The bus in a PC is the common pathway between the CPU and peripheral devices. Parallel buses use slots on the motherboard and provide multiple lines for data (32 bits, 64 bits) between the CPU and peripheral card. Cards plug into the bus inside the cabinet. Serial buses have external ports, and the cable that plugs into them can connect to multiple devices. Following are the buses used in the PC:
Parallel Buses (Current)
PCI - Peripheral Component Interconnect
The PCI bus, available in 32- and 64-bit versions, is the most popular bus architecture. It is used in PCs as well as many other platforms. In 2002, PCI Express was introduced, providing greatly enhanced speeds. See PCI and PCI Express.
AGP - Accelerated Graphics Port
The 32-bit AGP bus was designed for faster screen display. If used, there is just one AGP slot on the motherboard, and only the display adapter plugs into it. See AGP and display adapter.
Serial Buses (Current)
USB - Universal Serial Bus
One USB port connects up to 127 peripherals. The first version of USB was designed for low-speed peripherals, while USB 2.0 increased speed significantly. See USB.
FireWire (IEEE 1394)
FireWire connects up to 63 peripheral devices and has been mostly used for digital camera connections. See FireWire.
Parallel Buses (Earlier)
ISA - Industry Standard Architecture
Pronounced "eye-suh," ISA stems from the original PC. It was an 8-bit bus originally known as the PC bus and then the XT bus. It was later extended to 16 bits and became the AT bus and eventually the ISA bus. See ISA.
EISA - Extended ISA
Pronounced "ee-suh," this bus was a 32-bit extension of ISA created by major vendors to counter IBM's Micro Channel. EISA slots accepted both EISA and ISA cards, but clock speed was still at the slow ISA rate. EISA was used in servers but later abandoned for PCI. See EISA.
Micro Channel (MCA)
IBM switched to the 32-bit Micro Channel with its PS/2 line in 1987, then later added back ISA. Eventually, it gave up Micro Channel for PCI. See Micro Channel.
VL-bus - VESA Local Bus
The 32-bit VL-bus was introduced during the 486 era and offered higher speed than ISA. It then gave way to PCI. See VL-bus.
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