| Decimal | Binary | ||||||
|---|---|---|---|---|---|---|---|
| Value | SI | Value | IEC | JEDEC | |||
| 1000 | k | kilo | 1024 | Ki | kibi | K | kilo |
| 10002 | M | mega | 10242 | Mi | mebi | M | mega |
| 10003 | G | giga | 10243 | Gi | gibi | G | giga |
| 10004 | T | tera | 10244 | Ti | tebi | T | tera |
| 10005 | P | peta | 10245 | Pi | pebi | — | |
| 10006 | E | exa | 10246 | Ei | exbi | — | |
| 10007 | Z | zetta | 10247 | Zi | zebi | — | |
| 10008 | Y | yotta | 10248 | Yi | yobi | — | |
| 10009 | R | ronna | 10249 | Ri | robi | — | |
| 100010 | Q | quetta | 102410 | Qi | quebi | — | |
Abinary prefix is aunit prefix that indicates amultiple of aunit of measurement by an integerpower of two. The most commonly used binary prefixes arekibi (symbol Ki, meaning210 = 1024),mebi (Mi, 220 =1048576), andgibi (Gi, 230 =1073741824). They are most often used ininformation technology as multipliers ofbit andbyte, when expressing the capacity ofstorage devices or the size of computerfiles.
The binary prefixes "kibi", "mebi", etc. were defined in 1999 by theInternational Electrotechnical Commission (IEC), in theIEC 60027-2standard (Amendment 2). They were meant to replace themetric (SI)decimal power prefixes, such as "kilo" (k, 103 = 1000), "mega" (M, 106 =1000000) and "giga" (G, 109 =1000000000),[1] that were commonly used in the computer industry to indicate the nearest powers of two. For example, a memory module whose capacity was specified by the manufacturer as "2 megabytes" or "2 MB" would hold2 × 220 =2097152 bytes, instead of2 × 106 =2000000.
On the other hand, a hard disk whose capacity is specified by the manufacturer as "10 gigabytes" or "10 GB", holds10 × 109 =10000000000 bytes, or a little more than that, but less than10 × 230 =10737418240 and a file whose size is listed as "2.3 GB" may have a size closer to2.3 × 230 ≈2470000000 or to2.3 × 109 =2300000000, depending on theprogram oroperating system providing that measurement. This kind of ambiguity is often confusing to computer system users and has resulted inlawsuits.[2][3] The IEC 60027-2 binary prefixes have been incorporated in theISO/IEC 80000 standard and are supported by other standards bodies, including theBIPM, which defines the SI system,[1]: p.121 theUSNIST,[4][5] and theEuropean Union.
Prior to the 1999 IEC standard, some industry organizations, such as theJoint Electron Device Engineering Council (JEDEC), noted the common use of the termskilobyte,megabyte, andgigabyte, and the corresponding symbolsKB,MB, andGB in the binary sense, for use in storage capacity measurements. However, other computer industry sectors (such asmagnetic storage) continued using those same terms and symbols with the decimal meaning. Since then, the major standards organizations have expressly disapproved the use of SI prefixes to denote binary multiples, and recommended or mandated the use of the IEC prefixes for that purpose, but the use of SI prefixes in this sense has persisted in some fields.
| IEC prefix | Representations | ||||
|---|---|---|---|---|---|
| Name | Symbol | Base 2 | Base 1024 | Value | Base 10 |
| kibi | Ki | 210 | 10241 | 1024 | =1.024×103 |
| mebi | Mi | 220 | 10242 | 1048576 | ≈1.049×106 |
| gibi | Gi | 230 | 10243 | 1073741824 | ≈1.074×109 |
| tebi | Ti | 240 | 10244 | 1099511627776 | ≈1.100×1012 |
| pebi | Pi | 250 | 10245 | 1125899906842624 | ≈1.126×1015 |
| exbi | Ei | 260 | 10246 | 1152921504606846976 | ≈1.153×1018 |
| zebi | Zi | 270 | 10247 | 1180591620717411303424 | ≈1.181×1021 |
| yobi | Yi | 280 | 10248 | 1208925819614629174706176 | ≈1.209×1024 |
| robi | Ri | 290 | 10249 | 1237940039285380274899124224 | ≈1.238×1027 |
| quebi | Qi | 2100 | 102410 | 1267650600228229401496703205376 | ≈1.268×1030 |
In 2022, theInternational Bureau of Weights and Measures (BIPM) adopted the decimal prefixesronna for 10009 andquetta for 100010.[6][7] In 2025, the prefixesrobi (Ri, 10249) andquebi (Qi, 102410) were adopted by the IEC.[8]
The relative difference between the values in the binary and decimal interpretations increases, when using the SI prefixes as the base, from 2.4% for kibi vs. kilo to nearly 27% for the quebi vs. quetta.
