From: burns <burnsmacdonald@home.com>

READ THIS!
WARNING: Overclocking is not without danger. You can fry or otherwise damage certain parts of your system if you do it wrong. You will also be forever excommunicated by Intel if they find out you have overclocked your system... all warranties are violated by this activity. Anything I have written in the following is based upon my own personal experience - YMMV.

YOU UNDERTAKE ANY OVERCLOCKING AT YOUR OWN RISK!
I do NOT advise you to overclock, or in any other way, modify your system. Should you choose to do so, it is your decision - I accept no liability whatsoever for any misadventures that you may be inspired to experience after reading this article.

Overclocking is the practise of altering the conditions under which a CPU is operating for the express purpose of achieving performance levels beyond that intended by the device's manufacturer. In many ways overclocking computers is analogous to "hot-rodding" a car. Here, I've offered some things to think about regarding overclocking processors. These comments are directed toward PPGA Celerons on an Abit BP6 (or equivalent soft-jumpered) board. However, they apply generically to most overclocking situations:

WHICH CELERON?
Not all Celerons PPGAs clock well, or rather some do better than others. The PPGA 300's were *somewhat* clockable. The 366's were probably the most clockable of all. However it depended on when and where they were made. There are also two main form factors of Celerons that are commonly clocked. These are the PPGA's (Socket 370) and the Slot (edge) connectors.
 

Of these the PPGA's are the clear favorites and it is these processors that I am addressing here. While no rule is without exceptions, overclocking the Slot Celerons can be difficult, and frequently they can either not overclock at all, or perform poorly if they do.

NOT ALL CELERONS ARE CREATED EQUAL
Later Celeron production runs were better for overclocking and those produced in the Malaysian fab facility are more "clockable" than those produced in Costa Rico. Strong Celeron performers were the 366's produced in Malaysia after week 26 (I believe). You can tell by the first four digits of the serial number. Mine are 366 PPGA's with close serial numbers starting with 19932... this means that they are week 32 and were produced in the Malaysian fab.

You can't assume that all Celerons will overclock and run effectively. Some may not even POST, some may not allow your system to boot and some may run adequately, but will fail if put them under extended computational loads/stress. You can affect how well your processors run under these
conditions to a limited degree by controlling heat and adjusting the voltage.

DOING YOUR HOMEWORK
To overclock your processor, you first must do a bit of homework and preparation work. Failing to do this is where many people fail, or run into problems. Overclocking your processor not only affects your CPU, it also affects your hard drives, memory and internal devices such as graphics cards. If, for example, you intend to bump your system up to a bus speed of 100mhz, then you MUST make
sure that all affected devices are designed to cope with the increased clock speed. This means digging into manufacturers tech specs. Any one weak point can cause your entire system to fail, or worse
introduce instability or cause the corruption of data. This is not a good thing.

MULTIPLIERS AND CLOCK SPEEDS
Except for very very early limited distribution units, most Celerons are "clock-locked" by Intel. This means that the clock integer/multiplier cannot be changed (unless you are very good at micro-soldering). THEY ARE FACTORY FIXED PERMANENTLY at a given ratio which yields the advertised processor speed, based on the 66Mhz external clock/bus speed recommended by Intel. You can determine this ratio by dividing the advertised processor speed by 66 (for most models - some 400, 450 and all 500 Celerons use an external clock speed of 100, not 66) Thus, common examples are:

Processor Bus/External Clock Speed Multiplier
-----------------------------------------------
300 66 4.5
333 66 5.0
366 66 5.5
400 66 6.0
433 66 6.5
466 66 7.0
500 66 7.5
400 100 4.0
450 100 4.5
500 100 5.0

Overclocking means increasing the external clock (as an example) to 100mhz. For a Celeron 366 this would mean 100 x 5.5 = 550mhz. Some people try to compromise by using 83mhz instead of 100. However, this is not recommended, as it is not a standard speed and can adversely affect other
system devices.

IMPORTANT NOTE: Many motherboards are equipped with a Turbo Mode which yields an additional 2.5 percent in cpu speed. Based on past experience by myself and numerous others, I do NOT recommend using Turbo Mode on an overclocked system (or any other system, for that matter). It can cause far more problems that can be justified by such a negligible performance margin.

STARTING
Assuming you have checked all your devices and found that they are capable of running on a system employing a 100mhz external clock (and the resulting change in bus speed), you can simply change this speed in the SoftMenu bios for your system (as in the BP6), or you can change it using the mechanical ("hard") jumpers if you have an older style board. Booting the system should proceed normally with a successful post test and OS boot. Hanging or anomolies at any point indicates problems and should cause you to rethink your approach.

