PRESENTATION ON REAL ADDRESSING MODE AND VIRTUAL ADDRESSING MODE

PRESENTATION ON REAL ADDRESSING MODE AND VIRTUAL ADDRESSING MODE

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  SUBMITED BY:- ARIJIT CHAKRABORTY BETI1EC16002 ELECTRONIC& COMMUNICATION III year, V sem SUBMITED TO:- DR. SHYAM AKASHE PROFESSOR ELECTRONIC & COMMUNICATION
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  TABLE OF CONTAINS:- What is Real Addressing Mode  What is Virtual Addressing Mode
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  REAL ADDRESSING MODE:- oReal mode, also called real address mode, is an operating mode of all x86-compatible CPUs. Real mode is characterized by a 20- bit segmented memory address space (giving exactly 1 MB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels.
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  o Before therelease of the 80286, which introduced protected mode, real mode was the only available mode for x86 CPUs; and for backward compatibility, all x86 CPUs start in real mode when reset, though it is possible to emulate real mode on other systems when starting on other modes. CONT.….
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  CONT.…. o The 80286chip was introduced on 1 February 1982 and was made to start in 'real mode' – that is, in a mode which turned off the new memory protection features, so that it could run operating systems written for the 8086 and the 8088. As of 2018, current x86 CPUs (including x86- 64 CPUs) are able to boot real mode operating systems and can run software written for almost any previous x86 chip without emulation or virtualization. o The PC BIOS which IBM introduced operates in real mode, as do the DOS operating systems (MS-DOS, DR-DOS, etc.). Early versions of Microsoft Windows ran in real mode.
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  VIRTUAL ADDRESSING MODE:- oIn the 80386 microprocessor and later, virtual addressing mode (also called virtual real mode, virtual 8086 mode, V86-mode or VM86) allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system. It is a hardware virtualization technique that allowed multiple 8086 processors to be emulated by the 386 chip; it emerged from the painful experiences with the 80286 protected mode, which by itself was not suitable to run concurrent real mode applications well.
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  CONT.…. o VM86 modeuses a segmentation scheme identical to that of real mode (for compatibility reasons) which creates 20-bit linear addresses in the same manner as 20-bit physical addresses are created in real mode, but are subject to protected mode's memory paging mechanism. o To use virtual 8086 mode, an operating system sets up a virtual 8086 mode monitor, which is a program that manages the real-mode program and emulates or filters access to system hardware and software resources. The monitor must run at privilege level 0 and in protected mode. Only the 8086 program runs in VM86 mode and at privilege level 3.
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  o When thereal-mode program attempts to do things like access certain I/O ports to use hardware devices or access certain regions in its memory space, the CPU traps these events and calls the V86 monitor, which examines what the real mode program is trying to do and either acts as a proxy to interface with the hardware, emulates the intended function the real-mode program was trying to access, or terminates the real-mode program if it is trying to do something that cannot either be allowed or be adequately supported (such as reboot the machine, set a video display into a mode that is not supported by the hardware and is not emulated, or write over operating system code). CONT.….