You may have heard about overclocking recently as it has become a fairly popular practice. In part this due to the great overclocking success of the C300a over two years ago. Overclocking is achieved by running your CPU higher than it’s specified clock speed. This is done by modifying the CPU multiplier and/or the system I/O bus (i.e., Front Side Bus) clock speeds. Since Intel has been locking the multiplier settings, the way we overclock is to change the FSB clock speed. In my case, I’m overclocking a Pentium III 500E MHz FC-PGA Coppermine to 750MHz . The 500E has a locked multiplier of 5. The CPU speed is determined by multiplying the FSB setting by the multiplier. In this case, we have a multiplier of 5 and an FSB of 150MHz to achieve 750MHz. Normally, the 500E runs at a 100MHz (5 x 100) bus speed.
Unfortunately, not all chips overclock and some chips are better for overclocking than others. Fortunately, there are number of strategies available to the overclocker that can help to alleviate the problems that pop up. These strategies include, adjustable FSB settings, cooling, and voltage adjustments.
If you’re not afraid to push your system and get your hands dirty putting it together then I highly recommend trying it. However, keep in mind that overclocking can cause damage to your system and could result in potential loss of data on your hard disk.
I started learning about overclocking by joining a few news groups and looking at some do-it-yourself web pages. There are a lot of people out there with vast computer knowledge that are willing to share it. Here are a few sources for getting started:
News groups are a great source of learning and sharing information. The news groups are a good way to listen in on problems that others are experiencing and also get tips from more experienced people out there. Here are some links that I found particularly useful:
What Makes a Good Overclocking Chip?
The success of the Celerons created a great market for overclockers and for the most part it can be easy. There are several important factors that will determine success, of course the CPU itselfI chose the ABIT BE6 motherboard because it allows you to set the external clock speed, AGP clock, and voltage from the BIOS. This makes playing around with settings very convenient.
The Celerons were excellent overclocking chips for two main reasons, an on-die L2 cache running at core speed, and a FSB speed of 66MHz. The on-die L2 cache was critical since this allowed many Celerons to reach bus speeds of 100MHz without failing. Many chips such as the PII or K6 don’t have an on-die L2 cache and have less success handling the increases in bus speeds. Another critical factor was the Celeron’s default bus speed of 66MHz. Since the Intel 440BX chipset supports bus speeds of 66 and 100MHz this gives the Celeron a lot of room to play. Another added value is that a 100MHz bus speed is supported by the system and will not overclock the PCI, AGP buses or memory subsystems. A little more on this later.
Some of the key factors that lead to successful overclocking include the following:
Let’s take a brief look at each of these factors. You’ll want a motherboard that allows you to set change the CPU clock frequency or FSB settings, PCI and AGP multipliers, CPU Core Voltage, CPU L2 Cache Latency, and SDRAM settings.
FSB – The more settings that the motherboard allows the better your chances. The ABIT BE6 II has a wide number of FSB settings – 66, 75, 83-200(1MHz increments) that give the board extreme flexibility. You’ll want this to get the most out of your CPU. Since your chip might not be stable at specific FSB you can back down from to find an FSB that is stable.
PCI – Ideally you want your PCI devices to be unaffected by your changes to the FSB speed. Unfortunately, there will be some effect on your PCI bus speed but in most cases it is minimal. Normally, the PCI bus operates at 33MHz. You’ll want to stay as close as possible to this speed. The ABIT BE6 II motherboard supports PCI bus multipliers of 1/4, 1/3, and 1/2. For example, a FSB setting of 66 is multiplied by 1/2 to achieve 33MHz, 100FSB is multiplied by 1/3. This allows the overclocker to keep a PCI bus speed that is close to the original spec.
AGP – Similar to the PCI bus you will want a motherboard that provides a multiplier setting for the AGP bus so that your video card will run at the specified bus speed of 66MHz. The ABIT BE6 II provides AGP 1/1 and 2/3 mutipliers. At 100MHz the AGP bus is multiplied by 2/3 to yield 66MHz. Of course if you’re running at an FSB of say 83MHz your AGP bus will be slightly out of spec when multiplied by 2/3 (55MHz).
