Introduction
You can increase the gaming performance of your computer by overclocking your video card. Overclocking is a technique that makes a given hardware part to operate at a clock frequency above its standard frequency, thus increasing its performance. In this tutorial we will explain in details how to overclock your video card, with several tips and tricks.
If your PC has a video card embedded on the motherboard (i.e. “on-board video”) you won’t be able to overclock it, as you PC doesn’t have a real video card installed – the video is produced by the motherboard chipset. In this tutorial we deal exclusively with real video cards, the ones that are connected to your PC thru an expansion slot.
To learn how to overclock you video card you need to learn first how a video card works. On Figure 1 you can see a very basic diagram showing the video card main components and how they are connected together.
click to enlarge
Figure 1: Anatomy of a video card.
The heart of a video card is its graphics chip, also known as GPU, Graphics Processing Unit. It works at a certain clock rate, also known as “core clock” or “engine clock”. When we think of overclocking a video card, usually the first thing that comes to mind is to increase the GPU core clock.
The new GeForce 8 GPU series from nVidia has two clock signals, one used by its shader engines and another used by the rest of the chip (the core clock we’ve just described). So far we don’t know if this second signal (shader clock) can be overclocked or not, or if it is somehow connected to the core clock. We will update this tutorial as soon as we get one video card based on this new architecture in order to clarify this issue.
The GPU is connected to the video memory (which is physically located on the video card) using a dedicated memory bus (yellow on Figure 1). This bus also works at a certain clock rate, also known as “memory clock”. We can also increase this clock rate in order to increase the performance of your video card and of course we will show you how to do that.
One important thing to keep in mind right now is that the memory bus nowadays usually works transferring two data per clock cycle, technique known as DDR, Double Data Rate. Because of this technique the memory clock can sometimes be referred as the double of its real clock rate, because the transfer rate achieved by DDR technique is double the transfer rate of a regular memory transferring just one data per clock cycle. In order to avoid confusion during our tutorial we will add the letters DDR after clock rates that are “doubled”. For instance 300 MHz and 600 MHz DDR are the same thing, as this 600 MHz DDR clock rate is really 300 MHz transferring two data per clock cycle.
The memory bus – which can also be referred to as memory interface – transfers a certain number of bits per time between the GPU and the video memory – 64 bits, 128 bits, 256 bits, etc. This number is fixed and you cannot change it. In other words there is no way for you to transform your 128-bit video card into a 256-bit one. This is a physical limitation: each bit is transferred thru an individual wire on the video card printed circuit board, so a video card with a 128-bit memory interface has 128 wires connecting the GPU to the memory. So it is impossible to change this number, as you would need to add 128 more wires between the GPU and the memory chips (and also probably add or change the memory chips). The same thing goes for the video memory size: you cannot transform your 128 MB video card into a 256 MB one simply because you would need to add more memory chips to it.
The GPU is connected to the motherboard thru an I/O slot such as PCI Express and AGP. This connection is also done at a certain clock rate (100 MHz for PCI Express and 66 MHz for AGP) and some motherboards allow you to increase this clock rate, giving a third option to overclock your video card. Notice that this option depends on the motherboard and not on the video card, as it is the motherboard that controls the I/O slot where the video card is installed. Some overclocking-oriented motherboards also provide an option for you to increase the I/O slot voltage (i.e. the video card voltage), which can make your video card to achieve a higher overclocking.
Introduction (Cont’d)
So we can set up three kinds of overclocking: increasing the clock at which the video processor runs, increasing the clock the video processor uses to communicate with the video memory and increasing the clock the motherboard uses to communicate with the video card. You can even perform these three options at the same time in order to explore the maximum performance your video card is able to provide you. The first two overclockings are done configuring the video card and you can change these two clocks on any video card, while the third one is done on the motherboard setup and it will depend whether your motherboard provides this configuration option or not.
The first thing you need to do is to discover the core clock and the memory clock your video card is currently using. The best way to check this is using a program called PowerStrip. This is also the program we will use to overclock the video card. Depending on the version of the video driver you are using, it can provide the same functionalities of PowerStrip – including overclocking. Since we cannot tell for sure if your video driver has this feature, we prefer to use PowerStrip.
