To achieve higher memory subsystem capacity, some DIMMs have register logic chips (registers) that act as a pass-through buffer for address and command signals (Figure 6). Registers prevent the memory controller from having to drive the entire arrangement of DRAM chips on each module. Rather, the memory controller drives only the loading of the registers on each module. The register on each DIMM re-drives the address and command signals to the appropriate DRAM chip. Simultaneously, a phase lock loop chip on the registered DIMM generates a second clock signal that runs synchronously with the system bus clock and eliminates the need for the system bus clock signal from having to drive all the DRAM chips. It also allows adding more memory modules to the memory bus to increase memory capacity.
Information porvided by Hewlett-Packard Development Company, L.P.
Figure 6. Registered DIMMs
NOTE: Some CPU designs include the memory controller function integrated into processor module.
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