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58-615: Small Computer System Interface ( SCSI , / ˈ s k ʌ z i / SKUZ -ee ) is a set of standards for physically connecting and transferring data between computers and peripheral devices , best known for its use with storage devices such as hard disk drives . SCSI was introduced in the 1980s and has seen widespread use on servers and high-end workstations, with new SCSI standards being published as recently as SAS-4 in 2017. The SCSI standards define commands , protocols, electrical, optical and logical interfaces . The SCSI standard defines command sets for specific peripheral device types;

116-462: A parallel bus design. Since 2005, SPI was gradually replaced by Serial Attached SCSI (SAS), which uses a 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 ; others drop physical implementation entirely while retaining the SCSI architectural model . iSCSI , for example, uses TCP/IP as

174-427: A target . The initiator sends a command to the target, which then responds. SCSI commands are sent in a Command Descriptor Block ( CDB ). The CDB consists of a one byte operation code followed by five or more bytes containing command-specific parameters. At the end of the command sequence, the target returns a status code byte, such as 00h for success, 02h for an error (called a Check Condition), or 08h for busy. When

232-585: A "LUN number" or "LUN id". In modern SCSI transport protocols, there is an automated process for the "discovery" of the IDs. The SSA initiator (normally the host computer through the 'host adaptor') "walk the loop" to determine what devices are connected and then assigns each one a 7-bit "hop-count" value. Fibre Channel – Arbitrated Loop (FC-AL) initiators use the LIP (Loop Initialization Protocol) to interrogate each device port for its WWN ( World Wide Name ). For iSCSI, because of

290-403: A 21-bit LBA address. The Read(10), Read(12), Read Long, Write(10), Write(12), and Write Long commands all contain a 32-bit LBA address plus various other parameter options. The capacity of a "sequential access" (i.e. tape-type) device is not specified because it depends, amongst other things, on the length of the tape, which is not identified in a machine-readable way. Read and write operations on

348-550: A more expandable PC-2 model at a higher price point, this being announced alongside the PC-3 in November 1987. Responding to the introduction of the low-cost Amstrad PC1512 in the UK, price points for the initial PC model were given as around £400 including VAT for a 512 KB floppy-only model supporting CGA, EGA and Hercules graphics, rising to £1000 including VAT for a hard drive model. Later,

406-459: A much broader range of options for RAID subsystems together with the existence of nearline SAS (NL-SAS) drives. Instead of SCSI, modern desktop computers and notebooks typically use SATA interfaces for internal hard disk drives, with NVMe over PCIe gaining popularity as SATA can bottleneck modern solid-state drives . SCSI is available in a variety of interfaces. The first was parallel SCSI (also called SCSI Parallel Interface or SPI), which uses

464-459: A peripheral. This electronics-related article is a stub . You can help Misplaced Pages by expanding it . Atari Corporation Atari Corporation was an American manufacturer of home computers and video game consoles . It was founded by Jack Tramiel on May 17, 1984, as Tramel Technology, Ltd. , but then took on the Atari name less than two months later when Warner Communications sold

522-410: A sequential access device begin at the current tape position, not at a specific LBA. The block size on sequential access devices can either be fixed or variable, depending on the specific device. Tape devices such as half-inch 9-track tape , DDS (4 mm tapes physically similar to DAT ), Exabyte , etc., support variable block sizes. On a parallel SCSI bus, a device (e.g. host adapter, disk drive)

580-453: A transport mechanism, which is most often transported over Gigabit Ethernet or faster 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 SAS and SATA drives, provision for parallel SCSI on motherboards

638-518: A unified standard. In October 1981, the two companies agreed to co-develop SASI and present their standard jointly with ANSI. Until at least February 1982, ANSI developed the specification as "SASI" and "Shugart Associates System Interface". However, the committee documenting the standard would not allow it to be named after a company. Almost a full day was devoted to agreeing to name the standard "Small Computer System Interface", which Boucher intended to be pronounced "sexy", but ENDL's Dal Allan pronounced

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696-420: Is a "virtual" disk—a stripe set or mirror set constructed from portions of real disk drives. The SCSI ID, WWN, etc. in this case identifies the whole subsystem, and a second number, the logical unit number (LUN) identifies a disk device (real or virtual) within the subsystem. It is quite common, though incorrect, to refer to the logical unit itself as a "LUN". Sometimes, redundantly, the actual LUN may be called

754-427: Is a 5-bit field reported by a SCSI Inquiry Command ; defined SCSI Peripheral Device Types include, in addition to many varieties of storage device, printer, scanner, communications device, and a catch-all "processor" type for devices not otherwise listed. In larger SCSI servers, the disk-drive devices are housed in an intelligent enclosure that supports SCSI Enclosure Services (SES) . The initiator can communicate with

