Introduction of scsi
2022-08-01
SCSI is a once popular type of connection used for storage and other devices in PCs. The term refers to the cables and ports used to connect some types of hard drives, optical drives, scanners, and other peripherals to your computer.
The SCSI standard is no longer common in consumer hardware devices, but you will still find it used in some commercial and enterprise server environments. Newer versions include USB Attached SCSI (UAS) and Serial Attached SCSI (SAS).
Most computer manufacturers have stopped using onboard SCSI entirely and have used more popular standards such as USB and FireWire to connect external devices to the computer. USB is faster, with a maximum incoming speed approaching 40 Gbps.
Adaptec 2248700-R U320 PCI Express X1 1-lane SCSI host bus adapter
Adaptec SCSI host adapter. PMC-Sierra, Inc.
SCSI is based on an older interface called the Shugart Associates System Interface (SASI), which later evolved into the Small Computer System Interface, abbreviated SCSI and pronounced "scuzzy".
How does SCSI work?
A SCSI interface used inside a computer to connect different types of hardware devices directly to the motherboard or storage controller card. When used internally, the devices are connected via ribbon cables.
External connections are also common, usually using cables through external ports on the storage controller card.
Inside the controller is a memory chip that stores the SCSI BIOS, an integrated software used to control connected devices.
What are the different SCSI technologies?
There are several different SCSI technologies that support different cable lengths, speeds, and many devices that can be attached to a single cable. They are sometimes expressed in terms of bus bandwidth in MBps.
The first version of SCSI was introduced in 1986 and supported 8 devices with a maximum transfer speed of 5 MBps. A faster version followed at 320 MBps and supported 16 devices.
Here are some other SCSI interfaces that already exist:
Fast SCSI: 10 MBps; eight devices connected
Fast Wide SCSI: 20 MBps; 16 devices connected
Ultra Wide SCSI: 40 MBps; 16 devices connected
Ultra3 SCSI: 160 MBps; 16 devices connected
Ultra 640 SCSI: 640 MBps; 16 devices connected
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