require('os').cpus().length returns 24 .... can't understand how?

Question

I have a windows desktop with this configuration: Intel Xeon(R) CPU E5645 @2.40GHz (2 processors)
with 24 GB RAM and 64-bit OS

When I run following code.

var cpuCount = require('os').cpus().length;

It returns cpuCount as 24

Can someone please explain what exactly does this mean? And how does it determine that I have 24 CPUs with just 2 processors.

Answer 1

http://ark.intel.com/products/48768/Intel-Xeon-Processor-E5645-12M-Cache-2_40-GHz-5_86-GTs-Intel-QPI?q=Xeon%20e5645

Advanced Technologies section. It says that your CPU supports Hyper-Threading

From the Wikipedia:

For each processor core that is physically present, the operating system addresses two virtual or logical cores ...

So, you have two processors with 6 physical cores each (but 12 logical or virtual):

(2 x 6) x 2 = 24

Also check out node.js docs:

os.cpus()

Returns an array of objects containing information about each CPU/core installed: model, speed (in MHz), and times (an object containing the number of milliseconds the CPU/core spent in: user, nice, sys, idle, and irq).

That's why array returned by require('os').cpus() contains 24 elements.

Answer 2

Your computer processors contain physical cores which are actually physically present. -> https://en.wikichip.org/wiki/physical_core#:~:text=A%20physical%20core%20(also%20processing,one%20or%20more%20logical%20cores

It also has logical cores with is a result of some fancy logic hyper threading used to run process in parallel on a single core.

For example, two process can run on the same core at the same time in parallel. So out of one physical core, we now have two logical/virtual cores (Running a process each).

For example if you have 2 processors resulting into you have 6 physical cores on your machine (3 physical cores per processor).

Each physical core run two process in parallel giving 6 *2 = 12 logical cores.

Since you had 4 processors, now you have 4 * 3 * 2 = 24 logical cores.

Check out this article for more information on physical vs logical cores