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.

Important Notes

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.

Overclocking the Athlon XP

As we've mentioned earlier, multiplier x FSB = clock speed. We already know the FSB is adjustable, but normally, the multiplier is not. If you have a multiplier of 15, and your CPU's FSB is normally 133MHz, your chances of hitting 200 FSB are not that great.

By lowering the multiplier, your chances are better, but your milage will vary depending on the CPU stepping. Newer steppings (or core revisions) tend to be easier to overclock because AMD refined the manufacturing process.

The goal here is typically to increase the clock speed, but there will be instances where increasing the FSB will net better performance at lower clock speeds. Confused? Don't worry, we'll explain as we head into the BIOS.

Adjusting the Multiplier

Almost any decent motherboard worth it's weight will allow you to adjust the multiplier of an unlocked CPU in the BIOS. In rare cases, you may have to switch a jumper. Sometimes, such as with the DFI LANParty KT400, you'll need to switch from 133 to 166 (and up) to gain access to the higher FSB settings.

The location of the CPU adjustment settings in the BIOS vary from manufacturer to manufacturer, but typically, the multiplier options will be in the Advanced Chipset Features.

The only exception is the ABIT series of motherboards which rely on the Soft Menu III.

In either case, the multiplier options will be greyed out until you select an "Expert", "Manual" or "User Define" setting. This will open up all the tweak options you'll need for overclocking.

By selecting the Multiplier (or something similarly named) option, you'll have a choice of what multiplier you want to use.

Normally, we suggest taking a lower multiplier, something in the 9.5 - 12 range, but this is something you'll have to experiment with until you find a comfortable balance between the multiplier and FSB. Now, if you have a low stock multiplier, you might try moving it upwards and see how that does. In anycase, try not to do drastic jumps, and maybe adjust it 0.5 at a time.

Adjusting the FSB

Unlike the multiplier, which is something we normally suggest you lower, the FSB is something you will to increase. With a lower multiplier, increasing the FSB will be easier. The FSB adjustments can be found in the same screen as your multiplier adjustments. It may say "Front Side Bus", "External Clock" or something along those lines.

Either you'll have to move the cursor up or down, or key in a number within the minimum and maximum range of the motherboard (it will tell you if this is the case). 250 FSB is usually the maximum, but don't go setting it at 250 FSB right off the bat. Like the mulitplier, it's good practice to do a small adjustment, test for stability, and continue.

Important Notes

Overclocking successfully is not just about changing multipliers and FSB. There are a lot of factors to consider, such as your memory, ratios, dividers, and voltages. We stated at the beginning that a higher FSB is usually more effective than increasing the multiplier when overclocking a system. A higher FSB increases the speed of several key components, and the end result is a faster overall computer.

Therefore, while multiplier changes affect the CPU, FSB changes affect the entire motherboard.

Basically, you'll want quality memory, since running syncronously (aka 1/1), which means the memory bus runs at the same speed as the FSB, will push the memory harder. A good motherboard will provide additional ratio options in the cases where your memory can't handle the higher FSB speeds.

If you have PC2700 ram, which is 166MHz, and your CPU can hit 220FSB, I seriously doubt a 1/1 ratio will work. We'll have to run asyncronous, in otherwords, out of sync. Looking at the above image, let's use 4/3 and the aforementioned FSB speeds. At 4/3, your FSB remains at 220, but it gets divided by four, then multiplied by three. The net result for the memory is 220/4 x 3 = 165MHz, well within the memory's limits.

Dividers work the same way, except it deals with your PCI and AGP slots. PCI spots are rated at 33MHz, and AGP at 66MHz. The key is to keep the slots as close to the rated speeds as you can. Some motherboards even allow you to hard set (type in 66 for AGP) the speed, so you don't have to do any math.

Finally, anything running faster will need more power than before. The CPU will almost certainly need additional voltage to maintain stability. Make sure your cooling is up to it though as more power means more heat. Speaking of more power, a quality power supply is a must for successful overclocking. I personally recommend a 350W at the minimum, and anything from Antec, PC Power and Cooling, and Vantec are excellent PSUs.

Given that it isn't always possible to keep the PCI, AGP and memory within spec, even with ratios and dividers, you may need to increase the voltage to those components. Then again, video card and memory overclocking are popular options when jacking up system speed, so you'll need to play with their voltages if this applies to you.

Cooling Installation Tips

Installing an Athlon based CPU cooler has gotten easier over the past 18 months, but there are a couple things to be aware of:

1) They can still crack if you tilt the heatsink during installation.
2) Thermal paste (compound) is a must.

We've covered plenty of cooling products here, so I invite you to check those reviews out for some of our favorites.

Thermal paste is to be applied in a thin, even layer on top of the CPU core. This is a case of where "less is better". It's not a peanut butter sandwich, as more compound will hurt cooling performance.

Usually, a small drop of a compound of your choosing will be enough. I usually wrap my finger in Saran-Wrap to keep the paste free of any contaminants. Spread it around to cover the entire core, then gently run an edge of a credit/business card to remove excess paste. This is the right way to do it. The wrong way are as the images below:

Please excuse the obviously Photoshoped images, but I'm trying to illustrate a point. Do not put paste on the heatsink support pads, and do not put paste everywhere, minus the core.

The best way of installing the common heatsink (normally clip based) is to insert the CPU into the socket, then place the heatsink on top of it.