| Prefix | Binary ÷ Decimal | Decimal ÷ Binary | |||
|---|---|---|---|---|---|
| kilo | kibi | 1.024 (+2.4%) | 0.9766 (−2.3%) | ||
| mega | mebi | 1.049 (+4.9%) | 0.9537 (−4.6%) | ||
| giga | gibi | 1.074 (+7.4%) | 0.9313 (−6.9%) | ||
| tera | tebi | 1.100 (+10.0%) | 0.9095 (−9.1%) | ||
| peta | pebi | 1.126 (+12.6%) | 0.8882 (−11.2%) | ||
| exa | exbi | 1.153 (+15.3%) | 0.8674 (−13.3%) | ||
| zetta | zebi | 1.181 (+18.1%) | 0.8470 (−15.3%) | ||
| yotta | yobi | 1.209 (+20.9%) | 0.8272 (−17.3%) | ||
| ronna | robi | 1.238 (+23.8%) | 0.8078 (−19.2%) | ||
| quetta | quebi | 1.268 (+26.8%) | 0.7889 (−21.1%) | ||
There are severalnumeral prefixes in the English language that are binary prefixes, such assemi-,hemi-,di-,tetra- andocto-.
The originalmetric system adopted by France in 1795 included two binary prefixes nameddouble- (2×) anddemi- (1/2×).[9] However, these were not retained when theSI prefixes were internationally adopted by the 11thCGPM conference in 1960.
Early computers used one of two addressing methods to access the system memory; binary (base 2) or decimal (base 10).[10] For example, theIBM 701 (1952) used a binary methods and could address 2048words of 36bits each, while theIBM 702 (1953) used a decimal system, and could address ten thousand 7-bit words.
By the mid-1960s, binary addressing had become the standard architecture in most computer designs, and main memory sizes were most commonly powers of two. This is the most natural configuration for memory, as all combinations of states of theiraddress lines map to a valid address, allowing easy aggregation into a larger block of memory with contiguous addresses.
While early documentation specified those memory sizes as exact numbers such as 4096, 8192, or16384 units (usuallywords, bytes, or bits), computer professionals also started using the long-established metric system prefixes "kilo", "mega", "giga", etc., defined to be powers of 10,[1] to mean instead the nearest powers of two; namely, 210 = 1024, 220 = 10242, 230 = 10243, etc.[11][12] The corresponding metric prefix symbols ("k", "M", "G", etc.) were used with the same binary meanings.[13][14] The symbol for 210 = 1024 could be written either in lower case ("k")[15][16][17] or in uppercase ("K"). The latter was often used intentionally to indicate the binary rather than decimal meaning.[18] This convention, which could not be extended to higher powers, was widely used in the documentation of theIBM 360 (1964)[18] and of theIBM System/370 (1972),[19] of theCDC 7600,[20] of the DECPDP-11/70 (1975)[21] and of the DECVAX-11/780 (1977).[citation needed]
In other documents, however, the metric prefixes and their symbols were used to denote powers of 10, but usually with the understanding that the values given were approximate, often truncated down. Thus, for example, a 1967 document byControl Data Corporation (CDC) abbreviated "216 =64 × 1024 =65536 words" as "65K words" (rather than "64K" or "66K"),[22] while the documentation of theHP 21MX real-time computer (1974) denoted3 × 216 =192 × 1024 =196608 as "196K" and 220 =1048576 as "1M".[23]
These three possible meanings of "k" and "K" ("1024", "1000", or "approximately 1000") were used loosely around the same time, sometimes by the same company. TheHP 3000 business computer (1973) could have "64K", "96K", or "128K" bytes of memory.[24] The use of SI prefixes, and the use of "K" instead of "k" remained popular in computer-related publications well into the 21st century, although the ambiguity persisted. The correct meaning was often clear from the context; for instance, in a binary-addressed computer, the true memory size had to be either a power of 2, or a small integer multiple thereof. Thus a "512 megabyte" RAM module was generally understood to have512 × 10242 =536870912 bytes, rather than512000000.
