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Overclocking the Radeon HD 4850: Make Your Own "TOXIC" HD 4850
George Ross, August 4, 2008

How much more juice can one squeeze out of your new king of the midrange GPU's the HD 4850. Well as with all overclocks your results may vary, but this is a tale of one HD 4850 that I got to clock at 710 MHz core and 1125 MHz (2250 DDR) memory. One thing I would like to mention is if you are going to overclock your HD 4850 by bios editing as I have done here you really should purchase an aftermarket to cool your card. As this will not only improve your overclock, but it will also extend the lifespan of an overclocked GPU. This is where the VF900-Cu comes into play. As you may have noticed Sapphire has released an overclocked "TOXIC" version of the HD 4850 featuring the VF900-Cu by Zalman. I thought this to be an excellent model to try and emulate.

Installing the VF900-Cu
The VF900-Cu installs the same as the VF-1000 LED witch I have reviewed earlier, but the VF900-Cu has one less mounting hole than the VF-1000 LED making it compatible with fewer cards. The VF900-Cu only comes with thumbscrews to attach it to the PCB. The VF-1000 LED also had smaller Phillips head screws witch is what Sapphire used on the "TOXIC" edition. I like the thumbscrews my self. As I said before about the VF-1000 LED installation was a breeze. The same is true of the VF900-Cu.

Overclocking with the Catalyst OverDrive Utility
The Catalyst OverDrive Utility is a popular way to overclock the newer Radeons. Do to its ease of use and integration into the Catalyst Control Center. I have found it to be an easy way to get a good idea of a starting point for getting the maximum overclock. The OverDrive Utility yielded a 690 MHz core 1148 MHz (2296 DDR) memory overclock. This is where I would begin to find out what this particular card had to offer.

Overclocking with BIOS Flashing
In order to overclock the Radeon HD 4850 via the BIOS I suggest using the tools TechPowerUp Radeon Bios Editor and ATIFlash provided by techPowerUp.com.

I started off trying the 690 MHz core 1148 MHz (2296 DDR) memory clocks that the Catalyst OverDrive Utility maxed out at, but they did not work. GPU-Z would only report the memory working at 1125 MHz so that was all that the BIOS would allow me to run so I changed the memory to 1125 MHz and tried the core at 690 MHz again, but it still crashed. After lowering the core speed I found that 674 MHz was as high I could go without playing with the voltage. After looking though some forums I found that the highest voltage one could set with the BIOS was 1.2V. This allowed the HD 4850 to clock above 674 MHz. Up to 1.4V can be achieved by 'pencil mod'. The link is here. So after using 1.2V I noticed that the voltage regulators were putting off a little heat. This is probably why Sapphire decided to cool the voltage regulators on there HD 4850 "TOXIC" edition.

With this setup is was able to get the HD 4850 all the way up to 728 MHz core and complete my round of benchmarks without error, but when it came to the eight hour Unreal Tournament 3 botmatch that I used to test stability the driver would report that it had recovered from a crash after the match was complete. That stopped happening at 710 MHz and that is how I arrived at my final clocks.

Cooling Performance
The VF900-Cu is not quite as good as its big brother the VF-1000 LED, but is a far sight better than the stock cooler even at increased voltages and frequencies.

Now mind you these results are using the Tech Station from HighSpeed PC. Installing this into a case will yield higher temperatures because of less airflow. As I have been reminded when using better cooling methods more heat is extracted and needs to be expelled therefore make sure your case has adequate airflow.

Making It "TOXIC"
There is a little bit more to just overclocking a card and installing an aftermarket cooler. The Sapphire "TOXIC" edition has a custom heatsink for the voltage regulators and the VF900-Cu's fan plugs into the video card itself not the motherboard. These are the fine touches that make it professional. So how can you achieve these fine touches? With a little elbow grease and cannibalizing the stock cooler you can do it.

The first step in achieving the fine touches is to completely disassemble the stock cooler. Next cut off the voltage regulator portion of the stock cooler there is a visible line indicating where to cut on the underside. I used a dermal tool with a cutting wheel to cut mine. Next apply some sort of thermal grease to the voltage regulators (In this case I used Artic Silver 5) and attach the cutoff piece of heatsink using the screws that come with the stock cooler.

In order to get the fan to connect to the video card you will have to cut the fan connector off of the stock fan and splice it to the VF900-Cu's fan in some manner. I chose to cut the wire to length and solder the splice and insulating each conductor with electrical tape and covering it with heat shrink. The splice is to be connected black to black, red to red, and white to yellow. The stock connector has an additional colored conductor colored blue that I removed from the connector using the tip of a knife.

Test Hardware
Here are the specifics of the test system.

Processor Intel Core 2 Quad Q6700
Motherboard GIGABYTE GA-P31-S3G
Memory GeIL Evo One 4GB DDR2 1066 (PC2 8500) @ 5-7-7-20 Dual Channel Mode
Hard Drive Seagate Barracuda ES.2 ST3250310NS 250GB 7200 RPM 32MB cache SATA 3.0Gb/s
Video Cards SAPPHIRE Radeon HD 4850
Catalyst 8.6
SAPPHIRE Radeon HD 4850 @ 710 MHz core 1125 MHz (2250DDR) memory
Catalyst 8.6
Optical Disk Drive Pioneer DVR-215DBK
Operating System Windows Vista Ultimate x64

Gaming Benchmarks

As you can see there is a slight but noticeable difference across the board using the overclocked settings. Every bit helps with Crysis.

Power Consumption

The 1.2V that was used in order to proved to let the HD 4850 consume more power at full load, but the difference in idle power consumption is most likely due to the newer BIOS used in overclocking.

Now after all this work what is the end result a 3% increase in performance. The final overclock was 13% for both the GPU and memory. The HD 4850 has already proven itself a wonderful mainstream graphics offering. With a little effort you can squeeze a little more performance out of your HD 4850. Sometimes that last little bit can make all the difference.

If you want to get all that you can from your HD 4850 using Sapphire's "TOXIC" edition as a guide proves to be a good way to go.

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