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The Intel 80286 [4] (also marketed as the iAPX 286 [5] and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also the first with memory management and wide protection abilities.
When IBM used the 80286 in their IBM PC/AT, they solved this problem by including a software-settable gate to enable or disable (force to zero) the A20 address line, between the A20 pin on the 80286 and the system bus; this is known as Gate-A20 (the A20 gate), and it is still implemented in PC chipsets to this day. Most versions of the HIMEM ...
The 80286 had a 24-bit address bus. 32-bit i386 first 32-bit x86 processor. Introduced paging on top of segmentation which is the most commonly used memory protection ...
Industry Standard Architecture (ISA) is the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s. The bus was (largely) backward compatible with the 8-bit bus of the 8088-based IBM PC, including the IBM PC/XT as well as IBM PC compatibles.
The updated instruction set is grouped according to architecture (i186, i286, ... The new instructions added in 80286 add support for x86 protected mode.
The industry around the 8088- and 80286-based de facto standard of IBM PC and IBM AT designs also seldom used that naming scheme. As a result, the iAPX prefix is now, again, more closely associated with the (non-x86) iAPX 432 architecture (which, although a commercial failure, is often seen as historically important).
In 1982, the Intel 80286 added support for virtual memory and memory protection; the original mode was renamed real mode, and the new version was named protected mode. The x86-64 architecture, introduced in 2003, has largely dropped support for segmentation in 64-bit mode.
The native architecture of x86-64 processors: residing in the 64-bit Mode, lacks of access mode in segmentation, presenting 64-bit architectural-permit linear address space; an adapted IA-32 architecture residing in the Compatibility Mode alongside 64-bit Mode is provided to support most x86 applications 2003: Athlon 64/FX/X2 (2005), Opteron