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This article provides information about different types of memory DIMMS for Dell PowerEdge servers.

There are 3 types of memory DIMMS for servers available:

• Unbuffered DIMM: UDIMM, does not buffer either add, control, clock or data I/O lines
• Registered DIMM: RDIMM, buffers add, control, clock lines but does not buffer data I/O lines
• Load reduced DIMMs: LRDIMM, buffers both add, control, clock and data I/O lines

RDIMMs, by buffering and registering the address, control, and clock lines, removes loads from the system memory bus and isolates these to the well-defined signal paths on the DIMM itself. While this register introduces some latency to buffer these signals, the pipelined nature of the memory allows full speed access once the transfer begins. Rather than having eight or sixteen loads on these signals, the system memory bus only sees one load, that of the register. However, the data I/O signals on an RDIMM remain connected directly between the connector and the individual DRAMs (up to four loads on a 4-rank DIMM).

LRDIMMs are a new technology, introduced on the PowerEdge 12th generation servers. LRDIMMs buffer the data I/O signals between the DRAMs and the system memory bus by using a buffer device.

A complete configuration memory guide for each server generation is available here.

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