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The Need for SCSI Cables
SCSI cables are used to transfer data from computer devices such as scanners, cameras, printers to a computer. The SCSI (Small Computer System Interface) meets the demands of data transferring at a much larger scale than an USB can handle. SCSI commonly known as “scuzzy†is mostly used with hard disks and tape drives due to it higher capabilities. SCSI consists of definitions for commands, protocols, electrical and optical interfaces.
SCSI is the newly named SASI (Shugart Associates System Interface) which was developed in 1981 by Shugart Associates and NCR Corporation. The American National Standards Institute in 1986 developed SCSI from SASI to transfer data from larger devices. This newer interface is much faster at a speed of 380 Mbits/s. It can connect more devices to one SCSI and it also works with many computer systems.
There three different types of SCSIs, SCSI-1, SCSI-2 and SCSI-3. All types are parallel, which means data moves together at one time rather than individually. The SCSI-1 is the first SCSI and is now obsolete. In 1986, when this was developed it was designed with a width of 8 bits and a speed of 5 MHz. The SCSI-2 which was released in 1994 has a Common Command Set (CCS). The CCS has 18 commands and can handle speeds up to 10MHz. This SCSI could handle up to 15 devices with a width of 16 bits. The speed and width or number of handled devices are known as FAST and WIDE. It can also store commands to prioritize from the host computer (command queuing). SCSI-3 is the newest and most used bus interface and has a SCSI Parallel Interface (SPI) which are a set of standards that let devices transfer data. These standards are referred to as Ultra (SPI), Ultra2 (SPI-2) and Ultra3 (SPI-3). Serial Attached SCSI (SAS) is the newest type and can deliver data speeds up to 3 gigabit/s and handle up 128 devices.
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Cables for SCSI
A ribbon cable must be used for internal devices on a SCSI controller. These ribbon cables are thick rounded cables which connects each device in order. Many times, for external SCSI there will be two connectors so that each cable can be connected to the order of action for each device. Different SCSI standards use different SCSI cables; many use 50, 68 or 80 pins.
The Double Shielded SCSI-1 DB25M/C50M System Cable has a DB25-pin for SCSI host adapters and a 50-pin Centronic connector for peripherals. This cable has a Male-to-Male making it able to connect one peripheral to your SCSI host computer.
The SCSI-2 MD50/M Cable has a Micro-Density 50-pin connector. These connectors are most commonly found on the FAST SCSI-2 host adapters and SCSI peripherals. This cable can connect one peripheral to another or to a SCSI host adapter due to having a Male-to-Male connector.
The SCSI-3 MD68M/M Cable is the newest SCSI standard and is the best cable for the Iomega Zip Drive and other compatible devices. This cable will allow up to 32 devices over a 16 bit single cable bus. The cable will also allow up to 20 Mbps in a single-ended application, meaning that it will allow much more data through at one time. However, the single-ended SCSI-3 is limited to 4 devices over 3 meters or 8 devices over 1.5 meters. All SCSI cables are available in different lengths to accommodate devices and computer.
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