This article gives the information of Processor Mode. Processor Mode also called as CPU modes or CPU “privilege level”. The CPU modes are used by processor to create an operating environment for automatic. Specifically, the CPU mode controls how the processor sees and manages the system memory and task 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 Mode Real Mode.
  4. 64 bit extension Mode.

Real Mode:

The original IBM PC could only address 1MB of system memory and the original versions of DOS created to work on it were designed with this in mind.  DOS is it’s by nature a single tasking operating system meaning it can only handle one program running at a time. The decision made in this early days have carried forward until now and in each new processor care had to be taken to be able to put the processor in a mode that would be compatible with the original Intel 8088 chip. This is called Real Mode. Real mode is of course used by DOS and “standard” DOS application.

Modes of processor

Protected Mode:

Starting with the 80286 chip in the IBM AT, a new CPU mode was published called protected mode. This is much more powerful mode of operation than real mode and is used in all modern multitasking operating systems. The advantages of protected mode (compared to real mode) are:

  • Full access to all of the system memory. There is no1 MB limitation in mode
  • Ability to multiple tasking meaning having the operating system manages the execution of multiple programs simultaneously.
  • Preference to for virtual memory which gives the permission the system to use the hard disk to emulate additional system memory when needed.
  • Faster (32 bit) access to memory and faster 32 bit drivers to do        I/O transfer.

The name of this mode comes from its primary use which is multitasking operating system. Each program that is running has its own assigned memory location which is protected from conflict with other programs. If a program tryes to access a memory address that it isn’t allowed to a “protection fault” is generated.

Protected mode is now used by the most people use their PCs.

Virtual Mode:

This mode is also called virtual 8086 mode. The third mode of operation is actually an some more capability, an enhancement of protected mode. The use Protected mode is for to run graphical multitasking operating system such as the various types of windows. There is often desire to be able to run DOS program under the window, but DOS programs need to be run in the real mode not protected mode. Virtual real mode is used to solve this problem. Virtual real mode is also used when you use a DOS box or run a DOS game in Windows 95.

64 Bit Extension Mode:

This mode is also called Long Mode. 64 bit extension mode is the mode where a 64 bit application can access the 64 bit instruction and registers while 32 bit and 16 bit programs are executed in a compatibility sub mode. This is what about the processor modes.

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Written by Sourabh Bhunje

Sourabh Bhunje, B.E. IT from Pune University. Currently Working at Techliebe. Professional Skills: Programming - Software & Mobile, Web & Graphic Design, Localization, Content Writing, Sub-Titling etc.

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