The popularity of SCSI is increasing rapidly, but I
believe this is due to a misunderstanding. It is often thought that SCSI automatically
blows IDE away when it comes to performance. While SCSI does offer a faster throughput,
one’s activities on the machine affect just how much this performance will really matter.
Several factors must be considered when determining which is better for you.

Performance

Most PC’s use IDE drives because they are cheap and they
perform well. But, to look at performance, you need to look at the entire drive.

Many manufacturer release identical model drives in both
IDE and SCSI formats. If you look at these drives, they are identical except for the logic
board. this means that the HDA and other drive mechanics are the same. The difference lies
in the logic board. The IDE logic board has the disk controller and the built on AT bus
interface. The logic board on the SCSI drive contains one extra SBIC chip. Basically, this
chip is a SCSI adapter to allow the drive to operate on a SCSI bus. So, structurally, IDE
and SCSI drives are the same.

The performance overhead of SCSI over IDE comes from
structure of the bus, not the drive. The nature of the SCSI bus allows it much better
performance when doing data hungry tasks such as multi-tasking. The SCSI bus controller is
capable of controlling the drives without any work by the processor. Also, all drives on a
SCSI chain are capable of operating at the same time. With IDE, one is limited to two drives
in a chain, and these drives cannot work at the same time. In essence, they must
“take turns”.

Comparison

In some computers, SCSI is better. As mentioned above,
SCSI is a smarter bus than IDE. There are many steps in the SCSI data transfer. But, on
OSes that allow multitasking, or if you often use several programs at once, the SCSI drive
is a better choice because this extra intelligence of the SCSI bus is used.

SCSI devices can communicate independently from the CPU
over the SCSI bus. This is due to the fact that each device has its own embedded
controller. Data can then be transferred at high-speeds between the devices without taking
any CPU power. IDE, likewise, uses controllers on each device, but they cannot operate at
the same time and they do not support command queuing.

Last Thoughts

Finally, let me say that for most people, IDE is just
fine and offers very good performance. The reason I believe one does not need to get SCSI,
though, is that most users do not use their system in a way that would actually justify
the SCSI bus. While the nature of the bus is faster, it takes certain situations to
actually need it. Couple this with the significantly higher price, one can see that they
can easily live with IDE.