Editing Intel 80286 (section)

==Architecture==
[[File:Intel i80286 arch.svg|thumb|Simplified 80286 microarchitecture]]
[[File:Intel 80286 die.JPG|thumb|Intel 80286 die]]

Intel expected the 286 to be used primarily in industrial automation, transaction processing, and telecommunications, instead of in personal computers.<ref name="bloomberg19950305">{{cite news |last1=Gross |first1=Neil |url=https://www.bloomberg.com/news/articles/1995-03-05/the-technology-paradox |title=The Technology Paradox |date=1995-03-06 |work=Bloomberg |access-date=2020-03-19 |last2=Coy |first2=Peter |language=en}}</ref>

The CPU was designed for [[multi-user]] systems with [[computer multitasking|multitasking]] applications, including communications (such as automated [[private branch exchange|PBXs]]) and [[real-time computing|real-time]] [[process control]]. It had 134,000 [[transistor]]s and consisted of four independent units: the address unit, bus unit, instruction unit, and execution unit, organized into a [[loosely coupled]] (buffered) [[pipeline (computing)|pipeline]], just as in the 8086. It was produced in a 68-pin package, including PLCC ([[plastic leaded chip carrier]]), LCC ([[leadless chip carrier]]) and PGA ([[pin grid array]]) packages.<ref>{{cite web |title=Intel 80286 microprocessor family |publisher=CPU-World |url=http://www.cpu-world.com/CPUs/80286/ |access-date=May 19, 2012 |archive-date=March 31, 2012 |archive-url=https://web.archive.org/web/20120331094243/http://www.cpu-world.com/CPUs/80286/ |url-status=live }}</ref>

The performance increase of the 80286 over the 8086 (or 8088) could be more than 100% per [[clock cycle]] in many programs (i.e., a doubled performance at the same clock speed). This was a large increase, fully comparable to the speed improvements seven years later when the [[Intel 80486|i486]] (1989) or the original [[Pentium]] (1993) were introduced. This was partly due to the non-multiplexed address and data buses, but mainly to the fact that address calculations (such as [[addressing mode#Base plus index|base+index]]) were less expensive. They were performed by a dedicated unit in the 80286, while the older 8086 had to do effective address computation using its general [[arithmetic logic unit|ALU]], consuming several extra clock cycles in many cases. Also, the 80286 was more efficient in the prefetch of instructions, buffering, execution of jumps, and in complex [[microcode]]d numerical operations such as [[multiplication|MUL]]/[[division (mathematics)|DIV]] than its predecessor.<ref name=Bahadure2010>{{cite book |last=Bahadure |first=Nilesh B. |title=Microprocessors: 8086/8088, 80186/80286, 80386/80486 and the Pentium Family |publisher=PHI Learning Pvt. Ltd |year=2010 |isbn=978-8120339422 |chapter=15 Other 16-bit microprocessors 80186 and 80286 |pages=503–537 |chapter-url=https://books.google.com/books?id=XZzUyvghwnsC&pg=PA503 |access-date=October 11, 2016 |archive-date=February 27, 2017 |archive-url=https://web.archive.org/web/20170227204924/https://books.google.com/books?id=XZzUyvghwnsC&pg=PA503 |url-status=live }}</ref>

The 80286 included, in addition to all of the 8086 instructions, all of the new instructions of the 80186: ENTER, LEAVE, BOUND, INS, OUTS, PUSHA, POPA, PUSH immediate, IMUL immediate, and immediate shifts and rotates. The 80286 also added new instructions for protected mode: ARPL, CLTS, LAR, LGDT, LIDT, LLDT, LMSW, LSL, LTR, SGDT, SIDT, SLDT, SMSW, STR, VERR, and VERW. Some of the instructions for protected mode can (or must) be used in real mode to set up and switch to protected mode, and a few (such as SMSW and LMSW) are useful for real mode itself.

The Intel 80286 had a 24-bit address bus and as such had a 16&nbsp;[[megabyte|MB]] physical [[address space]], compared to the 1&nbsp;MB address space of prior x86 processors. It was the first x86 processor to support [[virtual memory]] supporting up to 1&nbsp;GB via segmentation.<ref>Intel Corporation, "New Product Focus Components: Highest Ranking 16-bit Microprocessor Meets Military Objectives", Solutions, September/October 1985, page 13</ref> However, memory cost and the initial rarity of software using the memory above 1&nbsp;MB meant that until late in its production, 80286 computers rarely shipped with more than 1&nbsp;MB of RAM.<ref name=Bahadure2010/> Additionally, there was a performance penalty involved in accessing extended memory from real mode as noted below.