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

Updated I/O technologies
Two capabilities are being used in the ProLiant ML570 and DL580 G3 servers which were not
present in previous generations of the 500-series servers: PCI Express (available on both servers) and
the use of the HP Smart Array 6i storage controller on the ProLiant DL580 G3.
The ProLiant ML570 G3 and DL580 G3 support PCI Express and PCI-X technology to give customers
the option to use whichever I/O cards fit their purposes. The ProLiant ML570 G3 includes ten I/O
slots: four PCI Express x4, two hot plug 64-bit/133 MHz PCI-X, and four 64-bit/100 MHz PCI-X.
The ProLiant DL580 G3 includes PCI Express slots as mezzanine options, with either two x4 PCI
Express slots or a single x8 PCI Express slot. Or, customers can use the mezzanine board that
provides two hot-plug PCI-X 64-bit/133 MHz slots. The five standard PCI-X slots in the DL580 G3
include three PCI-X 64-bit/133 MHz and two PCI-X 64-bit/100 MHz.
PCI Express
PCI Express provides point-to-point connections between devices. It sends data serially, one bit after
another, over each link rather than sending the data in parallel, one bit beside the other, as in PCI-X.
Serial interfaces allow for transmitting data at higher rates as opposed to parallel interfaces.
A PCI Express serial link consists of one or more dual-simplex lanes. Each lane contains a send pair
and a receive pair to transmit data at the signaling rate in both directions simultaneously. The serial
communication requires an 8b/10b encoder to convert parallel data into a serial bit stream and vice
versa. The encoding process adds about 20 percent overhead to the data stream. PCI Express 1.0
has a signaling rate of 2.5 Gb/s per direction per lane, resulting in an effective maximum bandwidth
of 250 MB/s per direction per lane after accounting for serial encoding overhead (Figure 9).
Therefore, a x4 link — which has 4 lanes, each with a send and receive pair — has an effective
bandwidth of 2 GB/s and a x8 link has an effective bandwidth of 4 GB/s.
Figure 9. PCI Express has an effective bandwidth of 250 MB/s after accounting for the overhead of serializing/deserializing
encoding.
For additional information about PCI Express technology, see the technology brief titled “HP local I/O
strategy for ProLiant servers.”
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Available on the HP ISS technology website at http://h18004.www1.hp.com/products/servers/technology/whitepapers/
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