Running this software for the first time you will see the clocks your video card is really using right away. From the second time on, PowerStrip will start minimized on System Tray and you will need to right click on its icon and choose Performance Profiles, Configure.
Pay attention as for ATI-based video cards PowerStrip will report the real memory clock but for nVidia-based video cards it will report the DDR clock (real clock x 2).
Let’s see two examples. On Figure 2 you can see the clocks used by our Radeon 9800 Pro: 378 MHz for video processor ("core clock") and 337 MHz for memory. And on Figure 3 you can see the clocks used by our GeForce 6800 GS: 425 MHz core and 1,000 MHz DDR memory.
click to enlarge
Figure 2: Clocks used by a Radeon 9800 Pro.
click to enlarge
Figure 3: Clocks used by a GeForce 6800 GS.
You can compare the clocks your video card uses with the manufacturer’s default clock for your video card. Click here to take a look on our ATI Chips Comparison Table or click here to take a look on our nVidia Chips Comparison Table. Please notice that the memory clock rates on these two tables are “doubled” (i.e. DDR).
As you can see on our table, Radeon 9800 Pro has default clocks of 380 MHz for core and 680 MHz DDR (340 MHz x 2) for memory, and GeForce 6800 GS has default clocks of 425 MHz core and 1,000 MHz DDR (500 MHz x 2) for memory. As you can see, our two video cards were using the default clock rates set by the chip manufacturer. Small differences below 5 MHz are normal and that doesn’t mean that your video card is running at a “wrong” clock rate.
Sometimes you will find that your video card is factory-overclocked, meaning that the manufacturer has already set it to run at a higher clock rate. Even if this is your case, you can try to overclock your video card even more.
Overclocking Your Video Card
Let’s now explain the basic procedure on how to overclock your video card.
After installing PowerStrip, it will be launched every time you turn on your computer and will be available as an icon on the task bar, near the system clock (system tray). To overclock your video card, right click on the program’s small icon and select Performance Profiles, Configure, like shown on Figure 4.
click to enlarge
Figure 4: Opening the overclocking screen on PowerStrip.
It is very important to notice that the changes made to your video card using PowerStrip aren’t permanent and are available only when PowerStrip is minimized on system tray. So if you disable PowerStrip (for example, by running Msconfig utility) or uninstall it your video card won’t be overclocked anymore.
This also means that if your system freezes or something goes wrong while you are overclocking your video card, just reboot your system and you will have your PC running just fine again.
On the screen that will be displayed you can freely set the GPU clock and the memory clock using the available sliders, see Figure 5.
click to enlarge
Figure 5: Overclocking your video card.
Note that overclocking can work or not. After adjusting the clock, run a 3D game on its benchmarking mode (Quake 4, for instance) and check whether the computer freezes or restarts on its own. If this happens, it means that you have set a clock beyond the capability supported by the video card.
The use of a game on its benchmarking mode is also good for you to see how much performance you are gaining with your overclocking: first run the game with your video card running without any overclocking, then you can compare the results with the score achieved under overclocking. If you don’t know how to use a 3D game on benchmarking mode, we’ve posted some tutorials on that: How to Use Battefield 2142 to Benchmark your PC, Testing the 3D Performance of Your PC With Quake 4 and Testing the 3D Performance of Your PC with Doom 3 and Far Cry.
Ideally, you should first find the maximum clock frequency supported by the GPU (i. e., the clock you can set without the computer freezing in a 3D game) and then the maximum clock supported by the video memory. If you try to set both at the same time, when the computer crashes you won’t be able to find out which clock is wrong, the GPU’s or the memory’s.
Overclocking is a boring trial-and-error process. Raise the GPU clock a little bit and run a 3D game under benchmarking mode. If the system ran fine, increase the GPU clock a little bit more and repeat the process, until you find the exact GPU clock that your system can run without crashing. After finding this out, you will need to repeat the same process for the memory clock. And then with the I/O bus, if you want to overclock it as well.
After finding the maximum overclocking spot of your video card, we recommend you to run more than one game on its benchmarking mode, at least three times each, so check if your video card overclocking is really stable.
