Technologies for the ProLiant ML570 G3 and ProLiant DL580 G3 Servers Technology Brief

Two-way interleaving
Like previous ProLiant servers, the ML570 G3 and the DL580 G3 servers use two-way, or dual-
channel, interleaving. Two-way interleaving works by dividing memory into 64-bit blocks that can be
accessed two at a time through the two memory channels in an XMB controller (Figure 5). This results
in twice the amount of data obtained in a single memory access and reduces the required number of
memory accesses. Because the data is split into the two separate memory channels and accessed
simultaneously, DIMMs must be installed in pairs in the ProLiant ML570 G3 and DL580 G3 servers,
and the pairs must contain identical DIMMs.
Figure 5. Interleaving between the two channels of memory allows 64-bits to go to memory controller (channel) 1, then the next
64 bits to go to memory controller 2, and so on.
XMB rank interleaving
Rank interleaving within the XMB groups several ranks of memory together so that cache lines are
sequentially read or written across the entire group. For example, suppose that bank A and bank B
are interleaved together. (In this example, all contain single-rank DIMMs, so bank A is equivalent to a
rank.) The first requested cache line would come from bank A DIMMs, then the next cache line from
bank B DIMMs, the next from bank A DIMMs, and so on (Figure 6). XMB interleaving is done on 2,
4, or 8 ranks at a time.
XMB rank interleaving reduces latencies by allowing multiple memory pages to be open at the same
time, rather than waiting for several cache lines to be read from a single bank.
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