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Practical Comparison: Serial ATA And SCSI

SATA Hard Drive with a Kick: Western Digital's Raptor Put to the Test
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In addition to the pure cost aspect, there are a number of factors that characterize and distinguish Serial ATA and SCSI from each other. There are always those who would like to see the end of parallel transmission technologies such as SCSI, for instance. However, this will not come about so soon. On the one hand, Ultra320 currently offers high performance reserves, while Serial ATA does not offer the necessary relief for the system processor under high loads - and this is where SCSI systems can still show off their advantages.

Going back to the topic of cabling mentioned earlier: whereas with Serial ATA all the drives are connected individually at the controller, SCSI requires a more sophisticated bus along with active termination (for eliminating signal reflections). However, there is no problem with this being several meters long, which, also permits drive configurations with large physical dimensions. Their usage in tower cases is simple and very clear, although things do become more difficult in 19" environments where space is at a premium.

In contrast to this, UltraATA always looked problematic with the 80-wire cable only being allowed to be 45 cm long. Although cables with twisted wires and a length of approximately 60 cm are not envisaged in the specification, they do, however, make for greater scope.

The solution comes only with the advent of Serial ATA. Both in the 19" sector as well as in conventional cases, cable lengths of up to one meter bring the long-awaited freedom. It is also possible to bind together numerous SATA cables in compact form without any difficulties, with star-shaped drive arrangements being possible, as well.

A further critical aspect is the ability to replace drives in the event of a breakdown. What is known as "hot swapping" is quite usual in the SCSI sector, with hot plugging supported by many controllers or realized by means of sophisticated interchangeable frames. This is not so with UltraATA, where disconnecting and connecting drives mostly results in the entire system crashing. The picture is different with Serial ATA, for which hot plugging is now envisaged. However, this must be supported both by drives as well as controllers.

Ultimately, not a great deal remains of the immense technical difference within the operating system. Drivers take care of addressing drives and, if necessary, entire RAID arrays. This situation is documented within the Device Manager because all the controllers (regardless of whether they are SCSI or ATA) are recognized as SCSI devices.

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