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Equation 5 · Comparing the Main Approaches to AI Memory Systems and the Bandwidth Wall

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WW

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WW

Symbol W

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with W the bus width in bits and fefff_{\mathrm{eff}} the effective transfer rate per pin. For a conventional DIMM interface, W is set by the number of package pins a processor can spare and a printed-circuit board can route, and that number has a hard physical ceiling — DDR5 alone specifies 288 pins per channel, and adding channels for more bandwidth becomes markedly more expensive under a CPU package’s pin budget [ 6 ] . Once W is capped by the board, the only lever left is fefff_{\mathrm{eff}} , and pushing per-pin speed higher costs power and signal-integrity margin at an increasing rate.

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