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60-457: The main machine in the line was the GE-225 (1961). It used a 20-bit word , of which 13 bits could be used for an address . Along with the basic central processing unit (CPU) the system could also have had a floating-point unit (the "Auxiliary Arithmetic Unit"), or a fixed-point decimal option with three six-bit decimal digits per word. It had eleven I/O channel controllers , and GE sold

120-404: A power of two multiple of the unit of address resolution (byte or word). Converting the index of an item in an array into the memory address offset of the item then requires only a shift operation rather than a multiplication. In some cases this relationship can also avoid the use of division operations. As a result, most modern computer designs have word sizes (and other operand sizes) that are

180-408: A " μ " key, so it is necessary to use a key-code; this varies depending on the operating system, physical keyboard layout, and user's language. The LaTeX typesetting system features an SIunitx package in which the units of measurement are spelled out, for example, \qty{3}{\tera\hertz} formats as "3 THz". The use of prefixes can be traced back to the introduction of the metric system in

240-426: A computer architecture is designed, the choice of a word size is of substantial importance. There are design considerations which encourage particular bit-group sizes for particular uses (e.g. for addresses), and these considerations point to different sizes for different uses. However, considerations of economy in design strongly push for one size, or a very few sizes related by multiples or fractions (submultiples) to

300-486: A count field, by a delimiting character, or by an additional bit called, e.g., flag, or word mark . Such machines often use binary-coded decimal in 4-bit digits, or in 6-bit characters, for numbers. This class of machines includes the IBM 702 , IBM 705 , IBM 7080 , IBM 7010 , UNIVAC 1050 , IBM 1401 , IBM 1620 , and RCA 301. Most of these machines work on one unit of memory at a time and since each instruction or datum

360-585: A driver, in order to maintain symmetry. The prefixes from tera- to quetta- are based on the Ancient Greek or Ancient Latin numbers from 4 to 10, referring to the 4th through 10th powers of 10 . The initial letter h has been removed from some of these stems and the initial letters z , y , r , and q have been added, ascending in reverse alphabetical order, to avoid confusion with other metric prefixes. When mega and micro were adopted in 1873, there were then three prefixes starting with "m", so it

420-463: A floating point instruction can only address words while an integer arithmetic instruction can specify a field length of 1-64 bits, a byte size of 1-8 bits and an accumulator offset of 0-127 bits. In a byte-addressable machine with storage-to-storage (SS) instructions, there are typically move instructions to copy one or multiple bytes from one arbitrary location to another. In a byte-oriented ( byte-addressable ) machine without SS instructions, moving

480-454: A fresh design has to coexist as an alternative size to the original word size in a backward compatible design. The original word size remains available in future designs, forming the basis of a size family. In the mid-1970s, DEC designed the VAX to be a 32-bit successor of the 16-bit PDP-11 . They used word for a 16-bit quantity, while longword referred to a 32-bit quantity; this terminology

540-460: A number of definitions for the non-SI unit, the calorie . There are gram calories and kilogram calories. One kilogram calorie, which equals one thousand gram calories, often appears capitalised and without a prefix (i.e. Cal ) when referring to " dietary calories " in food. It is common to apply metric prefixes to the gram calorie, but not to the kilogram calorie: thus, 1 kcal = 1000 cal = 1 Cal. Metric prefixes are widely used outside

600-404: A power of two times the size of a byte. As computer designs have grown more complex, the central importance of a single word size to an architecture has decreased. Although more capable hardware can use a wider variety of sizes of data, market forces exert pressure to maintain backward compatibility while extending processor capability. As a result, what might have been the central word size in

660-401: A primary size. That preferred size becomes the word size of the architecture. Character size was in the past (pre-variable-sized character encoding ) one of the influences on unit of address resolution and the choice of word size. Before the mid-1960s, characters were most often stored in six bits; this allowed no more than 64 characters, so the alphabet was limited to upper case. Since it

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720-483: A reintroduction of compound prefixes (e.g. kiloquetta- for 10 ) if a driver for prefixes at such scales ever materialises, with a restriction that the last prefix must always be quetta- or quecto- . This usage has not been approved by the BIPM. In written English, the symbol K is often used informally to indicate a multiple of thousand in many contexts. For example, one may talk of a 40K salary ( 40 000 ), or call

780-692: A shorter word (16 or 32 bits) may be used in contexts where the range of a wider word is not needed (especially where this can save considerable stack space or cache memory space). For example, Microsoft's Windows API maintains the programming language definition of WORD as 16 bits, despite the fact that the API may be used on a 32- or 64-bit x86 processor, where the standard word size would be 32 or 64 bits, respectively. Data structures containing such different sized words refer to them as: A similar phenomenon has developed in Intel's x86 assembly language – because of

