Hardware Reference
In-Depth Information
Figure 4.42. Conceptual diagram of the PCI bus.
The PCI bus often is called a mezzanine bus because it adds another layer to the traditional bus
configuration. PCI bypasses the standard I/O bus; it uses the system bus to increase the bus clock
speed and take full advantage of the CPU's data path. Systems that integrate the PCI bus became
available in mid-1993 and have since become a mainstay in the PC.
Information typically is transferred across the PCI bus at 33MHz and 32 bits at a time. The bandwidth
is 133MBps, as the following formula shows:
33.33MHz × 4 bytes (32 bits) = 133MBps
Until recently, 32-bit 33MHz PCI was the standard found in most PCs. However, most recent PCs
now feature PCI Express (PCIe) x1 and PCI Express x16 slots, and some late-model PCs have as few
as one PCI slot or have none; not surprisingly, as many recent chipsets no longer support PCI. Table
4.58 compares the specifications for PCI, PCI-X, and PCIe bus types.
Table 4.58. PCI Bus Types
 
 
 
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