CPU Multiplier – As mentioned above your CPU is a locked number that can’t be changed. For example the 300A had a 4.5 multiplier. One of the reasons why the Celeron 300A was such a great overclocking chip is that the 4.5 multiplier when multiplied against 100MHz yielded 450MHz! A 50% increase – not bad! You’ll need to know the multiplier for your chip so keep this in mind when you’re setting a target for your overclocking. It is a very important factor in the chips overclockability.
Core Voltage – Although most chips will overclock to some degree it is sometimes necessary to increase the core voltage being supplied to the CPU in order to stabilize the chip. The trade off here is that increasing the voltage often leads to more heat which in turn can cause the chip to be unstable and even shorten its lifespan. The Celerons had a default voltage of 2.0v. The new FC-PGA Coppermine chips come with a 1.6v core. Ideally, you want your chip to run stable at the default voltage, but it is often necessary to raise the voltage up to 20% higher in order to stabalize the chip. Adjusting the voltage is one most important variables in sucessful overclocking. Be aware that too much voltage can permanently damage the chip which is why we limit the voltage increase to 20% outside of spec.
CPU Cooling – The single most important factor to a stable overclocked CPU is cooling. Too much leads to system instability and a shorter CPU lifespan. The simple rule is – the cooler the better. Due to the popularity of overclocking there are now several commercially supported products that provide a variety of cooling methods. The current cooling techniques range from heatsinks, water coolers, and Peltier coolers. The most common method is to using a efficient heatsink and fan combination. In the case of the Intel Coppermine CPU the retail heatsink is great for normal operating temps but a larger heatsink is required when undertaking more extreme overclocking. The heatsink should be used in combination with thermal compound in order to ensure that there is good contact between the surface of the heatsink and CPU die. A very thin layer of thermal compound should be applied to the surface of the CPU (not the ceramic potion but the heatsink slug itself). Thermal compound is usually made of Zinc Oxide which has a low thermal resistance and is electrically non-conducting.
CASE Cooling – In order to make sure that your CPU is getting lots of cool air it is important to take a close look at your case. Your case should have a power supply that is located at the top of the case. The power is a source of heat and since heat rises the top is a good place for it. The power supply fan should be blowing air out of the case. This will help to remove the hot air from the top of the case. Next, your case should have another fan located at the bottom of the case that blows are into the case. This brings cool air into the case. Last, many cases come with a third vent located behind the CPU. This is a good spot to a fan in that blows air into the case and directly onto the CPU. This combination works pretty well. We here at Crazy PC have added a 4th fan to overclocked system. It is located at the top of our case and vents air directly out the top. This was done using one of the Radio Shack (Nidec) squirrel cage fans and cutting a small rectangular opening in the top of the case. With this setup we are consistently running at less than 10F above ambient room temp.
Overclocking Beyond 133MHz
As mentioned above when overclocking you want to avoid taking the AGP and PCI buses out of spec, but unfortunately this is not always avoidable. While the new FC-PGA chips are extremely overclockable they start a default bus speed of 100MHz. This means we can’t acheive the big jumps in clock speeds without overclocking the AGP and PCI buses as well as system memory. The three things too look at are the AGP video card, PCI devices, and RAM.
AGP Video Card – As mentioned above the BX chipsets provide1/1 and 2/3 multipliers for the AGP bus. Our current system is an overclocked 550E running at 150MHz. The 150MHz will set the AGP bus to 100MHz – or 51% out of spec (66MHz). Well, this doesn’t appear to be a problem for most NVIDIA GeForce cards. Our trust Leadtek GeForce 256 DDR is completely stable at 100MHz AGP! But, a lot of graphics cards will not be stable at that speed. You can test your video card by setting the AGP multiplier to 1/1 and at an FSB speed of 100MHz. This is a technique that can be used to determine if your video card is stable at the higher speeds.
