The Newest March 2009 iMac models have two memory expansion slots that use special 204 pin Mac spec DDR3-1066 SODIMM type modules. These 2.66GHz, 2.93GHz, or 3.06GHz models have either 2GB or 4GB installed from the factory. There are two memory expansion slots that can each address up to 4GB for a full maximum potential of a full 8GB of RAM in these models. Don't confuse these models with the previous models of the same processor speeds. These are DDR3 machines, the previous models use DDR2 memory.

MRD Premium HyperVelocity DDR3-1066 PC3-8500 modules
Special Apple spec DDR3-1066 PC3-8500 modules
2GB	1 2GB SODIMM	$128.56  $49.56
4GB	1 4GB SODIMMS	$658.56  $389.56
8GB	2 4GB SODIMMs (For those who need FULL POWER)	$1358.56  $759.56

HYNIX FACTORY ORIGINAL DDR3-1066 PC3-8500 Modules (These are the EXACT Apple factory original parts)
Apple Original Equipment OEM Modules
4GB	1 4GB HYNIX SODIMM	$758.33 $399.55
8GB	2 4GB HYNIX SODIMMs (For those who want FULL POWER!)	$1358.33 $799.55

 The 2008 Intel Core Duo powered iMac models have two memory expansion slots that use special 200 pin Mac spec DDR2-800 SODIMM type modules. The 2.4GHz, 2.66GHz, 2.8GHz, or 3.06GHz models have either 1GB or 2GB installed from the factory. There are two memory expansion slots that can each address up to 2GB for a full maximum potential of a full 4GB of RAM in these models.

MRD Premium HyperVelocity DDR2-800 PC2-6400 modules
Special Apple spec DDR2-800 PC2-6400 modules
1GB	1 1GB SODIMM	$45.61   $97.61
2GB	1 2GB SODIMM	$49.61   $127.61
4GB	2 2GB SODIMMs (For those who want FULL POWER!)	$79.61   $227.61

SAMSUNG FACTORY ORIGINAL DDR2-800 PC2-6400 Modules (For those who insist on using ONLY Apple factory original RAM)
Apple Original Equipment OEM Modules
1GB	1 1GB SAMSUNG SODIMM	$59.33 $128.33
2GB	1 2GB SAMSUNG SODIMM	$69.33 $199.33
4GB	2 2GB SAMSUNG SODIMMs (For those who want FULL POWER!)	$119.33 $227.33

 The First series Intel Core Duo and Core 2 Duo powered iMac models have two memory expansion slots that use special 200 pin Mac spec DIMM DDR2 type modules. The 1.83GHz models come from the factory with 512MB installed, the 2.0GHz and faster models have 1GB. There are two memory expansion slots that can address up to 1GB each in the 1.83GHZ machines with a maximum total potential being 2GB. The 2.0Ghz and faster Core Duo 2 models can expand up to 3GB maximum and the newest Aluminum models top out at a very nice 4GB!

MRD Premium HyperVelocity DDR2-667 PC2-5300 modules
Special Apple spec DDR2-667 PC2-5300 modules
512MB	1 512MB SODIMM	$77.66 $35.66
1GB	1 1GB SODIMM	$97.66 $45.66
2GB Kit	1 2GB SODIMM Kit (2X1GB)one MATCHED Pair 1GB (2X1GB)	$137.66 $55.66
2GB	1 2GB SODIMM 2.0GHz and faster Core2 Duo models ONLY	$117.66 $49.66
3GB	1 2GB+ 1 1GB SODIMM 2.0GHz and faster Core2 models ONLY	$168.66 $65.66
4GB	2 2GB SODIMMs (New Aluminum models ONLY)	$227.66 $69.66

SAMSUNG FACTORY ORIGINAL DDR2-667 PC2-5300 Modules (For those who insist on using ONLY Apple factory original RAM)
Apple Original Equipment OEM Modules
512MB	1 512MB SAMSUNG SODIMM	$77.68 $38.68
1GB	1 1GB SAMSUNG SODIMM	$117.68  $49.68
2GB Kit	2 1GB SAMSUNG SODIMMs one MATCHED Pair 1GB (2X1GB)	$227.68 $69.68
2GB	1 2GB SAMSUNG SODIMM , Core2 Duo 2.0GHz and faster ONLY!	$127.68 $59.68

 The DDR2 G5 Flat iMac "iSight" models have one memory expansion slot that use special 240 pin Mac spec DIMM DDR2 type modules. This model comes from the factory with 512MB soldered to the logic board. There is only one memory expansion slot that can address up to 2GB for a possible maximum total potential being 2.5GB.