There are some tips on improving your overclocking chances. Let's talk about this.
Memory Overclocking
Sometimes the video card's memory chips are running at speed lower than their maximum. For example, you have a video card with a memory chip capable of running up to 500 MHz but the memory is being accessed at 450 MHz.
If you were lucky to get one card like this you will find that the memory is highly overclockable. This happens because you will be able to put the memory running at a higher clock rate but still under its specs, and then push the memory over its specs.
First you need to know the maximum clock rate of the memory chips of your video card. You can find this out by taking a close look on the chips. The speed grade is marked on the chip's body after a dash (ex: -40, -50, -5, etc) as a number. This number is the memory clock, in nanoseconds. To find out the maximum clock rate in megahertz, divide one thousand by this number. In case of a two-digit number like 40, 45, 50, use a decimal dot between the two digits. So, for the calculation you would use 4.0, 4.5 and 5.0, respectively. There is one exception: memory chips from Samsung labeled as 2A actually are 2.8 ns chips, not 2 ns chips.
Pay attention because the number you will find is the real memory clock, not its DDR speed, which is the double of the number you will find.
Let's give you a couple of examples to clarify this. On Figure 6 you see two of the memory chips used on our GeForce 6800 GS. They are labeled as 2 ns, so their maximum labeled clock rate is 500 MHz (1,000 / 2). As we discussed before, on this video card the memory was accessed at 500 MHz, so in this case the memory was already working at its maximum labeled speed. Of course we can try to put it to work above its specs.
click to enlarge
Figure 6: 2 ns (500 MHz) chips from Samsung.
On Figure 7 you see one of the memory chips from a GeForce 7900 GT. As you can see, it is a 1.4 ns chip, meaning that it can officially run up to 715 MHz. Since on our GeForce 7900 GT the memory was accessed at 660 MHz, we know that we can push the memory clock at least up to 715 MHz that the video card will still work just fine, as the memory clock will still be inside the chips’ official specs. Of course we can still try pushing the memory clock even higher for a real overclocking.
click to enlarge
Figure 7: 1.4 ns (715 MHz) chip from Samsung.
On the next page we will present some tricks that can help you to achieve a higher memory clock.
Memory Overclocking (Cont’d)
A way to increase the video memory overclocking potential is checking the cooling system used by the memory chips. If you improve the memory chips cooling system you will probably achieve a higher memory overclocking. You can find three situations here:
- The memory chips are cooled down by the same cooler used by the GPU;
- The memory chips use an independent passive heatsink;
- The memory chips don’t use any cooling device at all.
If your memory chips already use passive heatsinks on them, great. You have already a good cooling solution for your memory chips. See an example on Figure 8.
click to enlarge
Figure 8: This video card came with passive heatsinks on its memory chips.
If the memory chips from your video card don’t come with any cooling device, you can buy memory heatsinks and install on them (Zalman ZMHRS1 and Thermaltake CL-C0025 are good examples of this kind of product). The installation process if very simple.
click to enlarge
Figure 9: The memory chips from this video card don’t come with any cooling device at all.
If on your video card the cooler used by the GPU is also used to cool down the memory chips, you can improve the video card cooling by installing a better GPU cooler, like the ones from Arctic Cooling. These high-end coolers will help you to increase both the GPU and the video memory overclocking potential. Read our first look article on Arctic Cooling Accelero X1 to see the step by step installation of this cooler on our GeForce 6800 GS.
click to enlarge
Figure 10: On this video card the GPU cooler cools down the memory chips.
Memory Overclocking (Cont’d)
As you could see on Figure 10, the memory chips from our video card were under the GPU cooler. The problem is that on some video cards the GPU cooler seems to be used to cool down the memory chips but actually they don’t even touch them. So pay close attention on video cards where the GPU cooler covers the memory chips to check whether it touches the memory chips or not. You can see an example of that on Figures 11 and 12. The GPU cooler appears to be used to cool down the memory chips but when you take a closer look, it doesn’t touch the chips! In cases like this the best solution is to replace the GPU cooler with a high-end GPU cooler that touches the memory chips, so you will be improving both GPU and memory chips cooling.
click to enlarge
Figure 11: On this video card the cooler seems to be cooling the memory chips…
click to enlarge
Figure 12: But it isn’t!