812-487: Is a protocol that specifies how to transport SCSI commands over a reliable RDMA connection. This protocol can run over any RDMA-capable physical transport, e.g. InfiniBand or Ethernet when using RoCE or iWARP . USB Attached SCSI allows SCSI devices to use the Universal Serial Bus . The Automation/Drive Interface − Transport Protocol (ADT) is used to connect removable media devices, such as tape drives, with

870-415: Is considered to be the "father" of SASI and ultimately SCSI due to his pioneering work first at Shugart Associates and then at Adaptec , which he founded in 1981. A SASI controller provided a bridge between a hard disk drive's low-level interface and a host computer, which needed to read blocks of data. SASI controller boards were typically the size of a hard disk drive and were usually physically mounted to

928-555: Is identified by a "SCSI ID", which is a number in the range 0–7 on a narrow bus and in the range 0–15 on a wide bus. On earlier models a physical jumper or switch controls the SCSI ID of the initiator ( host adapter ). On modern host adapters (since about 1997), doing I/O to the adapter sets the SCSI ID; for example, the adapter often contains a Option ROM (SCSI BIOS) program that runs when the computer boots up and that program has menus that let

986-403: Is typically for a CD-ROM drive. Note that a SCSI target device (which can be called a "physical unit") is sometimes divided into smaller "logical units". For example, a high-end disk subsystem may be a single SCSI device but contain dozens of individual disk drives, each of which is a logical unit. Further, a RAID array may be a single SCSI device, but may contain many logical units, each of which

1044-435: Is used which is also of serial nature. SCSI is popular on high-performance workstations, servers, and storage appliances. Almost all RAID subsystems on servers have used some kind of SCSI hard disk drives for decades (initially Parallel SCSI, interim Fibre Channel, recently SAS), though a number of manufacturers offer SATA -based RAID subsystems as a cheaper option. Moreover, SAS offers compatibility with SATA devices, creating

1102-582: The Atari ST . In 1985, they released their update to the 8-bit computer line—the Atari XE series—as well as the 16-bit Atari ST line. Then in 1986, Atari Corp. launched two consoles designed when Atari was under Warner's control: Atari 2600 Jr and Atari 7800 (which had a limited release in 1984). Atari Corp. rebounded, producing a $ 25 million profit for 1986. The Atari ST line proved very successful (mostly in Europe, not

1160-471: The Federated Group for $ 67.3 million. October 4, 1987, Atari completed the acquisition and gained full control of its own retail stores. In the final quarter of 1987, Federated lost $ 6.4 million in day-to-day operations. A post-acquisition audit ended on February 15, 1988, and identified $ 43 million in adjustments to Federated's balance sheet, far more than Atari anticipated. The net worth of its acquisition

1218-493: The Lynx , a handheld console with color graphics, to critical acclaim. However, a shortage of parts kept the system from being released nationwide for the 1989 Christmas season; the Lynx lost market share to Nintendo 's Game Boy , which had only a monochrome display, but a much better battery life, and was widely available. As the fortunes of Atari's computers faded, video games again became

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1276-717: The Macintosh Quadra 630 in 1994, and added it to its high-end desktops starting with the Power Macintosh G3 in 1997. Apple dropped on-board SCSI completely in favor of IDE and FireWire with the (Blue & White) Power Mac G3 in 1999, while still offering a PCI SCSI host adapter as an option on up to the Power Macintosh G4 (AGP Graphics) models. Sun switched its lower-end range to Parallel ATA (PATA) with introduction of their Ultra 5 and 10 low end workstations using CMD640 IDE controller and continued this trend with

1334-821: The Amiga 3000/3000T systems and it was an add-on to previous Amiga 500/2000 models. Starting with the Amiga 600/1200/4000 systems Commodore switched to the IDE interface. Atari included SCSI as standard in its Atari MEGA STE , Atari TT and Atari Falcon computer models. SCSI has never been popular in the low-priced IBM PC world, owing to the lower cost and adequate performance of ATA hard disk standard. However, SCSI drives and even SCSI RAIDs became common in PC workstations for video or audio production. Recent physical versions of SCSI‍—‌ Serial Attached SCSI (SAS), SCSI-over- Fibre Channel Protocol (FCP), and USB Attached SCSI (UAS)‍—‌break from

