How do you upgrade the RAM in the White iMac "Core Duo" and "Core 2 Duo" models? How much RAM of what type do these systems support?

Please note that all "White" iMac models have been discontinued. These systems were replaced by the "Aluminum" iMac Core 2 Duo line.

All of the "White" Intel-based iMac models use the same type of memory, but the maximum capacity and recommended configuration varies depending on the system.

The Apple Support Site provides a helpful document about "Installing and Replacing Memory" in all of the "White" Intel-based iMac models, and a follow up document with "Memory Specifications" for the iMac "Core 2 Duo" models, but even so, keeping the different systems straight can be a bit challenging.

Apple refers to the original "iMac 'Core Duo'" models -- the iMac "Core Duo" 1.83 17-Inch and 2.0 20-Inch -- as the "iMac (Early 2006)", the education-only iMac "Core Duo" 1.83 17-Inch (IG) as the "iMac (Mid 2006)", the iMac "Core 2 Duo" 1.83 17-Inch (IG) -- which uses effectively the same architecture as the education-only system -- as the the awkward "iMac (17-Inch Late 2006 CD)", and finally, the remaining iMac "Core 2 Duo" systems -- the iMac "Core 2 Duo" 2.0 17-Inch, 2.16 20-Inch, and 2.16 24-Inch -- as the "iMac (Late 2006)".

The Apple Support documents notes that all "White" Intel-based iMac models have "two SDRAM slots in the bottom of the computer" and "you can use small-outline dual inline memory modules (SO-DIMMS)" that "meet all of these criteria":

• PC2-5300
• unbuffered
• nonparity
• 200-pin
• 667 MHz DDR2 SDRAM

It also notes that "DIMMs with the following features are not supported":

• Registers or buffers
• PLLs
• ECC
• parity
• EDO RAM

The iMac "Core Duo" 1.83 17-Inch and 2.0 20-Inch -- the "iMac (Early 2006)" models -- shipped with "at least 512 MB of DDR2 SDRAM installed into the top slot" and can be upgraded to "2 GB total (a 1 GB SO-DIMM in each of the two slots)". There is not a performance penalty for populating a single slot or populating both slots with different capacity modules.

The iMac "Core Duo" 1.83 17-Inch (IG) and iMac "Core 2 Duo" 1.83 17-Inch (IG) -- the "iMac (Mid 2006)" and "iMac (17-Inch Late 2006 CD)", respectively -- shipped with "at least 512 MB of DDR2 SDRAM, in two 256 MB DIMMs; one in each of the memory slots" and also can be upgraded to "2 GB total (a 1 GB SO-DIMM in each of the two slots)". However, as these models use slower integrated graphics (IG) that "borrow" system memory, it is critical that you install two modules of equal capacity for optimum performance.

The iMac "Core 2 Duo" 2.0 17-Inch, 2.16 20-Inch, and 2.16 24-Inch -- the "iMac (Late 2006)" models -- shipped with "at least 512 MB DDR2 SDRAM installed into the top slot". There is not a performance penalty for populating a single slot or populating both slots with different capacity modules.

However, rather unusually, Apple notes that:

Although these iMacs will accept up to a 2 GB SO-DIMM in each of the two memory slots, the iMac will only support 3 GB total memory. If you want to maximize the amount of SDRAM in your computer, install a 2 GB SO-DIMM in one slot and a 1 GB SO-DIMM in the other. . .

If you do install a 2 GB SO-DIMM in both the bottom and top memory slots of the computer, the About This Mac window and Apple System Profiler will both show that you have 4 GB of SDRAM installed. However, Activity Monitor and other similar applications will reveal that only 3 GB of SDRAM has been addressed for use by the computer.

The "Installing and Replacing Memory" document continues with detailed instructions complete with photographs for replacing the RAM in both the top and bottom slot of these iMacs. By following the instructions closely, you should have the RAM upgraded in no time.