Memory-module board layout for use with memory chips of different data widths

摘要

A memory module substrate printed-circuit board (PCB) has multi-type footprints and an edge connector for mating with a memory module socket on a motherboard. Two or more kinds of dynamic-random-access memory (DRAM) chips with different data I/O widths can be soldered to solder pads around the multi-type footprints. When x4 DRAM chips with 4 data I/O pins are soldered over the multi-type footprints, the memory module has a rank-select signal that drives chip-select inputs to all DRAM chips. When x8 DRAM chips with 8 data I/O pins are soldered over the multi-type footprints, the memory module has two rank-select signals. One rank-select drives chip-select inputs to front-side DRAM chips while the second rank-select drives chip-select inputs to back-side DRAM chips. Wiring traces on the PCB cross-over data nibbles between the solder pads and the connector to allow two x4 chips to drive a byte driven by only one x8 chip.