Before doing that though, make sure you remove the protective sticker, if there is one. This sticker usually protects a thermal pad, which tends to suck, so feel free to discard that as well (especially if you're applied thermal paste to the CPU... do not use both).

Going back on topic, connect the clip to the first set of prongs. These prongs for the retention clip are opposite of the keyed (raised) area of the socket. Whatever you do, do not push down or tilt the heatsink while attaching it. This is how cores crack folks. It is alright to hold the heatsink steady with one hand, so long as you don't apply force downwards.

On the side where the keyed area is, this is where you'll need to push down to connect the retention clip to the prongs. Some clips don't require tools, whereas others require a flathead screwdriver.

Considering that you'll be overclocking, it's a good idea to spend a bit to get a quality heatsink and fan. Swiftech, Thermalright and Vantec are my personal favorites for air cooling, but more extreme methods are water cooling and phase change solutions. They are much more complicated to setup, and a lot more expensive, not to mention risky if you're not careful, but if you're going to be pushing the envelope, it's time to take the kid gloves off.

Test Setup

ABIT NF7-S nForce2: Barton 2500+, 2 x 256MB Corsair TWINX PC3200 Ram, MSI FX5200, 120GB Western Digital SE 8MB Cache, Windows XP SP1, nForce 2 Unified Driver Package 2.03, ATi Catalyst 3.6.

Before wrapping things up, we're going to have a good ole proof of concept demo. Is a higher FSB more important than a higher multiplier? We're not going for any crazy overclocks here (but you can read our latest CPU and motherboard reviews for those), and sticking within the 2GHz range, give or take a couple MHz.

SiSoft Sandra CPU Benchmark

SiSoft Sandra MMX Benchmark

As we can see, higher FSB is king, though it is a close call between 166FSB and 200FSB.

SiSoft Sandra Memory Benchmark

Here, the differences are more apparent. The extra FSB gives a nice bump in memory performance at a 1/1 ratio.

Unreal Tournament 2003, Min Detail, 640x480

As expected, the extra FSB scales with the performance accordingly. Now, we mentioned earlier about FSB being more important than pure clock speeds in some cases, and if you look at the 15x133 and 11.5x166 scores, this proves our point. I felt it was worth mentioning since I've seen some people more concerned with clock speeds (and low FSB) than trying to find a balance between the two.

Reader Tips:

Some readers have submitted a couple tips that may be worth noting. Here's some of the better ones:

EvlMinion writes: "Here's a heads-up for you, regarding whether nForce2 boards ignore the multiplier lock on Bartons with the new package. The Asus A7N8X, at least, is still capable of unlocking the new Bartons. I'm running a 2500+ with the new package, and have been able to successfully adjust the multiplier."

Omonk writes: "See with Athlon XP processors, (specifically Barton, I don't know about others) the 2500+ has the L3 bridge already closed, therefore you have access to multipliers 5.5-12.5 on most motherboards that allow for multiplier adjustments. (nforce2 for example).

However, a lot of the nForce2 boards do not read the 5th multiplier bit, so it will only give you a range of 5.5-12.5 OR 13 and up. Not all multipliers. SO with that bridge closed, you cannot select 13 or higher on a llot of motherboards. (specifically in my experience the ASUS A7N8X, but I believe this affects a lot more.)

So you have to CUT that L3 bridge to gain access to 13 and up. (That bridge is CUT for the athlon 3000+ for example.) So for people in my situation, (there are a lot of us in the nforcehq forums...) I am running PC2700 so I cannot get my FSB up to 200(x2), (175 (x2) Stable) soI would have to cut that bridge on my Barton 2500 to get access to the higher multipliers as I'm hitting the ceiling at 12.5, and I'm sure my processor will go farther than 2.19 with no voltage increase. Granted I COULD run in synchronous mode, but the performance hit on doing so is actually pretty large. More so than just leaving it as it is."

Ambian writes: "Thought I'd share with ya the 'other' way of unlocking a TBred. Just squeeze in a little conductive paint between these two pins, and... Voila! Wait a tick, those pins have a little bit of a ZIF in between them. The solution? Paint the motherboard pins together! Just pull out the motherboard, take a pin and draw a line of car rear window defogger repair paint between those two points and you're set! No mess, no tape, just a simple one step process."

Thanks for the tips guys (or gals).

Final Words

One thing I want to make clear is our multiplier and FSB options aren't the de facto standard. Don't think that a multiplier of 10 is required for a 200FSB. This is an area you'll have to experiment with to find the right balance of performance and reliability.

About the FSB argument... we've proven that FSB is more important than gunning for a high clock speed, but like we said, try to find the right mix. Although 15x133 will be about 90MHz faster than 11.5x166, and loses, 15x160 will be faster than 11.5x166.

With the right hardware and cooling, you can easily add 100 to 200MHz to most Athlon XPs, and in some cases, much higher. The only time you're going to hit a bump is if you have the higher clocked CPU. For example, a Barton 3200+ runs at 11x200 (2.2GHz), so since we've already reached the 200 FSB plateau here, you're not going to get as much of a "free" boost as you would from a lower clocked CPU.

Hopefully, some of you have found this guide useful. If you have any questions, we'll be happy to help you out in the forums. Problem with emails, is generally, questions repeat themselves. Posting inquiries will make it easier to help several people at once, and make me feel all warm and fuzzy inside.

If you have any comments, be sure to hit us up in our forums.

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