A rather sub-optimal solution that is offered as an alternative by some hard disk
manufacturers is the disk size reduction jumper. Certain hard disk size barriers
can cause a hard drive to not be seen by a system at all. If you set one of these jumpers
on the hard disk, this tells the disk to change the drive parameters it presents to the
system, reducing the size of the drive. Since the system sees the drive as being small
enough to avoid the size barrier, the barrier is avoided. Of course, this costs you
capacity: you lose the storage of the drive above the size barrier, unless you supplement
the jumper with a software overlay.
The first time size reduction jumpers were commonly used was to get around the 4,096 cylinder barrier. One of the common ways that a BIOS with
this barrier may treat a disk that is over about 2.1 GB is wrapping
around. So a 2.5 GB disk would be seen as only around 400 MB. The size reduction
jumpers would cause the hard disk to "pretend" that it had less than 4,096
cylinders, so it was only 2.1 GB in size. This is of course a waste of however much space
the disk really has over 2.1 GB, but it is better than only using 400 MB of the disk.
Similarly, some newer drives may come with size reduction or capacity limiting jumpers
to get around the 32 GB size barrier. These force the drive
to present a size small enough to avoid triggering that capacity barrier.
This "solution" is in some ways the hard disk equivalent of that old Marx
Brothers routine: "Doctor, it hurts when I do this"... "So don't do
that!" ;^) It's not really a solution, but rather a way to avoid the consequences of
the problem. It's better than having your PC hang when you try to boot the system, but
still, this solution is a very poor one. The only time these reduction jumpers really make
sense is when you use them in conjunction with drive overlay software--in some cases, without the jumpers you may not even
be able to get the system booteed so you can install the overlay! Proper hardware support
is still a better solution of course.
Next: Manually Entering Drive Geometry Parameters
