Memory Type: DDR PC2700, DDR PC3200, DDR (non-ECC)
Maximum Memory: 3.5GB
Supports 2 DDR 333/400 (PC2700/3200) DIMMs for a max of 2GB. Supports 3 unbuffered DDR 200/266 (PC1600/2100) DIMMS for a max of 3GB. Supports 4 registered DDR 200/266 (PC1600/2100) DIMMs for a max of 3.5GB.
How much memory your Windows OS will recognize depends on which version of Windows you are running. 32-bit versions of Windows will see (and utilize) only 3GB or 3.5GB. To utilize more memory, install a 64-bit version of your OS. More information about OS memory maximums can be found here.
Memory or DRAM is the "working" memory of the computer. It's used to store data for programs (sequences of instructions) on a temporary basis.
video - installing memory