What does an "unlocked multiplier" mean?

[Monkey_Business]

I was planning (at the end of this month) building a PC with a Phenom II X4 965 Black Edition. The black edition processors, as well as Intel's "extreme edition" have an unlocked multiplier. What exactly does this mean? How do I gain from this?

OT, When do the 3.6 GHz Phenom II X4 975 processors come out?

 

[TJCS]

CPU clock speed = multiplier x cpu frequency

- "unlocked multiplier" means you can change both multiplier and cpu frequency in your CPU settings to help overclock the system to higher speeds.

The real speed in overclocking is in changing the CPU frequency, because it not only increases the speed of your CPU, but also other parts of your system (ex:memory, gpu performance). Multiplier changes will only give you a marginal speed boost.

If you don't overclock then you don't even need to bother with it.

 

[Monkey_Business]

CPU clock speed = multiplier x cpu frequency

- "unlocked multiplier" means you can change both multiplier and cpu frequency in your CPU settings to help overclock the system to higher speeds.

The real speed in overclocking is in changing the CPU frequency, because it not only increases the speed of your CPU, but also other parts of your system (ex:memory, gpu performance). Multiplier changes will only give you a marginal speed boost.

If you don't overclock then you don't even need to bother with it.

How did you get your i7 920 to 4.1 GHz?

 

[TJCS]

You can this guide

 

[Axon]

In theory, an unlocked multiplier can make you clock a chip as high as it can handle before it burns out. In practice, an unlocked multiplier is just a feature that makes it easier to reach higher overclocks. As TJ said, the real boost comes from CPU Frequency speed, but that is more difficult and takes more time to stabilize. With the unlocked multiplier, you can just bump your clock speed by changing one setting.

To make it quick and dirty: each chip gets its stock ghz setting from this formula (more or less) - CPU freq. x multiplier = ghz.

On the i7 920, it would be 130 BLCK speed (CPU freq.) x 20 = 2600, or 2.6 ghz, which is the i7 920's stock setting. However, if you set that multiplier to 21, you'd now have a chip running at 2.730 ghz.

At multi of 30, you'd be at 3.9 ghz. But the 920 has a locked multiplier, so you can't do that.

My Phenom II, however, does not have a locked multiplier, and I can bump the multi to really high levels. Still, after a while, you have the same need to bump voltages and stabilize the system via the use of other settings, so I find that I typically bump the multiplier up a bit (usually to 18x) and bring the CPU freq. up with it to get the speed I want.

Read up a little more on it, there are far more detailed guides than what I've just said.

 

[Cogman]

Someone here, a while back, did a test of CPU multiplier vs CPU FSB overclocking and actually benchmarked it. The results were pretty much the same, with some very minor (0.1&#37 gains given from a FSB boost. Overall, a higher clock speed was far more important then a higher FSB.

Its roughly the same as using 800 fsb ram vs 1600 fsb ram. The differences are minimal and for most applications, unnoticeable. (yes, I realize that the PCI/PCI-E bus speeds will increase, however, they generally don't really affect anything).

The reason behind this is your CPU goes to GREAT lengths to optimize bandwidth. The whole 12MB of cache is your CPU grabbing huge chunks of memory and doing stuff to it, rather then waiting each time it wants to touch memory (See, Memory mountain).

In other words, the the highest clock possible, upping the FSB helps very little, you'll see bigger gains from a higher clocked processor.

 

[TJCS]

In general a higher clock speed is what you want to aim for for better output of processor power, but matching your max clock speed with your QPI link speed will ultimately give you the best overall system performance on the i7.

This guy is running at the same 4.1ghz speed as me on his i7 920, but his system is much faster by running lower multi and higher fsb/bclk to utilize his faster memory. I am running 4.1ghz with multi:21, BCLK/fsb:195 QPI Link Speed: 3511; if he ran his system at my settings even with his faster memory, the speed will be about the same.

The guy from the link above is using an older version of CPUz, the Rated FSB speed is the QPI Link speed in the current version.