processor usage in i-mac 2015

Hi all,
I am starting to work with a new desktop machine:
iMac (Retina 5K, 27-inch, Late 2015)
Processor: 4 GHz Intel Core i7

I am confused by output from the Activity monitor (see attached View attachment activ_monitor.pdf ) that suggests that 100% CPU is one eighth of the CPU load--since this is a quad-core machine.

I assume I am being dumb by misunderstanding something fundamental.

Thanks for any clarification.
jacob

pauxi said:

I am confused by output from the Activity monitor (see attached View attachment 25261 ) that suggests that 100% CPU is one eighth of the CPU load--since this is a quad-core machine.

Click to expand...

This computer has a quad-core CPU with a technology called "Hyper-Threading". Which basically means 2 threads/CPU core...or 8 total threads (can work on 8 things at the same time). This is how the one-eight part fits in.

- Nick

Thanks! Does this mean I should parallelize code as if for up to 8 cores?

Cheers
Jacob

pauxi said:

Thanks! Does this mean I should parallelize code as if for up to 8 cores?

Click to expand...

i wish everyone did this...since not that many Apple apps are written to take advantage of all available threads/cores. Many Apple computers sold today have 2 cores (4 threads)...with the exception being most iMac's, 15" MacBook Pro's, and the Mac Pro desktop.

I'm sure there must be extra time/cost/app size impacts to this. Otherwise everyone would do it.

- Nick

If you were writing multi-threaded code, you would query for the number of available cores and optimize your program that way, you wouldn't assume 8 on all instances for example. And Nick is correct that very few applications make effective use of the 4 physical cores let alone the additional 4 virtual cores which have a slight performance hit..

Where the extra cores come in handy is if you are running virtualization software like VirtualBox, Parallels or VMWare Fusion whereby you could assign the VM 2 cores and still have 6 available for macOS and so on..