Another case that you might want to replace the GPU cooler that comes with the video card with a high-end GPU cooler that touches the memory chips is when the GPU cooler prevents you from installing passive heatsinks on the memory chips. Take a look on Figure 13. On this video card the GPU cooler covers part of the memory chips without touching them, so the GPU cooler doesn’t cool down the memory chips and at the same time prevents you from installing passive heatsinks on the them.
click to enlarge
Figure 13: The cooler that came with this video card doesn’t allow you to install passive heatsinks on the memory chips.
Another trick advanced overclockers do is to play with memory timings. Usually increasing timings reduce the memory performance but allow you to achieve higher clocks. The trick is to check whether the higher clock rate you will be able to configure will really deliver a higher 3D performance or not – because of the increased timings, you may actually see loss of performance. Memory timing adjustment is done by editing the video card BIOS. We will discuss later how to edit your video card BIOS, however we won’t go into the details on how to change memory timings.
GPU Overclocking
The main trick to increase the GPU overclocking capability is also improving its cooling. GPUs can come with passive or active heatsinks, i.e. with or without a fan.
If you video card uses a passive heatsink, like the one portrayed on Figure 14, consider replacing it with a good VGA cooler. Take a look on our first look articles about Arctic Cooling NV Silencer 6 and Arctic Cooling Accelero X1 for a better idea on what we are talking about. Or if you don’t want to spend money, you can at least mod the heatsink to add a fan to it.
click to enlarge
Figure 14: Example of a video card with passive heatsink.
But even if your video card already uses an active heatsink, you may want to consider replacing it with a better cooling solution, like the Arctic Cooling products we’ve mentioned.
Another trick advanced overclockers do is to increase the GPU voltage. Increasing the GPU voltage usually helps the GPU to achieve a higher clock rate. One way of increasing the GPU voltage is by editing the video card BIOS. We will discuss later how to edit your video card BIOS, however we won’t go into the details on how to change the GPU voltage.
Tweaking the I/O Bus
As we mentioned, another option you have is to overclock the bus where the video card is connected to – AGP or PCI Express, depending on your motherboard.
Before going further, an important remark. Depending on your video card, you may not notice any performance gain by overclocking the I/O bus. This happens because you may have already enough free bandwidth on the I/O bus and it is not being a bottleneck for your 3D performance. So it is very important that you run games on their benchmarking modes before and after playing with the I/O bus in order to check whether you had any real performance gain by overclocking it. If you don’t get any performance improvement by tweaking the I/O bus, it makes no sense in keeping it overclocked. In this case, leave it back on its default configuration.
We, however, encourage you to at least try playing with the I/O bus if you want to extract the maximum performance your video card can give you and then, at the end, see if it was worthwhile of not.
Here the options you will have will depend on your motherboard model. We will explore all possible options, however your motherboard may not have all of them available.
The main problem here is that only overclocking-oriented motherboards will have a separated clock generator for the AGP or PCI Express x16 bus. On simpler motherboards, a single clock generator is used by all devices found on the motherboard and if you want to increase the AGP or PCI Express x16 clock rate you will have to increase the master clock generator rate, which will automatically increase the clock rate used by all other devices.
The problem with this setup is that everything will work overclocked as well, not only your video card. Thus you may face a situation where you won’t be able to pass a certain clock level not because your video card can’t go over it, but because some other devices on your system that is also overclocked has reached its clock limit.
Anyway, let’s see some examples on how to overclock your AGP or PCI Express x16 bus.
First you will need to enter your motherboard setup utility, which is done by pressing the Del key right after your turn you PC on. Inside the setup you will need to find where the overclocking options are located. The exact location varies according to the motherboard model. Please note that on some motherboard you need to change some configuration from “auto” to “manual” in order to see the overclocking options.
On Figures 15 and 16 you see two motherboards based on the AGP bus. The AGP bus runs at a default clock rate of 66 MHz.
