Intel 80286
 |
An Intel 80286 Microprocessor |
The
Intel 80286 (also called
iAPX 286 in the
Intel programmer's manual for the 286) is an
x86-family
16-bit microprocessor that was introduced by
Intel on
February 1,
1982. Initially released in 6 and 8
MHz editions, it was subsequently scaled up to 12.5 MHz. (AMD and
Harris later pushed the architecture to speeds as high as 20 MHz and 25 MHz, respectively.) It was widely used in
IBM PC compatible computers during the mid
1980s to early
1990s.
The 80286 performance is more than twice that of its predecessors (the
Intel 8086 and
Intel 80186) per
clock cycle. In fact, the performance increase per clock cycle may be the biggest among the generations of x86 processors. Calculation of the complex effective addresses (such as [BX+SI]) has less clock penalty because it is performed by a special circuit in the 286. The 8086, its predecessor, has to perform effective address calculation as a part of operation in general
ALU, taking many cycles. Also, complex mathematical operations (such as MUL/DIV) take fewer clock cycles compared to the 8086. The 286 is able to address up to 16
MiB of
RAM, in contrast to the 1 MiB the 8086 can work with. While
DOS machines were able to utilise this additional RAM capability via
extended memory emulation, few 286-based computers ever saw more than a megabyte of RAM.
The 286 was designed to run multitasking applications, including communications (such as automated
PBXs),
real-time process control, and multi-user systems.
An interesting feature of this processor is that it was the first x86 processor with the
protected mode, which enabled up to 16 MiB of memory addressed through the on-chip paged memory management unit (MMU). The MMU also provided some degree of prevention from (crashed or ill-behaved) applications writing outside their allocated memory zones. However, the 286 could not revert to the basic 8086-compatible "
real mode", without resetting the processor. In theory, real mode applications could be directly executed in 16-bit protected mode if certain rules were followed; however, as many DOS programs broke those rules protected mode was not widely used until the appearance of its successor, the
32-bit Intel 80386, which could go back and forth between modes easily. See
Protected mode#Compatibility with real mode applications for more info. Also it introduced the Virtual 8086 mode (which helped the 80386 to make a smoother transition from pure real mode to protected mode OSes).
*
Linux on 286 laptops and notebooks*
Intel 80286 images and descriptions at cpu-collection.de*
CPU-INFO: 80286, in-depth processor history
