Fright Of My Life (A8N Sli D)

So, I've had my 939 4200+ clocked nicely at 2.66ghz (242x11 or thereabouts). Ram was doing nicely at 333mhz on auto voltage through the A8n Sli.

"What the hell?" thinks I, "Let's bump it up to 400mhz"

Interesting result. Fans span up, drives whirred, but did I get ANYTHING on the monitor? Did I buggery. Nothing. Had to take the battery out of the mobo and reset everything.

Must read up on my memory overclocking. it's fairly good stuff, XMS3200 corsair stuff (the silver heatsink version). Maybe I wasn't giving it enough juice?

If the BIOS on the A8n Sli is anything like my A8N32-sli it not obvious what the memory clock speed will be when you boot up, it kind of ignores the CPU clock speed.

The memory was setting of 333mhz i used to select the divider of 13 at stock speed for your CPU

memory speed = cpu speed/mem divider

memory set to 166 (or 333 in ddr terms) 13 divider
stock:
200x11 2200/13 -> 169mhz (338mhz ddr)
your overclock:
242x11 2662/13 -> 204mhz (408mhz ddr) that's ok for XMS3200
the irony is that when your memory was set to 333 it was running at ~400mhz

memory set to 200 (or 400 in ddr terms) 11 divider
stock:
200x11 2200/11 -> 200mhz (400mhz ddr)
our overclock:
242x11 2662/11 -> 242mhz (484mhz ddr) that's probably not ok for XMS3200

If the above is like gibberish google some overclocking articles they should be able to explain it

Download CPU-Z it will show you what speed your memory is at.

You may need to relax your memory timings and maybe increase vdimm, but take great care with vdimm (memory voltage). Check the manufacturers website for info on what timings / voltage your ram can run at.

As noted above, selecting the memory "speed" in BIOS actually applies a divider rather than setting the absolute speed. With the CPU at 242 x 11 with the memory on the 333 setting, it will actually run at 380. Changing the memory setting to 400 with the same CPU parameters will actually make it run at DDR484.

There's a great little tool called A64 Memfreq that lets you plug in the values and see what the resulting memory frequency will be (google for it).

Using this tool, for example, I quickly determined that using the CPU multiplier of 11 and the memory setting of 333 in BIOS, if you can manage to overclock the CPU to 254 or 255 will get the memory actually running at 400 (or PC3200)

listen to scrandman - my assumptions about which memory divider is selected ... err are based on a divided and fragmented memory.

Ah, that makes it a lot clearer. Many thanks, gents.
Have got CPUz. Have been after another tool, so will get the recommended memory one.
Cheers.