Advanced guide
Whether you need
to solve PC boot problems, reallocate system resources or just improve
performance, your BIOS could hold the answer.
A quick question: what happens
when you turn on your PC? If your first thought is 'Windows loads', then you're
missing out rather a lot. In particular, you're missing out the contribution
made by the BIOS (basic input/output system), one of the most important parts of
your system.
What actually happens when your
PC starts is that the PSU runs some tests to check the voltages it's receiving.
Once they're stable, the PSU drops the CPU reset signal, which enables the
processor to begin running. This always starts by looking at a particular
address in memory, which points the CPU at the beginning of your BIOS code. The
CPU then begins executing it, and the boot process has finally started.
The first thing your BIOS will
do is access information stored in CMOS (complementary metal oxide
semiconductor) RAM. This small area of memory maintains its contents even when
your PC is switched off, thanks to a battery on the motherboard, and holds some
useful configuration settings. So useful, in fact, that one of them is needed
right away.
Power on self test
If your PC had an intermittent fault and Windows were permitted to load, then
the consequences could be disastrous. Faulty memory might corrupt the disk
cache, for instance, potentially trashing your most important data files. That's
why the BIOS always runs a power on self test (POST) soon after starting, to
ensure that at least the basic hardware functions are working as expected.
Everyone expects their PC to
load as quickly as possible, which means that these checks are very short and
not exactly reliable. Most people reduce these still further by a BIOS setup
program tweak, enabling a setting like 'Fast Boot', and normally it's safe to do
this. However, if your system is behaving erratically and you're wondering if
there might be hardware or RAM problems, remember that you can reverse this
step, too. Turn 'Fast Boot' off for a while to see if the POST picks up
anything.
If an error has been discovered,
then the boot process may not be able to continue. Obviously, you need to be
told about this, but there's a problem: your video card hasn't been initialised
yet and so error messages can't be displayed. The alternative is to use a
sequence of long and short beep codes instead, so you need to listen for these,
then read the documentation to find out what 'one long, two short, one long'
actually means. See Computer Hope at www.computerhope.com/beep.htm if you don't
have a motherboard manual to hand.
Search for adaptors
Next, your BIOS needs to initialise other hardware you've installed, such as a
video adaptor. Of course, it's no idea how to do this, but that's OK because
anything that needs initialising in this way has a ROM BIOS of its own. Your
BIOS searches through memory looking for the signature of other ROMs, and calls
the startup address of any it finds.
Normally this all works fine and
the most you'll see is an initialisation message from your network adaptor, RAID
card, whatever you've plugged in. However, if there's a problem with this device
then the entire boot process may fail in some way. So if your PC starts, but
doesn't get as far as loading Windows, then removing non-essential expansion
cards just might help.
Once all your adaptors have been
detected and initialised, the BIOS begins its task of allocating system
resources. More specifically, it decides which devices will share which
Interrupt Request Line (IRQ, the means by which a device informs your CPU that
it needs attention). Again, this usually works fine, but there are rare
exceptions. Use the BIOS setup program to turn off unused onboard features (such
as network adaptor, integrated sound and so on) to stand a chance of fixing
them.
Bootstrap loader
The final boot task any BIOS must perform is to load your Operating System.
Conventionally it'll look first for a bootable floppy, then a CD and finally
your hard drive, but this boot order may be changed in your BIOS setup program.
Under normal circumstances it's best to move your hard drive to the top of the
boot list: no floppy or CD access means that you'll shave a second or two off
the Startup time. You'll need to remember that you've done this, because you'll
need to switch it back to boot from CD, say, perhaps to reinstall Windows.
Your BIOS then works through
each drive in the boot order, looking for the first one that can be accessed,
then locating the code that makes the disk bootable. Exactly where this is
depends on the drive type: a floppy has its boot code in the very first sector,
for instance, while a hard drive has partition loader code stored in the
partition table. If there's a problem with any of this, such as your hard drive
partition not being marked as bootable, then the BIOS will display an error
message. Otherwise, the boot code will be loaded into memory, your CPU then
executes it and the real process of starting your OS finally begins.
Should I upgrade my BIOS?
BIOSes are regularly updated to add more features, improve performance and
stability, or fix problems. New BIOS code is made available online at your
motherboard manufacturer's site, along with flash upgrade utilities that will
carry out the upgrade for you.
This may all sound appealing,
but there's a problem. If the BIOS file is corrupted during the download, you
don't acquire the right BIOS for your motherboard or the flash upgrade utility
fails, then you could be left with a PC that won't even boot. This means that
you'll have no way of fixing the problem, either.Some motherboards have ways
around this. They employ a second BIOS chip that's ready to take over if the
first one is corrupted. Although this is welcome, it's still important to treat
the whole upgrade process with great care. If your PC is relatively new or
you're not experiencing any problems or bugs with the current BIOS version, then
it's probably safest to stick with your current setup. The risks outweigh any
likely benefits.
However, if your PC is old and
you're looking for extreme performance improvements, or you need a BIOS upgrade
for a specific reason (to support a CPU upgrade, say), then by all means give it
a try. Browse the Support section of your motherboard manufacturer's site for
more information and carefully follow the instructions you find.