Type of RAM

There are three main types of RAM: SDRAM, DDR and Rambus DRAM.

SDRAM ( Synchronous Dynamic Random Access Memory ):
Operating voltage is 3.3 volt.
168-pin SDRAM DIMMs.
Speed 133 MHz (PC133) .

DDR (Dynamic Random Access Memory) :
Operating voltage is 2.5 volt.
184 pins in its DIMMs
Speed 166MHz * 2 (aka PC333 / PC2700) or
133MHz*2 (PC266 / PC2100).

Rambus DRAM (RDRAM)
Operating voltage is 2.5 volt.
184 pins in its DIMMs
* PC600: 16-bit, single channel RIMM, specified to operate at 300 MHz clock rate, 1200 MB/s bandwidth
* PC700: 16-bit, single channel RIMM, specified to operate at 355 MHz clock rate, 1420 MB/s bandwidth
* PC800: 16-bit, single channel RIMM, specified to operate at 400 MHz clock rate, 1600 MB/s bandwidth
* PC1066 (RIMM 2100): 16-bit, single channel RIMM specified to operate at 533 MHz clock rate, 2133 MB/s bandwidth
* PC1200 (RIMM 2400): 16-bit, single channel RIMM specified to operate at 600 MHz clock rate, 2400 MB/s bandwidth
* RIMM 3200: 32-bit, dual channel RIMM specified to operate at 400 MHz clock rate, 3200 MB/s bandwidth
* RIMM 4200: 32-bit, dual channel RIMM specified to operate at 533 MHz clock rate, 4200 MB/s bandwidth
* RIMM 4800: 32-bit, dual channel RIMM specified to operate at 600 MHz clock rate, 4800 MB/s bandwidth
* RIMM 6400: 32-bit, dual channel RIMM specified to operate at 800 MHz clock rate, 6400 MB/s bandwidth