RAM – You will need RAM that runs stable at your target FSB. For example if you are running a 100MHz FSB you need at least PC100 SDRAM. If you’re shooting anything above 100MHz then PC133MHz will be the next choice. If your target speed is above 133MHz then you should look for RAM that is high quality and can potentially handle the higher speeds. We’re running at 150MHz with two brands of memory here at Crazy PC. We like the PC133 Corsair memory and the EMS HSDRAM.. Both are stable at 150MHz – your mileage may vary.
The basic technique to trouble shoot is the process of elimination. I like to start from the most common source of problems down to the least common. So here is a rough approach to take to isolate the cause of instability.
Since CPU overheating is very often the cause of stability problems. Try first to run with your case cover off and position a house fan to blow into cool are directly into the case. Many times this will be enough to pin-point heat as an issue.
If you still suspect that cooling is an issue try a better heatsink. In our case, we’re using the GlobalWin FKP-32 heatsink which provides excellent cooling at higher temps.
If you’ve exhausted the cooling options try increasing the voltage to your CPU. As mentioned above we don’t recommend going beyond 20% out of spec. Our system here at Crazy PC is running a PIII 500E @ 750MHz, 1.7volts (1.6v default).
If the system still isn’t stable take a look at your PCI and AGP bus speeds. Are they out of spec? If so, then consider swapping out one component at a time or remove it from the system completely. We recommend temporarily removing any components that aren’t critical in order to further isolate the cause of the problem and reduce the number of potential problems. Then try swapping out each component to see if one in particular is causing the problem. We were able to determine that our Matrox video card was the cause of instability at the higher bus speeds by using this approach and once we switched to the GeForce card are system ran stable.
Make sure your RAM is capable of running at the target bus speed. If you’ve tried everything else but are still getting application drop outs, or lock ups your RAM could be the problem. Try swapping out the RAM. If your have more than one stick of RAM in your system try only one at a time. Also, make sure your RAM is all the spec.
Lastly, make sure you have a good quality power supply.
If you’re not willing to take the risk of overclocking – DON’T.
Always use a grounding strap and attach it to your case. Don’t take unnecessary risks. Especially when you’re about to take a huge one!
Cool your CPU. Attach a fan with a big heatsink to it. Some people recommend a dual fan. I have only one with a big heatsink. – I’ve purchased a Radio Shack temperature sensor (Cat No. 277-123) that I will use to monitor my CPU temp. I hope to have more info on the site soon (including pics).
If you’re heat sink is bare metal on the side that abuts the CPU you should apply thermal compound (or heatsink grease). Apply a thin layer to CPU die surface and surface of heatsink that will make contact with the CPU. The layer should be thin and not dripping. Thermal compound will help conduct the heat from the CPU to the heatsink better by filling in the tiny gaps between the chip and the heatsink. Apply a thin layer to the CPU die surface that contacts the heatsink surface. It’s non-conducting but be careful not to be sloppy anyway. OK? You an buy heatsink compound from Radio Shack.
On tower cases make sure the air blows in from the bottom and out from the top. Cool air in the bottom, hot air out the top. The power supply fan should blow out. I installed an extra fan next to the power supply that sucks air out. My ambient temp is between 80F-86F. Some say your temp should be no more than 10F-20F more than room temp.
When you start overclocking start with default voltage and work your way up by small increments (.05). Remember cooling becomes more critical as you up your voltage as well.
I’ve read that some drives have problems with the non-standard bus speeds and UDMA which can lead to corrupted data. As a precaution, I recommend disabling DMA.
Some people recommend a burn-in period before overclocking. Make sure you have your system running stable for a period of time. The term “burn-in” is also used by some to mean running the CPU at a specific clock speed and voltage. Some believe the CPU adapts to the higher voltage after time and the voltage can then be lowered.