In specifying disk drive capacities, manufacturers have always used conventional decimal SI prefixes representing powers of 10. Storage in a rotatingdisk drive is organized in platters and tracks whose sizes and counts are determined by mechanical engineering constraints so that the capacity of a disk drive has hardly ever been a simple multiple of a power of 2. For example, the first commercially sold disk drive, theIBM 350 (1956), had 50 physical disk platters containing a total of50000 sectors of 100 characters each, for a total quoted capacity of 5 million characters.[25]
Moreover, since the 1960s, many disk drives used IBM'sdisk format, where each track was divided into blocks of user-specified size; and the block sizes were recorded on the disk, subtracting from the usable capacity. For example, the IBM 3336 disk pack was quoted to have a 200-megabyte capacity, achieved only with a single13030-byte block in each of its 808 × 19 tracks.
Decimal megabytes were used for disk capacity by the CDC in 1974.[26] The SeagateST-412,[27] one of several types installed in theIBM PC/XT,[28] had a capacity of10027008 bytes when formatted as 306 × 4 tracks and 32 256-byte sectors per track, which was quoted as "10 MB".[29] Similarly, a "300 GB" hard drive can be expected to offer only slightly more than300×109 =300000000000, bytes, not300 × 230 (which would be about322×109 bytes or "322 GB"). The first terabyte (SI prefix,1000000000000 bytes) hard disk drive was introduced in 2007.[30] Decimal prefixes were generally used by information processing publications when comparing hard disk capacities.[31]
Some programs and operating systems, such asMicrosoft Windows, still use "MB" and "GB" to denote binary prefixes even when displaying disk drive capacities and file sizes, as didClassic Mac OS. Thus, for example, the capacity of a "10 MB" (decimal "M") disk drive could be reported as "9.56 MB", and that of a "300 GB" drive as "279.4 GB". Some operating systems, such asMac OS X,[32]Ubuntu,[33] andDebian,[34] have been updated to use "MB" and "GB" to denote decimal prefixes when displaying disk drive capacities and file sizes. Some manufacturers, such asSeagate Technology, have released recommendations stating that properly-written software and documentation should specify clearly whether prefixes such as "K", "M", or "G" mean binary or decimal multipliers.[35][36]
Floppy disks useda variety of formats, and their capacities were usually specified with SI-like prefixes "K" and "M" with either decimal or binary meaning. The capacity of the disks was often specified without accounting for the internalformatting overhead, leading to more irregularities.
The early 8-inch diskette formats could contain less than a megabyte with the capacities of those devices specified in kilobytes, kilobits or megabits.[37][38]
The 5.25-inch diskette sold with theIBM PC AT could hold1200 × 1024 =1228800 bytes, and thus was marketed as "1200 KB" with the binary sense of "KB".[39] However, the capacity was also quoted "1.2 MB",[40] which was a hybrid decimal and binary notation, since the "M" meant 1000 × 1024. The precise value was1.2288 MB (decimal) or1.171875 MiB (binary).
The 5.25-inchApple Disk II had 256 bytes per sector, 13 sectors per track, 35 tracks per side, or a total capacity of116480 bytes. It was later upgraded to 16 sectors per track, giving a total of140 × 210 =143360 bytes, which was described as "140KB" using the binary sense of "K".
