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.

Further Reading

• Great Microprocessors of the Past and Present, Intel 8086: IBM's Choice, John Bayko

Low End PC (LEPC) launched September 2001. The entire LEPC site copyright ©2001-2003 by Cobweb Publishing, Inc., unless otherwise noted. Copyright of individual articles resides with the author. All rights reserved.
  Advice presented in good faith, but what works for one may not work for all. Computers are like that. Please report errors to the webmaster.
  Letters sent to LEPC may be published at our discretion. Email addresses will not be published unless specifically requested. If you prefer that your message not be published, clearly mark it "not for publication." Letters may be edited for length, context, and to match house style.
  LINK POLICY: This site allows and encourages links to any public page, so long as the linked page does not appear within a frame that prevents bookmarking the linked page.
  PRIVACY POLICY: In brief, we don't collect any personal information unless you explicitly provide it.
  Low End PC is an independent publication and has not been authorized, sponsored, or otherwise approved by Microsoft, Intel, or anyone else. Many company and product names may be trademarks or registered trademarks of the individual companies and are hereby acknowledged.
  For more details, see our Terms of Use.