Can't see artboard at real size

Hello to everyone,

Im working on my Imac(windows 10 system running on it)

I never experienced such a problem,but i cannot see at real size the artboard.

If i set 20cm for side than 100% view still the image it's smaller than reality.

I tried to fix it with pixels view as i read on some forum,but nothing happens.

On my window laptop and on another window machine  im running same Illustrator(Last version with same setting of the Imac) and i don't have such a problem.

What could it be?

I heard it could be the monitor?

DESKTOP-8OS4NT3 Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz 4.00 GHz Windows 10 Pro

Thanks in advance and sorry for my english

Francesco