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What is an SCSI Hard Drive?

SCSI hard drives are used in many personal computers.
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  • Written By: John Lister
  • Edited By: Bronwyn Harris
  • Last Modified Date: 10 October 2014
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A SCSI hard drive is a storage drive which uses a different system than that found in most home computers. Its main advantage is that multiple drives can be “daisy-chained” to a single connection. It also offers faster data transfer speeds, though the difference is often greater in theory than practice. SCSI is particularly suited to servers and other computer systems designed to be used 24/7.

SCSI stands for Small Computer System Interface. It’s usually an acronym rather than abbreviation, pronounced as “scuzzy.” The system can be used for connecting a variety of devices, though most consumers will normally encounter it in terms of a SCSI hard drive.

The biggest difference between a SCSI hard drive and one using a rival system such as SATA or ATA is that with SCSI, there is a processor on the drive itself. This means the performance of the drive is not as dependant on the computer’s specifications. Though this does not always outweigh SCSI’s disadvantages for the home user, it can be an important benefit for corporate users who are running multiple computers and need to use low-spec machines for economic reasons.

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It is possible to use a special adaptor to connect more than one SCSI hard drive to a single slot on the computer’s motherboard. Each adaptor can support up to 15 drives. Each drive has a jumper switch which can be set from 0 to 15, and each drive must be set to a different number to avoid conflicts. The ability to use multiple drives is particularly useful for systems which need continuous back-up facilities.

A SCSI hard drive will normally be considerably more expensive than a SATA or ATA drive of the same capacity. Because part of the cost is made up of components which control the drive rather than provide storage, the price of a SCSI drive is rarely very proportional to its capacity. This can produce even greater price disparities. For example, a SCSI drive may cost four or more times as much as a SATA drive which has double the capacity.

SCSI drives have historically had faster data transfer speeds than other types of hard drive, though this gap has shortened over time. A SCSI hard drive will also normally spin at a fast speed which can shorten the time it takes to read, write and access data. SCSI drives are also better suited to running continuously, rather than rival drive types which are designed and priced for personal computer use of a few hours each day. These advantages, and the high price, mean that a SCSI drive is usually most appropriate for systems which are permanently switched on and heavily used such as server set-ups.

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