Monday, March 02, 2009

Intel 80286

The Intel 286, introduced on February 1, 1982, (originally named 80286, and also called iAPX 286 in the programmer's manual) was an x86 16-bit microprocessor with 134,000 transistors.

It was widely used in IBM PC compatible computers during the mid 1980s to early 1990s.

After the 6 and 8 MHz initial releases, 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.) On average, the 80286 had a speed of about 0.21 instructions per clock. The 6 MHz model operated at 0.9 MIPS, the 10 MHz model at 1.5 MIPS, and the 12 MHz model at 1.8 MIPS.

The 80286's performance was more than twice that of its predecessors (the Intel 8086 and Intel 8088) per clock cycle. In fact, the performance increase per clock cycle of the 80286 over its immediate predecessor may be the largest among the generations of x86 processors. Calculation of the more complex addressing modes (such as base index) had less clock penalty because it was performed by a special circuit in the 286; the 8086, its predecessor, had to perform effective address calculation in the general ALU, taking many cycles. Also, complex mathematical operations (such as MUL/DIV) took fewer clock cycles compared to the 8086.

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