The G4 models all took PC2700 DDR RAM with a maximum amount of 1GB (only 1 DIMM slot).

When the Intel MacMini's arrived, Apple switched to DDR2 RAM and also utilizing an SODIMM (notebook RAM) along with making 2 RAM slots. The last Core Duo series and the current Core 2 Duo MacMini's support up to 3GB of DDR2 RAM.

In Spring 2009 Apple updated the MacMini to support DDR3 RAM and increased the max amount of RAM to 4GB. It continues to use SODIMMs just like previous models.

MacMini


G4 Processor

1.25/1.42 GHz G4
PC2700 RAM
Max RAM 1GB

1.33/1.5 GHz G4
PC2700 RAM
Max RAM 1GB



Intel Core Duo Processor

1.5 GHz Core Solo
PC2-5300 SODIMM RAM
Max RAM 2 GB

1.66 GHz Core Duo
PC2-5300 SODIMM RAM
Max RAM 2 GB

1.66/1.83 GHz Core Duo (Late 2006)
PC2-5300 SODIMM RAM
Max RAM 3 GB


Intel Core 2 Duo Processor

1.83/2.0 GHz Core 2 Duo (Aug 2007)
PC2-5300 DDR2 SODIMM RAM
Max RAM 3 GB


2.0 GHz Core 2 Duo (Spring 2009)
PC3-8500 DDR3 SODIMM RAM
Max RAM 4 GB

2.26/2.53 GHz Core 2 Duo (Fall 2009)
PC3-8500 DDR3 SODIMM RAM
Max RAM 4 GB