Question about CPU Core Speed

[Ranuka Perera]

Is the CPU speed provided by the manufacturer the speed of a single logical core or a single physical core?

Regards,
Ranuka Perera

[Kalinga Athulathmudali]

2010/8/29 Ranuka Perera <ran...@gmail.com>:

> Is the CPU speed provided by the manufacturer the speed of a single logical
> core or a single physical core?

Single physical core

Eg: an P4 HT 3Ghz will show the OS as 3Ghz x 2, but the CPU runs at
3Ghz, but it can do 2 threads each at 3Ghz, so that mean the CPU can
logical do 6Ghz, but not in most cases and the app need to have the
support

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[Ranuka Perera]

So, an i5 with 2 physical cores (4 logical) can logically do 2.4 * 4?
Practically is it less than that?


Regards,
Ranuka Perera

2010/9/2 Kalinga Athulathmudali <kali...@gmail.com>

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[Amila Banuka]

sppedup you gain is not linear. it is governed by Amdahl'a law. even you have 4 processing units you normally won't get 4 times speedup. it totally depends on the program. if the program is not written to support parallel computation you will not gain any speedup.

let's say 50% of the code can run in parallel then you get 1.6 speedup in 4 processing units...

see the link for more information: http://en.wikipedia.org/wiki/Amdahl's_law

2010/9/2 Ranuka Perera <ran...@gmail.com>

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Regards,
A.A.Banuka Amarasinghe,
Department of Computer Science and Engineering,
University of Moratuwa.

[Ranuka Perera]

I am aware of the practical limitations of utilizing resources due to coding limitations, but I am asking theoretically/practically assuming that the program is a perfect code that works perfectly on multi-core processors.

Regards,
Ranuka Perera

2010/9/3 Amila Banuka <amila...@gmail.com>

[Amila Banuka]

there are nor perfect codes. no coder can beat the critical path. only the rest can be parallelized. so in practically you cannot get linear speed up. 

[Ranuka Perera]

I am not asking about the speedup limit, but the hardware technological limit.
Regards,
Ranuka Perera