In a message dated 10/3/2003 8:36:44 PM Eastern Daylight Time,
[log in to unmask] writes:
Actually, there's a curious situation with hard drives, in that many drives
of varying size all have the same number of platters.
For instance, a typical 40Gb drive might consist of a double platter, ie, two
thin metal disks joined together but separated by 3-4 millimeters.
But a 20Gb drive might also have the same double-platter arrangement.
Obviously, in the case of the 20Gb, the extra capacity has been somehow disabled.
For anyone with an enquiring mind, I suggest you ask your local computer
store for an old hard drive that they were about to discard. They're easy enough
to open, a couple of screws and a bit of tape is all that holds them shut.
It's quite insightful to peer inside one of these intricately simple devices.
Ian Porter
Computer Guys Inc.
Arrowtown
New Zealand
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Hi,
Let me add my two cents worth...manufacturing hard drives is a VERY
competitive business, and no disk maker would stay in business long if they did not
cut costs to the bone (anyone remember Micropolis drives?). The reason a 20 gig
and a 40 gig drive may have the same number of platters can be because of two
things. The 40 gig drive is newer, and uses newer and better technology,
allowing more data to be squeezed onto each platter. Secondly they may use only
one side of a platter, on a smaller capacity drive. This can allow them to make
use of platters which have defects on one side that would otherwise have to be
scrapped.
The drive makers do allot a small amount of 'extra' space on drives. This
is for any 'bad blocks' that may exist, or develop during the drives lifetime.
The disk contains a map of these bad blocks and will not use them, instead
using 'spare' blocks allocated for this purpose. Back in the old days, drives
used to come with a label on them that had these bad blocks listed. You had to
enter these manually when setting up the drive to be used. Nowadays this is all
automatic, and transparent to the user.
Just my .02 worth,
Peter Hogan
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