When it comes to ATI hardware, one of the features we have been after for the longest time on Linux has been any overclocking support. Windows users have ATI's OverDrive at their disposal along with an arsenal of third-party utilities such as ATI Tool. NVIDIA also has various utilities for overclocking their graphics cards on Windows, but they also provide support for overclocking on Linux. Today though with the release of the Catalyst 8.8 Linux driver there is finally ATI OverDrive 5 support on Linux.
Since 2001 there has been the open-source NVClock utility on Linux, and while it's now more or less dead, it has allowed Linux users to overclock NVIDIA graphics cards using a CLI interface or Qt and GTK versions of the utility. On supported GPUs, NVClock allows modifying the graphics processor and memory frequencies. On some GPUs it supports manually adjusting the fan speed and soft-modding GeForce GPUs to being recognized as a Quadro part along with graphics pipeline modifications.
Originally, NVClock had its own backend for overclocking the NVIDIA graphics cards, but in June of 2005 NVIDIA had brought CoolBits to Linux. CoolBits allows the GPU and memory frequencies to be manipulated and even offers a feature for attempting to automatically detect the optimal frequencies. CoolBits is accessible on Linux through the GUI-based nvidia-settings panel or through the well-designed NV Extension. NVClock now largely relies upon using CoolBits through the NV Extension rather than its own overclocking backend.
Meanwhile, on the ATI side the only options up to this point had been using ATIpower and Rovclock and both options are less than ideal. Rovclock came about in 2005 and 2006 by a lone developer and allows manipulating the GPU and memory frequencies along with the memory timings. The problem with Rovclock though is that during its short time in existence it only supported a limited selection of graphics cards that were rather old even by standards two years ago. The Radeon R100 and R200 generations were supported and then later on support for the Radeon X800XL (R400) was appended. Rovclock was available only as a CLI program with limited options.
The other third-party program for ATI Linux overclocking was ATIpower, but that too had a limited lifespan and wasn't real overclocking. Once PowerPlay was brought to Linux for down-clocking the GPU/memory frequencies and voltages on notebook computers to conserve battery life and reduce heat output (since then PowerPlay has been added to desktop GPUs as well), ATIpower had come about. ATIpower only ever had one release and it just read the PowerPlay power states to expose all of the available steppings, since some of them weren't shown to the user when running aticonfig to manipulate PowerPlay.
Now, however, we finally have real (and official) ATI overclocking support on Linux. ATI OverDrive 5 is now supported with fglrx 8.52 / Catalyst 8.8 for the Radeon HD 3000 and Radeon HD 4000 series. This first-cut OverDrive support is only available through the CLI-based aticonfig utility, but in a future driver release, they will add an overclocking area to the AMD Catalyst Control Center Linux Edition (AMDCCCLE).