What is the difference between a CPU and an OS?

Everything. One is hardware, one is software. The CPU (central processing unit) is a programmable device capable of general purpose computation. It is composed of many integrated circuits on a single silicon package called a microprocessor. You can think of it as the core piece of hardware in a computer. read more

When you use them together they become so much useful and not so much when you see them apart. One is what the other uses to perform any single operation and the other is what decides (or instructs) what to do with the one. read more

An Operating System is the core software that allows applications to interface with the hardware. Operating Systems control the specific details of your system, presenting a more manageable interface for applications (and the user) to make use of. read more

By processor, you probably mean the chip that runs your computer - the central processing unit. It's a piece of hardware. The operating system is software. Windows is a common operating system; Mac OS-X is another, as is Linux (which comes in many different distributions). read more