[Sussex] Hard drive question

[John Crowhurst]

On Fri, October 27, 2006 17:04, linux at oneandoneis2.org wrote:
> Hard drives with multiple platters & therefore multiple heads: When
> writing to the disk, is only one head active at a time, writing the
> whole file to one platter; or do all the heads write at once, with
> head one writing the first bit of the file, head two writing the
> second bit, and so on?

Hard drives are accessed randomly, so one of the heads accesses the drive
on one platter. The file will be scattered over the different platters as
the drive writes in its most optimum pattern.

Drives don't 'fill' one platter before moving to the next, the data fills
up  in a pseudo random manner.

> I was under the impression that only one head could write at any one
> time, and most sites seem to bear this out, but others swear blind
> that all platters are written to at once, and you can see how that
> would make for a speed increase. . .

The only problem in the simultaneous logic idea is that data is stored
randomly across the disk and not sequentially, so there is little point
for a hard drive to read the heads at the same position.

Magneto-optical (MO) drives and tape drives use heads that read
simultaneously, as the data is stored sequentially on this media.

--
John