PC66 SDRAM memory modules

168-pin DIMM
144-pin SODIMM

SDRAM is the newer, faster type than the Extended data out (EDO) memory. SDRAM began to appear in systems in late 1996. The biggest difference between the two is that SDRAM is synchronized to the CPU clock. Most systems accept either EDO or SDRAM, but not both. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM modules come in several different speeds so as to synchronize to the clock speeds of the systems they'll be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz.

168-pin DIMM

144-pin SODIMM

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