Abit KN8 OC'ing issues

[Rickster]

Hi, Im new here, basically I'm having problems overclocking my Abit KN8 nForce4 board.

Im using:
CPU: Opteron 165 dual-core S939 (HTT: 200, CPU Multiplier: 9x is stock = 1800Mhz)
Motherboard: Abit KN8 (no SLI)
RAM: GSkill F14000 USU2 dual channel kit DDR500
PSU: Corsair HX620W

I set my settings as follows

HTT:300
CPU Multiplier:4X (the lowest the motherboard would allow)
CPU Voltages: 1.35v (stock)
Memory Voltages: 2.6V (stock)
nForce Voltages: 1.5V (stock)
CPU:RAM divider DDR400 (equilavent to 1:1 am I correct?)
HT Bus Multiplier: 3X

Passing memtest86+ v3.3 at these settings for over 5 cycles on test 1-8 and even 1 test on test 9. More or less it should be stable at such settings.

With these settings:
CPU frequency should be 300*4 = 1200Mhz
RAM frequency should be 300Mhz since CPU:RAM divider is 1:1. (my RAM at stock runs at 250Mhz just FYI)
I'am able to boot into windows with such settings.

So I wanted to try my CPU at stock speeds (1800Mhz) and my RAM running at 300Mhz. So I changed the settings to:
HTT:300
CPU Multiplier:6X
CPU Voltages: 1.35v (stock)
Memory Voltages: 2.6V (stock)
nForce Voltages: 1.5V (stock)
CPU:RAM divider DDR400
HT Bus Multiplier: 3X

Basically I only changed the CPU multiplier from the previous settings. And this is where I can't boot. Shouldn't my CPU frequency be 300*6=1800Mhz. And my RAM frequency be 300Mhz? Which should run fine since I've already tested my RAM at those frequencies. And obviously my CPU should run at stock speeds. This is where I'm getting confused. Is there something wrong with my calculations? When I set all the settings to HTT 200, CPU Multiplier 9x, HT bus multiplier 5x which is stock settings, it boots. Temps don't go higher than 44C at stock on CPU and 39C on NB.

Even running my CPU multiplier at 5X and HTT of 300 which should mean 300*5=1500Mhz it just won't boot into windows. Only CPU multiplier of 4X with HTT of 300 will boot. Is there a problem with the board?

[Tetras]

What did you use to verify memory clock? CPU-Z (http://www.cpuid.com)?

Technically no 1:1 divider exists for Athlon 64, all are manipulating internal memory clock. 300 Mhz RAM clock (600 Mhz effective) is very high for DDR, especially on stock volts, have others reached this speed with your memory commonly?

Generally overclocking memory with Athlon 64s is not worth it because they run optimally with PC3200/400 at tight timings and memory is quite sensitive to frequency and voltage changes (so more likely than CPU to produce hard to quickly detect errors, corruption and BSODs).

This thread can help explain how memory frequency is calculated with Athlon 64 memory controller:
http://www.ocforums.com/showthread.php?t=306418

Perhaps the reduced CPU clock frequency in the first case helps cover up the memory having issues with such a high frequency but I don't see why this would be the case. By my calculations both configs should still result in a 300 Mhz memory clock.

[scrandman]

When running at 4 x 300 with the RAM on DDR400 setting, the RAM is running at 240, but with 6 x 300 on DDR400 it is running at 300. Sounds like your RAM won't go as high.

Now, if you drop the RAM onto the DDR333 divider in BIOS it will run at 240 with the 6 x 300 setting.

Google for a small utility called A64 Memfreq - it was written by some German guy and allows you to play around with CPU settings, RAM dividers and see what the outcome would be. It doesn't actually change anything - just allows you to verify what the resulting DRAM frequency is.