-----Original Message-----
From: Andy Bovingdon [mailto:bov@xxxxxxx]
Sent: 17 April 2002
09:09
To: ukha_d@xxxxxxx
Subject: Re: [ukha_d] New PC recommendations
> In addition to an Athlon XP processor, think about 512Mb RAM
(don't
> bother about the Corsair stuff unless you want to overclock -
and
you
> won't need to unless you want to run the latest games - I run
a
very
> processor intensive simulator for my helicopter so I run an
XP1500
at
> the same speed as a 1900)
How do you actually go about
overclocking?
Apart from ensuring the
chip is kept cool?
Overclocking is based on the premise
that
with adequate cooling processors can be run at far faster than the rating
printed on them. This is for two reasons – in your average office
where
vents are typically blocked and pretty average cooling systems are employed
processors
need to run at the rated speed while they are pretty hot – reduce the
temperature of the CPU and you can get more speed out of it. The other one
is
that when the factory makes chips it doesn’t set out to make say 2000
chips one day and 1800 chips another. It makes chips and puts them on a
test
rig to see what speed they can get out of them. Generally all chips from
the
same batch of silicon will generate roughly the same speed. Now it gets
more
complicated, because one particular batch may be more than capable of
running
at 2000 speeds, but there may be demand for say 1800s. These chips will be
marked as 1800s and then copper links on the surface of the chip cut to set
the
speed of the chip electronically. Whether you get a good 1800 capable of
running at much higher speeds or an average one is pot luck. Overclocking
used
to bring with it massive cost savings (in the case of 486 processors), now
it
doesn’t yield as much of a saving, people tend to overclock
“because
they can”.
It actually gets more complicated with
each iteration of processors. AMD and Intel really don’t care about
people at home overclocking chips, what they don’t want is some Far
Eastern bucket shop re-marking chips and selling 1600s as 1800s. To this
end
they make it more and more difficult to overclock each time the hobbyists
find
a way to circumvent the protection they build in.
There are two methods to overclocking
–
the first and easiest is simply to turn up the bus-speed in the bios (most
Abit
and Asus boards amongst others will allow you to do this) so that instead
of
running at 10x133 (1333MHz) you run at 10x140 say (1400MHz). This means
that
you’ll be running everything though at faster than its rated speed
–
PCI bus, AGP, and most importantly the DDR memory bus (which is already
running
at twice the speed of the PCI bus!) Manufacturers of performance hardware
realise this, and so produce DDR ram rated at faster than the stock 266MHz.
My
Corsair ram is rated to 333MHz, and is actually capable of running reliably
at
360MHz.
The other, more complicated method involves keeping the bus speed
set
to standard and changing the multiplier in the bios. AMD and Intel
don’t
want you to do this so they build a number of bridges into the processor to
lock in the multiplier marked on the chip.
My current processor is an AMD so I
only
know how to unlock recent versions of their chips. It used to be relatively
simple use a pencil to join up all the relevant links – these are the
same links that AMD join on the test rig so they can set the multiplier in
software to find the maximum speed the processor can reliably run at. Then
the
pencil line didn’t reduce the resistance enough, so people started to
use
conductive paint for repairing PCB traces. In the latest generation of
Athlon
XP processors AMD cut through the top layer of substrate with a laser.
Beneath
this substrate lies a conductive grid – if the conductive paint gets
into
this grid it really screws with the multipliers you can set – and in
some
cases you’ll no longer be able to run at the speed you could before
you
started.
The answer is to fill these holes with
something before you start (I used 30 minute epoxy) and then join up the
dots. They
are tiny so need masking off with tape before you paint on the silver
lacquer
with a pin!
You’re now in a position that
you
can set any multiplier and clock speed, you like. The best position is to
run
the lowest multiplier and highest bus speed that you can. This determines
the
bandwidth between processor and main memory.
There’s more, but I’ve
spent
more time typing this than I originally intended.
Tim.