Nibble (data-processing)

A nibble (or, more rarely nybble ) is, in Informatique, an aggregate of 4 bits, that is to say a half byte. A nibble containing 4 bits, it can take sixteen (2⁴) different values and thus corresponds to only one figure Hexadécimal, from where its other name of hex digit or hexit ). Two hexadecimal digits forming a byte, this last is often represented by two nibble . One finds also the " terms; semioctet" or " quartet" in the fields of the network or Telecommunication S. In certain languages, one can also meet tetrad Greek will tetra (" quatre").

To nibble means to nibble, to corrode. That comes owing to the fact that in English, byte is a pun and drift of the word cock (bite). A nibble is a " small byte (byte) " just like nibbling is a small bite. Nybble takes again Y of byte and not the I of cock.

The nibble is used, in the Mainframe S of IBM, for the representation Décimal E of a figure. A byte is thus divided there into two and each nibble represents a figure, with share the last which represents the sign. A signed variable being able to contain to 9 digits will thus be contained in 5 bytes. That makes it possible to reduce the memory size of the variables, accelerates calculations and facilitates the débugage. This last point is explained simply: at the time of the débugage, the reading of the memory generally being done into hexadecimal, the numbers used there appear directly without least conversion not being necessary.

The term nybble was also used to indicate any group of less than 8 bits, not inevitably 4. It was the case, inter alia, of the computers of the range APPLE II. The majority of the disk players used on these machines were controlled logiciellement. The writing of the data was made there by page of 256 bytes converted into nibbles of 5 bits and, in the more recent machines, of 6 bits. Reading being done by carrying out opposite conversion. It should be noted that the term byte , often translated by byte , does not contain 8 bits inevitably. Nevertheless, the terms bytes and nibble represent today only seldom groupings other than those of 8 and 4 bits.

See too

Decimal coded into binary

References

Microprocessors and DIGITAL Systems , D.V. Hall, 1980, McGraw-Hill, Inc..

External bonds

Computer Maths Forum
Apple Assembly Line, May [[1981], Volume 1, Number 8]

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