1392-494: The Atari name almost vanished from the consumer market. On March 13, 1998, JTS Corporation sold the Atari name and assets to Hasbro Interactive for $ 5 million, less than a fifth of what Warner Communications had paid 22 years earlier. The transaction primarily involved the brand and intellectual property rights, which Hasbro Interactive largely used as a brand name for retro game releases. On January 29, 2001, Hasbro Interactive

1450-524: The Crescent Galaxy . In 1996, the company reverse merged with JTS Corp. , becoming a small de facto non-operating division which itself closed after JTS sold all Atari assets to Hasbro Interactive in 1998. The company was founded by Commodore International 's founder Jack Tramiel soon after his resignation from Commodore in January 1984. Initially named Tramel Technology, Ltd., the company's goal

1508-549: The Jaguar being a commercial failure, by February 1996, a series of successful lawsuits followed by profitable investments left Atari with millions of dollars in its bank account but no new products to sell at all. In addition, the Tramiel family wanted out of the business. On February 13, 1996, Atari agreed to merge with JTS Inc. , a short-lived maker of hard disk drives, in a reverse takeover to form JTS Corporation . The reverse merger

1566-554: The SCSI standards also include an extensive set of command definitions. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with iSCSI and serial SCSI. Other technologies which use the SCSI command set include the ATA Packet Interface , USB Mass Storage class and FireWire SBP-2 . In SCSI terminology, communication takes place between an initiator and

1624-530: The U.S. ), ultimately selling more than 5 million units. Its built-in MIDI ports made it especially popular among musicians. Still, after initially outselling the Amiga line, its closest competitor in the marketplace, the Amiga outsold it 3 to 2 in the end. Atari eventually released a line of inexpensive IBM PC compatibles , announcing a budget model at "a record-breaking price of under $ 599" in early 1987, to be followed by

1682-655: The company again. On January 2, 1996, at the Winter Consumer Electronics Show , Atari Corporation formally announced the formation of a PC division, Atari Interactive, to "address the worldwide PC market". Planning to initially launch with four titles, Tempest 2000 , Highlander: The Last of the MacLeods , Baldies , and FlipOut! , further releases would include Missile Command 3D , Return to Crystal Castles , Rocky Interactive Horror Show , and Virtual War . These plans did not materialize. Despite

1740-524: The company introduced an MS-DOS compatible palm computer called the Atari Portfolio . Atari, under Tramiel, had a poor reputation in the marketplace. In 1986 a columnist for Atari magazine ANALOG Computing warned that company executives seemed to emulate Tramiel's " 'penny-pinching' [and] hard-nosed bargaining, sometimes at the risk of everything else," resulting in poor customer service and documentation, and product release dates that were "perhaps not

1798-450: The company's main focus. In 1993, Atari released its last console, the Jaguar . One of the first entries in the fifth generation of game consoles , the Jaguar was marketed as the world's first 64-bit console. However, due to a games library which was low in both quantity and quality, as well as being extremely difficult to program games for the system because of its multi-chip architecture, it

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1856-526: The controllers of the libraries (automation devices) in which they are installed. The ADI standard specifies the use of RS-422 for the physical connections. The second-generation ADT-2 standard defines iADT, use of the ADT protocol over IP (Internet Protocol) connections, such as over Ethernet . The Automation/Drive Interface − Commands standards (ADC, ADC-2, and ADC-3) define SCSI commands for these installations. In addition to many different hardware implementations,

1914-451: The drive's chassis. SASI, which was used in mini- and early microcomputers, defined the interface as using a 50-pin flat ribbon connector which was adopted as the SCSI-1 connector. SASI is a fully compliant subset of SCSI-1 so that many, if not all, of the then-existing SASI controllers were SCSI-1 compatible. In around 1980, NCR Corporation had been developing a competing interface standard by

1972-414: The enclosure using a specialized set of SCSI commands to access power, cooling, and other non-data characteristics. Peripheral A peripheral can be categorized based on the direction in which information flows relative to the computer: Many modern electronic devices, such as Internet-enabled digital watches , video game consoles , smartphones , and tablet computers , have interfaces for use as

2030-465: The entire truth ... Pretty soon, you don't believe anything they say." He concluded, "I think Atari Corp. had better start considering how they're perceived by the non-Atari-using public." The company, however, was much more open to the press than its predecessor Atari Inc., which had refused to let Antic preview forthcoming announcements and even opposed the magazine printing the word "Atari" on its issues. On August 23, 1987, Atari agreed to purchase