840-495: A single byte from one arbitrary location to another is typically: Individual bytes can be accessed on a word-oriented machine in one of two ways. Bytes can be manipulated by a combination of shift and mask operations in registers. Moving a single byte from one arbitrary location to another may require the equivalent of the following: Alternatively many word-oriented machines implement byte operations with instructions using special byte pointers in registers or memory. For example,

900-414: A unit by the instruction set or the hardware of the processor. The number of bits or digits in a word (the word size , word width , or word length ) is an important characteristic of any specific processor design or computer architecture . The size of a word is reflected in many aspects of a computer's structure and operation; the majority of the registers in a processor are usually word-sized and

960-435: A variable number of cycles, depending on the size of the operands. The memory model of an architecture is strongly influenced by the word size. In particular, the resolution of a memory address, that is, the smallest unit that can be designated by an address, has often been chosen to be the word. In this approach, the word-addressable machine approach, address values which differ by one designate adjacent memory words. This

1020-412: A variety of add-ons including disks, printers, and other devices. The machines were built using discrete transistors, with a typical machine containing about 10,000 transistors and 20,000 diodes. They used magnetic-core memory , and a standard 8  kiloword system held 186,000 magnetic cores. They weighed about 2,000 pounds (1.0 short ton; 910 kg). The GE-215 (1963) was a scaled-down version of

1080-497: A variety of processors, even ones with different data word lengths or different address widths or both. Metric prefix A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic . Each prefix has a unique symbol that is prepended to any unit symbol. The prefix kilo- , for example, may be added to gram to indicate multiplication by one thousand: one kilogram

1140-483: Is efficient in time and space to have the word size be a multiple of the character size, word sizes in this period were usually multiples of 6 bits (in binary machines). A common choice then was the 36-bit word , which is also a good size for the numeric properties of a floating point format. After the introduction of the IBM System/360 design, which uses eight-bit characters and supports lower-case letters,

1200-482: Is equal to one thousand grams. The prefix milli- , likewise, may be added to metre to indicate division by one thousand; one millimetre is equal to one thousandth of a metre. Decimal multiplicative prefixes have been a feature of all forms of the metric system , with six of these dating back to the system's introduction in the 1790s. Metric prefixes have also been used with some non-metric units. The SI prefixes are metric prefixes that were standardised for use in

1260-405: Is natural in machines which deal almost always in word (or multiple-word) units, and has the advantage of allowing instructions to use minimally sized fields to contain addresses, which can permit a smaller instruction size or a larger variety of instructions. When byte processing is to be a significant part of the workload, it is usually more advantageous to use the byte , rather than the word, as

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1320-461: Is several units long, each instruction takes several cycles just to access memory. These machines are often quite slow because of this. For example, instruction fetches on an IBM 1620 Model I take 8 cycles (160 μs) just to read the 12 digits of the instruction (the Model II reduced this to 6 cycles, or 4 cycles if the instruction did not need both address fields). Instruction execution takes

1380-528: Is the x86 family, of which processors of three different word lengths (16-bit, later 32- and 64-bit) have been released, while word continues to designate a 16-bit quantity. As software is routinely ported from one word-length to the next, some APIs and documentation define or refer to an older (and thus shorter) word-length than the full word length on the CPU that software may be compiled for. Also, similar to how bytes are used for small numbers in many programs,

1440-510: Is the 64-bit member of that architecture family, continues to refer to 16-bit halfword s, 32-bit word s, and 64-bit doubleword s, and additionally features 128-bit quadword s. In general, new processors must use the same data word lengths and virtual address widths as an older processor to have binary compatibility with that older processor. Often carefully written source code – written with source-code compatibility and software portability in mind – can be recompiled to run on

1500-465: Is the same as the terminology used for the PDP-11. This was in contrast to earlier machines, where the natural unit of addressing memory would be called a word , while a quantity that is one half a word would be called a halfword . In fitting with this scheme, a VAX quadword is 64 bits. They continued this 16-bit word/32-bit longword/64-bit quadword terminology with the 64-bit Alpha . Another example

1560-596: The DATANET-30 (DN-30), which was a small computer that had evolved from an earlier process-control machine. DTSS actually ran on the DN-30. The DN-30 accepted commands one at a time from the terminals connected to it, and then ran their requested programs on the GE-235. The GE-235 had no idea it was not running in batch mode , and the illusion of multitasking was being maintained externally. In 1965 GE started packaging

