How many types of RAM are there ? DRAM : (Dynamic Random Access Memory) only generally used in 486 and earlier PC's
FP DRAM (Fast Page DRAM) generally used in 486 and earlier PC's though still supported in Pentium I class systems
EDO RAM (Extended Data Out) generally used in Pentium I and Pentium II class systems and is essentially faster than FP memory
SDRAM (Synchronous DRAM) significantly faster than edo and started as PC66 designed to run with 66MHz bus processors such as Pentium II. When 100MHz Pentium II processors (350 MHz and upwards) and others such as AMD K6-2 were released then faster memory designated PC100 (for 100MHz bus) was required. This was superceded with PC133 for systems that run 133Mhz bus such as some faster pentium III processors.
DDR SDRAM (Double Data Rate SDRAM) essentially designed to double the output of standard SDRAM the DDR equivalent of PC133 is PC2100. It can speed system performance over normal SDRAM though the motherboard needs to specifically support it and the difference should be more noticable on processors specifically designed for it such as some of the faster AMD Athlon processors.
DRD RAM (Direct Rambus DRAM) is another faster type of ram that competes directly with DDR SDRAM and is currently the only type of ram supported by Pentium IV (since the licence for this type of ram is owned by Intel and Rambus Technologies)
DVD RAM is not ram at all but is a device that will write special DVD disks, normally used now with recordable DVD Players and DVD Camcorders
