Types of Memory

Type of Memory	Description
DRAM (Dynamic RAM)	Memory that must be refreshed.
SRAM (Static RAM) (L1, L2, L3)	Does not require refresh. Used for cache memory.
SDRAM (Synchronous Dynamic RAM)	Synced with the CPU clock. 168-pin.
DDR (Double Data Rate) SDRAM	Data read on rising and falling edge of computer clock to double the bandwidth of SDRAM. 184-pin, 64-bit DIMM.
DDR2	Similar to DDR but 240-pin, 64-bit DIMM. Faster than DDR.
Single Ranked DDR	Uses one DDR module in a single slot.
Double Ranked DDR	Uses two DDR modules in two slots to double bandwidth to the system bus.

Form Factors

Form Factor	Description
DIMM (Dual Inline Memory Module)	168, 184, or 240-pin. Pins on both sides are independent. SDRAM uses DIMM. 64-bits.
SoDIMM (Small outline DIMM)	Used in notebook computers. 72-pin is 32-bits and 144-pin is 64-bits.
MicroDIMM	Smaller than a SoDiMM, used in sub-notebook computers. 144-pin SDRAM, 172-pin DDR, 214-pin DDR2.
RIMM (Rambus Inline Memory Module)	184 or 168-pin, 16 or 32-bit, 800-1600 MHz, 2 notches. Each RIMM slot must be filled. C-RIMM can fill empty slots. Uses heat spreader. Current DDR and DDR2 is faster and less expensive.

Calculating DDR Memory performance:

MHz x Clock Cycles x Bus Width

Example:

500 MHz x 2 clock cycles x 8 bytes = 8,000

500 x 2 x 8 = 8,000

This memory would have a throughput value of 8,000 MB per second (or 8 GB per second) and would be referred to as PC2-8000