Difference between real mode and protected mode.

Difference between real mode and protected mode.


The 80286 mode called the protected mode in the x86 architecture. Protected mode was different to the initial mode of 8086 which was constantly referred to as "Real Mode" in order to avoid illegal writes of programs placed in memory from being physically isolated by the processor itself. Multiple programs could run simultaneously in the memory before protected mode, but any program could reach any memory region and thus, for instance, bring down the entire system if malicious or errant.

Difference between real mode and protected mode.
Difference between real mode and protected mode.

In real mode programming, information were handled between 0 and 1 MB.  And while there weren't usually many programs operating simultaneously in memory, the OS had to establish the stuff called "interrupt handlers" because the x86 architecture is guided interruptly.

Interrupting oriented architectures means that programs run sequentially, but are interrupted occasionally to manage external applications. The processor is informed by a external device called an APIC in the chipset that an external interrupt is pending. The processor then branches to the suitable interrupt handler when the current instruction is completed. The keyboard interrupt handler would include reading the keyboard's physical code and then using some logic to determine what sort of keyboard is in use and what the keystroke symbol is.There are many more interrupts that can also happen externally. The disputes between many elderly PC users are IRQ. An IRQ is an "interrupt request" and any individual interrupt request has its own IRQ to signal the suitable handler. You would not like a keyboard handler or Vice-vera to process the time interrupt. It wouldn't operate and the system would not operate.

In the 80286, protected mode has been implemented, which can be isolated by enabling the OS to dictate where each application should operate. While the design of the 80286 expanded the initial 8086 memory by adding fresh parts for each memory command block the initial 8086 memory was still a 16-bit processor. I will now migrate to the future generation of the design 80386 and its 32-bit capabilities to describe the complete implications of protected mode programming.


What is real mode


Real mode is an operational mode that allows newer Intel 286 processors to acquire the characteristics of the reduced 8086 or 8088 processors, enabling them to operate older programs. Real mode provides a higher clock speed, but only restricts the processor to a 16-bit and a minimum of 1 mb RAM  instructions.

Difference between real mode and protected mode.
8086 chip- Difference between real mode and protected mode.


The real mode is based on intel processors 8086 & 8088.

The original IBM computers contained 8088 processors that could use 16 bit internal registration to execute 16 bit instructions with 1 mb using 20 address lines.

The Intel 80286 and subsequent processors support an execution mode. The Intel 8088 and 8086 microprocessors are imitated in real mode although they operate at a faster speed. The other accessible mode is known as protected mode.In virtual mode, these microprocessors can run several real-mode programs at once. 80386 and later microprocessors support a third-mode called virtual 8086 mode.

The real mode is called the 16-bit instruction mode for 8088 processors.

All software must use only 16 bit instruction and operate in 20 bit memory architecture in real mode.

In real mode there is no multitasking,no protection  to keep one program from overwriting another program.

The real mode is used by DOS  and its applications.

What is protected mode


The protected mode is a 32-bit operating mode that is identified on Intel 80286 or later on.This mode allows the termination of a failed program without restarting the computer or running programs. It offers access to addressing by virtual memory, expanded memory, and multiple tasks while it protecting programs against memory overwriting. 


Protected mode is an Intel 80286-compatible Intel operating mode. It allows operating system to use functionalities like virtual memory, paging, and  multi-tasking. It is also intended to improve the control of the Operating system over software applications.

Difference between real mode and protected mode.
80286 chip - Difference between real mode and protected mode.

Protected mode is a programming mode in an Intel-based computer where the program is limited to addressing an adjacent 640-kilobyte contiguous field. The original Intel PC microprocessor 8088 provided a random access memory (RAM) with an 1 megabyte. For the basic input / output system data, signals from your display and other system information the memory was divided into several areas.

In the beginning of 1982, Intel's x86 architecture utilized protected mode. It then became a basic basis for all additional Intel x86 architectures. The original releases did not allow a real mode switch or enable the protected mode. An option was provided, however, to save RAM stack pointers, registers and masks via a keyboard controller. After the advent of the 386 processor, the protected mode could easily be turned into enables eliminating complex steps involved in the 286 architecture, which have no internal exit mechanism in the protected mode.

Difference between real mode and protected mode.

80286 chip -Difference between real mode and protected mode.


The memory was divided into several area for bios signal for display and other system information.All operating system code and application program run in protected mode to ensure that data is not over written.

The protected mode support virtual memory concepts in which allows the system to use the hard disk to emulate additional system memory when needed.

Conclusion

The architecture of protected mode presents many protection elements, which really isolate one from the memory of other operating programs. If another program is attempting the memory region the OS didn't specifically allocate to that region, then an error or failure will be reported, which the OS intercepts and then handles.

It is worth noting that the precise same real mode is accessible on current systems 80386 and later, instead of the initial 16-bit system, within a 32-bit framework.  It is a secondary effect of the lazy selector processing that is carried out within a CPU once it returns to real mode from protected mode.

The protected mode design of 80386 also allows a true 32-bit machine to run in the protected mode version of the unreal mode. This type of setup is seldom discovered typically in custom Linux installations and the like. In fact, the CPUs produced today are so much quicker than the operating systems such as Linux and Windows do. Paging alone presents a great slowdown, which I have experienced almost 2 times the slowdown of a non-paged scheme.


Thank you so much for reading the Difference between real mode and protected mode.

Difference between real mode and protected mode.

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