Regardless of which socket you are on, 754, 939, or AM2, the process of overclocking (henceforth OCing) an Athlon 64 or Athlon X2 is the same. The basic process is this: lower the RAM speed and HTT multiplier (to eliminate them as points of instability) and then raise the HTT speed (from which the CPU speed is derived). In more detail:
0. Don't touch any voltages! Save some fun for later after all, and build up some experience before you kill any of your components.
1. Isolating the CPU. Get into the BIOS, usually by pressing the DEL key when prompted during system POST (just after you turn on the computer when it's looking for disk drives). Immediately go find the Hypertransport multiplier (also called LDT multiplier or HTT multiplier) and move it down a notch. For 754 systems move it down from 4 to 3; for 939 and AM2 systems move it down from 5 to 4 (or go ahead and move it to 3 if you're feeling confident
) Next, find the memory multiplier and move it down to one speed grade below what your RAM is actually rated for. You can leave the RAM timings set to AUTO or you can specifically lock them in to what your RAM is rated for if you want. At the end of step-1 here, you've effectively removed your chipset and your RAM as points of failure.2. Overclocking the CPU. Find the Hypertransport speed, also called HTT, or it's even sometimes called CPU speed or even FSB (:roll:). As far as I know, this is set at 200 on all Athlon64 sockets. Raise this number by 10 so now it should be set at 210. Your CPU speed is determined as the product of the CPU's multiplier (set at the factory and can only be changed downward) and the HTT speed. So if the multi is 10 and the HTT is 210 then the CPU is running at 2100.
3. Testing. Boot into Windows and run Orthos Prime 95 for 10 minutes, and also run CPUZ. Now the short term goal is to run Orthos Prime 95 for 10 minutes without getting any errors - once you go 10 minute without errors then restart you computer and go into the BIOS and raise the FSB (CPU Frequency) another 10 then go into windows and test with Orthos again. Keep doing this until Orthos fails.
4. Fine Tuning. Once Orthos fails, restart the computer and in the BIOS go to the the CPU Frequency and back that down by 5 (So if you failed at 270HTT move it back to 265HTT). Back into windows you go so you can run Orthos again. This time let Orthos run for as long as you can - let it run overnight. If you don't get any errors after that long, then you can be fairly certain that you have just found your CPU's maximum overclock at stock voltage. If Orthos does fail again then go back to the BIOS and decrease the HTT by 1 then Orthos test again. If you're still getting errors in Orthos then just keep dropping the FSB by 1 until you get Orthos to run for at least 8 hours without any errors. Again, what you're trying to do is find your maximum CPU overclock at stock voltage.
4.1 Even Finer Tuning. If you get the HTT speed high enough, you RAM or your chipset may become an OC bottleneck once again. Keep an eye on your RAM speed by checking it in CPUZ each time you go into windows to do some testing. Don't get distracted and try to OC your RAM and CPU all at once!!!eleventy. Keep your RAM at or below its rated speed and keep it at it's rated timings and just concentrate on finding your CPU's maximum overclock. And as for the LDT / HTT multiplier, as far as I know, setting this lower doesn't really cause any drop in performance but my gut feeling is that it shouldn't be set below 3. Really what you're shooting for is to keep the Hypertransport bus running at it's standard speed, so if at stock settings it runs at 200*5 = 1000 and you lower the LDT multi to 3 then you'd have to get up to a whopping 333*3 before that happens, and I just don't hear of many Athlon64 chipsets making it up that high anyway. It is very likely that you will reach 250HTT though, above which an LDT of 4 could cause instability. So at 250HTT and above you're going to want to put the LDT multi at 3.
OVERCLOCKING THE CORE 2 DUO
0. Don't touch any voltages!
1. Isolate the CPU. Set your DRAM Frequency down one step from it's stock settings, so if it's DDR2-800, set it to DDR2-667. The goal is to remove the RAM as a point of instability. With any luck by the time you're done OCing your RAM will be running right up at it's stock speed despite the lowered mulitplier.
2. Slowly raise the CPU Frequency in increments of, say, 20. So you'll go from 266 to 286 to 306 and so on. Each time you take a step up, boot into Windows and run Orthos Prime 95 for 10 minutes, and also run CPUZ. When you open CPUZ, pay attention to your memory speeds, making sure they don't get too far above what your RAM is rated for. Now the short term goal is to run Orthos Prime 95 for 10 minutes without getting any errors - once you go 10 minute without errors then restart you computer and go into the BIOS and raise the FSB (CPU Frequency) another 20 then go into windows and test with Orthos again. Keep doing this until Orthos fails.
3. Once Orthos fails, restart the computer and in the BIOS set the DRAM Frequency down one more multiplier level and go into windows and run Orthos again. If Orthos still fails then you have just determined by this process that the errors are coming from the CPU and not the RAM. Go back into the BIOS, set the DRAM Frequency mulitplier back up again and then go to the the CPU Frequency and decrease it by 10. Back into windows you go so you can run Orthos again. This time let Orthos run for as long as you can - let it run overnight. If you don't get any errors after that long, then you can be fairly certain that you have just found your CPU's maximum overclock at stock voltage. If Orthos does fail again then go back to the BIOS and decrease the FSB (CPU Frequency) by 5 and go into Orthos testing again. If it fails go to the BIOS and drop FSB by 1 then Orthos test again. If you're still getting errors in Orthos then just keep dropping the FSB by 1 until you get Orthos to run for at least 8 hours without any errors. Again, what you're trying to do is find your maximum CPU overclock at stock voltage.
My advice is to go through this process of finding the maximum CPU overclock (OC) and don't worry about OCing the RAM at this moment. Why? OCing the CPU gets you a lot more benefit than OCing the RAM. Also, RAM testing is a little more complex, and there are A LOT more settings involved in OCing the RAM.
HAVE FUN! Your mileage may vary!!! I've only built one C2D system but it didn't overclock worth a spit!
I only got 300MHz more out of a c2d6300. I've never heard of anyone else getting such a crappy OC so even if you only get 600MHz just remember me and feel better 
External Sources / Guides:
A really nice general guide: http://www.overclock.net/overclock.php? ... -guide.htm
Neoseekers guide
Anandtech explains the memory divider on the Athlon 64 platform
Overclokers Online has a guide
Discussion on Venice's max vcore
EOC Athlon 64 wiki
HAVE FUN! Your mileage may vary! Most 90-nano Athlons can do 2.4GHz or higher but there's no guarantee! I have one myself that needs an uncomfortable amount of voltage to run at 2.4 so I'm running it at 2.32 (stock is 2.0 so only 320MHz OC
) It's too early to tell, but it's my gut feeling that the 65-nano Athlons will all do 2.6 or more. My 65-nano Brisbane whose stock is 1.9GHz runs at 2.75GHz on stock voltage for crying out loud, and I have yet to hear of any sample of this chip (x2-3600) that won't do 2.7GHz and then some.Please feel free to PM me if any part of this guide needs clarification or if any errors or terminology needs to be corrected!!!
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You are joking with the liquid nitrogen thing eh Jigar?