2088-486: The faster serial SCSI (SAS) host adapters. The "small" reference in "small computer system interface" is historical; since the mid-1990s, SCSI has been available on even the largest of computer systems. Since its standardization in 1986, SCSI has been commonly used in the Amiga , Atari , Apple Macintosh and Sun Microsystems computer lines and PC server systems. Apple started using the less-expensive parallel ATA (PATA, also known as IDE ) for its low-end machines with

2146-411: The home gaming and computing assets of Atari, Inc. to Tramiel. Its chief products were the Atari ST , Atari XE , Atari 7800 , Atari Lynx and Atari Jaguar ; in addition to hardware, the company also published video games for its home systems and also had an in-house development team for Lynx and Jaguar software for porting , or developing original titles such as Warbirds and Trevor McFur in

2204-429: The jumpers are typically located; the switch emulates the necessary jumpers. While there is no standard that makes this work, drive designers typically set up their jumper headers in a consistent format that matches the way that these switches implement. Setting the bootable (or first) hard disk to SCSI ID 0 is an accepted IT community recommendation. SCSI ID 2 is usually set aside for the floppy disk drive while SCSI ID 3

2262-471: The later Blade 100 and 150 entry level systems and did not switch to contemporary SATA interface even with the introduction of the Blade 1500 in 2003 while the higher end Blade 2500 released at the same time used Ultra320 Parallel SCSI-3. Sun moved to SATA and SAS interfaces with their last UltraSPARC-III based workstations in 2006 with the entry level Ultra 25 and mid-range Ultra 45. Commodore included SCSI on

2320-638: The most commonly used being: Each device on the SCSI bus is assigned a unique SCSI identification number or ID. Devices may encompass multiple logical units, which are addressed by logical unit number (LUN). Simple devices have just one LUN, more complex devices may have multiple LUNs. A "direct access" (i.e. disk type) storage device consists of a number of logical blocks, addressed by Logical Block Address ( LBA ). A typical LBA equates to 512 bytes of storage. The usage of LBAs has evolved over time and so four different command variants are provided for reading and writing data. The Read(6) and Write(6) commands contain

2378-508: The name of BYSE. In the summer of 1981, NCR abandoned their in-house efforts in favor of pursuing SASI and improving on its design for their own computer systems. Fearing that their extension of the SASI standard would induce market confusion, however, NCR briefly cancelled their contract with Shugart. NCR's proposed improvements to the design of SCSI piqued the interest of Optimem, a subsidiary of Shugart, who requested that NCR and Shugart collaborate on

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2436-566: The new acronym as "scuzzy" and that stuck. The NCR facility in Wichita, Kansas developed the industry's first SCSI controller chip, the NCR 5385, released in 1983. According to its developers, the chip worked the first time it was tested. A number of companies, such as Adaptec and Optimem, were early supporters of SCSI. By late 1990 at least 45 manufactures offered 251 models of parallel SCSI host adapters Today, such host adapters have largely been displaced by

2494-414: The operator choose the SCSI ID of the host adapter. Alternatively, the host adapter may come with software that must be installed on the host computer to configure the SCSI ID. The traditional SCSI ID for a host adapter is 7, as that ID has the highest priority during bus arbitration (even on a 16 bit bus). The SCSI ID of a device in a drive enclosure that has a back plane is set either by jumpers or by

2552-470: 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. Internal parallel SCSI cables are usually ribbons , with two or more 50–, 68–, or 80–pin connectors attached. External cables are typically shielded (but may not be), with 50– or 68–pin connectors at each end, depending upon

2610-515: The presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements. The initial Parallel SCSI was most commonly used for hard disk drives and tape drives , but it can connect a wide range of other devices, including scanners and CD drives , although not all controllers can handle all devices. The ancestral SCSI standard, X3.131-1986, generally referred to as SCSI-1,

2668-588: The shift to serial interfaces is the clock skew issue of high-speed parallel interfaces, which makes the faster variants of parallel SCSI susceptible to problems caused by cabling and termination. The non-physical iSCSI preserves the basic SCSI paradigm , especially the command set, almost unchanged, through embedding of SCSI-3 over TCP/IP . Therefore, iSCSI uses logical connections instead of physical links and can run on top of any network supporting IP. The actual physical links are realized on lower network layers , independently from iSCSI. Predominantly, Ethernet

2726-409: The slot in the enclosure the device is installed into, depending on the model of the enclosure. In the latter case, each slot on the enclosure's back plane delivers control signals to the drive to select a unique SCSI ID. A SCSI enclosure without a back plane often has a switch for each drive to choose the drive's SCSI ID. The enclosure is packaged with connectors that must be plugged into the drive where

