i5-2557M

[cclloyd]

So I was looking at the 13" MBA, and the processor (i5-2557M) was shown at 1.7 on apple.com. But when I went to intels site, it said it was 1.7, with a max at 2.7.

So is it basically a 2.7 GHz cpu, but it just goes lower when not in use to save power? Like can it change quickly between a high and low frequency.

 

[NikFinn]

Correct. It's called Turbo Boost.

I found this, from AnandTech after a quick Google search.

 

[nebulos]

So is it basically a 2.7 GHz cpu, but it just goes lower when not in use to save power? Like can it change quickly between a high and low frequency.

turbo boost is a bit subtle. i'm not an expert, but i think it might be better to think of it as a 1.7GHz that can boost up. if you're doing something very processor intensive, it will boost, but it won't maintain constant max turbo speed. it does it in waves, i believe; in a previous discussion, someone reported that during a video encode, CPU frequency bounced between the high and low range continuously throughout.

to really understand it, you gotta read up on it, as above.

 

[KPOM]

Turbo Boost is actually pretty interesting. The i5-2557 can and actually does run at 2.4GHz much of the time even when both processor cores are operating. If only one processor core is running, it can shut down the unused one and speed up to 2.7GHz. The 1.7GHz rating is the "base" speed, at which it can operate both cores pretty much indefinitely while maintaining an acceptable operating temperature. All Core i5s and i7s can slow down to 800MHz to preserve power when they are not in use.

By contrast, the "1.6GHz" i5-2467 can boost both cores at 2.0GHz, and one core at 2.3GHz. That's why there's a noticeable difference between the 1.6GHz and 1.7GHz i5s (even more so than between the 1.7GHz i5 and 1.8GHz i7).

As noted above, if you encode a video in Handbrake, the processor will spend as much time as possible at the boosted speed (2.4GHz), slowing down to 1.7GHz when necessary to cool off.

 

[cclloyd]

So it boosts the power near instantly as much as needed, while slowing down to calculator speed to preserve power when idle, and when needed, slow back down to 1.7 GHz to keep a nice temperature?

 

[KPOM]

So it boosts the power near instantly as much as needed, while slowing down to calculator speed to preserve power when idle, and when needed, slow back down to 1.7 GHz to keep a nice temperature?

Yes, that's how it works.