With more and more graphics chips being released every day it became very complicated for the user who does not follow the video card market to know the differences among all ATI graphic chips in the market today. To facilitate knowing and understanding the difference among major ATI chips, we have compiled the following table.

It is important to notice that starting 2007 both ATI and nVidia started referring to the memory clock of their video cards with the real clock rate used. In the past manufacturers referred the memory clocks with double their real clock rate, because DDR and subsequent technologies (DDR2, GDDR3, etc) allow the memory chip to transfer two data per clock cycle. So a video card with a memory chip running at 500 MHz would be referred as having a 1 GHz memory. In order to keep the compatibility of our table, we are still referring the memory clocks with the DDR naming convention – i.e. double the real clock rate – on cards with memories based on DDR or subsequent technologies.

• Click here to see nVidia Chips Comparison Table

* ATI doesn't set a default clock for Radeon X800 SE chip. The specs depend on the video card manufacturer. So you have to take care when comparing video cards using this chip.

** Depends on the model. There are boards based on Radeon X800 GT using DDR, DDR2 and GDDR3 memories running at different speeds. We've seen GDDR3 models running at 980 MHz and DDR models running at 700 MHz. You can calculate the memory transfer rate using the formula memory clock x number of bits / 8. A model with GDDR3 memory running at 980 MHz and 256-bit interface has a transfer rate of 31.36 GB/s.

*** There are models using DDR memories and running at lower clock rates.

**** There are three video card versions using this chip with very different specs, depending on the memory chips used. If they are 128 MB DDR, then the graphics chip runs at 400 MHz, the memory runs at 500 MHz, a 128-bit memory interface is used and the memory has a maximum theoretical transfer rate of 8 GB/s. If the card has 128 MB DDR2, then the graphics chip runs at 325 MHz, the memory runs at 666 MHz, a 64-bit memory interface is used and the memory has a maximum theoretical transfer rate of 5.3 GB/s. And finally if the card has 256 MB DDR2 then the graphics chip runs at 400 MHz, the memory runs at 666 MHz, a 128-bit memory interface us used and the memory has a maximum theoretical transfer rate of 10.6 GB/s.

***** The shader unit is unified, meaning that this chip doesn't have separated pixel shader and vertex shader units. Read our article AMD ATI Radeon HD 2000 Series Architecture for more information. On video cards from Radeon HD 2400 and HD 2600 series the video card manufacturer can use a different clock for the memory (usually lower, thus achieveing a lower performance compared to the reference model); the clock rates published here are the official one.

^ Based on PCI Express 2.0, which doubles the available I/O bandwidth from 2.5 GB/s to 5 GB/s if a PCI Express 2.0 motherboard is used.

+ Radeon HD 3870 X2 and HD 4870 X2 use two Radeon chips working in parallel (CrossFire). The specs published are for only one of the chips.

When you compare chips, you have to be very careful. Judging from the table, a Radeon 9800 may seem slower than a Radeon 9600 Pro, since its clock is inferior, and a Radeon X700 Pro seems faster than a Radeon X800 since it uses a higher clock rate.

However, Radeon 9800 accesses its memory using a 256-bit interface and processes eight pixels per clock pulse, while the Radeon 9600 Pro accesses its memory using a 128-bit interface and processes four pixels per clock pulse. This means that memory access and processing performance of the Radeon 9800 would the double of that of the Radeon 9600 Pro if they were working at the same clock. In other words, a Radeon 9600 Pro would have work at 650 MHz and access the memory at 1.360 MHz to have the same performance of the Radeon 9800.

The same idea goes for the Radeon X700 Pro example, it accesses memory using a 128-bit interface and processes data at 8 pixels per clock tick, while Radeon X800 accesses memory using a 256-bit interface and processes data at 12 pixels per clock tick.

Therefore, it is not correct to compare graphic chips only through their clocks. For the processing performance you will have to compare the clocks and the number of pixels per clock. As of the memory, the right way to compare its performance among different chips is through their memory transfer rate, which is calculated using the formula (clock x bits per clock)/ 8.

As you can see in the table, "SE" chips are the simplest and access the memory at only 64 bits per time. Another detail is that ATI uses the letters "XT" to indicate the fastest chip in a series, while its competitor, nVidia, uses the same letters to indicate the simplest chip in a series.

"PE" stands for "Platinum Edition" and are models even faster than the "XT" models, aimed to gamers with money.

As for the DirectX version, check the table below:

For a detailed discussion on the subject, read our DirectX tutorial.