CPU architecture

A system's CPU architecture is generally 32-bit or 64-bit. When you download the VirtualBox or Vagrant software package-installer, you will have to define which version you require. 

We can run the sysctl hw.cpu64bit_capable command, which lets us know whether our system is capable of running 64-bit software. In this screenshot of my system, you can see the returned value is 1:

This means that I have a 64-bit-capable Mac system. If your value returns as empty or 0, then your system only supports 32-bit.