Processor mode also called as CPU modes or CPU privilege level. The processor modes are used by processor to create an operating environment for itself. Specifically, the processor mode controls how the processor sees and menages the system memory and the tasks that use it.

There are three different modes of operation, but one more mode is added for new 64 bit processor.

  1. Real Mode
  2. Protected Mode
  3. Virtual Real Mode
  4. 64 bit extension Mode

Real Mode: When the processor is running in real mode, it acts like an 8088. What this means is that it has the advantage of speed, but it otherwise accesses memory with the same restrictions of the original 8088: a limit of 1 MB of addressable RAM, and slow memory access that doesn’t take full advantage of the modern CPU´s.

Protected Mode: This is a much powerful mode of operation than real mode, and it is used in all modern multitasking operating systems. It has full access to all of the system´s memory. There is no 1 MB limit like the real mode. It has the ability to multitask, as compared to the single tasking real mode.

Virtual Real Mode: This mode is an addition capability, an enhancement of protected mode. Protected mode is normally used to run graphical multitasking operating systems like windows. There is often a desire to be able to run DOS programs under Windows, but DOS programs need to be run in real mode and not the protected mode. So basically this mode virtually creates a real mode in order to run DOS programs.

Processor modes
A software known as Dos Box is used to execute Dos programs in Windows even when it is in protected mode.