Here's a better writeup for you guys.
The original R300 design was based on the 0.15 micron LV process from Taiwan Semiconductor Manufacturing Co. (TSMC). This process was already relatively mature at the time, and offered the best combination of high performance and reasonable power consumption. However, further testing showed that clock speeds could be improved by increasing or “over-driving†the core voltage, while maintaining acceptable yields. The RADEON 9700 PRO shipped using this modified process, called 0.15 micron LVOD, at 38 MHz above the design target clock speed.
Soon after, work began on the follow-up to this flagship product. After evaluating the available process technologies, including the new 0.13 micron processes, it was determined that a tweaked version of the 0.15 micron LVOD could provide the required performance improvement with minimal risk. ATI worked closely with TSMC to come up with a custom variation dubbed the “HS†process, which involved modifying transistor dimensions and other characteristics to further improve rise times. The designers also focused on isolating and eliminating hold time issues that were limiting the maximum clock speeds. The net result of these efforts was a further 55 MHz core clock improvement for the RADEON 9800 PRO.
Over the next 6 months, the 0.15 micron HS process continued to mature and yields continued to improve. This opened up the opportunity to push clock speeds even higher. However, it was first necessary to overcome two new issues that the higher speeds introduced. The first was a clock skew issue that was arising between the chip’s I/O pads and core logic. These two portions of the chip operate on separate clocks and use different types of transistors with slightly different response times, which sometimes resulted in timing problems at higher clock speeds. The problem was solved by implementing a set of structures called Delay Lock Loops between the two parts of the chip. By tuning these to introduce just the right amount of delay, most of the clock skew could be eliminated.
The combination of greater process maturity and the added delay lock loops resulted in another 32 MHz clock speed increase for the RADEON 9800 XT.