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.

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 -- 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 -- 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 -- officially support 3 GB of memory. There is not a performance penalty for populating a single slot or populating both slots with different capacity modules.

Rather unusually -- for the "iMac (Late 2006)" models -- 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 "Late 2006" iMac models have the same memory limitations as the "Late 2006" MacBook Pro "Core 2 Duo" models. Ultimately, 4 GB of RAM may be installed, but not all RAM in excess of 3 GB can be used due to the possibility of memory "overlap".

Nevertheless, in a series of tests, site sponsor Other World Computing found that most -- but not all -- tasks are faster in these systems with 4 GB of RAM installed compared to the official maximum of 3 GB of RAM.

Apple's "Installing and Replacing Memory" document continues with detailed instructions complete with photographs for replacing the RAM, and this absolutely should be read in its entirety before one installs memory, but perhaps even better, site sponsor Other World Computing provides a convenient step-by-step video of the process:

In addition to instructional videos, as you would expect, Other World Computing has quality compatible memory for sale.