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16-bit computing

January 01, 1970

"16-bit" redirects here. For the color encoding, see 16-bit color. For the video gaming era, see 16-bit era. For other uses, see 16-bit (disambiguation).

In computer architecture, 16-bit integers, memory addresses, or other data units are those that are 16 bits (2 octets) wide. Also, 16-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size. 16-bit microcomputers are microcomputers that use 16-bit microprocessors.

A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two most common representations, the range is 0 through 65,535 (216 − 1) for representation as an (unsigned) binary number, and −32,768 (−1 × 215) through 32,767 (215 − 1) for representation as two's complement. Since 216 is 65,536, a processor with 16-bit memory addresses can directly access 64 KB (65,536 bytes) of byte-addressable memory. If a system uses segmentation with 16-bit segment offsets, more can be accessed.

16-bit architecture edit

The MIT Whirlwind (c. 1951)[1][2] was quite possibly the first-ever 16-bit computer. It was an unusual word size for the era; most systems used six-bit character code and used a word length of some multiple of 6-bits. This changed with the effort to introduce ASCII, which used a 7-bit code and naturally led to the use of an 8-bit multiple which could store a single ASCII character or two binary coded decimal digits.

The 16-bit word length thus became more common in the 1960s, especially on minicomputer systems. Early 16-bit computers (c. 1965–70) include the IBM 1130,[3] the HP 2100,[4] the Data General Nova,[5] and the DEC PDP-11.[6] Early 16-bit microprocessors, often modeled on one of the mini platforms, began to appear in the 1970s. Examples (c. 1973–76) include the five-chip National Semiconductor IMP-16 (1973),[7] the two-chip NEC μCOM-16 (1974),[8][7] the three-chip Western Digital MCP-1600 (1975), and the five-chip Toshiba T-3412 (1976).[7]

Early single-chip 16-bit microprocessors (c. 1975–76) include the Panafacom MN1610 (1975),[9][10][7] National Semiconductor PACE (1975), General Instrument CP1600 (1975), Texas Instruments TMS9900 (1976),[7] Ferranti F100-L, and the HP BPC. Other notable 16-bit processors include the Intel 8086, the Intel 80286, the WDC 65C816, and the Zilog Z8000. The Intel 8088 was binary compatible with the Intel 8086, and was 16-bit in that its registers were 16 bits wide, and arithmetic instructions could operate on 16-bit quantities, even though its external bus was 8 bits wide.

16-bit processors have been almost entirely supplanted in the personal computer industry, and are used less than 32-bit (or 8-bit) CPUs in embedded applications.

16/32-bit Motorola 68000 and Intel 386SX edit

The Motorola 68000 is sometimes called 16-bit because of the way it handles basic arithmetic. The instruction set was based on 32-bit numbers and the internal registers were 32 bits wide, so by common definitions, the 68000 is a 32-bit design. Internally, 32-bit arithmetic is performed using two 16-bit operations, and this leads to some descriptions of the system as 16-bit, or "16/32".

Such solutions have a long history in the computer field, with various designs performing math even one bit at a time, known as "serial arithmetic", while most designs by the 1970s processed at least a few bits at a time. A common example is the Data General Nova, which was a 16-bit design that performed 16-bit math as a series of four 4-bit operations. 4-bits was the word size of a widely available single-chip ALU and thus allowed for inexpensive implementation. Using the definition being applied to the 68000, the Nova would be a 4-bit computer, or 4/16. Not long after the introduction of the Nova, a second version was introduced, the SuperNova, which included four of the 4-bit ALUs running in parallel to perform math 16 bits at a time and therefore offer higher performance. This was invisible to the user and the programs, which always used 16-bit instructions and data. In a similar fashion, later 68000-family members, starting with the Motorola 68020, had 32-bit ALUs.

One may also see references to systems being, or not being, 16-bit based on some other measure. One common one is when the address space is not the same size of bits as the internal registers. Most 8-bit CPUs of the 1970s fall into this category; the MOS 6502, Intel 8080, Zilog Z80 and most others had 16-bit address space which provided 64 KB of address space. This also meant address manipulation required two instruction cycles. For this reason, most processors had special 8-bit addressing modes, the zero page, improving speed. This sort of difference between internal register size and external address size remained in the 1980s, although often reversed, as memory costs of the era made a machine with 32-bit addressing, 2 or 4 GB, a practical impossibility. For example, the 68000 exposed only 24 bits of addressing on the DIP, limiting it to a still huge (for the era) 16 MB.[11]

A similar analysis applies to Intel's 80286 CPU replacement, called the 386SX, which is a 32-bit processor with 32-bit ALU and internal 32-bit data paths with a 16-bit external bus and 24-bit addressing of the processor it replaced.

16-bit application edit

In the context of IBM PC compatible and Wintel platforms, a 16-bit application is any software written for MS-DOS, OS/2 1.x or early versions of Microsoft Windows which originally ran on the 16-bit Intel 8088 and Intel 80286 microprocessors. Such applications used a 20-bit or 24-bit segment or selector-offset address representation to extend the range of addressable memory locations beyond what was possible using only 16-bit addresses. Programs containing more than 216 bytes (65,536 bytes) of instructions and data therefore required special instructions to switch between their 64-kilobyte segments, increasing the complexity of programming 16-bit applications.

