IDE:
As the name implies, IDE (Integrated Drive
Electronics) combines both the disk and the
controller on the same unit. Only a simple
interface is needed and typically it is built
directly into the motherboard. If the interface
is not built into the motherboard, a simple
paddle-board is used and, because so little
electronics are needed, an additional serial and
parallel port is sometimes included.
The IDE drive transfers only data and doesn't
need to send format and sector information as
does ESDI. Therefore, the data transfer rate can
be 3-4 times faster then ESDI.
The IDE drive is not a device level interface
and has the ability to lie to the BIOS and give
the logical appearance of a known device type,
while physically it may be totally different.
You won't see bad tracks on an IDE drive,
because the drive hides them. Because of this,
you can not low level format an IDE drive
without specific utilities for that drive.
IDE uses a single 40 pin cable. Limited to a 2
foot cable length and 2 addresses, no termina-
tion is needed. The first drive is configured as
the master and the second as the slave.
IDE has a transfer rate of .625 - 2M bytes per
second and a storage capacity of 20 - 500 MB.
SCSI:
SCSI (Small Computer Systems Interface),
pronounced "scuzzy", is a more general version
of the IDE interface. SCSI hard disks boast the
fastest transfer rates of all the discussed
technologies, with SCSI 2 having a transfer rate
up to 40M bytes per second.
SCSI implements 2 ways of boosting transfer
rates, fast and wide. FAST SCSI doubles the
clock speed, and WIDE SCSI increases the bus
width.
SCSI also implements other performance features,
including controller based RAM caching and tag
command queuing. By queuing commands, the SCSI
controller can free up the CPU to do other tasks
while it finishes its task. SCSI also has the
ability to transfer data to another SCSI device
without CPU involvement.
SCSI uses a single 50 pin cable with devices
daisy chained together and terminated on both
ends. Seven devices can be installed per
controller with up to four controllers.
SCSI 1 has a data transfer rate of 1-5M bytes
per second and a storage capacity of 20 MB - 1.5
GB.
SCSI 2 has a data transfer rate of 1-40M bytes
per second and a storage capacity of 40 MB - 3
GB.
WHICH IS BEST?
Performance isn't without price. Many applica-
tions don't need the performance of SCSI, which
is, by far, the most expensive. IDE or ESDI will
usually suffice for most applications. IDE is
presently the cheapest of the three. SCSI, how-
ever, has the added advantage of the greatest
expandability. So, if you need SCSI, the money
is well spent.
Thanks Alan.
Well, good luck with your Z-100 MFM Hard Drive
installation. If you have questions or comments,
I can be reached at
Cheers,
S.W. Vagts
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