Pci Express Technology - HP BL680c - ProLiant - G5 Introduction Manual

Figure 1. Typical parallel bus architecture
The PCI and PCI-X specifications maintain full forward and backward compatibility with conventional
3.3-V, 33-MHz PCI; existing conventional 3.3-V, 33-MHz PCI, conventional 66-MHz PCI, PCI-X 66,
PCI-X 133, PCI-X 266, and PCI-X 533 add-in cards will operate in any PCI (3.3 V) or PCI-X system.
PCI-X 133 and 66-MHz PCI systems support universal add-in cards and 3.3-V PCI cards; however,
they do not support 5-V-only PCI cards, which operate only at 33 MHz.
The parallel bus system is highly cost effective with its small silicon footprint and low-frequency design
rules. However, economics have changed. Backward compatibility has become increasingly
expensive as speeds increase. Higher bus speeds require physically shorter connections, which yields
fewer slots. And as Moore's Law dictates, silicon costs have decreased much faster than package and
pin count. As a result, the industry has transitioned to PCI Express technology, which has proven to be
a more cost-effective solution to provide the bandwidth required for future peripheral devices.

PCI Express technology

PCI Express 1.0 has a signaling rate of 2.5 Gigabits/second per direction per lane, for a combined
receive and transmit bandwidth of 500 Megabytes/second per lane. Multiple lanes can be combined
to form higher bandwidth links. For example, four lanes can be combined to form a 2-
Gigabyte/second link, designated "x4" (pronounced "by four").
Today, the entire ProLiant server line incorporates support for PCI Express (PCIe) devices, as well as
support the PCI-X standard.
In January of 2007, the base specification for PCI Express 2.0 was released by PCI SIG. As
expected, the primary change is a doubling of the signaling rate to 5 Gb/s, resulting in doubling of
the aggregate bandwidth for PCIe 2.0 slots.
Introduction of PCIe 2.0 slots is currently planned to coincide with the release of the next generation
of HP ProLiant server designs.
CPU
DRAM
Memory
Controller
DRAM
I/O
Bridge
RAID
Controller
PCI-X
100-MHz
NIC
Slots
Standard
Peripherals
(KB, video,
mouse, etc.)
iLO
I/O
Bridge
PCI-X 133 Slots
3