SCSI-1. A basic connection using a 25-pin connector, supporting transfer rates up to 4 MB per second.
SCSI-2. Uses a 50-pin connector and supports multiple devices with a transfer rate of 4MB per second.
Wide SCSI. These drives have a wider cable and a 68-pin connection that supports 16-bit data transfers.
Fast SCSI. Uses an 8-bit bus but transfers data at 10 MB Per second.
Fast Wide SCSI. Doubles both the bus (16-bit) and the data transfer rate (20 MB per second).
Ultra SCSI or Ultra Wide SCSI. Uses an 8-bit bus and transfers data at 20 MB per second.
SCSI-3. Features a 16-bit bus and transfers data at 40 MB per second.
Ultra2 SCSI. Uses an 8-bit bus and transfer data at a rate of 40 MB per second.
Wide Ultra2 SCSI. Uses a 16-bit bus and supports data transfer rates of 80 MB per second.
SCSI Hard Drives
Ultra320 SCSI Hard Drives
FIREWIRE (IEEE 1394)
The FireWire standard is becoming popular in portable hard drives because it can be connected and removed without having to reboot the computer. It supports data transfer rates of 50 MB per second, which means it is ideal for video, audio and multimedia applications. FireWire requires a dedicated add-in card and the hard drives in use require an external power source, but the interface can support up to 63 devices simultaneously.
FireWire Hard Drives
USB 1.1 (UNIVERSAL SERIAL BUS)
Pretty much all computers today include USB ports on their motherboards. (On older model, you can install an add-in card.) USB controllers can be used to connect external hard drives, and can support as many as 127 devices simultaneously either through USB port hubs or linked in a daisy chain fashion. USB controllers do delivery power to devices connected to them, but many hard drives still use an external power source. USB is limited by its data transfer speed, the maximum rate being about at 1.5 MB per second.
USB Hard Drives
USB 2.0 (HI-SPEED USB)
A more recently introduced and far better connection standard that offers backward compatibility and data transfer rates of up to 60 MB per second. USB 1.1 system can use a USB 2.0 device; it will need a USB 2.0 controller card to achieve the higher transfer rates.
USB 2.0 Hard Drives
FIBRE CHANNEL
Fibre Cabling is mainly used for high-bandwidth network servers and workstations, providing very fast data transfer rates (up to 106MB per second), and connection at long cabled distances, although it is expensive and you need to install a special interface card.
Spin rate
Data transfer rate is crucial to how well your computer performs for you. Apart from the connection types above, the performance of your hard drive depends on its spin rate, measured in RPM. Higher RPM generally means faster data transfer rate. The lowest spin speed that is acceptable in computing today is 5400 RPM. The common standard at present is 7200 RPM. But higher speeds are available in SCSI drives, and it is one area of computer system technology that is constantly being developed.
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