You can increase the gaming performance of your computer by overclocking your video card. Overclocking is a technique that enables 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 detail how to overclock your video card by using 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 your PC doesn’t have a real video card installed – the video is produced by the motherboard chipset. In the following pages, we deal exclusively with real video cards, the ones that are connected to your PC through an expansion slot.
To learn how to overclock your video card, first you need to learn how a video card works. In Figure 1, you see a very basic diagram showing the video card’s main components and how they are interconnected.
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, sometimes referred to as “core clock” or “engine clock.” When we think of overclocking a video card, the first thing that usually comes to mind is to increase the GPU’s core clock.
The GPUs from NVIDIA have 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), and this second signal (shader clock) is linked to the core clock, so increasing the core clock you automatically increase the shader clock.
The GPU is connected to the video memory (which is physically located on the video card) using a dedicated memory bus (yellow in Figure 1). This bus, known as a “memory clock,” also works at a certain clock rate. We can increase this clock rate in order to increase the performance of your video card, which we will show you how to do.
One important thing to remember is that nowadays the memory bus usually works by transferring two data per clock cycle, a technique known as DDR (Double Data Rate). Because of this technique, the memory clock can sometimes be referred to as the double of its real clock rate, because the transfer rate achieved by the DDR technique is double the transfer rate of a regular memory transferring just one datum 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 the 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 one that is 256 bits. This is a physical limitation. Each bit is transferred through 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. 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 holds true 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 through an I/O slot such as PCI Express and AGP. This connection is also performed at a certain clock rate (100 MHz for PCI Express and 66 MHz for AGP). Some motherboards allow you to increase this clock rate, providing a third option to overclock your video card. Notice that this option depends on the motherboard rather than 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 afford an option to increase the I/O slot voltage (i.e., the video card voltage), which can make your video card achieve a higher overclocking.