Computer Busses

See also Bus systems and interfaces

On the PC, a rough progression occurred from ISA to microchannel/EISA to PCI and PCI64, the 64-bit version of PCI. Graphics buses migrated from VL to PCI to AGP.

The Accelerated Graphics Port (AGP) has a speed of 533 MB/s, using a clock speed of 66 MHz and pipelining.

Memory speeds are increased for synchronous DRAM (SDRAM), which is clocked rather than triggered by control signals. Page-mode DRAM has slow (60 ns) access to the first byte, but then 10 ns access to the following bytes within a row. This burst mode is particularly useful for filling cache lines. Storage FAQ

name	type	parallel/serial	topology	access control	speed	physical (cable, pins, etc.)	distance	devices	example use
USB: Universal Serial Bus	external peripheral	serial	chain with hubs	?	12 Mb/s	?	?	127	medium to low-speed peripherals (*)
IEEE 1394 TI	external peripheral	serial	branch, daisy chain	bus controller	100, 200, 400 Mb/s; 800 Mb/s planned	six-wire shielded twisted-pair	?	?	digital video cameras
SCSI: Small computer system interconnect	external/internal storage peripherals	parallel (8-32 bits)	chain with termination		80 - 640 Mb/s	ribbon or shielded cable, various connectors	few ft	7?	disks, scanners
ISA	internal	8/16 parallel	bus	DMA	42.4 Mb/s (8 MHz)	98-signal edge connector, 24 address lines	enclosure	>12	serial/parallel ports, network, disks, ...
S-bus	internal	32 parallel	bus	DMA		pins	enclosure
VME				DMA
PCI	internal	32 parallel	bus	DMA	960 Mb/s (33 MHz), up to 100 MHz	card-edge		10, typically 3	disk, network

(*) This broad category includes telephones, digital cameras, modems, keyboards, mice, digital joysticks, some CD-ROM drives, tape and floppy drives, digital scanners and specialty printers. USB's data rate also accomodates a whole new generation of peripherals, including MPEG-2 video-base products, data gloves and digitizers.

Last updated by Henning Schulzrinne