[ The PC Guide | Systems and Components Reference Guide | System Memory | Memory Speed, Access and Timing ]

Memory Bus Speed and Required DRAM Speed

Most modern systems generally require the DRAMs they use to be a certain minimum speed. The speed required is normally a function of the speed of the memory bus. Faster memory buses require faster speed DRAMs and in some cases, faster technologies. While it is not always cut-and-dried what speed is necessary, the table below is a guideline. It is usually possible to use slower memory in any system if you slow down the memory timing, but of course we're trying to make our systems run as fast as we can.

Processor Generation

Memory Bus Speed

Usual DRAM Technology

Usual Required DRAM Speed (ns)

First, Second

4.77-20

Conventional

100-120

Third, Fourth

16-40

Conventional, Page Mode, FPM, EDO

70-100

Fifth, Sixth

50-100

FPM, EDO, BEDO, SDRAM

8-10 (SDRAM) 50-70 (Asynchronous)

Future

125+

SDRAM, DDR SDRAM, DRDRAM, SLDRAM, Other?

?

Next: System Timing and Wait States


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