Editing SCSI (section)

==Interfaces==
{{Main|SCSI connector}}
SCSI is available in a variety of interfaces. The first was parallel SCSI (also called SCSI Parallel Interface or SPI), which uses a [[parallel communications|parallel]] [[Bus (computing)|bus]] design. Since 2005, SPI was gradually replaced by [[Serial Attached SCSI]] (SAS), which uses a [[Serial communications|serial]] design but retains other aspects of the technology. Many other interfaces which do not rely on complete SCSI standards still implement the [[#SCSI command protocol|SCSI command protocol]]; others drop physical implementation entirely while retaining the [[SCSI architectural model]]. [[iSCSI]], for example, uses [[TCP/IP]] as a transport mechanism, which is most often transported over [[Gigabit Ethernet]] or faster [[computer network|network]] links.

SCSI interfaces have often been included on computers from various manufacturers for use under [[Microsoft Windows]], [[classic Mac OS]], [[Unix]], [[Amiga]] and [[Linux]] operating systems, either implemented on the [[motherboard]] or by the means of plug-in adaptors. With the advent of [[Serial Attached SCSI|SAS]] and [[SATA]] drives, provision for parallel SCSI on motherboards was discontinued.<ref>{{cite book|author1=Shuangbao Paul Wang|title=Computer Architecture and Security: Fundamentals of Designing Secure Computer Systems|isbn=978-1118168813|edition=1st|date=2013-01-10|publisher=John Wiley & Sons }}</ref>

===Parallel SCSI===
[[Image:Scsi-connectors.jpg|thumb|Assorted Parallel SCSI connectors]]
{{Main|Parallel SCSI}}

Initially, the ''SCSI Parallel Interface'' (SPI) was the only interface using the SCSI protocol. Its standardization started as a [[single-ended signaling|single-ended]] 8-bit [[system bus|bus]] in 1986, transferring up to {{nowrap|5 MB/s}}, and evolved into a low-voltage [[differential signaling|differential]] 16-bit bus capable of up to {{nowrap|320 MB/s}}. The last SPI-5 standard from 2003 also defined a {{nowrap|640 MB/s}} speed which failed to be realized.

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.

