<P> Initially, the SCSI Parallel Interface (SPI) was the only interface using the SCSI protocol . Its standardization started as a single - ended 8 - bit bus in 1986, transferring up to 5 MB / s, and evolved into a low - voltage differential 16 - bit bus capable of up to 320 MB / s . The last SPI - 5 standard from 2003 also defined a 640 MB / s speed which failed to be realized . </P> <P> Parallel SCSI specifications include several synchronous transfer modes for the parallel cable, and an asynchronous mode . The asynchronous mode is a classic request / acknowledge protocol, which allows systems with a slow bus or simple systems to also use SCSI devices . Faster synchronous modes are used more frequently . </P> <Table> <Tr> <Th> Interface </Th> <Th> Alternative names </Th> <Th> Specification body / document </Th> <Th> Width (bits) </Th> <Th> Clock </Th> <Th> Line code </Th> <Th_colspan="3"> Maximum </Th> </Tr> <Tr> <Th> Throughput </Th> <Th> Length </Th> <Th> Devices </Th> </Tr> <Tr> <Td> SSA </Td> <Td> Serial Storage Architecture </Td> <Td> T10 / INCITS 309 - 1997 </Td> <Td> serial </Td> <Td> 200 Mbit / s </Td> <Td> 8b10b </Td> <Td> 20 MB / s (160 Mbit / s) </Td> <Td> 25 m </Td> <Td> 96 </Td> </Tr> <Tr> <Td> SSA 40 </Td> <Td> T10 / INCITS 309 - 1997 </Td> <Td> serial </Td> <Td> 400 Mbit / s </Td> <Td> 40 MB / s (320 Mbit / s) </Td> <Td> 25 m </Td> <Td> 96 </Td> </Tr> <Tr> <Td> Fibre Channel 1Gbit </Td> <Td> 1GFC </Td> <Td> T11 / X3T11 / 94 - 175v0 FC - PH Draft, Revision 4.3 </Td> <Td> serial </Td> <Td> 1.0625 Gbit / s </Td> <Td> 8b10b </Td> <Td> 98.4 MB / s (850 Mbit / s) </Td> <Td> 500 m / 10 km </Td> <Td> 127 (FC - AL) 2 (FC - SW) </Td> </Tr> <Tr> <Td> Fibre Channel 2Gbit </Td> <Td> 2GFC </Td> <Td> T11 / X3T11 / 96 - 402v0 FC - PH - 2, Rev 7.4 </Td> <Td> serial </Td> <Td> 2.125 Gbit / s </Td> <Td> 197 MB / s (1,700 Mbit / s) </Td> <Td> 500 m / 10 km </Td> <Td> 127 / 2 </Td> </Tr> <Tr> <Td> Fibre Channel 4Gbit </Td> <Td> 4GFC </Td> <Td> T11 / INCITS Project 2118 - D / Rev 6.10 </Td> <Td> serial </Td> <Td> 4.25 Gbit / s </Td> <Td> 394 MB / s (3,400 Mbit / s) </Td> <Td> 500 m / 10 km </Td> <Td> 127 / 2 </Td> </Tr> <Tr> <Td> Fibre Channel 8Gbit </Td> <Td> 8GFC </Td> <Td> T11 / INCITS Project 2118 - D / Rev 6.10 </Td> <Td> serial </Td> <Td> 8.5 Gbit / s </Td> <Td> 788 MB / s (6,800 Mbit / s) </Td> <Td> 500 m / 10 km </Td> <Td> 127 / 2 </Td> </Tr> <Tr> <Td> Fibre Channel 16Gbit </Td> <Td> 16GFC </Td> <Td> T11 / INCITS Project 2118 - D / Rev 6.10 </Td> <Td> serial </Td> <Td> 14.025 Gbit / s </Td> <Td> 64b66b </Td> <Td> 1,575 MB / s (13,600 Mbit / s) </Td> <Td> 500 m / 10 km </Td> <Td> 127 / 2 </Td> </Tr> <Tr> <Td> SAS 1.1 </Td> <Td> Serial attached SCSI </Td> <Td> T10 / INCITS 417 - 2006 </Td> <Td> serial </Td> <Td> 3 Gbit / s </Td> <Td> 8b10b </Td> <Td> 300 MB / s (2,400 Mbit / s) </Td> <Td> 6 m </Td> <Td> 16,256 </Td> </Tr> <Tr> <Td> SAS 2.1 </Td> <Td> T10 / INCITS 478 - 2011 </Td> <Td> serial </Td> <Td> 6 Gbit / s </Td> <Td> 600 MB / s (4,800 Mbit / s) </Td> <Td> 6 m </Td> <Td> 16,256 </Td> </Tr> <Tr> <Td> SAS 3.0 </Td> <Td> T10 / INCITS 519 </Td> <Td> serial </Td> <Td> 12 Gbit / s </Td> <Td> 1,200 MB / s (9,600 Mbit / s) </Td> <Td> 6 m </Td> <Td> 16,256 </Td> </Tr> <Tr> <Td> SAS 4.0 </Td> <Td> T10 / INCITS 534 (draft) </Td> <Td> serial </Td> <Td> 22.5 Gbit / s </Td> <Td> 128b150b </Td> <Td> 2,400 MB / s (19,200 Mbit / s) </Td> <Td> tbd </Td> <Td> 16,256 </Td> </Tr> <Tr> <Td> IEEE 1394 - 2008 </Td> <Td> Firewire S3200, i. Link, Serial Bus Protocol (SBP) </Td> <Td> IEEE Std. 1394 - 2008 </Td> <Td> serial </Td> <Td> 3.145728 Gbit / s </Td> <Td> 8b10b </Td> <Td> 315 MB / s (2,517 Mbit / s) </Td> <Td> 4.5 m </Td> <Td> 63 </Td> </Tr> <Tr> <Td> SCSI Express </Td> <Td> SCSI over PCIe (SOP) </Td> <Td> T10 / INCITS 489 </Td> <Td> serial </Td> <Td> 8 GT / s (PCIe 3.0) </Td> <Td> 128b130b </Td> <Td> 985 MB / s (7,877 Mbit / s) </Td> <Td> short, backplane only </Td> <Td> </Td> </Tr> <Tr> <Td> USB Attached SCSI 2 </Td> <Td> UAS - 2 </Td> <Td> T10 / INCITS 520 </Td> <Td> serial </Td> <Td> 10 Gbit / s (USB 3.1) </Td> <Td> 128b132b </Td> <Td> ~ 1,200 MB / s (~ 9,500 Mbit / s) </Td> <Td> 3 m </Td> <Td> 127 </Td> </Tr> <Tr> <Td> ATAPI over Parallel ATA </Td> <Td> ATA Packet Interface </Td> <Td> T13 / NCITS 317 - 1998 </Td> <Td> 16 </Td> <Td> 33 MHz DDR </Td> <Td> none </Td> <Td> 133 MB / s (1,064 Mbit / s) </Td> <Td> 457 mm (18 inches) </Td> <Td> </Td> </Tr> <Tr> <Td> ATAPI over Serial ATA </Td> <Td> serial </Td> <Td> 6 Gbit / s </Td> <Td> 8b10b </Td> <Td> 600 MB / s (4,800 Mbit / s) </Td> <Td> 1 m </Td> <Td> 1 (15 with port multiplier) </Td> </Tr> <Tr> <Td> iSCSI </Td> <Td> Internet Small Computer System Interface, SCSI over IP </Td> <Td> IETF / RFC 7143 </Td> <Td> mostly serial </Td> <Td_colspan="2"> implementation - and network - dependent </Td> <Td> 1,187 MB / s or 1,239 MB / s </Td> <Td> implementation - and network - dependent </Td> <Td> 2 (IPv6) </Td> </Tr> <Tr> <Td> SRP </Td> <Td> SCSI RDMA Protocol (SCSI over InfiniBand and similar) </Td> <Td> T10 / INCITS 365 - 2002 </Td> <Td_colspan="5"> implementation - and network - dependent </Td> <Td> </Td> </Tr> </Table> <Tr> <Th> Interface </Th> <Th> Alternative names </Th> <Th> Specification body / document </Th> <Th> Width (bits) </Th> <Th> Clock </Th> <Th> Line code </Th> <Th_colspan="3"> Maximum </Th> </Tr>

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