Dust Buster

April 1996 / Reviews / One Gig to Go / Dust Buster

Hard disk technology is fast, but making it removable introduces the problem of media contamination. Dust in a Jaz or SyQuest cartridge can cause data errors or worse.
Iomega uses several steps to control contamination. First is avoiding most of it by sealing the cartridge. A hermetic seal (like that on a hard drive) isn't possible with a removable cartridge because the drive's read/write heads must get in and out. Jaz cartridges have a flexible metal gate that slides tightly in its channel and opens only after the cartridge is fully inserted.
To control the dust that does make it inside, the Jaz design uses air flow (from spinning at 5400 rpm), baffles, and filters to move contaminants from clean zones and tr ap them in "not-so-clean" zones. The heads also track across the data area when the disk first comes up to speed--for calibration, but also to plow dust from the medium and into the airstream for filtering.
Finally, the Jaz data format includes 24 bytes of error-correction code (ECC) at the end of each 512-byte block of data. That's less than the 52 bytes Iomega uses in its Bernoulli flexible-media products, but over twice as much as typical hard disks have been using.

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Matthew Wilson
My approach to software engineering is far more pragmatic than it is theoretical--and no language better exemplifies this than C++.

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