x86 (also known as 80x86[2] or the 8086 family[3]) is a family of complex instruction set computer (CISC) instruction set architectures[a] initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introduced in 1978 as a fully 16-bit extension of Intel's 8-bit 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486 processors.
A few years after the introduction of the 8086 and 8088, Intel added some complexity to its naming scheme and terminology as the "iAPX" of the ambitious but ill-fated Intel iAPX 432 processor was tried on the more successful 8086 family of chips,[c] applied as a kind of system-level prefix. An 8086 system, including coprocessors such as 8087 and 8089, and simpler Intel-specific system chips,[d] was thereby described as an iAPX 86 system.[8][e] There were also terms iRMX (for operating systems), iSBC (for single-board computers), and iSBX (for multimodule boards based on the 8086-architecture), all together under the heading Microsystem 80.[9][10] However, this naming scheme was quite temporary, lasting for a few years during the early 1980s.[f]
Intel 8086 Hardware Architecture Pdf Download
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Although the 8086 was primarily developed for embedded systems and small multi-user or single-user computers, largely as a response to the successful 8080-compatible Zilog Z80,[11] the x86 line soon grew in features and processing power. Today, x86 is ubiquitous in both stationary and portable personal computers, and is also used in midrange computers, workstations, servers, and most new supercomputer clusters of the TOP500 list. A large amount of software, including a large list of x86 operating systems are using x86-based hardware.
The 8086 had 64 KB of eight-bit (or alternatively 32 K-word of 16-bit) I/O space, and a 64 KB (one segment) stack in memory supported by computer hardware. Only words (two bytes) can be pushed to the stack. The stack grows toward numerically lower addresses, with .mw-parser-output .monospacedfont-family:monospace,monospaceSS:SP pointing to the most recently pushed item. There are 256 interrupts, which can be invoked by both hardware and software. The interrupts can cascade, using the stack to store the return address.
Real Address mode,[35] commonly called Real mode, is an operating mode of 8086 and later x86-compatible CPUs. Real mode is characterized by a 20-bit segmented memory address space (meaning that only slightly more than 1 MiB of memory can be addressed[p]), direct software access to peripheral hardware, and no concept of memory protection or multitasking at the hardware level. All x86 CPUs in the 80286 series and later start up in real mode at power-on; 80186 CPUs and earlier had only one operational mode, which is equivalent to real mode in later chips. (On the IBM PC platform, direct software access to the IBM BIOS routines is available only in real mode, since BIOS is written for real mode. However, this is not a property of the x86 CPU but of the IBM BIOS design.) 2ff7e9595c
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