The most recent version of the physical hardware, the "3.5-inch diskette" cartridge, had 720 512-byte blocks (single-sided). Since two blocks comprised 1024 bytes, the capacity was quoted "360 KB", with the binary sense of "K". On the other hand, the quoted capacity of "1.44 MB" of the High Density ("HD") version was again a hybrid decimal and binary notation, since it meant 1440 pairs of 512-byte sectors, or1440 × 210 =1474560 bytes. Some operating systems displayed the capacity of those disks using the binary sense of "MB", as "1.4 MB" (which would be1.4 × 220 ≈1468000 bytes). User complaints forced both Apple[citation needed] and Microsoft[41] to issue support bulletins explaining the discrepancy.
When specifying the capacities of opticalcompact discs, "megabyte" and "MB" usually meant 10242 bytes. Thus a "700-MB" (or "80-minute") CD has a nominal capacity of about700 MiB, which is approximately730 MB (decimal).[42]
On the other hand, capacities of otheroptical disc storage media likeDVD,Blu-ray Disc,HD DVD andmagneto-optical (MO) have been generally specified in decimal gigabytes ("GB"), that is, 10003 bytes. In particular, a typical "4.7 GB" DVD has a nominal capacity of about4.7×109 bytes, which is about4.38 GiB.[43]
Tape drive and media manufacturers have generally used SI decimal prefixes to specify the maximum capacity,[44][45] although the actual capacity would depend on theblock size used when recording.
Computerclock frequencies are always quoted using SI prefixes in their decimal sense. For example, the internal clock frequency of the originalIBM PC was4.77 MHz, that is4770000 Hz.
Similarly, digital information transfer rates are quoted using decimal prefixes. TheParallel ATA "100 MB/s" disk interface can transfer100000000 bytes per second, and a "56 Kb/s" modem transmits56000 bits per second. Seagate specified the sustained transfer rate of some hard disk drive models with both decimal and IEC binary prefixes.[35] The standard sampling rate of musiccompact disks, quoted as44.1 kHz, is indeed44100 samples per second.[citation needed] A "1 Gb/s"Ethernet interface can receive or transmit up to 109 bits per second, or125000000 bytes per second within each packet. A "56k" modem can encode or decode up to56000 bits per second.
Decimal SI prefixes are also generally used forprocessor-memory data transfer speeds. APCI-X bus with66 MHz clock and 64 bits wide can transfer66000000 64-bit words per second, or4224000000 bit/s =528000000 B/s, which is usually quoted as528 MB/s. APC3200 memory on adouble data rate bus, transferring 8 bytes per cycle with a clock speed of200 MHz has a bandwidth of200000000 × 8 × 2 =3200000000 B/s, which would be quoted as3.2 GB/s.
The ambiguous usage of the prefixes "kilo ("K" or "k"), "mega" ("M"), and "giga" ("G"), as meaning both powers of 1000 or (in computer contexts) of 1024, has been recorded in popular dictionaries,[46][47][48] and even in some obsolete standards, such asANSI/IEEE 1084-1986[49] andANSI/IEEE 1212-1991,[50]IEEE 610.10-1994,[51] andIEEE 100-2000.[52] Some of these standards specifically limited the binary meaning to multiples of "byte" ("B") or "bit" ("b").
