-----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.