Motherboards and Buses - Upgrading and Repairing PCs - page 278

ThePCIbusofteniscalleda mezzanine bus becauseitaddsanotherlayertothetraditional
bus configuration. PCI bypasses the standard I/O bus; it uses the system bus to increase
the busclock speed andtake full advantage ofthe CPU'sdata 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, 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. Table 4.56 compares the specifications for PCI,
PCI-X, and PCIe bus types.
Table 4.56 PCI Bus Types