Differentiate between the real mode and the protected mode o

Differentiate between the real mode and the protected mode of the Intel 80286, 80386, 80486, and Pentium microprocessors operation.

• Explain why it is important for programmers to understand the details of the real mode and the protected mode of a microprocessor.

Solution

Protected mode of the Intel 80286 differ from the real mode in the areas of memory could be physically isolated by the processor itself to prevent illegal writes to other programs running in memory at the same time.Before the use of protected mode, multiple programs used to run in memory at the same time and any program could corrupt any part of the memory at any time which can lead the entire system down as result.

80386 is the baseline for the today\'s modern 64 bit processors and it is also an advance version for the 80286.Real mode drivers were ceated to run under the MS DOS operating system.Protected mode drivers are more secure and robust than real mode drivers.

A protected mode driver is also called as virtual device driver, or VxD which allows for faster, shared access to the device with no use of the lower 640K of memory.

The 80386 protected mode architecture introduces an “absent” bit in memory control blocks related to paging. The processor interrupts the program when a program attempts to run a program or access data in an area of memory which has been swapped out to the paging file, task switches to the OS’s “page not present” handler, waits for the OS to do the needful to restore the memory, and then proceeds further.

80486 is an upgraded version of the 80386 architecture.It is 3 to 5 times faster than the 80386 version.

It is important for programmers to understand the details of the real mode and the protected mode of a microprocessor.Processor modes are different ways of how a processor makes operating environment for itself.

Real mode or real address mode is an operating mode for all x86 architectures.It provides no support for memory protection, multitasking, or code privilege levels. Prior to 80286 protected mode introduction , real mode was the only mode available for the x86 CPUs.A processor which runs in real mode acts as \"8088 on steroids\".This means 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 advantage of the full 32-bit processing of modern CPUs.This rel mode is available in all the processors and in fact computer normally starts in real mode.

A new processor mode was introduced called protected mode with the 80286 chip in the IBM AT. This is a much more powerful mode of operation than real mode, and is used in all modern multitasking operating systems. The advantages of protected mode are as follows -

1) There is full acess to all of the system memory and it overcomes the disadvantage of 1 MB limit.

2)It has the ability to multitask.The OS can manage to execute multiple task simultaneously.

3)It supports virtual memory which allows the hard disk to emulate additional system memory when needed.

4)It is faster in performance compared to real mode.