i7 3930K - How to overclock it?

Overclocking on X79

The realm of overclocking has changed in recent months, especially in the hands of Intel. If we take the previous enthusiast platform, X58 and LGA 1366, a full array of BCLK and multiplier adjustments were available. Personally, I moved from that platform (and my trusty i7-920 D0) to P67 and Sandy Bridge, where due to the clock generator arrangement, I had access to the multiplier and perhaps +/- 2-5 MHz on the BCLK. In terms of the joy of overclocking, this was a bit of a let down – but Intel has (sort of) met in the middle with X79.

On a basic level, we have a standard clock generator pumping out 100 MHz. This is split several ways, most notably one way to the CPU and memory through a buffer chip, and one way to everything else. Using this buffer chip, we can select four gears/ratios: 1.00x, 1.25x, 1.66x and 2.50x. As a result, we can send 100 MHz, 125 MHz, 166 MHz and 250 MHz to the CPU/memory, while restricting everything else to 100 MHz. The basic 100 MHz, like P67/Z68, can be adjusted – usually by +/- 2-5 MHz as Sandy Bridge was able. On top of all this, we also have multiplier adjustment.

With this in mind, I can already tell you that the majority of overclocks from system builders will be on the 1.25x ratio. It provides a simple 25% overclock if the multipliers are not changed, and providing they are using Intel’s all-in-one liquid cooling as a minimum (or a high end air cooler), temperatures should not be an issue. No doubt we will see motherboards that implement this as a one-button option on the motherboard – ASUS’ auto overclock option does something similar. In order to push the memory, users may opt for the 1.25x ratio, and then decrease the multiplier to a reasonable temperature level.

In terms of the ASUS’ board performance, I first had a go at the auto OC options.

Auto OC

ASUS offers a ‘Fast’ and an ‘Extreme’ mode in their software options. ‘OC Tuner’ in the BIOS, and activating the TPU switch on board, both default to the Fast mode. In this fast mode, we see a jump to the 1.25x CPU ratio, and a slight increase in the BCLK with a multiplier adjustment. Instantly, this equates to a 34x multiplier with a 126.4 MHz BCLK, giving 4296 MHz, which hits 68ºC in Cinebench (20ºC ambient max).

In Extreme mode, ASUS uses a series of algorithms and stress tests to determine the maximum frequency. Usually, I am underwhelmed by this option in my previous reviews, providing no real insight into the depth of the CPU. Despite this, the Extreme mode did run tests, BSOD and eventually reach a final speed without any intervention. A simple 35x multiplier and 127.9 MHz BCLK (4476 MHz) is good enhancement over the Fast auto OC option. However, it may worry some people that the CPU registered an 88ºC temperature when stress tested.

Manual OC

In terms of manual adjustment, my main focus here was the multiplier. Booting at 45x, with auto voltages and the CPU fan/pump set at 100%, the board was stable. However, it was pulling 1.496 V at load, resulting in 90ºC under full OCCT stress – far too hot for my liking, and this is outside a case! But setting the voltage manually to 1.4 V, the board still booted happily at 45x, giving only 82ºC under stress. The board would boot at 46x, but was unstable at 47x.

At the 46x multiplier, at 1.4 V, with load line calibration at auto, the CPU would hit 82ºC under OCCT or Blender Stress, and only 73ºC for the 3DPM multithreaded (3DPM-MT) benchmark. At this speed (4.6 GHz, 6 cores, 12 threads), our 3DPM-MT gave a score of 1145.66, up from 914.76 at stock.

Memory

Of note with this BIOS (0709), is that when I populated the memory slots with 4x4GB DDR3, the board would default to the nearest JEDEC speed timings of the kit to 1600 MHz – in this case, my G.Skill kit has a JEDEC of 1676 MHz at 11-11-11, so the board defaulted to 1600 11-11-11. When I selected 1866 MHz memory, it shifted to 9-9-9, disregarding JEDEC vales.

The XMP profile was easy enough to enable with the XMP mode. For more performance, I pushed the board on to the 2400 MHz strap, which booted at auto values of 10-11-10 2T, and was completely stable. Moving towards the 2666 MHz strap caused failed boots. The nearest strap while on the 1.25x ratio was only at 2333 MHz, suggesting that 2400 MHz on the 1.00x strap is a safe memory overclock.

Originally Posted by A14M3D 

With regards to your worry of destroying the chip, just keep the voltages in a reasonable range and you will be fine, to be extra safe may be stay around 1.3-1.35V?