Advertisement
Although the ST-506
drive has a low data transfer rate it only takes a minor modification to free
it from this transaction. Originally the IDE drive was invented as a way of
making disk systems cheaper by incorporating the disk controller within the
drive itself. This effectively produced a drive that could plug more or less
directly into the ISA bus. By combining the controller and drive electronics on
one printed circuit board the interface between the two could be simplified. At
this stage in the IDE’s development it was thought of just as a way of
packaging the standard ST-506 drive and
doing away with the need to have a controller. Many main boards were designed
with 40- way IDE connectors that allowed the drive to be directly connected.
This freed an adapter slot and even allowed the manufacturer to claim that the
machine had a hard disk controller built into the mainboard!
The importance of the
IDE interface was slow to dawn but in
retrospect it is obvious. Once you have
combined the disk controller with the
disk there is no need to keep to
any standard. The drive manufacturer is free to modify the way the drive works in any way as long as the final interface connects to the ISA bus . In this sense the
IDE drive’s interface with the outside world is
the ISA bus and so data can be
transferred at any speed up to the limit
of the ISA bus! This puts the upper limit
on the data transfer rate of
around 6.5MByte/s. Most IDE drivers do not achieve this high rate of data transfer and -1-2MByte/S is more
typical.
IDE drivers achieve
their higher data transfer rate by a range
of methods. Some rotate faster than the standard 3600 rpm and some pack
in more than the standard 17 sectors per track. This change in the
number of sectors per track can be
something of a problem in that
the BIOS setup program usually only recognizes standard 17 sector
drives. When a drive is installed in a machine, the BIOS setup program has to be run to set the number of cylinders, heads and sectors per track. IN
most systems you do this by selecting a drive type
number form a table – each drive
type number corresponds to a giving number of cylinders, heads and
sectors per track. This isn’t a problem
as long you can find the drive type number that
corresponds to the drive being
installed. It not then some BIOS
setup routines will allow you to enter a
user-defined type then most IDE
drives will emulate a different drive
geometries – i.e they will pretend to
have a different number of cylinders,
heads and sectors per track. The only problem that the user has is to select a supported drive type that has a
total storage capacity as close
to, but not bigger than, the
actual capacity of the IDE drive. This ability to emulate almost any drive
geometry is often referred to as translation mode as opposed to the drive’s native mode.
You can fit an IDE
drive to most machines even if they don’t have an IDE connectors built in to the main board. In this case you
have to use an IDE controller card but as
this is mainly a simple connector it is
possible to combine it with other
facilities. For example , you can buy an IDE controller, serial port parallel port and games port. There are some minor problems in using an IDE drives. The
following is a list of dates and
revision numbers of BIOS ROMs that do:
AMI dated
4/9/90 or later
Award version
3.04 or higher
Quad-tel any
version supports a single IDE drive but
only 3.04 or
later
supports dual IDE drivers
Phoenix Plus
386 version 1.10 or higher
Phoenix BIOS version 1.00 or higher
Another minor incompatibility is that IDE drives are
low-level or physically , formatted at the factory. This means that
to install them all you have to do is
partition the drive and then use the
standard FORMAT command to perform a logical format. This makes life much simpler
for the user but it makes it impossible
to use some advanced disk diagnostic and maintenance programs such
us Spin Rite (see later).
In spite of these minor
problems, IDE drivers are the most cost-effective choice for all single-user
systems. The only situation in which it
is necessary to consider other
types of drive is when you need to extend
by the ISA bus. If you want to make full
use of the EISA or MCA bus then SCSI and ESDI are your
only reasonable choices.
( Best Hosting site for godady )
