Buying a Harddisc (SCSI)?
Introduction
SCSI harddisks are for those who demand a lot from their harddisk. Typical uses for SCSI harddisks are in servers and high
end workstations used for tasks such as digital video and graphics work. There is no reason for a home user to purchase a
SCSI harddisk. Furthermore, SCSI harddisks require you to have a SCSI controller, which can cost over £100 depending on the
type needed. There are a few motherboards available with SCSI controllers onboard.
Size
One can purchase harddisks in many sizes - from 2,1 Gigabytes up to 34 Gigabytes. A 'normal' home user
should find that a drive around 6,4 to 13 Gigabytes is plenty. If you don't find this to be plenty, you're probably not
organising your files properly and have loads of things installed that you never use! Installing an extra harddisk in a computer
is a relatively simple process, so you can always buy more space later if you need it. It's definitely worth waiting rather than
buying a big disk now, since prices are constantly falling.
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 specifik 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, areal 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. Areal density has been rapidly increasing the last few years
and a harddisk with very good areal 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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