1620-793: The International System of Units (SI) by the International Bureau of Weights and Measures (BIPM) in resolutions dating from 1960 to 2022. Since 2009, they have formed part of the ISO/IEC 80000 standard. They are also used in the Unified Code for Units of Measure (UCUM). The BIPM specifies twenty-four prefixes for the International System of Units (SI) . The first uses of prefixes in SI date back to

1680-502: The PDP-10 byte pointer contained the size of the byte in bits (allowing different-sized bytes to be accessed), the bit position of the byte within the word, and the word address of the data. Instructions could automatically adjust the pointer to the next byte on, for example, load and deposit (store) operations. Different amounts of memory are used to store data values with different degrees of precision. The commonly used sizes are usually

1740-653: The Year 2000 problem the Y2K problem . In these cases, an uppercase K is often used with an implied unit (although it could then be confused with the symbol for the kelvin temperature unit if the context is unclear). This informal postfix is read or spoken as "thousand", "grand", or just "k". The financial and general news media mostly use m or M, b or B, and t or T as abbreviations for million, billion (10 ) and trillion (10 ), respectively, for large quantities, typically currency and population. The medical and automotive fields in

1800-534: The year , equal to exactly 31 557 600  seconds ( ⁠365 + 1  / 4 ⁠  days). The unit is so named because it was the average length of a year in the Julian calendar . Long time periods are then expressed by using metric prefixes with the annum, such as megaannum (Ma) or gigaannum (Ga). The SI unit of angle is the radian , but degrees , as well as arc-minutes and arc-seconds , see some scientific use. Common practice does not typically use

1860-437: The 11th CGPM conference in 1960. Other metric prefixes used historically include hebdo- (10 ) and micri- (10 ). Double prefixes have been used in the past, such as micromillimetres or millimicrons (now nanometres ), micromicrofarads (μμF; now picofarads , pF), kilomegatonnes (now gigatonnes ), hectokilometres (now 100  kilometres ) and the derived adjective hectokilometric (typically used for qualifying

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1920-619: The 1790s, long before the 1960 introduction of the SI. The prefixes, including those introduced after 1960, are used with any metric unit, whether officially included in the SI or not (e.g., millidyne and milligauss). Metric prefixes may also be used with some non-metric units, but not, for example, with the non-SI units of time. The units kilogram , gram , milligram , microgram, and smaller are commonly used for measurement of mass . However, megagram, gigagram, and larger are rarely used; tonnes (and kilotonnes, megatonnes, etc.) or scientific notation are used instead. The megagram does not share

1980-426: The 36-bit word being especially common on mainframe computers . The introduction of ASCII led to the move to systems with word lengths that were a multiple of 8-bits, with 16-bit machines being popular in the 1970s before the move to modern processors with 32 or 64 bits. Special-purpose designs like digital signal processors , may have any word length from 4 to 80 bits. The size of a word can sometimes differ from

2040-526: The DN-30 and GE-235 systems together as the GE-265 . The GE-265 achieved fame not only for being the first commercially successful time-sharing system, but it was also the machine on which the BASIC programming language was first created. Word (computer architecture) In computing , a word is the natural unit of data used by a particular processor design. A word is a fixed-sized datum handled as

2100-556: The GE-225, including only six I/O channels and only 4 kilowords or 8 kilowords of core. The GE-205 (1964). The GE-235 (1964) was a re-implementation of the GE-225 with three times faster memory than the original. The GE-235 consisted of several major components and options: The series was designed by a team led by Homer R. “Barney” Oldfield , and which included Arnold Spielberg (father of film director Steven Spielberg ). GE chairman Ralph J. Cordiner had forbidden GE from entering

2160-591: The Latin annus ), is commonly used with metric prefixes: ka , Ma, and Ga. Official policies about the use of SI prefixes with non-SI units vary slightly between the International Bureau of Weights and Measures (BIPM) and the American National Institute of Standards and Technology (NIST). For instance, the NIST advises that "to avoid confusion, prefix symbols (and prefix names) are not used with

2220-484: The United States use the abbreviations cc or ccm for cubic centimetres. One  cubic centimetre is equal to one  millilitre . For nearly a century, engineers used the abbreviation MCM to designate a "thousand circular mils " in specifying the cross-sectional area of large electrical cables . Since the mid-1990s, kcmil has been adopted as the official designation of a thousand circular mils, but