List of 16-bit CPUs edit

See also edit

References edit

  1. ^ "Year 1951". Computer History Museum. (see also "Year 1943".).
  2. ^ Digital Press, Digital at Work 2013-07-02 at the Wayback Machine, Pearson, 1992, ISBN 1-55558-092-0, pp. 4, 23.
  3. ^ "The IBM 1130 computing system". IBM Archives.
  4. ^ "HP 2116". Computer History Museum.
  5. ^ . Computer History Museum. Archived from the original on 2013-05-17. Retrieved 2012-06-11.
  6. ^ Pearson, Jamie Parker (September 1992). Digital at work: snapshots from the first thirty-five years. Digital Press. pp. 58–61. ISBN 978-1-55558-092-6.
  7. ^ a b c d e Belzer, Jack; Holzman, Albert G.; Kent, Allen (1978). Encyclopedia of Computer Science and Technology. Vol. 10 – Linear and Matrix Algebra to Microorganisms: Computer-Assisted Identification. CRC Press. p. 402. ISBN 9780824722609.
  8. ^ (PDF). Semiconductor History Museum of Japan. Archived from the original (PDF) on 2019-06-27. Retrieved 2019-06-27.
  9. ^ "16-bit Microprocessors". CPU Museum. Retrieved 5 October 2010.
  10. ^ "History". PFU. Retrieved 5 October 2010.
  11. ^ Motorola M68000 Family, Programmer's Reference Manual (PDF). Motorola, Inc. 1992. sec. 2.4, pp. 2–21. Retrieved 2023-06-05.

