Definitions

So in recap we have!

Athlon64 System speeds to consider.

1. CPU Speed= CPU multiplier x HTT bus.

2. HTT bus=how CPU interfaces with motherboard. Default speed is 200 MHz HTT, similar to traditional front side bus.

3. HT multiplier/LDT=Multiplier used to help determine overall Hypertransport bus speed. Initial boards supported 800 MHz Hypertransport buses (1600 MHz effective when factoring in DDR nature of bus). LDT of 4x times 200 MHz HTT=800 MHz Hypertransport bus. Limited to 3x on initial NF3 150 boards or 3 x 200 MHz = 600 MHz Hypertransport or 1200 MHz effective. Newer boards support up to 1000 MHz Hypertransport and use a 5X LDT/HT multiplier.

4. Ram speed=speed at which ram interacts with HTT buses.

5. AGP and PCI MHz levels. Defaults are 66 MHz and 33 MHz respectively. Boards that do not support AGP/PCI locks will not tolerate being too far out of spec. Newer PCI Express frequencies are 100MHz and appear locked on samples I have looked at with NVidia NF4 boards.


Variables

So by now we've weeded out the suckers right! No really, there is a method to this madness. You should now have a basic understanding of how the A64 interacts with the system it interfaces with. So let’s recap the variables to overclocking our Athlon64 system.

Overclocking variables:

1. CPU MHz. Equation of CPU Multiplier and the HTT bus. Will be limited by quality of CPU core, CPU voltage supplied (vcore), and cooling (the cooler the CPU, the higher the stable speeds we can obtain in general). CPU Multipliers are downward unlocked (all multipliers lower than default available) in all Athlon64’s and fully unlocked in FX series cpus.

2. Motherboard and chipset type. NVIDIA NForce or VIA chipset, default Hypertransport speeds. Bios revision. I would currently recommend either the Nvidia NF3 250/Ultra or Nvidia NF4/Ultra Chipset boards for those wishing to gain the best overclock from their system.

3. HTT Bus. Default speed is 200 MHz. Can be raised by which we will overclock system and CPU speed. Attention must be paid too many factors when scaling HTT bus. Limited by board quality, CPU speed, HT multiplier, and Ram quality and compatibility.

4. HT/LDT multiplier. Can be limited by board type and quality. Some overclockability should be allowed but figure on keeping overall system bus within 100 MHz of rated Hypertransport bus speed.

5. Ram speed. Seeing a pattern here? Will be limited by CPU quality (remember memory controller on CPU), vdimm voltage and ram speed and quality.

6. AGP, PCI Express and PCI MHz levels. Limits overall overclockability of system as a whole. If your board does not support AGP/PCI Express or PCI locks figure on 20 MHz average overclock to HTT bus, which will really limit your fun with overclocking your system.

7. Power supply. Have a crappy power supply? Plan on upgrading, enough said! Low or unstable voltage rails will drive you insane troubleshooting system instability. Figure on a high quality 400-500W power supply.
System specs to be used as reference:

CPU: Athlon64 3500+ 0.09u Socket 939 CPU
Cooling: EverCool WC202
Motherboard: MSI K8N Neo2 Platinum Socket 939, bios rev 1.3b6
Ram: G. Skill PC4400 2x512mb Timings of CAS 2.5 3:3:7 @2.65 memory voltage
Video: EVga Geforce 6800Ultra
Power Supply: Fortron 530W ATX