The first motherboard (Figure 15) uses a single clock generator, and to overclock the AGP bus you need to increase the CPU external bus. Increasing the CPU external bus you will overclock not only the AGP bus but also the CPU, the PCI bus and all other devices found on the motherboard. On this motherboard you need to change the “CPU Host Clock Control” option to “Enabled” in order to have access to the external clock rate configuration (“CPU Host Frequency”). Note how you don’t have access to the option “PCI/AGP Frequency”, this option only displays the new PCI/AGP clock rates based on the new external bus configuration you entered.
click to enlarge
Figure 15: On this motherboard you can’t configure the AGP bus clock rate separately.
But on the second motherboard (Figure 16) there is a separated clock generator for the AGP bus. We know that because there is an option called “Adjust AGP Frequency”, which defaults to 66 MHz.
click to enlarge
Figure 16: On this motherboard you can configure the AGP bus clock rate separately.
Tweaking the I/O Bus (Cont’d)
The same idea goes for the PCI Express bus. This bus uses a default clock rate of 100 MHz. If your motherboard doesn’t have a separated clock generator for this bus, you will have to increase the motherboard master clock generator, which will increase all clock rates used by all devices on the motherboard.
On Figure 17 you can see a motherboard without a separated clock generator for the PCI Express bus. The only possibility here is to increase the motherboard master clock generator, which will overclock everything connected to the motherboard.
click to enlarge
Figure 17: On this motherboard you can’t configure the PCI Express clock rate separately.
Some motherboards have a separate configuration for the PCI Express bus, but they don’t have a separated clock generator for the PCI Express x16 slot, which is the one used by the video card. They have instead a single clock generator for all PCI Express slots and connections, so when you increase the PCI Express clock rate, you will also overclock all devices that use this bus, including the ones connected directly on the motherboard, such as the SATA ports – and hard disk drives are very sensitive to any increase on the SATA clock. This is the case of the motherboard shown on Figure 18. It has a separated clock configuration for the PCI Express bus (“PCIE Clock” option), but this configuration will increase the clock rate of all PCI Express connections, not only the one used by the x16 slot.
click to enlarge
Figure 18: This motherboard has a separated clock generator for all PCI Express connections.
The best option is to have a motherboard with a separated clock configuration for the PCI Express x16 slot, like the one shown on Figure 19. On this motherboard the clock configuration for the main PCI Express x16 slot is called “C51 PCI-Express Frequency”. The clock that will be used by the other PCI Express connections is called “MCP55 PCI-Express Frequency” and should be left at 100 MHz.
click to enlarge
Figure 19: Motherboard with separated clock configuration for the PCI Express x16 slot.
So, how to find out the maximum clock rate your AGP or PCI Express x16 bus will support? Like everything related to overclocking, by trial-and-error. Increase the clock rate a little bit, save the changes and exit setup, load Windows, run a 3D game like Quake 4 on its benchmarking mode and see if the system stays stable. If it does, go back and increase a little bit more and repeat all the process, until you find the maximum clock rate your I/O bus will run without crashing the system.
Tweaking the I/O Bus (Cont’d)
Besides increasing the I/O bus clock rate, you can also increase its voltage. Usually by increasing its voltage you will be able to set it at higher clock rates without making the system to crash. But we recommend you to first find out the maximum clock rate the I/O bus will run with stability (i.e. without crashing), and only then increase the I/O bus voltage to see if your system will run without crashing with a higher clock rate. Keep in mind that sometimes you won’t be able to increase the clock rate even increasing the bus voltage.
Not all motherboards provide this option. But from all the motherboards we shown above, only the one portrayed on Figure 17 didn’t provide it. On the motherboard on Figure 15 it was called “AGP OverVoltage Control”, on Figure 16 it was called “AGP Voltage”, on Figures 18 and 19 you would have to select “Advanced Voltage Control” and then would see this option as “NB Core/PCI-E Voltage” (see Figure 20) or “NB to PCIE VGA Voltage” (see Figure 21).
click to enlarge
Figure 20: Option for increasing the PCI Express x16 voltage.
click to enlarge
Figure 21: Option for increasing the PCI Express x16 voltage.
