Small computer system interface(SCSI)

SCSI defined as 

       A small computer systems interface (SCSI) is a standard interface for connecting peripheral devices to a PC. Depending on the standard, generally it can connect up to 16 peripheral devices using a single bus including one host adapter. SCSI is used to increase performance, deliver faster data transfer transmission and provide larger expansion for devices such as CD-ROM drives, scanners, DVD drives and CD writers. SCSI is also frequently used with RAID, servers, high-performance PCs and storage area networks SCSI has a controller in charge of transferring data between the devices and the SCSI bus. It is either embedded on the motherboard or a host adapter is inserted into an expansion slot on the motherboard. The controller also contains SCSI basic input/output system, which is a small chip providing the required software to access and control devices. Each device on a parallel SCSI bus must be assigned a number between 0 and 7 on a narrow bus or 0 and 15 on a wider bus. This number is called an SCSI ID. Newer serial SCSI IDs such as serialattached SCSI (SAS) use an automatic process assigning a 7-bit number with the use of serial storage architecture initiators

How Does SCSI Work?

   SCSI interfaces used internally in computers to connect different types of hardware devices directly to a motherboard or storage controller card. When used internally, devices are attached through a ribbon cable.

External connections are also common and typically connect via an external port on a storage controller card using a cable.

Within the controller is a memory chip that holds the SCSI BIOS, which is a piece of integrated software that's used to control the connected devices.

What Are the Different SCSI Technologies?

Several SCSI technologies support different cable lengths, speeds, and number of devices that can be attached to one cable. They're sometimes referred to by their bus bandwidth in MBps.

Debuting in 1986, the first version of SCSI supported eight devices with a maximum transfer speed of 5 MBps and a maximum cable length of six meters. Faster versions came later with support for 16 devices and a 12-meter maximum cable length.

Here are some of the other SCSI interfaces that have existed:

Fast SCSI: 10 MBps; connects eight devices

Fast Wide SCSI: 20 MBps; connects 16 devices

Ultra Wide SCSI: 40 MBps; connects 16 devices

Ultra2 Wide SCSI: 80 MBps; connects 16 devices

Ultra3 SCSI: 160 MBps; connects 16 devices

Ultra-320 SCSI: 320 MBps; connects 16 devices

Ultra-640 SCSI: 640 MBps; connects 16 devices