2280-404: The astronomical unit is mentioned in the SI standards as an accepted non-SI unit. Prefixes for the SI standard unit second are most commonly encountered for quantities less than one second. For larger quantities, the system of minutes (60 seconds), hours (60 minutes) and days (24 hours) is accepted for use with the SI and more commonly used. When speaking of spans of time,

2340-744: The definition of kilogram after the French Revolution at the end of the 18th century. Several more prefixes came into use, and were recognised by the 1947 IUPAC 14th International Conference of Chemistry before being officially adopted for the first time in 1960. The most recent prefixes adopted were ronna- , quetta- , ronto- , and quecto- in 2022, after a proposal from British metrologist Richard J. C. Brown. The large prefixes ronna- and quetta- were adopted in anticipation of needs for use in data science, and because unofficial prefixes that did not meet SI requirements were already circulating. The small prefixes were also added, even without such

2400-416: The expected due to backward compatibility with earlier computers. If multiple compatible variations or a family of processors share a common architecture and instruction set but differ in their word sizes, their documentation and software may become notationally complex to accommodate the difference (see Size families below). Depending on how a computer is organized, word-size units may be used for: When

2460-515: The flexibility allowed by official policy in the case of the degree Celsius (°C). NIST states: "Prefix symbols may be used with the unit symbol °C and prefix names may be used with the unit name degree Celsius . For example, 12 m°C (12 millidegrees Celsius) is acceptable." In practice, it is more common for prefixes to be used with the kelvin when it is desirable to denote extremely large or small absolute temperatures or temperature differences. Thus, temperatures of star interiors may be given with

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2520-480: The fuel consumption measures). These are not compatible with the SI. Other obsolete double prefixes included "decimilli-" (10 ), which was contracted to "dimi-" and standardised in France up to 1961. There are no more letters of the Latin alphabet available for new prefixes (all the unused letters are already used for units). As such, Richard J.C. Brown (who proposed the prefixes adopted for 10 and 10 ) has proposed

2580-456: The general purpose computer business, rejecting several proposals by Oldfield by simply writing "No" across them and sending them back. Oldfield, somewhat deceptively, claimed that the GE-200 series would be industrial control computers. By the time Cordiner found out otherwise, it was too late and the machine was in production; Cordiner fired Oldfield at the product rollout. Even though the machine

2640-422: The hectolitre (100 litres). Larger volumes are usually denoted in kilolitres, megalitres or gigalitres, or else in cubic metres (1 cubic metre = 1 kilolitre) or cubic kilometres (1 cubic kilometre = 1 teralitre). For scientific purposes, the cubic metre is usually used. The kilometre, metre, centimetre, millimetre, and smaller units are common. The decimetre is rarely used. The micrometre is often referred to by

2700-926: The largest datum that can be transferred to and from the working memory in a single operation is a word in many (not all) architectures. The largest possible address size, used to designate a location in memory, is typically a hardware word (here, "hardware word" means the full-sized natural word of the processor, as opposed to any other definition used). Documentation for older computers with fixed word size commonly states memory sizes in words rather than bytes or characters. The documentation sometimes uses metric prefixes correctly, sometimes with rounding, e.g., 65 kilowords (kW) meaning for 65536 words, and sometimes uses them incorrectly, with kilowords (kW) meaning 1024 words (2 ) and megawords (MW) meaning 1,048,576 words (2 ). With standardization on 8-bit bytes and byte addressability, stating memory sizes in bytes, kilobytes, and megabytes with powers of 1024 rather than 1000 has become

2760-418: The length of the day is usually standardised to 86 400  seconds so as not to create issues with the irregular leap second . Larger multiples of the second such as kiloseconds and megaseconds are occasionally encountered in scientific contexts, but are seldom used in common parlance. For long-scale scientific work, particularly in astronomy , the Julian year or annum (a) is a standardised variant of

2820-429: The metric SI system. Common examples include the megabyte and the decibel . Metric prefixes rarely appear with imperial or US units except in some special cases (e.g., microinch, kilofoot, kilopound ). They are also used with other specialised units used in particular fields (e.g., megaelectronvolt , gigaparsec , millibarn , kilodalton ). In astronomy, geology, and palaeontology, the year , with symbol 'a' (from

2880-450: The norm, although there is some use of the IEC binary prefixes . Several of the earliest computers (and a few modern as well) use binary-coded decimal rather than plain binary , typically having a word size of 10 or 12 decimal digits, and some early decimal computers have no fixed word length at all. Early binary systems tended to use word lengths that were some multiple of 6-bits, with

