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Can someone explain what a CPU thread / logical core is?

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December 15, 2009 9:55:18 PM

Hi,

Just been looking into CPU terms and what actually is in a CPU and I need some things clearing up. Firstly after reading this article

http://www.macrumors.com/2009/12/15/details-of-core-i7-...

I read the next intel chip will have 6 cores and can use 12 threads (logical cores I believe)

So could someone clear up for me

What is a thread? How does this threading work?

I understand number of physical cores eg Core 2 duo - 2 CPUs, Athlon X2 - 2 cores.

But is a Core 2 Quad, 2 physical cores ad 2 logical cores / threads. and how does this threading roughly work

Might be completely wrong what I just wrote but looking for an explanation. Wikipedia didn't really help.

Thanks
December 15, 2009 10:25:04 PM

Well, first of all, the upcoming Gulftown is a 6-core CPU with Intel's HyperThreading.
HyperThreading allows each core to execute two threads simultaneously.
Your computer would see this CPU as having 12 cores - in reality, its 6 cores handling 12 threads.

From wikipedia: A thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.

I'm no programmer so that's as far as my knowledge extends. I think of them as "sub-processes" as they exist within the process itself (explorer.exe, firefox.exe). Applications that are "heavily threaded", as in they've been written to take advantage of multiple CPU cores, benefit greatly from multiple cores and even more so from features like HyperThreading.

Core 2 Quad's are strictly 4 CPU cores - no HyperThreading.
They can run 4 threads concurrently.

I'm sure an experienced programmer can explain this better. If you're running something like Photoshop or Maya/3D Studio Max, the more cores the better.
Games are beginning to take more advantage of multiple cores (see: GTA4) but generally, beyond dual core, performance isn't hugely improved by going with a quad-core.

EDIT: A great thread that's stickied at the top of this forum...
There's a good definition of what a CPU thread is, as well as tons of other useful information.
December 26, 2010 2:12:57 PM

2 cores with hyper threading appear as 4 logical cores in your system, but they are not the same as a true quad core which has 4 physical cores. hyper threading allows a core to do 2 task at the same time as they have 2 threades on a single core, but those 2 threads share the core memory, it is faster than a dual core w/o hyper threading of course specially in applications or softwares that can run multiple threads, but its not as fast as a true quad core that has 4 physical cores, because those threads dont share memory, they have their own core memory, so they can do task independently. its like comparing to a person, a dual core w/o HT are 2 person each carry a sack of rice , while dual core w/HT are 2 person that each carry one and a half sack of rice for a total of 3 sacks of rice. while a true quad core with 4 physical cores are 4 persons.. so you know who wins.
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December 26, 2010 2:37:05 PM

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