Before the IEC standard, several alternative proposals existed for unique binary prefixes, starting in the late 1960s. In 1996,Markus Kuhn proposed the extra prefix "di" and the symbolsuffix orsubscript "2" to mean "binary"; so that, for example, "one dikilobyte" would mean "1024 bytes", denoted "K2B" or "K2B".[53]
In 1968, Donald Morrison proposed to use the Greek letter kappa (κ) to denote 1024, κ2 to denote 10242, and so on.[54] (At the time, memory size was small, and only K was in widespread use.) In the same year,Wallace Givens responded with a suggestion to use bK as an abbreviation for 1024 and bK2 or bK2 for 10242, though he noted that neither the Greek letter nor lowercase letter b would be easy to reproduce on computer printers of the day.[55]Bruce Alan Martin ofBrookhaven National Laboratory proposed that, instead of prefixes, binary powers of two were indicated by the letterB followed by the exponent, similar toE indecimal scientific notation. Thus one would write 3B20 for3 × 220.[56] This convention is still used on some calculators to present binary floating point-numbers today.[57]
In 1969,Donald Knuth, who uses decimal notation like 1 MB = 1000 kB,[58] proposed that the powers of 1024 be designated as "large kilobytes" and "large megabytes", with abbreviations KKB and MMB.[59]
The ambiguous meanings of "kilo", "mega", "giga", etc., has caused significantconsumer confusion, especially in thepersonal computer era. A common source of confusion was the discrepancy between the capacities of hard drives specified by manufacturers, using those prefixes in the decimal sense, and the numbers reported by operating systems and other software, that used them in the binary sense, such as theApple Macintosh in 1984. For example, a hard drive marketed as "1 TB" could be reported as having only "931 GB". The confusion was compounded by fact that RAM manufacturers used the binary sense too.
The different interpretations of disk size prefixes led to class action lawsuits against digital storage manufacturers. These cases involved both flash memory and hard disk drives.
Early cases (2004–2007) were settled prior to any court ruling with the manufacturers admitting no wrongdoing but agreeing to clarify the storage capacity of their products on the consumer packaging. Accordingly, many flash memory and hard disk manufacturers have disclosures on their packaging and web sites clarifying the formatted capacity of the devices or defining MB as 1 million bytes and 1 GB as 1 billion bytes.[60][61][62][63]
On 20 February 2004,Willem Vroegh filed a lawsuit against Lexar Media, Dane–Elec Memory,Fuji Photo Film USA,Eastman Kodak Company, Kingston Technology Company, Inc.,Memorex Products, Inc.;PNY Technologies Inc.,SanDisk Corporation,Verbatim Corporation, andViking Interworks alleging that their descriptions of the capacity of theirflash memory cards were false and misleading.
Vroegh claimed that a 256 MB Flash Memory Device had only 244 MB of accessible memory. "Plaintiffs allege that Defendants marketed the memory capacity of their products by assuming that one megabyte equals one million bytes and one gigabyte equals one billion bytes." The plaintiffs wanted the defendants to use the customary values of 10242 for megabyte and 10243 for gigabyte. The plaintiffs acknowledged that the IEC and IEEE standards define a MB as one million bytes but stated that the industry has largely ignored the IEC standards.[64]
The parties agreed that manufacturers could continue to use the decimal definition so long as the definition was added to the packaging and web sites.[65] The consumers could apply for "a discount of ten percent off a future online purchase from Defendants' Online Stores Flash Memory Device".[66]
On 7 July 2005, an action entitledOrin Safier v.Western Digital Corporation, et al. was filed in the Superior Court for the City and County of San Francisco, Case No. CGC-05-442812. The case was subsequently moved to the Northern District of California, Case No. 05-03353 BZ.[67]
Although Western Digital maintained that their usage of units is consistent with "the indisputably correct industry standard for measuring and describing storage capacity", and that they "cannot be expected to reform the software industry", they agreed to settle in March 2006 with 14 June 2006 as the Final Approval hearing date.[68]
