HARD DISKS

There are a lot of issues involved in buying a hard disk, more than can really
be covered in a single written document. I'll try to make some notes on the
important features you'll be concerned with, adding details as things change --
this is a rapidly-changing field.

Size
----

As I write this, disk capacities range from around 270 megabytes up through
2 gigabytes and above. As you look through the ads, you'll see common sizes
popping up -- if you don't already know, a "megabyte" is roughly one million
characters and is abbreviated MB, and a gigabyte is around one billion and is
abbreviated GB. The disk will never have exactly the advertised amount of
space, because some overhead is required in formatting and a megabyte isn't
really exactly one million bytes anyway. It's not a big issue as long as you
are prepared for it.


Internal vs. External
---------------------
You're paying about $200 for the box and the mechanism, regardless of how
big the capacity of the drive is. If you're adding a hard disk to an existing
system, therefore, it might turn out to be cost-effective to buy an internal
disk with and replace the one you've already got. This is also a factor if
you want a self-contained system with fewer parts.

SCSI connections
----------------
If you buy an external drive, it will have to be connected to your Mac with
a cable. The SCSI (Small Computer System Interconnect) cables carry standard
signals but the plugs, unfortunately, are not standard.
(hopefully I'll get some pictures of 25-pin vs. 50-pin cables to put here)

Reliablity
----------
Expect your disk to fail. That's all I'll say for right now until I have time
to give you the details, but basically all disks should be expected to fail
after some number of years of use. They even have ratings for this, called
the MTBF (mean time between failures) for a particular device. As long as it
works, you can think of the disk drive as "permanent" storage, but someday
it will stop working. So be prepared for that day.