Intel 80286
From Free net encyclopedia
Image:Intel 80286.jpg Image:Am80286-12.jpg 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 special circuit of 80286. The 8086, its predecessor, has to perform effective address calculation as a part of operation in general ALU, taking many cycles. Also, complex math operations (such as MUL/DIV) take fewer clock cycles comparing to the 8086. The 80286 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 capable of switching from real mode to protected mode, enabling the use of up to 16 MiB of system memory, and allowing certain degree of protection of the memory zones used by applications. However, the 286 could not revert to 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#compatiblity 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).
External links
- Linux on 286 laptops and notebooks
- Intel 80286 images and descriptions at cpu-collection.de
- CPU-INFO: 80286, indepth processor history
|
Intel processors 4004 | 4040 | 8008 | 8080 | 8085 | 8086 | 8088 | iAPX 432 | 80186 | 80188 | 80286 | 80386 | 80486 | i860 | i960 | Pentium | Pentium Pro | Pentium II | Celeron | Pentium III | XScale | Pentium 4 | Pentium M | Pentium D | Pentium Extreme Edition | Xeon | Core | Itanium | Itanium 2 (italics indicate non-x86 processors) |