The Intel 80286
Dan Knight - September 2001
In their overview of CPUs, even Intel skips past the 80186/80188. It wasn't really significant to personal computing. A few accelerators adopted it, but as far as I know the Tandy 2000 was the only computer ever designed around the 80186.
The 80286 was a much more powerful CPU than the 8086. It was capable of addressing 16 MB of RAM and 1 GB of virtual memory, started life at 6 MHz and eventually reached 12.5 MHz, and offered 3-6x the performance of the 8086, according to Intel's estimate. (That's just for genuine Intel processors - Siemens, an Intel licensee, pushed the design to 16 MHz. AMD reached 20 MHz, and Harris managed to ship a 25 MHz 80286.)
In contrast to the 3 micron, 29,000 transistor design of the 8086, the more powerful '286 had a 1.5 micron design containing 134,000 transistors. Byte magazine (May 1993) noted that the 80286 had a MIPS (million instructions per second) rating of 1.2 (6 MHz) to 2.66 (for the 12.5 MHz CPU).
The earlier 8086 had a MIPS score of about 0.07 per MHz of CPU speed, compared with about 0.21 for the '286, making the newer CPU up to 3x more powerful at the same MHz rating, although we must keep in mind that MIPS is not an accurate pedictor of real world CPU performance.
The 6 MHz 80286 was the heart of the 1984 IBM AT, which also introduced a 16-bit motherboard and 16-bit expansion bus to the PC world. However, despite new addressing modes available with the 286, it typically ran "real mode," which was compatible with the older 8086, leaving it generally working more quickly but with the same 640 KB memory limit.
Running in "protected mode" allowed the 286 to address a lot more 64 KB segments, but it had the same problems using data structures over 64K as the 8086/88.
Some operating systems, such as OS/2 and Windows/286, took advantage of the more advanced memory models available to the 286.
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