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Computer hardware problems
Auto detect & hard
disc drive parameters
Enjoy playing with your computer’s CMOS
setup? Well, watch out. If you change the
hard disc setup from a “User” type to “Auto
Detect”, the machine may no longer boot.
Here’s why auto detect doesn’t always work.
When you buy a new hard disc
drive, one of the first things to do is
to check the manual for the drive’s
“parameters”. Alter
natively, these
parameters are usually also printed on
a sticker attached to the drive itself.
Your Drive parameters consist
of: (1) number of heads; (2) number
of cylinders; (3) number of sectors
(4) landing zone; and (5) write pre
compression. These parameters are
required by the computer so that it
knows how big the drive is and, more
importantly, where to go on the drive
in order to retrieve data.
For example, to retrieve a certain
string of data, it may read sector 7
head 3 on the drive. That’s fine but
what if you change the parameters
of the drive, either intentionally or
accidentally? This can easily happen
if you install a new motherboard or
transfer the drive to another comput
er, for example.
The most common error is using
Auto Detect (in the system BIOS) on
a drive that’s come from a machine
in which it was “assigned” it’s para
meters by the person who originally
installed it.
If it’s a boot disc, you may find that
the machine will no longer boot up.
Alternatively, if it’s a non-boot disc,
you may no longer be able to retrieve
files or the files may be corrupted,
with lots of lost clusters.
The reason for this is quite simple.
Auto detect doesn’t actually read
the settings that have been manually
assigned to the drive. Instead, it re
trieves the drive’s parameters by read
ing the manufacturer’s data from the
drive itself. Because of this, it follows
that if the original manually-assigned
parameters differ from the parameters
stored in the ROM, then using auto
detect will cause data errors.
This doesn’t matter if it’s not a boot
drive and you no longer need the data
that’s stored on it. In this case, you can
just reformat the drive and carry on.
The drive will be auto-detected each
time you start the computer and all
will be well.
If it is a boot drive and/or you do
need access to the data, then you will
have to manually assign the required
drive parameters if auto-detect causes
problems. How do you know if it’s
wrong or not? The most simple checks
to do are:
(1). Try to boot the machine. If the
settings are incorrect, the machine
won’t boot (because it can’t find the
system). Be sure not to run Scandisk
with the autofix option, otherwise you
could trash your data;
(2). Run CHKDSK or Scandisk (no
autofix) on the drive. This quickly
checks the drive and if the settings
are incorrect then you will receive
hundred’s of errors.
Parameter selection is very im
portant. If you lose your parameters
you can spend hours trying different
combinations and still not guess the
correct settings. My advice is to al
ways write them down.
Before leaving this subject, it’s
worth noting that many BIOS’s offer
two different auto detect options.
The first is the auto detect in the
BIOS setup. You activate this in or
der to automatically enter the correct
drive parameters in the main menu
when it is first installed. You then
save those parameters so that the
machine doesn’t have to auto detect
the drive each time it’s started.
This is used for most computer
setups and the detected parameters
can be written down and stored with
the computer (so that they can be later
manually re-entered in a different
setup if necessary).
The other method involves select
ing ‘Auto’ as the drive type in the
main menu. This way, the system
will auto detect the drive every time
you start up. This is a simple way of
installing drives, however you are
generally not presented with the set
tings. Only the size is shown so that
if you transfer the drive to another
machine without auto detect and you
don’t know the settings, it can’t be
correctly set up.
Finally, I have seen different moth
erboards return different para-meters
for the same hard disc drive when
using auto detect. Admittedly, this
only occurs with some older mother
boards; I haven’t encountered any
modern motherboards that give this
sort of problem.
So be careful when playing with
hard disc drives – it’s all to easy to
lose your precious data and wind up
with a door stop if you don’t know
SC
exactly what you are doing.
March 1998 83
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