Measuring unit in data processing

The following measuring units are used in Informatique to quantify the memory size of a Ordinateur, space usable on a Hard drive, the size of a file, a repertory or other.

  • Bit: basic measuring unit, its symbol is B or bit . The bit (English binary digit , “binary digit”) represents the smallest storage unit usable on a computer. This memory can take only two values, interpreted most of the time like 0 or 1. The other measuring units correspond only to regroupings of bits.

  • Word: basic unit for the operations in a processor given, according to its architecture. A processor 32 bits uses words of 32 bits. Sometimes used to say 16 bits, independently of the processor.
  • Four-bit byte or nibble: half of a byte, is four bits. (cf Guingay, Dictionary of data processing )
  • Septet: seven bits. Little used nowadays.
  • Byte: a byte is composed of eight bits. Its symbol is O . It is the current price of a byte . It can take 28, that is to say 256, possible values (from 0 to 255 or -128 to 127, according to the convention of reading).
  • Seizet : sixteen bits. See the ISO/CEI 10646 (F) and the seizets of indirection in UTF-16. On the model of byte and quarter of a crown (part of 16 worms). Little used nowadays.
  • Trente-deuxet : thirty-two bits. On the model of byte and trente-deuxain (cloth of which the chain was made up of 32 times hundred wire). Little used nowadays.
  • Rune : sixteen bits. This term was introduced to try to dissipate confusion reigning around the term “word” (English Word ), which often means 16 bits but can also be worth 32 or 64 bits according to the processor. Little used nowadays.
  • Quad : thirty-two bits. Like Rune, this term was introduced to try to dissipate confusion reigning around the term “word”. Today, it can be question of a " Quad" float, of a word in precision quadruples compared to a word of simple precision (float on 32 bits) or double (double on 64 bits). In floating number, it is about a number coded 128 bits. These terms derived from those are used by the language C.

Measuring units the speed of posting

These units are very often used in the play-videos, in order to know the fluidity of animation precisely.
  • Screens a second (tps): Many images posted in one second, also (fps).

Conventions of measurement of posting

The pixel is the smallest addressable unit on the screen (finally, almost, taking into account the easy way of the technique ClearType). The definition of a screen is expressed in width × height. By ex: 1024×768 means 1024 pixels broad on 768 pixels top.

Current definitions of the screens of Computer

Note: certain manufacturers vary the characteristics of their screens, in particular the vertical dimension of the screens 16/9 is often slightly increased with format 16/10 in order to allow the posting of a bar of tool or navigation under the image. They often omit to specify the extensions after the letters " GA" , and confuse certain nomenclatures (by specifying only the initials on their specifications, but not the effective resolution…).

Less current definitions of the screens of Computer

Units of flow

These measuring units are used to measure a flow (maximum) of information between two points of a Data-processing network.
  • measurements are generally carried out in bit/s (bits a second, bps in English) or Baud S (many symbols a second).
These units are used for the Modem S, ADSL, the ports series, the Concentrateur S, and the charts networks.

At the time of the access to a disc (CD-ROM, DVD, CD-RW, Hard drive, Diskette, Key USB), different units are perhaps used.

Units speed of treatment in floating decimal point

The speed of treatment of the part floating decimal point, known as FPU (Floating Point Links), of a processor is expressed in operations a second, FAILURES (Floating Point Per Operations Second).

  • Failures (unit)
  • Kiloflops (10^3 Failure, (1000 Failure))
  • Mégaflops (10^6 Failure, (1000 kKlop))
  • Gigaflops (10^9 Failure, (1000 MFlop))
  • Teraflops (10^12 Failure, (1000 GFlop))

Anglo-Saxon measuring units

Because of the size of the Anglo-Saxon market and dynamism of the Research and development in data processing with the the United States, dimensions are frequently expressed in Anglo-Saxon Measuring units, and in particular in inches, although this is contrary with the international standard. The French law (R.643-2 article of the Penal code) obliges the salesmen to indicate the equivalent in Mètre (or for example Centimètre), in order to guarantee information right of the Consommateur, customer (possibility of comparison).

The table opposite gives some examples of equivalence. Fact cocasse, the diskettes of “three inches and half” in fact are specified as making 90 mm (the standard is of Japanese origin) and measure actually 1/32 inch more than 3 ½.

On the other hand, the millimetre is universally adopted for the thicknesses of hard drives (9 mm, 9,5 mm, etc)

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