Turbo Boost vs Speedstep

Apologies if the answer to this is obvious, but I've been wondering.

How is Turbo Boost different from having a permanently downclocked processor that just ran at the higher speed?

For example, I have an i5-450m. It's supposed to run at 2.4 GHz which is a multiplier of x18. When it turboboosts, it goes up to 2.66 GHz, a multiplier of x20. How exactly is that different from a 2.66 GHz processor with speedstep to lower its multiplier to 18?

I know Turboboost can boost a single core, but in the case of the 450m, it doesn't support any single core boosts (running only one core will still only bring it up to 2.66GHz). Does that mean it's basically a 2.66 GHz processor?

 

Speedstep is meant to reduce power usage/heat based on the load of the processor. (slow down an idle processor)

Turbo boost increase processor speed based on load and temperature. So it will find the so called sweet spot between temperature and performance up to a certain clock speed.

But yeah you are right in some ways it depends on how you look at it.

I wouldn't say its basically a 2.66Ghz processor though because it won't run at this speed unless its cool enough and you may find that if your playing a game and the system gets hot it will run at a much lower speed.

In my M11x I'd be lucky to see 2.26GHZ while playing a game.

 

The way it should work is like this.

You have a CPU that runs at a nominal frequency. We will call this speed [stock] its how fast the cpu should run at normal and safe temps/power.

Speed step was a way to reduce heat and save power by lowering the frequency of the cpu when the demand is not needed.

So you have it like this [speed step][stock]

It makes the speed go in the backwards direction in the name of effiency.

Then turboboost came out, its supposed to raise the speed of the cpu on demand if a higher demand is needed, almost the exact oposite of speed step.

So you have this [turbo boost]

Its not one or the other they actually work together like this.

<---------CPU Speed--------->
[speed step][stock][turbo boost]

The idea is that the cpu can not run the turbo boost speeds 100% of the time nor on all 4 cores of a quad core cpu thats why there is a different turbo boost speed based on the number of cores in use.

So its pushing the cpu past its [stock] / normal limits.

It seems like your thinking they simply just reduced the cpus frequency and created this new thing called turbo boost rather than run the cpu where it should be and let speed step do its thing.

Sure the turbo boost limits and things may be lax and a manual overclock can be higher but if you follow what I said above it should make sense that it is a new thing and its on the opposite side of speed step to increase the cpu power, not some method of marketing/neutering a cpu.

I think the key thing to help you understand is that turbo boost was probably primarily an i7 thing for the high power/heat quad cores to get new and greater limits that would have not been possible otherwise, a automatic laymans on demand overclock and it was smart to use only 2 or 1 core to get higher OC since it was a lower heat generation/power demand.

Intel probably just assumed since it was a good thing to pass it down to other cpus in the family even if they cant use it to the same extent.

 

So turbo boost is for increasing the cpu speed while turbo boost is for decreasing the speed. The cpu basically looks at how much power it's using and what the temperatures are to decide how fast to run.

It just seems like you could pick any speed to be your "stock" speed and call every time the cpu goes above it "overclocking" and "turbo boost" and every time it goes below "speedstep". Or even saying that it's a 1.33 GHz processor (in the case of the 450m) with 1.33GHz of turboboost . It sounds like an arbitrary distinction when turbo boost and speedstep are just different directions to go from a baseline.

 

Back when Turbo Boost was first introduced (with Nehalem), the difference was that Turbo Boost could overclock 1 core by more than it could overclock 3 or 4. I can think of two reasons why they would call something like the i5-450m a 2.4GHz processor when it can push both cores to 2.66Ghz. The first is marketing -- they're selling a much more expensive 2.66GHz CPU and they don't want to sell anything at the same clock speed. The second is that they might be covering themselves in case the CPU is not good enough: it could be that it can't reliably hit 2.66GHz in some reasonable circumstances (e.g. on a hot summer day). If people see that their 2.66GHz processor isn't going any higher than 2.4GHz, they'll complain, but if the Turbo Boost feature on a 2.4GHz processor doesn't kick in, there is a built-in clause about heat to preempt such expectations.

 

Ah I see. I was hoping there might be some special trick to it but marketing always plays a role. Thanks for that answer.

 

Well, the only "special trick" that I know of is that with Turbo Boost, there's more control over individual cores than with the previous Speedstep. Back in Core 2 days, the rated speed was what the processor was designed to run when all cores were working at full speed, with Speedstep slowing down individual cores when the processing power was unnecessary. Thus even if you had, say, a quad core, and you only needed one of the cores working, you were still limited to that rated speed, because the CPU controls weren't "smart" enough to realize that with the other 3 cores down, you have the thermal overhead to overclock that single core. Turbo Boost is a result of the control being smart enough now to realize that.

Or, for a rough analogy, think of a old C2D quad core as 4 blindfolded people (or 2 if it's a dual core) dumping water into a tub. The drain in the tub is just big enough to empty out the tub just as fast as the 4 people are filling it. Now, if any of those people slow down or stop dumping water (Speedstep), the others _could_ dump more water (increase speed), but because they're blind, they don't know that they can (half-true, there is IDA which will slightly overclock one core when the other is idle, but that just complicates things). Turbo-Boost is taking the blindfolds off those people so they can see exactly how full or empty the tub is getting as they work, so if one or more slows down, the others could speed up as necessary until they're working as fast as the drain allows again.

 

Nicely done sir, I approve of your analogy...and I am picky when it comes to analogies..lol