2784-785: The specific SCSI bus width supported. The 80–pin Single Connector Attachment (SCA) is typically used for hot-pluggable devices Fibre Channel can be used to transport SCSI information units, as defined by the Fibre Channel Protocol for SCSI (FCP). These connections are hot-pluggable and are usually implemented with optical fiber. Serial attached SCSI (SAS) uses a modified Serial ATA data and power cable. iSCSI (Internet Small Computer System Interface) usually uses Ethernet connectors and cables as its physical transport, but can run over any physical transport capable of transporting IP . The SCSI RDMA Protocol (SRP)

2842-518: The target returns a Check Condition in response to a command, the initiator usually then issues a SCSI Request Sense command in order to obtain a key code qualifier ( KCQ ) from the target. The Check Condition and Request Sense sequence involves a special SCSI protocol called a Contingent Allegiance Condition. There are four categories of SCSI commands: N (non-data), W (writing data from initiator to target), R (reading data), and B (bidirectional). There are about 60 different SCSI commands in total, with

2900-456: The traditional parallel SCSI bus and perform data transfer via serial communications using point-to-point links. Although much of the SCSI documentation talks about the parallel interface, all modern development efforts use serial interfaces. Serial interfaces have a number of advantages over parallel SCSI, including higher data rates, simplified cabling, longer reach, improved fault isolation and full-duplex capability. The primary reason for

2958-896: The unlimited scope of the (IP) network, the process is quite complicated. These discovery processes occur at power-on/initialization time and also if the bus topology changes later, for example if an extra device is added. SCSI has the CTL (Channel, Target or Physical Unit Number, Logical Unit Number) identification mechanism per host bus adapter , or the HCTL (HBA, Channel, PUN, LUN) identification mechanism, one host adapter may have more than one channels. While all SCSI controllers can work with read/write storage devices, i.e. disk and tape, some will not work with some other device types; older controllers are likely to be more limited, sometimes by their driver software, and more Device Types were added as SCSI evolved. Even CD-ROMs are not handled by all controllers. Device Type

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3016-432: Was completed on July 30, 1996. Financially, the merge consisted of Atari's "acquisition" of JTS for approximately $ 112.3 million. Atari's role in the new company largely became a holder for most of its properties. Most of Atari's staff members were either dismissed or resigned, and its Atari Interactive division was quickly shut down, with the remainder of its employees being relocated to JTS's headquarters. Consequently,

3074-545: Was discontinued. 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. Parallel SCSI specifications include several synchronous transfer modes for

3132-765: Was published by the X3T9 technical committee of the American National Standards Institute (ANSI) in 1986. SCSI-2 was published in August 1990 as X3.T9.2/86-109, with further revisions in 1994 and subsequent adoption of a multitude of interfaces. Further refinements have resulted in improvements in performance and support for ever-increasing data storage capacity. SCSI is derived from the Shugart Associates System Interface (SASI), developed beginning 1979 and publicly disclosed in 1981. Larry Boucher

3190-582: Was purportedly to offset the unanticipated losses in the purchase of Federated. In March 1989, Atari announced that it would treat Federated as a discontinued operation and took an additional one-time charge of $ 57 million. Federated was eventually sold to Silo in 1989. In 1988, Stewart Alsop II said that Atari was among several companies that "have already been knocked out" of the GUI market by Apple , IBM / Microsoft , and others, but Atari's sales hit their peak that year, at $ 452 million. In 1989, Atari released

3248-585: Was reduced by $ 33 million. Atari's CFO later claimed that they would never have done the deal had they known at the time. Federated's operational losses increased, reaching $ 67 million for its first full year under Atari in 1988. The FBI began an investigation of Atari in May of that same year for an ongoing scheme involving the profitable import and resale of Japanese DRAM chips in the US, "in violation of U.S. import laws and contrary to import agreements." This alleged DRAM scheme

3306-504: Was to design and sell a next-generation home computer. On July 1, 1984, TTL bought the Consumer Division assets of Atari, Inc. from Warner, and TTL was renamed Atari Corporation. Warner sold the division in exchange for $ 240 million in stock in the new company. Under Tramiel's ownership, Atari used the remaining stock of game console inventory to keep the company afloat while they finished the development of their 16-bit computer system,

3364-532: Was unable to compete effectively against the incumbent fourth generation consoles ; the Sega Saturn and Sony PlayStation would outsell the Jaguar in very large numbers late in its lifespan. Atari sustained a net loss of $ 49.6 million for 1995, with $ 27.7 million in losses during the last quarter of the year alone. In December 1995, Sam Tramiel suffered a mild heart attack, forcing him to step down as Atari's president, causing Jack Tramiel to come back and lead

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