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The View From The Top

Round-Up: Comparison Testing of 22 Hard Disk Drives
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As we write this story, the switchover from UltraATA to Serial ATA (SATA) remains in full swing. Actually, there are now more SATA drives for sale than UltraATA models, though both types will probably continue to be offered side-by-side for some years to come. There are still too many UltraATA systems in circulation for them to be ignored, and many of those are likely to be upgraded at least once more before they are retired.

It's also still true that Serial ATA works faster than UltraATA only in a very few cases. Though both 150 and 300 MBytes/s SATA versions may be theoretically faster than UltraATA/133 and UltraATA/100, in practice most hard disks top out at speeds somewhat slower than 80 MBytes/s anyway, regardless of interface type; most run at about 70 MBytes/s. In actual use, there's little more that these devices can deliver, because the underlying file system (this means NTFS for most Windows installations) takes its toll and sequential disk access to a substantial number of sectors happens only rarely.

Seek times for typical 7,200 RPM drives are normally rated between 8 and 9 ms, which results in average access times of 12 to 15 ms. The only exception to this rule occurs in the Raptor family of 10,000 RPM drives from Western Digital, which feature shorter access times and higher average transfer rates.

SATA offers one additional advantage - above and beyond its compact and simple cabling - one that can boost performance under heavy loads. Native Command Queuing (aka NCQ) is now supported by disk controllers and hard drives. It enables the drive to analyze and sort all pending read and write requests into the most efficient service order. The goal of this exercise is to limit or minimize drive head motion as much as possible.

Thankfully, nearly all vendors have also addressed the most significant cause of hard disk noise, by switching from ball bearings to fluid dynamic bearings. Switching from horizontal to perpendicular magnetic fields (like those used for perpendicular recording) should also enable higher data densities (usually expressed in terms of bits per square inch) and hence, drives with even greater capacity than those available today. So far vendors have offered up to 140 GB per drive platter, and boosted total drive capacity by combining more platters within a single drive enclosure. As time goes on, the capacity of each platter will also go up.

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