Any Overclocking Experts Out There?

[Jason Dunn]

As I continue to experiment with overclocking the Intel Core 2 Duo E6700 CPU and D975XBX2 motherboard (http://www.digitalmediathoughts.com/articles.php?action=expand,12002), I find myself running into the wall of my own inexperience with overclocking. Over the years, I've done a fair bit of overclocking, but it's always been the same type: bumping up the front-side bus speed, and perhaps the CPU multiplier (if available) and going faster and faster until something breaks. Most of the computers I've had over the years weren't designed for overclocking enthusiasts, so I haven't had the option to change much beyond those two things.

The Intel D975XBX2, on the other hand, has a lot of options and I'm struggling to figure out how best to manipulate them all to get the most speed possible. I've been reading up on DDR2 speeds and how dropping the RAM speed from 800mhz to 533mhz changes the FSB:DRAM ratio from 3:2 to 1:1. It seems like 1:1 is where you want to be for overclocking. I was able to get the machine up to 3000 mhz using that setup, but when I tried to jump to 3200 mhz it boots but Windows Vista gives me a BSOD when it tries to load. I tried doing a voltage bump from 1.84 up to 1.92 (I tried each increment up to 1.92) and it didn't help. One of the questions I have is how do you tell which component is causing Windows to not load? Is it the RAM, and does it need more power? Or is it the CPU and does that need a voltage bump?

Wondering if I could answer the RAM question, I ran Memtext x86 to see if it would cough up errors - and so far, 15 minutes in, there are no memory errors. So should I take that to mean that it's a CPU problem and I need to bump the voltage for that?

[Jeremy Charette]

What FSB are you running? Keep in mind that DDR2 ram runs at double the FSB, so if you're running the FSB at 400 mhz, the DDR2 modules run at 800 mhz. If you want to overclock to a 500 mhz FSB, the ram will run at 1000 mhz. You'll need RAM that can support that. If you're using run of the mill 800mhz sticks, that's likely where your problem is coming from.

I'd suggest running the FSB at a maximum of half your ram sticks. If you're running 800 mhz DDR2, stay at 400 mhz FSB. Use the clock multiplier to bump up the CPU speed from there. Whatever you do, DON'T exceed half your rated ram speed. Most memory these days is tested to tight tolerances, and doesn't take well to overclocking.

If you hit a wall with the CPU multiplier, you can try bumping up the voltage, but I don't recommend exceeding spec plus 5%. Any higher and you risk turning your CPU into a coaster.

[Jason Dunn]

What FSB are you running?

Right now? 310.2 mhz.

Keep in mind that DDR2 ram runs at double the FSB, so if you're running the FSB at 400 mhz, the DDR2 modules run at 800 mhz.

Aha. Interesting. I had read that somewhere, but I got confused by the fact that CPU-Z was reporting my FSB:DRAM ratio was 1:1, so I wasn't sure if the RAM speed was really 400mhz or 800mhz. I did down-clock the RAM from 800mhz to 533mhz in order to get the 3.1 Ghz overclock working...meaning the RAM is really running at 1066 mhz, right?

I'd suggest running the FSB at a maximum of half your ram sticks. If you're running 800 mhz DDR2, stay at 400 mhz FSB. Use the clock multiplier to bump up the CPU speed from there.

I think one of the things I find baffling is the number of overclocking options in the Intel BIOS. My options are:

CPU Voltage Override
Enhanced Power Slope
Front-Side Bus Voltage Override
MCH/ICH Voltage Override

And there's no manual from Intel telling me what these do... :?

If you hit a wall with the CPU multiplier, you can try bumping up the voltage, but I don't recommend exceeding spec plus 5%. Any higher and you risk turning your CPU into a coaster.

With the FSB set to 320 mhz and the RAM set to 400 mhz, I played around with the voltages a little bit, bumping the CPU up two notches to 1.35v and the FSB Override one bump to 1.25v. Windows Vista would boot, but then it would lock up on it either at the login screen or just afterward.

I downclocked to 3.1 Ghz, stock voltages on everything, and 533 mhz RAM speeds, and it's running solid so far (I haven't done a 24 hour torture test though). Interestingly my Windows Experience RAM score went from 5.5 up to 5.9 by the time I finsihed with all of this - so that RAM is really cranking.

[Jason Dunn]

Follow up: with the FSB set to 310 and the RAM set to 533mhz, I tried playing Neverwinter Nights and during the game it locked up at one point. So I've clocked the RAM down to 400mhz and now CPU-Z reports my FSB:DRAM ratio as 4:3...but does that mean the RAM is still running at 800mhz? I think that makes sense because the FSB is 310 x 10 = 1310mhz...

[Jason Dunn]

Sonofa...my game locked up again! I've down-clocked to 3000 mhz and put the RAM back to the normal 800mhz (default) setting. CPU-Z says the RAM is at frequency 434.9 mhz and the FSB:DRAM ratio is 2:3.

Should I be adding some juice to the CPU in order to make it stable at the higher speeds, even if Windows boots and works OK? Or if Windows boots and works, that means you don't need the CPU voltage bump?

[Jeremy Charette]

What RAM are you running?

Also, keep in mind that there is an internal and external bus speed. FSB (as you see it in the BIOS menus), is the internal bus speed. The external bus speed is 4x the internal speed. So at stock settings, the internal bus speed should be 266 mhz, the external bus speed should be at 1066 mhz, and the ram should run at whatever it's default is.

In an ideal situation, the ram runs at a 1:1 ratio. In other words, an internal bus speed of 400 mhz, an external bus speed of 1600 mhz, and the ram set at 800 mhz (matching double the internal bus speed, i.e. 2x400 mhz = 800 mhz, i.e. a 1:1 ratio). If the CPU multiplier is set to 8x, the CPU should run at 3.2 mhz. I'd be surprised if you couldn't coax that out of an e6700.

[Jeremy Charette]

Ah, it looks like with the Core 2 Duo you can't set the CPU multiplier to anything other than 6x or the board default. If you use a Core 2 Extreme, you'll be able to monkey with the CPU multiplier and get more performance out of the board.

My suggestion: stick with the rated RAM speed, and keep clocking up the FSB and FSB voltage until the system locks up. Then back down 1 or 2 notches and run some stress tests overnight to see if it's stable.

If you get your hands on a Core 2 Extreme, my suggestions:

FSB: 400 mhz
Ram (if your sticks support it): 800 mhz
CPU Multiplier: 7.5x or 8x
CPU Speed: 3000 or 3200 mhz

[cw823]

I've had several E6*00 chips, all are multiplier unlocked, but only at stock or lower. On my 6600, i can select 9,8,7,6.

Most recommend to set multiplier as low as possible (in my case 6), set RAM at lowest speed possible, and increase your FSB (may need to add voltage, I set mine to 1.425 which with vdroop ends up at around 1.38).

You should really head to ocforums dot com for more specific advice.

[Jason Dunn]

Thanks for taking the time to make this your first post in our forums. :-)

I've had several E6*00 chips, all are multiplier unlocked, but only at stock or lower. On my 6600, i can select 9,8,7,6.

My CPU is locked at 10, and I can't seem to change that in the BIOS in any way. It's greyed out as a non-changeable option. I've tried going back to stock and lower speeds, but it's still not something I can change. Is this a function of the Intel motherboard perhaps?

which with vdroop ends up at around 1.38).

What's vdroop?

You should really head to ocforums dot com for more specific advice.

Thank you, I may do just that.