As you may have noticed, the exact name of each option varies a lot, and we tried to give some examples, but of course it is impossible to cover all motherboard models available at the market and tell you how each option will be called on your motherboard in particular. We hope that with our examples you at least got a clue on how to identify these options.
Making Changes Permanent (nVidia-Based Cards)
As we mentioned before, all changes made to your video card aren’t permanent. This happens because the video card's BIOS will instruct the VGA to run on its default configuration every time you reboot your PC. That’s why you need to keep PowerStrip loaded: it will load your personalized configurations and reconfigure your video card every time you load Windows. If you shut down PowerStrip your video card will use the BIOS default configuration again.
You can edit the video card BIOS and make your overclocking permanent, if you want to. With this option, you won’t need to load PowerStrip anymore and the video card will always work under the clocks you programmed at its BIOS.
But don’t worry: in the future you can revert this change and make your video card to run back on its original configuration.
For doing this you will need two programs, a BIOS editor (used to edit the BIOS contents, i.e. to change your video card clock rates) and a BIOS programmer (used to save the new modified BIOS to the video card). The programs you will need depends if your video card is based on an nVidia or on an ATI chip. Below we will show you how to modify your nVidia-based video card BIOS, and on next page we will talk about on how to do the same thing on an ATI-based video card.
For your nVidia-based card you will need two programs: NiBiTor, which is a BIOS editor, and nvFlash, which is a BIOS programmer. Both can be downloaded from our download section. Please download the latest version available.
Run NiBiTor and first backup the BIOS your video card is currently using. So if in the future you want to restore your video card original BIOS, just update your video card BIOS this file.
Go to Tools, Read BIOS, Select device and select your video card. Then go to Tools, Read BIOS, Read into File. Give a name for your file. This will backup your video card BIOS to a file.
Then go to File, Open BIOS and load the BIOS file you’ve just saved. You will see a screen similar to Figure 22.
click to enlarge
Figure 22: Editing your nVidia-based video card BIOS.
As you can see, there are two places you will want to change, “Core” and “Memory”. Just type in the maximum core and memory clocks you know your video card can run stable.
After editing these two fields, save the BIOS into a new file, by going to File, Save BIOS. Now you have a BIOS file with your overclocked settings.
The next step is to create a bootable floppy disk. Go to http://www.bootdisk.com, select a DOS boot disk, download the .exe file and run it to create your bootable floppy. Copy nvFlash.exe and your overclocked BIOS file to the floppy disk. Then boot your PC using this floppy (you may need to enter the motherboard setup and change the boot order).
At the command prompt, type:
nvflash file_name_of_your_overclocked_bios
Restart your computer and your work is done.
Making Changes Permanent (ATI-Based Cards)
The process for ATI-based cards is similar but you will need to use different programs: RaBiT, which is a BIOS editor, and ATIWinFlash, which is a BIOS programmer. Both can be downloaded from our download section. Please download the latest version available.
Run ATIWinFlash and first backup the BIOS your video card is currently using. So if in the future you want to restore your video card original BIOS, just update your video card BIOS this file. Just click on Save to save your video card BIOS to a file.
click to enlarge
Figure 23: ATIWinFlash.
Then run RaBiT and open the BIOS file by going to Open, BIOS file. Then click on the Clocking tab to edit the core and memory clocks. After editing these two fields, save the BIOS into a new file, by clicking on Save as. Now you have your overclocked BIOS saved to a file.
click to enlarge
Figure 24: Editing your ATI-based card BIOS.
Run ATIWinFlash again and click on Load Image and select your overclocked BIOS file. Click on Program and ATIWinFlash will save your overclocked BIOS to your video card.
Restart your computer and your work is done.
Originally at http://www.hardwaresecrets.com/article/141
© 2004-9, Hardware Secrets, LLC. All Rights Reserved.
Total or partial reproduction of the contents of this site, as well as that of the texts available for downloading, be this in the electronic media, in print, or any other form of distribution, is expressly forbidden. Those who do not comply with these copyright laws will be indicted and punished according to the International Copyrights Law.
We do not take responsibility for material damage of any kind caused by the use of information contained in Hardware Secrets.