Editor's Note: Please be advised that the following article deals with overclocking and possible modifications to your AMD processor. This will void your warranty, and VL will accept no responsibilities if your computer melts down and flaming midgets exit your floppy drives.
It's a matter of days before the latest in AMD's arsonal splashes on to the scene, and you're probably looking at that brand new CPU you just bought 15 minutes ago and asking yourself why? Truth is, there really isn't a good time to buy a CPU, as there is always something newer on the horizon.
All is not lost though, as there is a strong chance you got a fair amount of headroom for overclocking. For those of you who do not know, overclocking is the art of pushing a piece of hardware beyond manufacturer specifications. From CPUs, to memory, to video cards, each item can be pushed a little harder to squeeze more performance out of your setup. Today, we're going to focus on CPUs, the AMD Athlon XP in particular, and we'll be covering the Palomino, the Thoroughbred and the Barton models. We'll be covering how to unlock them, how to overclock them, cooling tips, and some benchmarks to prove a point regarding the CPU Ratio and Front Side Bus.
In order to save a bit of time, and get right to the point, I'm not going to go into great details about each of the chip's particular architecture, 166/333 FSB explanations, debate about performance ratings, and ramble on about motherboard technology. We covered several AMD CPUs and motherboards here at VL, so please feel free to go over the reviews if you would like to know more about those topics.
Clock Speeds Explained
Using an Athlon XP 2400+ Thoroughbred as an example, this CPU runs at 1995MHz. To get this number, a combination of a specific Front Side Bus (FSB) setting and a specific CPU Ratio (Multiplier) is used. Officially, the Palomino and Thoroughbred launches sported 133 FSBs, whereas the Barton supported 166 FSB. Later on, both the Thoroughbred (TBred) and Barton supported faster FSB speeds, but we've covered those topics in our CPU reviews. Now, depending on which class of CPU you had(ve), your CPU will have a multiplier that determines "what" times "what" equals "what". Therefore:
CPU Ratio (Multiplier) x Front Side Bus (FSB) = Clock Speed
In the case of the Athlon XP 2400+, it is 15 x 133 = 1995MHz. For a Barton 2500+, it is 11.5 x 166 = 1909MHz. Both CPUs have similar clock speeds, but use different settings to get there.
Unlocking the Athlon XP
Since the Athlon 1.4 Thunderbird, all retail and OEM CPUs come factory locked. Unless you have an engineering sample (if you have to ask, then you probably do not have one), your multiplier is at a set number, and in many cases, there is no way to change that number without some sort of a modification. How did AMD do this?
With the later Thunderbird CPUs, the L1 bridges were connected. With the later CPUs, AMD "cut the bridges", much like the initial Thunderbirds. However, to defeat the "pencil trick", AMD created depressions, or pits, so that you can no longer just run a pencil from one connection to the next to create the bridge. The pits now have to be filled, which isn't a terribly complicated process, but it will discourage very casual overclockers.
As for your FSB, no matter what class of Athlon XP you have, you have some "official" FSB speed. As of this writing, 133 FSB, 166FSB, and 200 FSB are AMD's offical supported FSB speeds. Of course, any enthusiast motherboard will support changing the FSB, but before you salivate too much, there is only so high your CPU's FSB can go. There's a lot of work to be done, so the first thing we'll have to do is fix that locked multiplier.
To unlock the processors, we chose HighSpeed PC's Athlon XP Unlocking Kit. You can use items such as windshield repair kits, wax and pencils, conductive ink and so on, but we chose HighSpeed PC's kit for it's ease of use, and low price.
Unlocking Kit and CPU
In each case, what we want to do here is connect bridges with conductive material. Depending on the CPU, these connections open up the CPU's multipliers, allowing you to change them at will. Although we'll be using a kit designed for unlocking, the theory applies to any practical alternative method you choose.
The Palomino Athlon XP
The Palomino is easily the most time consuming of the Athlon XPs to unlock. There are five bridges to connect here, but the payoff will be worth it.
The first thing we'll be needing to do is to fill those pits. Apply a piece of tape to protect the other bridges. This isn't required, but given how small the area we're working on is, this would be a good idea.
Using the HighSpeed PC's Athlon XP Unlocking Kit's filler material, we just spread it around, being sure to cover all the pits. This process fills the pits, creating a smooth surface to connect the bridges. The filler material we're using is designed to rub off cleanly, so don't go spreading it like this if you choose to use Crazy Glue.
After rubbing off the filler material, you can see above that all the pits are now filled. You can apply another piece of tape to the other side to prevent the conductive material from making contact to the rest of the CPU.
You then apply the conductive material, connecting each bridge to each other. Only connect the connections adjacent to each other as above. Any decorative criss cross patterns will not work. That's it, the Palomino is now officially unlocked. Remember to remove any tape that you may have used.
The Thoroughbred and Barton Athlon XPs
Unlocking both brands of CPUs is identical, so the following steps will work on both. The difference between this method and the Palomino is that you only have one bridge to connect. Ain't life grand?
Unlike the Palomino, for the TBred and Barton, you'll need to connect the L3 #5 bridge. We begin by taping off all the bridges to prevent making any mistakes.
Like before, we'll need to fill in the pit with some filler material. After removing the tape, you should only have one pit filled where the L3 #5 bridge is. Dip the needle into some conductive material...
... connect the bridge, and you're done. Now your TBred or Barton is setup for some real overclocking fun.
A couple of things to let you know. A large number of nVidia based nForce 2 motherboards allow you to unlock the TBred and Barton with simple BIOS adjustments (we'll explain on the next page). In otherwords, if you have one of those CPUs, you will probably not need to physically unlock the CPU as we've described. For Palomino owners, you're out of luck, as you still need to unlock the CPU. At this time, I know ASUS, ABIT, FIC and Epox unlock via the BIOS, but others may as well. I do know MSI does not.
Due to the fact that we have not reviewed many VIA based KT400 or KT600 motherboards, I cannot say for certain if any of these boards "magically" unlock TBreds and Bartons, but there are plenty of reviews out there for you to check.
One thing to note is that for some Palominos (the 2100+ I'm fairly certain of) require a different unlocking method. Our very own Scott Harness has some experience with this, but you can , and try out their techniques.
Second item that works against us is they've begun implementing. It will be near impossible to modify the CPU, and our methods here will almost certainly not work. Right now I cannot say if nForce 2 mobos still unlock these chips, but when we learn more, we'll pass the info to you.
Update: A reader submitted his discovery here.