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Windows 3.0 actually had several modes: "real mode", "standard mode" and "386-enhanced mode"; the latter required some of the virtualization features of the 80386 processor, and thus would not run on an 80286. Windows 3.1 removed support for real mode, and it was the first mainstream operating environment which required at least an 80286 processor.
In computing, protected mode, also called protected virtual address mode, [1] is an operational mode of x86-compatible central processing units (CPUs). It allows system software to use features such as segmentation, virtual memory, paging and safe multi-tasking designed to increase an operating system's control over application software.
The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 [5] and June 8, 1978, when it was released. [6] The Intel 8088, released July 1, 1979, [7] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM PC design.
To support old software, the processor starts up in "real mode", a mode in which it uses the segmented addressing model of the 8086. There is a small difference though: the resulting physical address is no longer truncated to 20 bits, so real mode pointers (but not 8086 pointers) can now refer to addresses between 100000 16 and 10FFEF 16.
The x86 processors support five modes of operation for x86 code, Real Mode, Protected Mode, Long Mode, Virtual 86 Mode, and System Management Mode, in which some instructions are available and others are not. A 16-bit subset of instructions is available on the 16-bit x86 processors, which are the 8086, 8088, 80186, 80188, and 80286.
An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere. In computer programming, addressing modes are primarily of interest to those who write in assembly languages and to compiler writers.
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.
Microprocessor modes for the x86 architecture; Real mode ; 8080 emulation mode (NEC V20/V30 only) Protected mode (Intel 80286) Unreal mode (Intel 80286) Virtual 8086 mode (Intel 80386) System Management Mode (Intel 386SL) Long mode (AMD Athlon 64) x86 virtualization (Intel Pentium 4, AMD Athlon 64) AIS mode (VIA C3 only)