==={{Anchor|SCSI-EXPRESS}}SCSI interfaces===
{| class="wikitable" 
|- 
! rowspan=2 | Interface
! rowspan=2 | Alternative<br />names
! rowspan=2 | Specification<br />body / document
! rowspan=2 | Width<br />(bits)
! rowspan=2 | Clock{{Efn|Clock rate in [[MHz]] for parallel, or [[bitrate]] (per second) for serial interfaces.}}
! rowspan=2 | [[Line code]]
! colspan=3 | Maximum
|-
! Throughput
! Length{{Efn|For daisy-chain designs, length of bus, from end to end; for point-to-point, length of a single link}}
! Devices{{Efn|Including any host adapters (i.e., computers count as a device)}}
|-
| Ultra-320 SCSI
| Ultra-4; Fast-160
| SPI-5 (INCITS 367-2003)
| 16
| 80&nbsp;MHz DDR
| none
| {{nowrap|320 MB/s}} (2560&nbsp;Mbit/s)
| 12 m
| 16
|-
| [[Serial Storage Architecture|SSA]]
| rowspan=2 | Serial Storage Architecture
| T10&nbsp;/ INCITS 309-1997
| serial
| 200&nbsp;Mbit/s
| rowspan=2 | [[8b10b]]
| {{nowrap|20 MB/s}}{{Efn|name="spatial_reuse"|spatial reuse}}{{Efn|name="fdx"|[[Duplex (telecommunications)|full duplex]]}}{{Efn|name="per_dir"}} (160&nbsp;Mbit/s)
| 25&nbsp;m
| 96
|-
| SSA 40
| T10&nbsp;/ INCITS 309-1997
| serial
| 400&nbsp;Mbit/s
| {{nowrap|40 MB/s}}{{Efn|name="spatial_reuse"}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (320&nbsp;Mbit/s)
| 25&nbsp;m
| 96
|-
| [[Fibre Channel]] 1&nbsp;Gbit
| 1GFC
| T11&nbsp;/ X3T11/94-175v0 FC-PH Draft, Revision 4.3
| serial
| 1.0625&nbsp;Gbit/s
| rowspan=4 | 8b10b
| {{nowrap|98.4 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"|per direction}} (850&nbsp;Mbit/s)
| 500&nbsp;m&nbsp;/&nbsp;10&nbsp;km{{Efn|name="fcdist"|500 meters for [[Multi-mode optical fiber|multi-mode]], 10 kilometers for [[Single-mode optical fiber|single-mode]]}}
| 127&nbsp;([[FC-AL]])<br />2<sup>24</sup>&nbsp;([[switched fabric|FC-SW]])
|-
| Fibre Channel 2&nbsp;Gbit
| 2GFC
| T11&nbsp;/ X3T11/96-402v0 FC-PH-2, Rev 7.4
| serial
| 2.125&nbsp;Gbit/s
| {{nowrap|197 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (1,700&nbsp;Mbit/s)
| 500&nbsp;m&nbsp;/&nbsp;10&nbsp;km{{Efn|name="fcdist"}}
| 127/2<sup>24</sup>
|-
| Fibre Channel 4&nbsp;Gbit
| 4GFC
| T11&nbsp;/ INCITS Project 2118-D / Rev 6.10
| serial
| 4.25&nbsp;Gbit/s
| {{nowrap|394 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (3,400&nbsp;Mbit/s)
| 500&nbsp;m&nbsp;/&nbsp;10&nbsp;km{{Efn|name="fcdist"}}
| 127/2<sup>24</sup>
|-
| Fibre Channel 8&nbsp;Gbit
| 8GFC
| T11&nbsp;/ INCITS Project 2118-D / Rev 6.10
| serial
| 8.5&nbsp;Gbit/s
| {{nowrap|788 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (6,800&nbsp;Mbit/s)
| 500&nbsp;m&nbsp;/&nbsp;10&nbsp;km{{Efn|name="fcdist"}}
| 127/2<sup>24</sup>
|-
| Fibre Channel 16&nbsp;Gbit
| 16GFC
| T11&nbsp;/ INCITS Project 2118-D / Rev 6.10
| serial
| 14.025&nbsp;Gbit/s
| [[64b/66b encoding|64b66b]]
| 1,575&nbsp;MB/s{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (13,600&nbsp;Mbit/s)
| 500&nbsp;m&nbsp;/&nbsp;10&nbsp;km{{Efn|name="fcdist"}}
| 127/2<sup>24</sup>
|-
| [[Serial attached SCSI|SAS]] 1.1
| rowspan=4 | Serial attached SCSI
| T10&nbsp;/ [http://www.t10.org/drafts.htm#SCSI3_SAS INCITS 417-2006]
| serial
| 3&nbsp;Gbit/s
| rowspan=3 | 8b10b
