@Darkk - That's only true if you also:
- Remove the optical drive and other removable media drives.
- Remove any wireless or bluetooth adapters.
- Block up the network port.
- Remove any peripherals that have their own data inputs, multifunction printers, flash card readers etc.
- Block up all the USB ports, unless they are needed for keyboard on mouse, in which case super glue those devices into the ports.
- Block up any other port such and Firewire or Thunberbolt.
- Tack weld the case shut.
Then maybe the computer will be safe for the next couple of years, of course it will impossible to get data on or off the computer, other than manually enter it or print it out, there will also be no way to backup, but hey it will be safe, as long as the hard drive doesn't fail.
Air Gapping a PC only works if you have total control over what is connected to it at all times. I can't count the number of PC I've seen total owned by a virus, because someone thought because it wasn't on the network it was safe. But of course they want to get files on off the pc using a flash drive, or they wanted that one file off the backup media over the long weekend, so they opened it on their home PC, or someone needed a convenient USB port to charge there smartphone. Then it's as helpless as the Indians were to smallpox.
In the typical work environment an Air Gapped computer is a lamb to the slaughter, an internet connected computer with a modern OS, antivirus, and the ability to keep itself up to date, has a hell of a lot better chance of staying virus free.