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Product : Radeon 9600XT
Company : ATI Technologies
Author : Mark 'Ratchet' Thorne
Editor : Robin 'roki' Kim
Date : February 16th, 2004

OverDrive

Though both the 9600XT and the 9800XT have hardware monitoring capabilities, they go about it in different ways. There was a recent discussion in our forums on how ATI had implemented the feature, which prompted ATI employees Terry "Catalyst Maker" Makedon and Eric "SirEric" Demers to make the following clarifications:
  1. The 9600XT's have an on-die thermal diode, and we are using that for thermal checks and as the reported temperature
  2. The 9800XTs do not have an on-die thermal diode. They have an on package thermistor and an on-board thermal sensor chip. The thermistor is very close to the ASIC die and the thermal transfer is very close to being constant, so a constant delta is fine.
  3. We've done HW qualification testing on 9800XT's in various configurations, and we've found that there's a very consistent delta differential between reported thermal data and measure ON DIE temperature.
  4. We can use the reported thermal data from both sources for OC calibration
  5. The offset of 20 degrees is an approximation of the temperature differential on 9800XT's, and is only used in the control panel temperature report. This temperature does not need to be exact, it just needs to be roughly accurate, which it is within a degree or two. This was experimentally gathered information
  6. Future changes might refine this process, as we deem fit. We are constantly developing this technology and from the 9600 onward, we plan to have (not guaranteeing we will though) on die thermal diodes in all of our products and in the future, other much more complex on die thermal logic.

Taking advantage of the new on-die thermal monitor is OverDrive. OverDrive monitors and dynamically adjusts the 9600XT core speed based on the temperature the on-die thermal monitor reports. If the temperature is between 44°C and 67°C OverDrive adjusts the core speed to 513MHz. If the temperature falls to between 0°C and 47°C, OverDrive adjusts the core speed to 527MHz. Between 64°C and 127°C, the core is clocked at its default value of 500MHz:

9800XT OverDrive Temperature Levels
500MHz 64°C or hotter
513MHz From 44°C to 67°C
527MHz From 0°C to 47°C

Like I first did in my ABIT 9800XT review, I decided to run some quick benchmarks comparing performance with and without OverDrive enabled.

Default 2x AA / 4x AF 4x AA / 8x AF
Call of Duty - OverDrive
Application Preferences
 1024x768 
 71.6
 72.8
 1280x1024 
 58.8
 59.7
 1600x1200 
 42.4
 43.0
 
0 40 80
Average Framerate
ATI 9600XT
ATI 9600XT w/OD

I also jotted down the temperature of the core before and after the 4xAA run of Call of Duty to see how how the core was getting:

9800XT OverDrive Temperature Levels
Idle 31°C
Load 39°C





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