| {{nowrap|300 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (2,400&nbsp;Mbit/s)
| 6&nbsp;m
| 16,256{{Efn|name="128per"|128 per expander}}
|-
| SAS 2.1
| T10&nbsp;/ [http://www.t10.org/drafts.htm#SCSI3_SAS INCITS 478-2011]
| serial
| 6&nbsp;Gbit/s
| {{nowrap|600 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (4,800&nbsp;Mbit/s)
| 6&nbsp;m
| 16,256{{Efn|name="128per"}}
|-
| SAS 3.0
| T10&nbsp;/ [http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas3r06.pdf INCITS 519]
| serial
| 12&nbsp;Gbit/s
| 1,200&nbsp;MB/s{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (9,600&nbsp;Mbit/s)
| 6&nbsp;m
| 16,256{{Efn|name="128per"}}
|-
| SAS 4.0
| T10&nbsp;/ [http://www.t10.org/cgi-bin/ac.pl?t=f&f=sas4r01.pdf INCITS 534] (draft)
| serial
| 22.5&nbsp;Gbit/s
| [[128b/150b encoding|128b150b]]
| 2,400&nbsp;MB/s{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (19,200&nbsp;Mbit/s)
| tbd
| 16,256{{Efn|name="128per"}}
|-
| [[IEEE 1394]]-2008
| Firewire S3200, i.Link, Serial Bus Protocol (SBP)
| [https://ieeexplore.ieee.org/document/4659233 IEEE Std. 1394-2008]
| serial
| 3.145728&nbsp;Gbit/s
| 8b10b
| {{nowrap|315 MB/s}} (2,517&nbsp;Mbit/s)
| 4.5&nbsp;m
| 63
|-
| SCSI Express
| SCSI over [[PCIe]] (SOP)
| T10&nbsp;/ [http://www.t10.org/drafts.htm#SCSI3_PCI INCITS 489]
| serial
| 8&nbsp;[[GT/s]] ([[PCIe]]&nbsp;3.0)
| [[128b/130b encoding|128b130b]]
| {{nowrap|985 MB/s}}{{Efn|name="fdx"}}{{Efn|name="per_dir"}}{{Efn|per PCIe&nbsp;3.0 lane}} (7,877&nbsp;Mbit/s)
| short, [[backplane]] only
| 2<sup>58</sup>
|-
| [[USB Attached SCSI]] 2
| UAS-2
| T10 / [http://www.t10.org/drafts.htm#SCSI3_UAS INCITS 520]
| serial
| 10&nbsp;Gbit/s ([[USB 3.1|USB&nbsp;3.1]])
| [[128b/132b encoding|128b132b]]
| ~1,200&nbsp;MB/s{{Efn|name="fdx"}}{{Efn|name="per_dir"}} (~9,500&nbsp;Mbit/s)
| 3&nbsp;m{{Efn|not specified, practical limitation of USB 3.1}}
| 127
|-
| [[ATAPI]] over [[Parallel ATA]]
| rowspan=2 | ATA Packet Interface
| rowspan=2 | T13&nbsp;/ {{webarchive |url=https://web.archive.org/web/20131215111345/http://www.t10.org/t13/project/d1153r18-ATA-ATAPI-4.pdf |title=NCITS 317-1998}}
| 16
| 33&nbsp;MHz [[double data rate|DDR]]
| none
| {{nowrap|133 MB/s}}{{Efn|half duplex}} (1,064&nbsp;Mbit/s)
| {{convert|457|mm|in|0|abbr=in}}
| 2
|-
| [[ATAPI]] over [[Serial ATA]]
| serial
| 6&nbsp;Gbit/s
| 8b10b
| {{nowrap|600 MB/s}}{{Efn|half duplex}} (4,800&nbsp;Mbit/s)
| 1&nbsp;m
| 1 (15 with [[port multiplier]])
|-
| [[iSCSI]]
| Internet Small Computer System Interface, SCSI over [[TCP/IP|IP]]
| [[IETF]]&nbsp;/ RFC 7143
| mostly serial
| colspan=2 style="text-align: center;" | implementation- and network-dependent
| 1,187&nbsp;MB/s{{Efn|over [[Ethernet]], per 10 Gbit/s, [[Maximum Transfer Unit|MTU]] 1500}} or 1,239&nbsp;MB/s{{Efn|over Ethernet, per 10&nbsp;Gbit/s, MTU 9000}}
| style="text-align: center;" | implementation- and network-dependent
| 2<sup>128</sup> ([[IPv6]])
|-
| [[SCSI RDMA Protocol|SRP]]
| SCSI RDMA Protocol (SCSI over [[InfiniBand]] and similar)
| T10&nbsp;/ [http://www.t10.org/drafts.htm#SCSI3_SRP INCITS 365-2002]
| colspan=5 style="text-align: center;" | implementation- and network-dependent
|
|}