tore apart an "Early 2009" Aluminum iMac model and noted that the processor "appeared to be socketed", just as it is in their predecessors. It is a ZIF socket in these models, too.

Processor Mounting - 21.5" & 27" Aluminum iMac Models

Kodawarisan jumped back on the scene to disassemble the 21.5-Inch "Late 2009" Aluminum iMac model and iFixit did the same for the 27-Inch "Late 2009" Aluminum iMac design and both noted that the processors on these models are socketed.

More precisely, the Core 2 Duo-based "Late 2009" iMac models -- the iMac "Core 2 Duo" 3.06 21.5" and "Core 2 Duo" 3.06 27" -- use an LGA 775 Socket T and the iMac "Core i5" 2.66 27" uses an LGA 1156 Socket H.

The usual suspects declined to disassemble one of the "Mid-2010" iMac models -- the iMac "Core i3" 3.06 21.5", "Core i3" 3.2 21.5", "Core i3" 3.2 27" and "Core i5" 2.8 27" -- but Intel provides information on the default mounting for the processors these Macs use.

Specifically, Intel reports that the applicable Core i3 processors each support an FCLGA 1156 socket and the applicable Core i5 processor supports an LGA 1156 socket. It isn't entirely clear how, or if, the FCLGA 1156 socket that the Core i3 supports is different from the LGA 1156 socket that the Core i5 supports, but it is believed that the sockets are the same and just the Core i3 "package" is different.

For the "Sandy Bridge"-powered "Mid-2011" iMac models -- the stock configurations of which are the iMac "Core i5" 2.5 21.5", "Core i5" 2.7 21.5", "Core i5" 2.7 27" and "Core i5" 3.1 27" -- Intel reports that all have an LGA 1155 socket (also referred to as an "H2 socket"). The custom-configured models -- the iMac "Core i7" 2.8 21.5" and "Core i7" 3.4 27" -- as well as the education-only iMac "Core i3" 2.1 21.5" (Late 2011) likewise all have the same LGA 1155 (H2) socket.

Processor Upgrade Experiment Results

Knowing how the processor is mounted in a particular Mac only is half the battle. Determining whether or not a processor upgrade will function originally required experimentation by brave souls.

The now defunct HardMac was able to successfully upgrade an iMac "Core i5" 2.66 27" (Late 2009) -- equipped by default with a 2.66 GHz "Core i5" I5-750 processor -- to a 2.93 GHz "Core i7" I7-870 processor. It is worth noting that this model also could be equipped with a 2.8 GHz "Core i7" I7-860 processor at the time of purchase via build-to-order configuration.

Although no details are provided, multiple third-party forum readers also reported that swapping the stock 3.2 GHz "Core i3" I3-550 processor in the iMac "Core i3" 3.2 27" (Mid-2010) with a 2.93 GHz "Core i7" I7-870 processor worked without a problem. By default, this model was available via build-to-order with a faster 3.6 GHz "Core i5" I5-680 processor.

However, there are limits to the processor upgrade options, as well. In response to a request for reader input, Jason Riley of Sydney, Australia kindly shared the results of his efforts to upgrade a iMac "Core i3" 3.06 21.5" (Mid-2010) with an LGA 1156-socketed 2.93 GHz "Core i7" (I7-870) processor. He discovered:

The new processor physically fits fine but the computer wont boot with the new chip. I tried swapping the CPUs back and forth a couple of times just in case I missed anything but each time the i7 CPU failed to boot.

I suggest there are one of three possibilities:

1. Apple have restricted the logicboard firmware to specific CPUs.
2. There is not enough power for the i7 (95W as opposed to 74W).
3. The logicboard requires the graphics capabilities of the FCLGA 1156 Socket chips.
   

Additional readers -- in particular the very helpful Andy Hucko of Bratislava, Slovakia -- were able to confirm that there are not logicboard firmware restrictions, and the above upgrade was restricted only by power, or specifically, the TDP (Thermal Design Power), which refers to the heat dissipation capability of a particular CPU cooling system.

Andy was able to successfully upgrade the entry-level iMac "Core i3" 3.06 21.5" (Mid-2010) with a 3.6 GHz "Core i5" (I5-680) processor, which is the fastest available CPU with the same TDP as the original processor in this model.

Processor Upgrade Summary

From the above experiments, one can safely conclude that thankfully there are not restrictions on processor upgrades in firmware for any of the Aluminum iMac models.

However, one only can upgrade the processor in an Aluminum iMac with a socket-compatible processor that has the same, or lower, TDP as the originally installed processor.

If you have additional information about upgrading the processor in any Aluminum iMac model based on hands-on experience please share. Thank you.