Western Digital offered to compensate customers with agratis download of backup and recovery software that they valued at US$30. They also paid$500000 in fees and expenses to San Francisco lawyers Adam Gutride and Seth Safier, who filed the suit. The settlement called for Western Digital to add a disclaimer to their later packaging and advertising.[69][70][71]Western Digital had this footnote in their settlement. "Apparently, Plaintiff believes that he could sue an egg company for fraud for labeling a carton of 12 eggs a 'dozen', because some bakers would view a 'dozen' as including 13 items."[72]
A lawsuit (Cho v. Seagate Technology (US) Holdings, Inc., San Francisco Superior Court, Case No. CGC-06-453195) was filed againstSeagate Technology, alleging that Seagate overrepresented the amount of usable storage by 7% on hard drives sold between 22 March 2001 and 26 September 2007. The case was settled without Seagate admitting wrongdoing, but agreeing to supply those purchasers with gratisbackup software or a 5% refund on the cost of the drives.[73]
On 22 January 2020, the district court of the Northern District of California ruled in favor of the defendant,SanDisk, upholding its use of "GB" to mean1000000000 bytes.[2] TheNinth Circuit affirmed in February 2021.[3]
In 1995, theInternational Union of Pure and Applied Chemistry's (IUPAC) Interdivisional Committee on Nomenclature and Symbols (IDCNS) proposed the prefixes "kibi" (short for "kilobinary"), "mebi" ("megabinary"), "gibi" ("gigabinary") and "tebi" ("terabinary"), with respective symbols "kb", "Mb", "Gb" and "Tb",[74] for binary multipliers. The proposal suggested that the SI prefixes should be used only for powers of 10; so that a disk drive capacity of "500 gigabytes", "0.5 terabytes", "500 GB", or "0.5 TB" should all mean500×109 bytes, exactly or approximately, rather than500 × 230 (= 536870912000) or0.5 × 240 (= 549755813888).
The proposal was not accepted by IUPAC at the time, but was taken up in 1996 by theInstitute of Electrical and Electronics Engineers (IEEE) in collaboration with theInternational Organization for Standardization (ISO) andInternational Electrotechnical Commission (IEC). The prefixes "kibi", "mebi", "gibi" and "tebi" were retained, but with the symbols "Ki" (with capital "K"), "Mi", "Gi" and "Ti" respectively.[75]
In January 1999, the IEC published this proposal, with additional prefixes "pebi" ("Pi") and "exbi" ("Ei"), as an international standard (IEC 60027-2 Amendment 2)[76][77][78] The standard reaffirmed the BIPM's position that the SI prefixes should always denote powers of 10. The third edition of the standard, published in 2005, added prefixes "zebi" and "yobi", thus matching all then-defined SI prefixes with binary counterparts.[79]
The harmonizedISO/IECIEC 80000-13:2025 standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005 (those defining prefixes for binary multiples). The only significant change is the addition of explicit definitions for some quantities.[80] In 2009, the prefixes kibi-, mebi-, etc. were defined byISO 80000-1 in their own right, independently of the kibibyte, mebibyte, and so on.
The BIPM standard JCGM 200:2012 "International vocabulary of metrology – Basic and general concepts and associated terms (VIM), 3rd edition" lists the IEC binary prefixes and states "SI prefixes refer strictly to powers of 10, and should not be used for powers of 2. For example, 1 kilobit should not be used to represent1024 bits (210 bits), which is 1 kibibit."[81]
The IEC 60027-2 standard recommended operating systems and other software were updated to use binary or decimal prefixes consistently, but incorrect usage of SI prefixes for binary multiples is still common. At the time, the IEEE decided that their standards would use the prefixes "kilo", etc. with their metric definitions, but allowed the binary definitions to be used in an interim period as long as such usage was explicitly pointed out on a case-by-case basis.[82]
The IEC standard binary prefixes are supported by other standardization bodies and technical organizations.
