Buying a Harddisc (IDE)?
Introduction
For the vast majority of computer users, IDE harddisks are the best choice. The prices for these drives are far
lower than for SCSI drives and performance is almost as good. You should make sure any drive you purchase is
DMA/33 compatible (nowdays DMA/66 is standard, but so far not many motherboards support it reliably).
DMA/33 means that your harddisk can transfer up to 33 Megabytes of data in one second in a burst. However,
the standard sustained transfer rate of modern harddisks is more like 5 to 8 Megabytes a second. Almost all
motherboards have a controller for IDE built in and this can support up to 4 devices (for example you could
have two harddisks, one DVD drive and a CDRW drive - after this you would need either an expansion card or
to move to SCSI).
Speed
Here it all gets rather technical - feel free to skip this section! There are four main factors that determine
how fast a harddisk is: spindle speed, seek time, cache size and areal density. Often, only the first two of
these factors are shown in adverts, despite the last factor being just as important. Spindle speed is a measure
of how fast the disk physically spins - this is normally 5400 or 7200 RPM, although high end SCSI devices can
be faster. Obviously, the faster the disk spins, the quicker you can read data from its surface. Seek time is
a measure of how quickly, on average, a harddisk can find a specific file location on the disk. Don't take too
much notice of seek times, as their measurement isn't always reliable and the relation between this and performance
seems to be somewhat non-linear. Generally, however, the lower the seek time, the better the disk. Cache size is
a measure of how much high-speed memory is installed in the harddisk - the more the better, but it's not too
important a factor for home computers. Finally, area 1 density is a measure for how closely data is packed on
the surface of the disk. If data is very close together, the disk won't have to travel so far to read a given
amount of data. Area l density has been rapidly increasing the last few years and a harddisk with very good area l
density and a spindle speed of 5400 rpm may well be able to outperform the first generation of 7200 rpm drives,
which had lower areal density. However, we are now seeing second and third generation 7200rpm IDE harddisks which
also have high areal density and thus superb performance.
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