X-bit labs

ATI RADEON 9600 XT: to OVERDRIVE, or not to OVERDRIVE?

Category: Video

by Anton Shilov

[ 02/10/2004 | 04:27 AM ]

A number of readers asked us about distinguishing between different RADEON 9600 XT based graphics cards with and without OVERDRIVE capability. Apparently, not all “Powered by ATI” performance mainstream solutions of the most recent generation sport the highly advertised feature.

OVERDRIVE technology is a combination of hardware and software means that allow the graphics card to dynamically adjust clock-frequency of the chip depending on its temperature that is measured by a special on-chip thermal sensor. The OVERDRIVE capability has been available on mobile VPUs from ATI for some time now, while desktop graphics cards acquired the technique only in their latest generation – the “XT” series of processors.

Virtually all RADEON 9800 XT-based graphics cards, except those from ASUSTeK that handle their own SmartDoctor technology, have the OVERDRIVE feature enabled and fully functional – graphics cards adjust their speed flawlessly, if you are lucky, you will get a substantial performance boost, if you are not lucky, you will get a tiny improvement you will hardly feel.

It is not that easy with the RADEON 9600 XT-based products, we realize now. A number of products from companies like PowerColor or GeCube do not sport the OVERDRIVE. Apparently, there is a special chip needed to control the on-die thermal sensor of ATI’s graphics processor and report ATI CATALYST software current condition of the VPU. ATI Technologies itself suggests using LM63 controller from National Semiconductor for its RADEON 9600 XT graphics cards. If no such, or similar, controller is present, you will not be able to utilize OVERDRIVE feature.

The LM63 is a remote diode temperature sensor with integrated fan control. The LM63 accurately measures its own temperature and the temperature of a diode-connected transistor, such as a 2N3904, or a thermal diode commonly found on CPUs, GPUs, VPUs and so on. The LM63 also features an integrated, pulse-width-modulated (PWM), open-drain fan control output, according to National Semiconductor. Fan speed is a combination of the remote temperature reading, the lookup table and the register settings. The 8-step Lookup Table enables the user to program a non-linear fan speed vs. temperature transfer function often used to quiet acoustic fan noise. 

The LM63 chip should be located on the backside of a RADEON 9600 XT graphics cards near the edge of AGP, close to the sticker – as shown on pictures below.

The LM63 is available on this Built by ATI card to allow OVERDRIVE operation!

The LM63 is not mounted. OVERDRIVE will not work.

There is a simple rule, if the LM63 is there, so will be the OVERDRIVE.

Basically speaking, ATI uses a chip for controlling fans to tell its software when is the right time to pump up the clock-speed. ATI might program up to 8-steps of OVERDRIVE to enable RADEON 9800 XT and 9600 XT graphics cards working on very flexible frequencies. This step should not be too significant, e.g., 50MHz, so not to damage the processor, it looks like for the majority of the graphics cards the first speed gear is something like 13MHz, the second is a bit higher and so on.

Please keep in mind that OVERDRIVE should be supported by ATI CATALYST drivers. We recommend using CATALYST 4.1 and later for correct OVERDRIVE work on the RADEON 9600 XT-based graphics cards.

ATI’s OVERDRIVE is not a Nitrous Oxide booster for the RADEON series, 13-26MHz will hardly make a graphics card with VPU already clocked in the 400MHz - 500MHz range much faster. Though, if you pay for it, you should probably get it. Keep your eyes open!