The United StatesNational Institute of Standards and Technology (NIST) supports the ISO/IEC standards for"Prefixes for binary multiples" and has a web page[83] documenting them, describing and justifying their use. NIST suggests that in English, the first syllable of the name of the binary-multiple prefix should be pronounced in the same way as the first syllable of the name of the corresponding SI prefix, and that the second syllable should be pronounced asbee.[5] NIST has stated the SI prefixes "refer strictly to powers of 10" and that the binary definitions "should not be used" for them.[84]
As of 2014, the microelectronics industry standards bodyJEDEC describes the IEC prefixes in its online dictionary, but acknowledges that the SI prefixes and the symbols "K", "M" and "G" are still commonly used with the binary sense for memory sizes.[85][86]
On 19 March 2005, the IEEE standardIEEE 1541-2002 ("Prefixes for Binary Multiples") was elevated to a full-use standard by theIEEE Standards Association after a two-year trial period.[87][88] as of April 2008[update], the IEEE Publications division does not require the use of IEC prefixes in its major magazines such asSpectrum[89] orComputer.[90]
TheInternational Bureau of Weights and Measures (BIPM), which maintains theInternational System of Units (SI), expressly prohibits the use of SI prefixes to denote binary multiples, and recommends the use of the IEC prefixes as an alternative since units of information are not included in the SI.[91][1]
TheSociety of Automotive Engineers (SAE) prohibits the use of SI prefixes with anything but a power-of-1000 meaning, but does not cite the IEC binary prefixes.[92]
The European Committee for Electrotechnical Standardization (CENELEC) adopted the IEC-recommended binary prefixes via the harmonization document HD 60027-2:2003-03.[93] The European Union (EU) has required the use of the IEC binary prefixes since 2007.[94]
Some computer industry participants, such as Hewlett-Packard (HP),[95] and IBM[96][97] have adopted or recommended IEC binary prefixes as part of their general documentation policies.
As of 2023, the use of SI prefixes with the binary meanings is still prevalent for specifying the capacity of themain memory of computers, ofRAM,ROM,EPROM, andEEPROMchips andmemory modules, and of thecache ofcomputer processors. For example, a "512-megabyte" or "512 MB" memory module holds 512 MiB; that is, 512 × 220 bytes, not 512 × 106 bytes.[98][99][100][101]
JEDEC continues to include the customary binary definitions of "kilo", "mega", and "giga" in the documentTerms, Definitions, and Letter Symbols,[102] and, as of 2010[update], still used those definitions in theirmemory standards.[103][104][105][106][107]
On the other hand, the SI prefixes with powers of ten meanings are generally used for the capacity of external storage units, such asdisk drives,[108][109][110][111][112]solid state drives, andUSB flash drives,[63] except for someflash memory chips intended to be used asEEPROMs. However, some disk manufacturers have used the IEC prefixes to avoid confusion.[113] The decimal meaning of SI prefixes is usually also intended in measurements of data transfer rates, and clock speeds.[citation needed]
Some operating systems and other software use either the IEC binary multiplier symbols ("Ki", "Mi", etc.)[114][115][116][117][118][119] or the SI multiplier symbols ("k", "M", "G", etc.) with decimal meaning. Some programs, such as theGNUls command, let the user choose between binary or decimal multipliers. However, some continue to use the SI symbols with the binary meanings, even when reporting disk or file sizes. Some programs may also use "K" instead of "k", with either meaning.[120]
While the binary prefixes are predominantly used with units of data, bits and bytes, they may be used with other unit of measure. For example, insignal processing it may be convenient to use a binary prefix with the unit of frequency,hertz (Hz), to produce a unit such as thekibihertz (KiHz), which is equal to1024 Hz,[121][122] or mebihertz (MiHz), equal to1048576 Hz.[123]
[Side note:] These SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The IEC has adopted prefixes for binary powers in the international standard IEC 60027-2: 2005, third edition,Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics. The names and symbols for the prefixes corresponding to 210, 220, 230, 240, 250, and 260 are, respectively: kibi, Ki; mebi, Mi; gibi, Gi; tebi, Ti; pebi, Pi; and exbi, Ei. Thus, for example, one kibibyte would be written: 1 KiB = 210 B = 1024 B, where B denotes a byte. Although these prefixes are not part of the SI, they should be used in the field of information technology to avoid the incorrect usage of the SI prefixes.
Art. 8. Dans les poids et mesures de capacité, chacune des mesures décimales de ces deux genres aura son double et sa moitié, afin de donner à la vente des divers objets toute la commodité que l'on peut désirer. Il y aura donc le double-litre et le demi-litre, le double-hectogramme et le demi-hectogramme, et ainsi des autres.[Art. 8. In the weights and measures of capacity, each of the decimal measures of these two kinds will have its double and its half, in order to give to the sale of the various articles all the convenience that one can desire. There will therefore be the double-litre and the half-litre, the double-hectogram and the half-hectogram, and so on.]
