Editing Microprocessor (section)

===16-bit designs===
{{x86 processor modes}}
The first multi-chip [[16-bit]] microprocessor was the [[National Semiconductor]] [[IMP-16]], introduced in early 1973. An 8-bit version of the chipset was introduced in 1974 as the IMP-8.

Other early multi-chip 16-bit microprocessors include the [[MCP-1600]] that [[Digital Equipment Corporation|Digital Equipment Corporation (DEC)]] used in the [[LSI-11]] OEM board set and the packaged [[PDP-11|PDP-11/03]] [[minicomputer]]—and the [[Fairchild Semiconductor]] MicroFlame 9440, both introduced in 1975–76. In late 1974, National introduced the first 16-bit single-chip microprocessor, the [[National Semiconductor PACE]],<ref>{{cite web | url=https://www.cpu-world.com/CPUs/PACE/index.html | title=National Semiconductor PACE CPU family | access-date=25 November 2022 | archive-date=25 November 2022 | archive-url=https://web.archive.org/web/20221125202308/https://www.cpu-world.com/CPUs/PACE/index.html | url-status=live }}</ref> which was later followed by an [[NMOS logic|NMOS]] version, the [[INS8900]].

Next in list is the [[General Instrument CP1600]], released in February 1975,<ref>{{Cite web |last=EDN Staff |date=2000-01-01 |title=General Instrument's microprocessor aimed at minicomputer market |url=https://www.edn.com/general-instruments-microprocessor-aimed-at-minicomputer-market/ |access-date=2023-01-01 |website=EDN |language=en-US |archive-date=25 November 2022 |archive-url=https://web.archive.org/web/20221125201445/https://www.edn.com/general-instruments-microprocessor-aimed-at-minicomputer-market/ |url-status=live }}</ref> which was used mainly in the [[Intellivision]] console.

Another early single-chip 16-bit microprocessor was TI's [[TMS 9900]], which was also compatible with their [[TI-990]] line of minicomputers. The 9900 was used in the TI 990/4 minicomputer, the [[TI-99/4A]] home computer, and the TM990 line of OEM microcomputer boards. The chip was packaged in a large ceramic 64-pin [[Dual in-line package|DIP package]], while most 8-bit microprocessors such as the Intel 8080 used the more common, smaller, and less expensive plastic 40-pin DIP. A follow-on chip, the TMS 9980, was designed to compete with the Intel 8080, had the full TI 990 16-bit instruction set, used a plastic 40-pin package, moved data 8&nbsp;bits at a time, but could only address 16&nbsp;[[Kilobyte|KB]]. A third chip, the TMS 9995, was a new design. The family later expanded to include the 99105 and 99110.

The [[Western Design Center]] (WDC) introduced the CMOS [[65816]] 16-bit upgrade of the WDC CMOS [[65C02]] in 1984. The 65816 16-bit microprocessor was the core of the [[Apple IIGS]] and later the [[Super Nintendo Entertainment System]], making it one of the most popular 16-bit designs of all time.

Intel "upsized" their 8080 design into the 16-bit [[Intel 8086]], the first member of the [[x86]] family, which powers most modern [[IBM PC compatible|PC]] type computers. [[Intel]] introduced the 8086 as a cost-effective way of porting software from the 8080 lines, and succeeded in winning much business on that premise. The [[8088]], a version of the 8086 that used an 8-bit external data bus, was the microprocessor in the first [[IBM PC]]. Intel then released the [[80186]] and [[80188]], the [[80286]] and, in 1985, the 32-bit [[80386]], cementing their PC market dominance with the processor family's backwards compatibility. The 80186 and 80188 were essentially versions of the 8086 and 8088, enhanced with some onboard peripherals and a few new instructions. Although Intel's 80186 and 80188 were not used in IBM PC type designs,{{dubious|Intel 80186 and IBM PC-style computers|date=November 2016}} second source versions from NEC, the [[NEC V20|V20]] and V30 frequently were. The 8086 and successors had an innovative but limited method of [[memory segmentation]], while the 80286 introduced a full-featured segmented [[memory management unit]] (MMU). The 80386 introduced a flat 32-bit memory model with paged memory management.

The 16-bit Intel x86 processors up to and including the 80386 do not include [[Floating-point unit|floating-point units (FPUs)]]. Intel introduced the [[8087]], [[80187]], [[80287]] and [[80387]] math coprocessors to add hardware floating-point and transcendental function capabilities to the 8086 through 80386 CPUs. The 8087 works with the 8086/8088 and 80186/80188,<ref>Intel 8087 datasheet, pg. 1</ref> the 80187 works with the 80186 but not the 80188,<ref>The 80187 only has a 16-bit data bus because it used the 80387SX core.</ref> the 80287 works with the 80286 and the 80387 works with the 80386. The combination of an x86 CPU and an x87 coprocessor forms a single multi-chip microprocessor; the two chips are programmed as a unit using a single integrated instruction set.<ref>"Essentially, the 80C187 can be treated as an additional resource or an extension to the CPU. The 80C186 CPU together with an 80C187 can be used as a single unified system." Intel 80C187 datasheet, p. 3, November 1992 (Order Number: 270640-004).</ref> The 8087 and 80187 coprocessors are connected in parallel with the data and address buses of their parent processor and directly execute instructions intended for them. The 80287 and 80387 coprocessors are interfaced to the CPU through I/O ports in the CPU's address space, this is transparent to the program, which does not need to know about or access these I/O ports directly; the program accesses the coprocessor and its registers through normal instruction opcodes.