ISRO2014-10

Question

The number of logical CPUs in a computer having two physical quad-core chips with hyper threading enabled is ______

• A. $1$
• B. $2$
• C. $8$
• D. $16$

Answer 1

2 * 4 physical cores * 2 = 16 logical cores. I'm not sure if we can call this logical CPU. But Hyper Threading is vendor specific and hence out of GATE scope. 

https://en.wikipedia.org/wiki/Hyper-threading 

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Hyper Threading is Intel implementation of Simultaneous Multi-Threading (SMP). SMP means the CPU executes instructions from 2 different threads on the same physical core. For the OS, this appears as 2 different logical cores and this enables to have better pipeline efficiency in hardware.

Comments

Arjun sir why we multiply .with again  2 for logical CPU.

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answer should be 8 or 16?

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In hyperthreading, every physical CPU corresponds to 2 logical CPU

There are two quad core chips

so total no. of physical CPU = 2*4 =8

now, 8 physical CPU corresponds to 2*8 = 16 logical CPU