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MacBook Pro showing 4 Cores!?

Consultant

Consultant

macrumors G5
Original poster
Jun 27, 2007
13,314
36
Was just checking out the 17" MacBook Pro with i7 at Apple Store.

Turned on activity monitor to see Flash performance on it, and noticed that the CPU usage display shows 4 graphs. What does it mean? Quad core? :confused:
 
I think I read somewhere that the i7 "virtualizes" two cores. So that means you have to physical cores and two virtual ones. Correct me if I'm wrong.....
 
Neolithium said:
The Core i7's are 4 cores, it's the Core i5 that have hyperthreading, 2 physical and 2 logical cores.
Click to expand...
The i7s in the MBPs are 2 cores + hyperthreading. Intel makes a 4 core i7, but Apple doesn't use it for the MBP. A workmate has a Dell laptop with a 4 core i7, and it has a slower clock speed (like 2GHz or so). He complains about it running hot.
 
Saying 2 physical + 2 logical cores is sort of bad. It is more like 4 virtual cores running on 2 physical.

If 2 logical cores are at full load running on top of only one physical core. Each of this logical cores is slowed down but by a little less than 50%, thus it is making one core act as two slow cores.
Putting the same workload on these two slow virtual cores instead of one makes them finish about 20% or less.
According to Intel they need about 5% more DIE Space for upto 25% more speed (or non at all or less, HT does hamper performance in some situations like games). AMD with Bulldozer says their double Integer Module speeds up about 80% (because most workload is Integer stuff and they basically have almost two full Integer Cores) but needs only 12% additional DIE Space per Module.
 
The i7 either has 4 physical cores or either 2 physical and 2 logical cores.

The only benefit is the way data is transferred, because the computer thinks there are 4 physical cores.

This is a nice way intel puts it. Click the HT tab. It applies to all processors with HT (hyper threading)

http://www.intel.com/business/resources/demos/xeon5500/performance/demo.htm


Intel® Hyper-Threading Technology is a performance feature on our new Intel(R) Core(TM) i7 processor and the Xeon(R) 5500 series processors. Put simply, it allows one core on the processor to appear like 2 cores to the operating system. This doubles the execution resources available to the O/S, which potentially increases the performance of your overall system
 
hyperthreading_image1.gif

That's how it works
 
Consultant said:
Cool thanks. So hyperthreading makes each core act as 2?
Click to expand...

Each hyperthreading core acts either as a single core running at full speed, or as two cores running at about 60 percent of the full speed (the clock speed is the same, but they do less work per clock). So these two cores will do about 120% of the work that a single core would do. All in all, the i7 in the MBP (two cores + hyperthreading) is a bit faster than just two cores with hyperthreading, but not nearly as fast as four cores without hyperthreading.

A real core will often do nothing because it is waiting for previous operations to finish. Say the core wants to multiply a and b, then add c. It cannot add c until the result of the multiplication is ready, and in between it's twiddling its thumbs. That's where the second virtual core comes in: When one virtual core is doing nothing, the second virtual core can do things. So while the first virtual core cannot use the "adder" in the core, the second one can use it (that's a rough model what happens, reality is a bit more complicated).
 
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