How do measure memory?

Megabytes and Gigabytes.

1024 Megabytes = 1 Gigabyte.

The computer has L2 Cache on the CPU. this is very fast memory that cannot be changed.

The other type of RAM (Random Access Memory) is Main Memory, which is in "sticks" on the motherboard, usually 2-3 inches from the CPU. this memory is supplied in (DDR2):

256mb; 512mb; 1gb; 2gb; 4gb.