January 01, 1970
computing, redirects, here, color, encoding, color, video, gaming, other, uses, disambiguation, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challeng. 16 bit redirects here For the color encoding see 16 bit color For the video gaming era see 16 bit era For other uses see 16 bit disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources 16 bit computing news newspapers books scholar JSTOR March 2023 Learn how and when to remove this message In computer architecture 16 bit integers memory addresses or other data units are those that are 16 bits 2 octets wide Also 16 bit central processing unit CPU and arithmetic logic unit ALU architectures are those that are based on registers address buses or data buses of that size 16 bit microcomputers are microcomputers that use 16 bit microprocessors A 16 bit register can store 216 different values The range of integer values that can be stored in 16 bits depends on the integer representation used With the two most common representations the range is 0 through 65 535 216 1 for representation as an unsigned binary number and 32 768 1 215 through 32 767 215 1 for representation as two s complement Since 216 is 65 536 a processor with 16 bit memory addresses can directly access 64 KB 65 536 bytes of byte addressable memory If a system uses segmentation with 16 bit segment offsets more can be accessed Contents 1 16 bit architecture 1 1 16 32 bit Motorola 68000 and Intel 386SX 2 16 bit application 3 List of 16 bit CPUs 4 See also 5 References16 bit architecture editThe MIT Whirlwind c 1951 1 2 was quite possibly the first ever 16 bit computer It was an unusual word size for the era most systems used six bit character code and used a word length of some multiple of 6 bits This changed with the effort to introduce ASCII which used a 7 bit code and naturally led to the use of an 8 bit multiple which could store a single ASCII character or two binary coded decimal digits The 16 bit word length thus became more common in the 1960s especially on minicomputer systems Early 16 bit computers c 1965 70 include the IBM 1130 3 the HP 2100 4 the Data General Nova 5 and the DEC PDP 11 6 Early 16 bit microprocessors often modeled on one of the mini platforms began to appear in the 1970s Examples c 1973 76 include the five chip National Semiconductor IMP 16 1973 7 the two chip NEC mCOM 16 1974 8 7 the three chip Western Digital MCP 1600 1975 and the five chip Toshiba T 3412 1976 7 Early single chip 16 bit microprocessors c 1975 76 include the Panafacom MN1610 1975 9 10 7 National Semiconductor PACE 1975 General Instrument CP1600 1975 Texas Instruments TMS9900 1976 7 Ferranti F100 L and the HP BPC Other notable 16 bit processors include the Intel 8086 the Intel 80286 the WDC 65C816 and the Zilog Z8000 The Intel 8088 was binary compatible with the Intel 8086 and was 16 bit in that its registers were 16 bits wide and arithmetic instructions could operate on 16 bit quantities even though its external bus was 8 bits wide 16 bit processors have been almost entirely supplanted in the personal computer industry and are used less than 32 bit or 8 bit CPUs in embedded applications 16 32 bit Motorola 68000 and Intel 386SX edit The Motorola 68000 is sometimes called 16 bit because of the way it handles basic arithmetic The instruction set was based on 32 bit numbers and the internal registers were 32 bits wide so by common definitions the 68000 is a 32 bit design Internally 32 bit arithmetic is performed using two 16 bit operations and this leads to some descriptions of the system as 16 bit or 16 32 Such solutions have a long history in the computer field with various designs performing math even one bit at a time known as serial arithmetic while most designs by the 1970s processed at least a few bits at a time A common example is the Data General Nova which was a 16 bit design that performed 16 bit math as a series of four 4 bit operations 4 bits was the word size of a widely available single chip ALU and thus allowed for inexpensive implementation Using the definition being applied to the 68000 the Nova would be a 4 bit computer or 4 16 Not long after the introduction of the Nova a second version was introduced the SuperNova which included four of the 4 bit ALUs running in parallel to perform math 16 bits at a time and therefore offer higher performance This was invisible to the user and the programs which always used 16 bit instructions and data In a similar fashion later 68000 family members starting with the Motorola 68020 had 32 bit ALUs One may also see references to systems being or not being 16 bit based on some other measure One common one is when the address space is not the same size of bits as the internal registers Most 8 bit CPUs of the 1970s fall into this category the MOS 6502 Intel 8080 Zilog Z80 and most others had 16 bit address space which provided 64 KB of address space This also meant address manipulation required two instruction cycles For this reason most processors had special 8 bit addressing modes the zero page improving speed This sort of difference between internal register size and external address size remained in the 1980s although often reversed as memory costs of the era made a machine with 32 bit addressing 2 or 4 GB a practical impossibility For example the 68000 exposed only 24 bits of addressing on the DIP limiting it to a still huge for the era 16 MB 11 A similar analysis applies to Intel s 80286 CPU replacement called the 386SX which is a 32 bit processor with 32 bit ALU and internal 32 bit data paths with a 16 bit external bus and 24 bit addressing of the processor it replaced 16 bit application editIn the context of IBM PC compatible and Wintel platforms a 16 bit application is any software written for MS DOS OS 2 1 x or early versions of Microsoft Windows which originally ran on the 16 bit Intel 8088 and Intel 80286 microprocessors Such applications used a 20 bit or 24 bit segment or selector offset address representation to extend the range of addressable memory locations beyond what was possible using only 16 bit addresses Programs containing more than 216 bytes 65 536 bytes of instructions and data therefore required special instructions to switch between their 64 kilobyte segments increasing the complexity of programming 16 bit applications List of 16 bit CPUs editThis list is incomplete you can help by adding missing items November 2021 Angstrem 1801 series CPU Data General Nova Eclipse Digital Equipment Corporation PDP 11 for LSI 11 see Western Digital below DEC J 11 DEC T 11 EnSilica eSi 1600 Fairchild Semiconductor 9440 MICROFLAME Ferranti Ferranti F100 L Ferranti F200 L General Instrument CP1600 Hewlett Packard HP 21xx 2000 1000 98xx BPC HP 3000 Honeywell Honeywell Level 6 DPS 6 IBM 1130 1800 System 7 Series 1 System 36 Infineon XE166 family C166 C167 family XC2000 Intel Intel 8086 Intel 8088 Intel 80186 Intel 80188 Intel 80286 Intel MCS 96 Lockheed MAC 16 MIL STD 1750A Motorola Motorola 68HC12 Motorola 68HC16 National Semiconductor IMP 16 PACE INS8900 NEC mCOM 16 NEC V20 and V30 Panafacom MN1610 Renesas Renesas M16C jp 16 bit registers 24 bit address space Ricoh Ricoh 5A22 WDC 65816 clone used in SNES Texas Instruments Texas Instruments TMS9900 TI MSP430 Toshiba T 3412 Western Design Center WDC 65816 65802 Western Digital MCP 1600 used in the DEC LSI 11 used in the Pascal MicroEngine used in the WD16 Xerox Alto Zilog Zilog Z8000See also editMicroprocessor 16 bit designs Influence of the IBM PC on the personal computer market Before the IBM PC s introduction 74181 key component of some early 16 bit and other CPUs Audio bit depth as 16 bit is the most common bit depth used e g on CD audio References edit Year 1951 Computer History Museum see also Year 1943 Digital Press Digital at Work Archived 2013 07 02 at the Wayback Machine Pearson 1992 ISBN 1 55558 092 0 pp 4 23 The IBM 1130 computing system IBM Archives HP 2116 Computer History Museum Data General Nova minicomputer Computer History Museum Archived from the original on 2013 05 17 Retrieved 2012 06 11 Pearson Jamie Parker September 1992 Digital at work snapshots from the first thirty five years Digital Press pp 58 61 ISBN 978 1 55558 092 6 a b c d e Belzer Jack Holzman Albert G Kent Allen 1978 Encyclopedia of Computer Science and Technology Vol 10 Linear and Matrix Algebra to Microorganisms Computer Assisted Identification CRC Press p 402 ISBN 9780824722609 1970s Development and evolution of microprocessors PDF Semiconductor History Museum of Japan Archived from the original PDF on 2019 06 27 Retrieved 2019 06 27 16 bit Microprocessors CPU Museum Retrieved 5 October 2010 History PFU Retrieved 5 October 2010 Motorola M68000 Family Programmer s Reference Manual PDF Motorola Inc 1992 sec 2 4 pp 2 21 Retrieved 2023 06 05 Retrieved from https en wikipedia org w index php title 16 bit computing amp oldid 1190825005, wikipedia, wiki, book, books, library,

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