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Overclocking the inexpensive AMD TBred-B Duron (1)
 AndyB 24 Aug 2004

Standard disclaimer: the author assumes no responsibilities if you damage your computer, burn down your house or the sky falls on your head, as a result of this article. And as usual, YMMV (Your Mileage May Vary).

Acknowledgments

All the overclocking techniques I'll use here have been perfected before by others, so really I am just "standing on the shoulders of giants". To name a few people I have met at OCWorkbench: my thanks first to Bluetooth, Eversor, Grumpy, Gortok, RayvenX, Bismark, Europe and many others.

Introduction: what's a TBred-B Duron?

AMD nowadays manufactures two different models of its K7 core:
  1. Barton cores. These come with 512kB of L2 cache.
  2. Thoroughbred "B" cores, a.k.a. TBred-B cores. TBred-Bs have smaller cores (84 mm2 vs. 108mm2 for the Bartons) with just 256kB of L2 cache.
It is generally accepted that at the same clock frequency, Bartons have slightly better general performance than TBred-Bs because of their larger L2 cache. The CPU core itself and the L1 cache are thought to be the same.

Because of their smaller die size, TBred-Bs cost less to manufacture, and so AMD have been selling them as their "value" line, recently rebranded to Sempron. But AMD also have an even cheaper brand of microprocessors, the Duron line. These are also based on TBred-B cores, but have had 3/4 of their L2 cache disabled, either because the die was in part defective, or simply AMD didn't bother testing all the L2 cache; these TBred-B based Durons have 128kB L1 cache, just like all K7 microprocessors, but only 64kB of L2 cache.

How much does that affect performance? There is no clear answer to that question, because cache size has different effects on different programs. One thing is sure, Durons are in general slower than normal TBred-Bs, and TBred-Bs are slower than Bartons.

An Duron CPU, based on the TBred-B core.

The sample in the picture has the core still covered with a thin layer of thermal compound. The 0403 denotes the year and week it was manufactured (third week, 2004). The 1600 denotes the speed rating, which in this case is 1600MHz (12x133MHz).

Durons are tested and guaranteed to work with a 133MHz FSB with a 1.5V supply voltage. Any higher FSB means we are entering overclocking territory. Normal TBred-B cores, on the other hand, like those used in Sempron CPUs, are specified to work with a 166MHz FSB. And TBred-B cores are known to handle voltages up to 1.85V with adequate cooling. This raises interesting overclocking possibilities...

Mainboard choice

The AMD Duron is the least expensive x86 CPU found in retail right now. This particular sample seen above cost me 38 Euros, with taxes. It would not make sense to use it with a 200 Euros mainboard! I have been using the ASROCK K7S8X line of mainboards for some time now and they make a perfect match to the Durons: stable, simple to setup and inexpensive. And what's best, there is a great support forum for ASROCK mainboards at OCWorkbench.com!

The ASROCK K7S8X mainboard.

There are three similar models in the ASROCK K7S8X line, with slightly different features:
  1. The K7S8X rev. 3, seen above, based on the SiS 746 northbridge and 963L southbridge. Around 32 Euros.
  2. The K7S8XE, based on the SiS 748 northbridge and 963L southbridge. Around 40 Euros.
  3. The K7S8XE+, also based on the SiS 748 northbridge and 964L southbridge. Around 48 Euros.
ASROCK mainboards are not designed for heavy overclocking but for our purposes they'll do fine. I used the plain K7S8X for some tests, the K7S8XE for others, and a K7S8XE+ for the final test. Note that these mainboards draw the CPU power from the +5V lines, so your Power Supply Unit (PSU) should be specified for at least 25A on the +5V line if you are going to overclock.

First step: 2GHz at 1.65V Vcore

The first test is to simply change the FSB_SEL jumpers on the mainboard to set the FSB to 333MHz, and set an option in the BIOS to raise the voltage by 5%. But wait, 1.5V + 5%, equals 1.575V! Like this:

The FSB_SEL jumpers set to 333MHz.

The BIOS Overvoltage option allows + 5% Vcore.

The BIOS reports a voltage of 1.575V.

Well, I have found that at 2GHz, most TBred-B Durons would require 1.65V to be 100% stable. Your mileage may vary, but raising the voltage is as easy as inserting two small pieces of wire in the CPU socket before you lock the CPU in place. Easy, reversible, does not require a soldering iron or any special skills, and 100% safe. Just make sure you put the wires in the correct holes (as shown in red below) or you could damage your CPU:

The CPU socket and red lines showing where two jumpers should be inserted to get 1.675V Vcore.

The appropriate socket holes to insert jumpers can be found at the excellent Interactive Pin-Mod Guide. I recommend choosing a 1.675 target voltage which requires just two very small pieces of wire, as shown above. The wire must be really thin (like a hair, almost) and the small u-shaped jumpers are very, very small, like this:
A very small U-shaped bit of thin copper wire.

I found another article with some good shots of the small bits of wire here.

The result is this:

The Duron running at 2GHz.

These Durons run quite cool at 2.0GHz at 1.65V Vcore, so an inexpensive heatsink/fan is OK. Note that I have used either PC2700 (for the 333MHz FSB tests) or PC3200 (for the 400MHz FSB tests) noname 256 and 512MB DDR SDRAM DIMMs. The power supply is an inexpensive 400W standard model with a single exhaust fan. As shown this mod will work fine on the SiS 746-based K7S8X with an official BIOS.

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