The second generation of x86 16-bit processors, Intel 80286, was
released in 1982. The major new feature of the 80286 microprocessor
was protected mode. When switched to this mode, the CPU could address
up to 16 MB of operating memory (previous generation of 8086/8088
microprocessors was limited to 1 MB). In the protected mode it was
possible to protect memory and other system resources from user
programs - this feature was necessary for real program multitasking.
There were many operating systems that utilized the 80286 protected
mode: OS/2 1.x, Venix, SCO Xenix 286, and others. While this mode was
useful for multitasking operating systems, it was of limited use for
systems that required execution of existing x86 programs. The
protected mode couldn't run multiple virtual 8086 programs, and had
other limitations as well:
- 80286 was a 16-bit microprocessor. Although in protected mode
the CPU could address up to 16 MB of memory, this was implemented
using memory segments. Maximum size of memory segment was still 64
KB.
- There was no fast and reliable way to switch back to real mode from
protected mode.
Currently the 80286 protected mode is not used by x86 operating
systems. All modern 32-bit x86-based operating systems use 80386
protected mode that was introduced by
next generation of Intel x86
processors.
The Intel 80286 microprocessor included new protected mode and all real-mode
instructions that were introduced by
80186/80188
processors. Execution time of many real-mode instructions was reduced.
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