MRD Premium HyperVelocity DDR2-533 PC2-4200 modules
Special Apple spec DDR2-533 PC2-4200 modules
512MB	1 512MB DIMM	$39.77
1GB	1 1GB DIMM	$45.77
2GB	1 2GB DIMM	$55.77

SAMSUNG FACTORY ORIGINAL DDR2-533 PC2-4200 Modules (For those who insist on using ONLY Apple factory original RAM)
Apple Original Equipment OEM Modules
512MB	1 512MB SAMSUNG DIMM	$39.74
1GB	1 1GB SAMSUNG DIMM	$59.74
2GB	1 2GB SAMSUNG DIMM	$69.74

 The Original G5 Flat iMac models have two memory slots that use two DIMM DDR type modules. The original factory installed module is a single special Apple spec 256MB DDR DIMM. There are two memory slots that can each address up to 1GB for a possible maximum total potential being 2 full GB.

MRD Premium HyperVelocity DDR400 PC3200 Modules
Special Apple spec DDR400 PC3200 Modules
512MB	1 512MB DIMM	$39.93
1GB	1 1GB DIMM	$59.93
1GB Kit	2 512MB DIMMs	$69.93
2GB Kit	2 1GB DIMMs	$99.93

SAMSUNG FACTORY ORIGINAL DDR400 PC3200 Modules (For those who insist on using ONLY Apple factory original RAM)
Apple Original Equipment OEM Modules
512MB	1 512MB SAMSUNG DIMM	$59.94
1GB	1 1GB SAMSUNG DIMM	$79.94

 The G4 DDR Flat iMac models have two memory slots, one easily accessible"User slot" under the base plate and a second more internal "Apple slot". The User slot requires a SODIMM type module while the Apple slot uses a DIMM type. The original factory installed modules reside in the Apple slot leaving the User slot empty. The User slot can accept up to 512MB and expanding beyond that requires replacing the factory Apple slot module with a 512MB module as well.

DDR266 PC2100 modules
US=User slot, AS=Apple slot (factory original supplied RAM is in the Apple slot)
512MB US	1 512MB SODIMM	$49.69
512MB AS	1 512MB DIMM	$39.93
1GB Kit US+AS	1 512MB SODIMM, 1 512MB DIMM	$87.69

 The Original PC133 Flat iMac models have two memory slots, one easily accessible"User slot" under the base plate and a second more internal "Apple slot". The User slot requires a SODIMM type module while the Apple slot uses a DIMM type. The original factory installed modules reside in the Apple slot leaving the User slot empty. The User slot can accept up to 512MB and expanding beyond that requires replacing the factory Apple slot module with a 512MB module as well.

PC133 modules
US=User slot, AS=Apple slot (factory original supplied RAM is in the Apple slot)
256MB US	1 256MB SODIMM	$49.97
512MB US	1 512MB SODIMM	$59.97
512MB AS	1 512MB DIMM	$59.95
1GB Kit US+AS	1 512MB SODIMM, 1 512MB DIMM	$99.89

 The Second Generation of the iMac include the SE , DV and Graphite models to name a few. RAM max jumps to 1GB via a pair of 512MB PC133 DIMMs. These machines were a major upgrade over the Original iMac models and still have some kick in them with the full 1GB installed.

PC133 modules (Mac RAM Direct's recommended upgrade)
Two identical memory slots reside under memory cover
256MB	1 256MB DIMM	$39.95
512MB	1 512MB DIMM	$59.95
1GB Kit	2 512MB DIMMs	$89.95

 The machine that started it all... again. The second coming of Commodore Jobs at the helm and a brand new Mac for the masses. These new iMacs sold like hotcakes. PC66 SODIMM (upgradable to PC100) memory that could expand to 512MB maximum with a pair of 256MB modules installed. Load her up with RAM and she'll still run just fine for you.

PC100 modules (Mac RAM Direct's recommended upgrade)
US=Upper slot, LS=Lower slot (lower slot requires low profile) (factory original supplied RAM is in the Apple slot)
256MB US	1 256MB SODIMM	$59.91
256MB LS	1 256MB SODIMM	$69.91
512MB Kit	2 256MB SODIMMs	$119.91