Power, Heat, and OverclockingPower and Heat
We have three generations of process tech at play in this article. The 8800 GT was fabbed on TSMC’s 65 nm process, while the HD 4870 was a 55 nm part. Of course the HD 5750 is based on the newest bulk process from TSMC. The G92 that powers the 8800 GT is around 754 million transistors, the RV770 which powers the HD 4870 is 956 million transistors, and the Juniper chip that powers the HD 5750 is 1.04 billion transistors.
The differences are actually quite dramatic. The HD 5750 is by far the more efficient performer of the group, and almost 100 watts lower than the slightly faster overall HD 4870. The temperatures of the cards was measured on the PCB behind the chip with a laser thermometer. The HD 5750 hit a max of 50.9C, the 8800 GT went to 77.6C, and the HD 4780 was at a still toasty 69.3C. The actual temperature of the dies is going to be higher.
I had high expectations for this card. Not only was it supposed to have a much more efficient cooler, but the tools that Asus provided were supposed to send the core clocks sky high. Of course, nobody from Asus actually told me any of those things, I’m just the eternal optimist.
The Asus overclocking tool only goes to 780 MHz, which is far short of the HD 5770’s stock 850 MHz speed. I was expecting to get to at least 850 MHz with this setup, and luckily AMD’s Overdrive in the Catalyst Control Center does allow for higher clockspeeds. Neither the Asus or AMD control panels allow for voltage modifications on this card, as it is not supported in the hardware.
I wonder if that tail helps provide more downforce when the GPU is rendering at full bore?
Setting the clock to 850 MHz resulted in a near instant freeze once a 3D game or benchmark was run. Undaunted, I went for 840 MHz. Same result. It only completed a full benchmark at 800 MHz, but the performance at this speed was actually 20% lower than at the stock 700 MHz clock. It only started to act nice around 760 MHz. I was sorely disappointed in the overclocking potential of this particular card. Mileage will of course vary, and I have seen overclocks of this particular model from 780 MHz to 860 MHz. I was not so lucky. I was not expecting to get to 1 GHz, but I certainly expected to get to HD 5770 speeds.