by Peter Bjørn Perlsø
created 12th of March, 2005 , updated 22nd of June 2007 and 30aug2009.
This article briefly explains the historical background and evolution of the Personal Computer databus systems.
|bus||width (bits)||clock||theoretical peak bandwidth (MBps)||burst capable||year||comments|
|Industry Standard Architecture (ISA) - 8 bit||8||4.77 MHz||4.77||1981||used in PC XT|
|ISA - 8 bit||8||8.33 MHz||8.33|
|ISA - 16 bit||16||8.33 MHz||16.67||1984||used in PC AT|
|Micro Channel Architecture (MCA)||16, 32||10.33 MHz||up to 41.32||1987||
Used exclusively in IBM's PS/2 systems - was IBM's attempt to marginalize Compaq - failed miserably because it was incompatible with the commonly used ISA.
Launched by the "Gang of Nine" consortium of computer makers (AST, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse and Zenith) as an alternative to IBM's attempt to freeze out PC clone makers by way of MCA.
"New Bus" - primarily used in Apple Macintoshes
|VESA Local Bus (VLB)||32||up to 40 MHz||100, 133 or 160||1992||Used with 486 boards. Ran syncronously with the CPU, ie. at 25, 33 or 40 MHz|
|Peripheral Component Interconnect (PCI)||32||33 MHz||132||yes||1992||
developed by Intel, for use with Pentium systems. Asynchronous.
|PCI 2.1||64||66 MHz||528||yes|
|Accellerated Graphics Port (AGP)||32||66 MHz||264||Spring 1997||AGP 1.0, allows sideband addressing (demultiplexed (seperated) addresses from data -> faster data transfers) and AGP texturing ("direct execute mode" - system memory can be used as texture storage)|
|2x AGP||32||2x66 MHz||528||"|
|4x AGP||32||4x66 MHz||1056||AGP 2.0, allows write combining|
|8x AGP||32||8x66 MHz||2112||AGP 3.0|
|PCI-X 100||64||100 MHz||792||yes|
|PCI-X 133||64||133 MHz||1056||yes|
|PCI-X (2.0) 266||64||266 MHz||2.15 GBps||yes||2003|
|PCI-X (2.0) 533||64||533 MHz||4.3 GBps||yes||2003|
|PCI Express (PCIe) x16||2||?||up to 4 GBps||yes||250 MBps per lane, up to 16 lanes (x16), more or less mainstream in late 2006|
|bus||width (bits)||clock||peak bandwidth (MBps)||burst capable||year||comments|
|AT Attachment (ATA), IDE||8||4,77 MHz||8,3||1981||used in PC AT (as the name suggests)|
|Fast ATA (ATA-2), EIDE||8||16,7|
|ATA-7||16||133||>127 GB drive capacity|
|Serial ATA (SATA)||1||1.5 GHz||150|
|SATA 6G (SATA-3)||1||6 GHz||600||2007??|
|Fast SCSI (SCSI-2)||8||10 MHz||10|
|Fast Wide SCSI (Wide SCSI-2)||16||10 MHz||20|
|Ultra SCSI (SCSI-3)||8||20 MHz||20|
|Ultra Wide SCSI (Wide SCSI-3)||16||20 MHz||40|
|Ultra-2 SCSI||8||40 MHz||40||uses LVD cabling and connectors|
|Ultra-2 Wide SCSI||16||40 MHz||80||"|
|Ultra160 SCSI||16||80 MHz||160||", (Ultra 3 Wide)|
|Ultra320 SCSI||16||160 MHz||320||", (Ultra 4 Wide)|
The term "Ultra Fast SCSI" is misleading and should be avoided. Ultra SCSI is actually an "extra Fast" SCSI, hence don't use the "Fast" term in conjunction with any Ultra SCSI name. Avoid misleading terms such as "Ultra Fast SCSI" and "Ultra Fast SCSI-3"
Ultra-2 SCSI is sometimes mistakenly referred to as "Ultra SCSI-2". Don't make that mistake.
Low Voltage Differential (LVD) SCSI and Differental SCSI are NOT the same things! Mixing up two of these bus/cabling types can have catastrophic consequences due to different signalling tensions and methods being used - beware!
ALL Wide SCSI variants use 68-pin connectors, and they all allow for 16 storage units per channel.
SCSI info based on my old article "SCSI Demystified! (or how I learned to rid myself of the confusion and love SCSI)", based on a draft from 1998.
"How can they do that? THEY'RE CABLES, MAN!"
- Hudson, Aliens
cc, 1998-2009, Peter Bjørn Perlsø