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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 .
8086 first x86 processor; initially a temporary substitute for the iAPX 432 to compete with Motorola, Zilog, and National Semiconductor and to top the successful Z80. The 8088 version, with an 8-bit bus, was used in the original IBM Personal Computer. 186 included a DMA controller, interrupt controller, timers, and chip select logic. A small ...
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
The processor executes the SMM code in a separate address space (SMRAM) that has to be made inaccessible to other operating modes of the CPU by the firmware. [7] System Management Mode can address up to 4 GB memory as huge real mode. In x86-64 processors, SMM can address >4 GB memory as real address mode. [8]
With the release of the 386, protected mode offers what the Intel manuals call virtual 8086 mode. Virtual 8086 mode is designed to allow code previously written for the 8086 to run unmodified and concurrently with other tasks, without compromising security or system stability. [34] Virtual 8086 mode, however, is not completely backward ...
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)
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.