Of 187 different relevant systems, 131 utilize a straight binary system internally, whereas 53 utilize the decimal system (primarily binary coded decimal) and 3 systems utilize a binary coded alphanumeric system of notation.This lengthy report describes many of the early computers.
Also, random access devices are advantageous over serial access devices for backing store applications only when the memory capacity is less than 1 Mbyte. For capacities of 4 Mbyte and 16 Mbyte serial access stores with shift register lengths of 256 bit and 1024 bit, respectively, look favorable.
On a 32K core size 704 computer, approximately28000 data may be analyzed, ... without resorting to auxiliary tape storage.Note: the IBM 704 core memory units had 4096 36-bit words. Up to32768 words could be installed
In computing and storage systems, a kB (kiloByte) is actually 1,024 (2^10) bytes, since the measurement is based on a base 2, or binary, number system. The term kB comes from the fact that 1,024 is nominally, or approximately, 1,000.
kB (kilobyte; actually 1024 bytes) KB (kilobyte; kB is preferred)
when describing the performance of IT systems the larger units 'kilobytes' (kB) [...] Strictly speaking, k means the 'binary thousand' 1024
All-monolithic storage ... (1024-bit NMOS) This new improvement of processor storage makes system expansion more economical. Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes.
One type, designated as the small core memory (SCM) is a many bank coincident current type memory with a total of 64K words of 60 bit length (K=1024).
memory size (8k bytes to 4 megabytes).
Central Memory is organized into 32K, 65K, or 131K words (60-bit) in 8, 16, or 32 banks of 4096 words each.
196K-word memory size
CDS 100 ... stores over 600 kilobits, Model 650 ... store 1.5 megabits ...
kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 210, or 1024. mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 220, or 1048576.
Kbyte. Kilobyte. Indicates 210 bytes. Mbyte. Megabyte. Indicates 220bytes. Gbyte is used in the Foreword.
gigabyte (gig, GB). This term may mean either a)1000000000 bytes or b) 230 bytes. ... As used in this document, the terms kilobyte (kB) means 210 or 1024 bytes, megabyte (MB) means 1024 kilobytes, and gigabyte (GB) means 1024 megabytes.
[...] the industry-standard definition of a megabyte (MByte) for flash devices is one million (1,000,000) bytes, where the operating system uses two to the twentieth power, or 1,048,576 bytes. Similarly, for a gigabyte (GByte), the number is 1,000,000,000 and 1,073,741,824 respectively.
The definitions of kilo, giga, and mega based on powers of two are included only to reflect common usage.
These devices contain the following number of bits: 4Gb has 4,294,967,296 bits ... 32Gb has 34,359,738,368 bitsFree registration required to download the standard.
This standard is prepared with two goals in mind: (1) to preserve the SI prefixes as unambiguous decimal multipliers and (2) to provide alternative prefixes for those cases where binary multipliers are needed. The first goal affects the general public, the wide audience of technical and nontechnical persons who use computers without much concern for their construction or inner working. These persons will normally interpret kilo, mega, etc., in their proper decimal sense. The second goal speaks to specialists – the prefixes for binary multiples make it possible for persons who work in the information sciences to communicate with precision.
1541-2002 (SCC14) IEEE Trial-Use Standard for Prefixes for Binary Multiples[No negative comments received during trial-use period, which is now complete; Sponsor requests elevation of status to full-use.]Recommendation: Elevate status of standard from trial-use to full-use. Editorial staff will be notified to implement the necessary changes. The standard will be due for a maintenance action in 2007.
The definitions of kilo, giga, and mega based on powers of two are included only to reflect common usage. IEEE/ASTM SI 10-1997 states "This practice frequently leads to confusion and is deprecated."(Requires free registration and login.)
When the Linux kernel boots and sayshda: 120064896 sectors (61473 MB) w/2048KiB Cache the MB are megabytes and the KiB are kibibytes.