What is the difference between cpu and core? <lscpu>

**black8** · May 21st, 2015

Hey, here is my lscpu output:

Code:

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:   2 
Core(s) per socket:    2
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 58
Stepping:              9
CPU MHz:               774.000
BogoMIPS:              3591.87
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              3072K
NUMA node0 CPU(s):     0-3

What does this mean? Does it mean that there is a socket with two cores, and each core with two cpus?

What is the difference between core and cpu?

**dino99** · May 21st, 2015

that wording is false, should be "Core(s): 4" instead of "CPU(s): 4"

**black8** · May 21st, 2015

But then i have 4 cores. It says I have 2 cores per socket and only one socket. So what happened to the other two cores? Something is wrong.

**Yellow Pasque** · May 21st, 2015

It looks like a dual core with Hyperthreading (4 virtual cores).

**tgalati4** · May 21st, 2015

You can read about Hyper Threading technology. It is a way of multiplexing operations to the compute engine in such a way that it doubles the throughput per clock cycle. So that is counted as 2 "threads" per core. A core is a complete compute engine where an instruction could be sent to either core to get executed. A CPU (computer processing unit) has changed it's meaning slightly with modern computer architectures and multiple compute engines on a single silicon die. These are typically called "cores". You could have 2, 4, 6, 8 cores on a die. One die will fit on one socket.

In your case, the operating system thinks there are 4, single CPU's, and will divide the workload according to those 4 "CPU's". In reality, you have a single socket (single die), with 2 compute engines (cores) and each core can support 2 threads (hyper threading). So you can crunch 4 sets of instructions at a time. You can verify with the following:

Open a terminal:

Code:

sudo apt-get install htop cpuburn
htop

Now open another terminal and watch what happens:

Code:

burnP6 &
burnP6 &
burnP6 &
burnP6 &

To kill the instances:

Code:

sudo killall burnP6

On some computers you can turn Hyper Threading off in BIOS. If your system is working properly, you will see all 4 processing threads pushed to 100%. If you turn off HT, then htop will only show 2 processing threads.

In the old days, computers had 1 socket, 1 die, 1 CPU, 1 Core, and no Hyper Threading, so the notion that 1 CPU==1 compute engine==1 processing thread. This notion is probably throughout the kernel code, so you will sometimes see "CPU" which implies a single processing thread.