VOLTAGE AND STABILITY
Increasing the voltage increases the amplitude of the signal and, therefore tends to make the processor more stable. This can cause many overclocked systems which do not boot well , to do so. However there is a direct relationship between heat and voltage. Processor life is also a factor and is often quoted as a reason not to overclock at all. Most Celerons run at 2.0v. It's your decision, but frankly if you stay within accepted, sensible bounds (+-0.2v max. variation) then your processor will be obsolete long before any shortened life span is likely to be an issue.

The rule of thumb here is to use the lowest possible voltage that will still allow your system to run reliably in a stable and cool condition. NOTE: I consider 2.2v to be the absolute MAXIMUM voltage for PPGAs. The lower the level below that, the better.

The change of even one-tenth of a volt can make a difference of as much as 5 deg. Celsius in the temperature of your CPU core. You will often hear of doing a BURN -IN on newly overclocked systems. This refers to, as an example, clocking a system and 2.0 volts is the intended final voltage
setting, but running it under load for an extended period at 2.1 or 2.2 volts. The consensus in the overclocking community is that, once burned in, overclocked systems will perform more reliably at the lower final voltage than an identical system which has not undergone this process. People use looping system tests, looping Quake demos and SETI for this purpose. This also performs the dual function of testing the stability of the system. Most burn ins are conducted over a 48 hour period.

HEAT IS YOUR ENEMY
Failures and, ultimately, damage suffered through overclocking are invariably caused by resistance and heat. Intel advertises a maximum heat specification for the Celeron PPGAs of 90C. However, experience has shown that Celerons will fail (ie; lock-up and shutdown) long before that temperature is reached. Out of the box, Celerons normally run between 35 and 45C, depending on the design of the case and the heatsink and fan that comes with them, or in the case of the OEM models, what heatsink and fan is provided by the reseller.

Most overclockers consider 35C or less desirable (the lower the better - some even use freon coolers!), 35 - 40 undesirable but tolerable, 40 -45 time to do something radical, and anything approaching 50C is critical - shut it down NOW and rethink your whole system!

COOLING
There is NO length that overclockers will not go to improve cooling - it has become a sub-cult in itself. Some use refrigeration or peltier coolers. Others (such as myself) use massive special market heatsinks and fans. Some even carefully lap the surface of the heatsink and the cpu to match perfectly and maximize heat transfer. However, for most purposes, a high-capacity roller bearing fan, a good quality heatsink and a sparing application of thermal paste between the heatsink and cpu slug, is all that is needed for most mild overclocking ventures.

Don't overlook your case. The heat that is drawn away from your CPU needs to go somewhere. High ambient internal case temps will eventually result in abnormally high system and cpu temps. Cases should have plenty of adequate cooling and be free of unnecessary clutter that obstructs airflow. The case I use is a mid-tower with a 3 inch intake toe fan on the bottom of the front, a 3 inch exhaust chimeny fan on the top of the case, a four inch exhaust fan on the side directly over the cpus and graphics cards, a exhaust fan for the power supply (rather than the usual intake fan) and two micro drive cooler fans on each of the two high speed bulk hard drives. This may be a little extreme (and noisy) but I have an extremely cool, reliable and stable SMP system as a result.

BAD SIGNS
Failing to boot, hanging, locking, poor video performance, memory errors and corrupted hard drives are all signs that you have got it wrong and your system is retaliating. These, along with damaged cpu's, are the risks involved in overclocking - especially if you don't approach it with respect and due prudence. Some folks overclock and see no apparent problem until they start to perform cpu-intensive applications such as very large scale compiling, unarchiving/unzipping, high speed backups, or SETI. Failures under these circumstances indicate that there is some underlying
instability which needs to be addressed... quickly. YMMV

MORE READING (This Was Just A Start)
Please don't take this as the one and only gospel on overclocking Celerons (or any other processor). I have just scratched the surface. In overclocking, as in anything else, the more reading you do and the more informed you become, the more likely you will achieve success and minimize the pitfalls.

* There are a number of Usenet newgroups devoted to overclocking. You should at least consider lurking in them for a while. However, they do tend to attract a few "cowboys" as well as some genuine gurus. Treat the advice you receive in these forums accordingly.

* TOM's Hardware Guide ( www.tomshardware.com ) One of the many excellent sites which offer a wealth of information on this subject. This is put out by Tom Pabst, a German doctor living in the UK. Those of us who have been around for a while remember when this was THE definitive reference for overclocking and independant chipset reviews. Since that time, Tom has (unfortunately) been seduced by creeping commercialsim and, according to some, become less objective in his reviews. However it is still an excellent place to start. His overclocking guide can be found here:
http://www6.tomshardware.com/guides/overclocking/index.html

That's all - make up your own mind and good luck.

--
burns
 

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