2940-453: The older non-SI name micron , which is officially deprecated. In some fields, such as chemistry , the ångström (0.1 nm) has been used commonly instead of the nanometre. The femtometre , used mainly in particle physics, is sometimes called a fermi . For large scales, megametre, gigametre, and larger are rarely used. Instead, ad hoc non-metric units are used, such as the solar radius , astronomical units , light years , and parsecs ;

3000-423: The prefixes formerly used in the metric system have fallen into disuse and were not adopted into the SI. The decimal prefix for ten thousand, myria- (sometimes spelt myrio- ), and the early binary prefixes double- (2×) and demi- ( ⁠ 1 / 2 ⁠ ×) were parts of the original metric system adopted by France in 1795, but were not retained when the SI prefixes were internationally adopted by

3060-477: The risk of confusion that the tonne has with other units with the name "ton". The kilogram is the only coherent unit of the International System of Units that includes a metric prefix. The litre (equal to a cubic decimetre), millilitre (equal to a cubic centimetre), microlitre, and smaller are common. In Europe, the centilitre is often used for liquids, and the decilitre is used less frequently. Bulk agricultural products, such as grain, beer and wine, often use

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3120-426: The standard size of a character (or more accurately, a byte ) becomes eight bits. Word sizes thereafter are naturally multiples of eight bits, with 16, 32, and 64 bits being commonly used. Early machine designs included some that used what is often termed a variable word length . In this type of organization, an operand has no fixed length. Depending on the machine and the instruction, the length might be denoted by

3180-590: The support for various sizes (and backward compatibility) in the instruction set, some instruction mnemonics carry "d" or "q" identifiers denoting "double-", "quad-" or "double-quad-", which are in terms of the architecture's original 16-bit word size. An example with a different word size is the IBM System/360 family. In the System/360 architecture , System/370 architecture and System/390 architecture, there are 8-bit byte s, 16-bit halfword s, 32-bit word s and 64-bit doubleword s. The z/Architecture , which

3240-440: The time-related unit symbols (names) min (minute), h (hour), d (day); nor with the angle-related symbols (names) ° (degree), ′ (minute), and ″ (second)", whereas the BIPM adds information about the use of prefixes with the symbol as for arcsecond when they state: "However astronomers use milliarcsecond, which they denote mas, and microarcsecond, μas, which they use as units for measuring very small angles." Some of

3300-415: The unit of MK (megakelvin), and molecular cooling may be given with the unit mK (millikelvin). In use the joule and kilojoule are common, with larger multiples seen in limited contexts. In addition, the kilowatt-hour , a composite unit formed from the kilowatt and hour, is often used for electrical energy; other multiples can be formed by modifying the prefix of watt (e.g. terawatt-hour). There exist

3360-438: The unit of address resolution. Address values which differ by one designate adjacent bytes in memory. This allows an arbitrary character within a character string to be addressed straightforwardly. A word can still be addressed, but the address to be used requires a few more bits than the word-resolution alternative. The word size needs to be an integer multiple of the character size in this organization. This addressing approach

3420-598: Was created, it included the " μ " symbol for micro at codepoint 0xB5 ; later, the whole of ISO 8859-1 was incorporated into the initial version of Unicode . Many fonts that support both characters render them identical, but because the micro sign and the Greek lower-case letter have different applications (normally, a Greek letter would be used with other Greek letters, but the micro sign is never used like that), some fonts render them differently, e.g. Linux Libertine and Segoe UI . Most English-language keyboards do not have

3480-520: Was necessary to use some other symbol besides upper and lowercase 'm'. Eventually the Greek letter "μ" was adopted. However, with the lack of a "μ" key on most typewriters, as well as computer keyboards, various other abbreviations remained common, including "mc", "mic", and "u". From about 1960 onwards, "u" prevailed in type-written documents. Because ASCII , EBCDIC , and other common encodings lacked code-points for " μ ", this tradition remained even as computers replaced typewriters. When ISO 8859-1

3540-503: Was selling well, Cordiner ordered that GE leave the computer business within 18 months (it actually took several years). Through the early 1960s GE worked with Dartmouth College on the development of a time-sharing operating system , which would later go on to become the Dartmouth Time-Sharing System (DTSS). The system was constructed by attaching a number of teletypewriters to a smaller GE machine called

3600-457: Was used in the IBM 360, and has been the most common approach in machines designed since then. When the workload involves processing fields of different sizes, it can be advantageous to address to the bit. Machines with bit addressing may have some instructions that use a programmer-defined byte size and other instructions that operate on fixed data sizes. As an example, on the IBM 7030 ("Stretch"),

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