I'm going to purchase an e6300 and conroe to be used in a silent PC.. either Zalman 7700 or XP-120+Nexus120 for cooling.
I leave my machine on always, so I want a stable OC with an asus P5B. I'm not greedy, looking to get somewhere in the range of 2.4-2.8Ghz extremely stable and quiet.
I've never done it before, so I think I'll just go with what is available in the bios. I'm not sure i understand what speedstepping is it the Asus advertises AI NOS, which will dynamically boost the CPU into an overclock only when required?
Speedstep allows a CPU to alter its clock speed and voltage dynamically based on the CPU load. It changes clock speed by altering the multiplier but keeps the FSB constant. The lowest multiplier for all C2Ds is currently 6 and for the E6300 the highest multiplier is 7; E6400 = 8, E6600 = 9 etc.
Using the E6300 that you want to purchase as an example we have the following if the CPU is not overclocked:
Lowest Speedstep clock speed = 6 * 266 = 1.6 GHz
Highest Speedstep clock speed = 7 * 266 = 1.86 GHz
To achieve 2.8GHz with the E6300 will require a FSB of 400, which gives:
Lowest Speedstep clock speed = 6 * 400 = 2.4 GHz
Highest Speedstep clock speed = 7 * 400 = 2.8 GHz
This should be possible to achieve with almost any E6300 and using the stock voltages. You will need to use DDR2-800 as the FSB of 400 will mean that the RAM will be running at an affective minimum of 800 MHz (2 * 400) with the P965 chipset. Although many DDR2-667 modules will run at DDR2-800 when over-volted, this is not guaranteed and is dependent on the BIOS being able to over-volt the RAM. Iâ€™m not sure if the P5B offers this feature; the deluxe version does.
At this speed and voltage a C2D is easy to silence quietly with a good heatsink/fan.
The other part of the Speedstep equation is CPU voltage control. This is of less importance with the E6300 as the difference between its two speeds is quite small when overclocked to 2.8GHz; 2.4 â€“ 2.8 = 400 MHz
As a comparison an E6600 overclocked to 2.8GHz would have a lower Speedstep speed of 1.87GHz, which gives a difference of 1.87 â€“ 2.8 = 930MHz.
So there is much more scope to run a significantly lower VCore setting at idle with the E6600 than there is with the E6300. Since many motherboards donâ€™t allow you to lower the VCore below ~1.15V, this isnâ€™t as big a deal as it sounds. An E6300 at 2.4GHz might only need 1.2-1.25V, so the difference at the voltage level isnâ€™t dramatic.
I have a P5B Deluxe which does allow me to use as low as 1.05V when over-clocking, even when the VCore is set to auto in the BIOS. This is useful as when used with an E6600 I get these settings:
FSB = 360
Idle: 2.16 GHz, 1.05V â€“ tested Prime95 stable for 2 hours.
Load: 3.24 GHz, 1.376V â€“ tested Prime95 stable for 6 hours.
[Edit] These VCore values as reported by CPU-Z are incorrect. The power consumption stays constant regardless of the VCore that I select with RMClock, which strongly suggests that the VCore is always at a high state, even when CPU-Z says otherwise. No other utility shows a vaguely meaningful value for VCore with this board and BIOS version. [Edit]
Iâ€™m not sure if the non-deluxe version works in the same way though!
A new BIOS for both the P5B boards has just been released, so who knows how these boards behave now anyway!