In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...
, a nibble
(occasionally nybble, nyble, or nybl to match the spelling of
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
) is a four-
bit aggregation,
or half an
octet
Octet may refer to:
Music
* Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble
** String octet, a piece of music written for eight string instruments
*** Octet (Mendelssohn), 1825 com ...
. It is also known as half-byte
or tetrade.
In a
networking
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematic ...
or
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...
context, the nibble is often called a semi-octet,
quadbit,
or quartet.
A nibble has sixteen () possible values. A nibble can be represented by a single
hexadecimal digit (–) and called a hex digit.
A full
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
(octet) is represented by two hexadecimal digits (–); therefore, it is common to display a byte of information as two nibbles. Sometimes the set of all
256-byte values is represented as a table, which gives easily readable hexadecimal codes for each value.
Four-bit
In computer architecture, 4-bit integers, or other data units are those that are 4 bits wide. Also, 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, or data buses of that si ...
computer architectures use groups of four bits as their fundamental unit. Such architectures were used in early
microprocessor
A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...
s,
pocket calculators and
pocket computer
A pocket computer was a 1980s-era user programmable calculator-sized computer that had fewer screen lines,
Some had only one line and often fewer characters per line, than the Pocket-sized computers introduced beginning in 1989. Manufacturers in ...
s. They continue to be used in some
microcontrollers. In this context, 4-bit groups were sometimes also called ''
character
Character or Characters may refer to:
Arts, entertainment, and media Literature
* ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk
* ''Characters'' (Theophrastus), a classical Greek set of character sketches attributed to The ...
s''
rather than nibbles.
History
The term ''nibble'' originates from its representing "half a byte", with ''byte'' a
homophone
A homophone () is a word that is pronounced the same (to varying extent) as another word but differs in meaning. A ''homophone'' may also differ in spelling. The two words may be spelled the same, for example ''rose'' (flower) and ''rose'' (pa ...
of the
English
English usually refers to:
* English language
* English people
English may also refer to:
Peoples, culture, and language
* ''English'', an adjective for something of, from, or related to England
** English national ...
word ''bite''.
In 2014, David B. Benson, a professor emeritus at
Washington State University, remembered that he playfully used (and may have possibly coined) the term ''nibble'' as "half a byte" and unit of storage required to hold a
binary-coded decimal (BCD) decimal digit around 1958, when talking to a programmer of
Los Alamos Scientific Laboratory. The alternative spelling ''nybble'' reflects the spelling of ''byte'', as noted in editorials of ''
Kilobaud'' and ''
Byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
'' in the early 1980s. Another early recorded use of the term ''nybble'' was in 1977 within the consumer-banking technology group at Citibank. It created a pre-
ISO 8583 standard for transactional messages between
cash machines and Citibank's
data centers that used the basic informational unit 'NABBLE'.
The nibble is used to describe the amount of memory used to store a digit of a number stored in
packed decimal format (BCD) within an IBM mainframe. This technique is used to make computations faster and debugging easier. An 8-bit byte is split in half and each nibble is used to store one decimal digit. The last (rightmost) nibble of the variable is reserved for the sign. Thus a variable which can store up to nine digits would be "packed" into 5 bytes. Ease of debugging resulted from the numbers being readable in a
hex dump where two
hex numbers are used to represent the value of a byte, as . For example, a five-byte BCD value of represents a decimal value of .
Historically, there are cases where nybble was used for a group of bits greater than 4. In the
Apple II microcomputer line, much of the disk drive control and
group-coded recording was implemented in software. Writing data to a disk was done by converting 256-byte pages into sets of
5-bit (later,
6-bit) nibbles and loading disk data required the reverse.
Moreover, 1982 documentation for the
Integrated Woz Machine refers consistently to an "8 bit nibble".
The term ''byte'' once had the same ambiguity and meant a set of bits but not necessarily 8, hence the distinction of ''bytes'' and ''
octet
Octet may refer to:
Music
* Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble
** String octet, a piece of music written for eight string instruments
*** Octet (Mendelssohn), 1825 com ...
s'' or of ''nibbles'' and ''quartets'' (or ''quadbits''). Today, the terms ''byte'' and ''nibble'' almost always refer to 8-bit and 4-bit collections respectively and are very rarely used to express any other sizes.
Table of nibbles
The sixteen nibbles and their equivalents in other numeral systems:
Low and high nibbles
The terms ''low nibble'' and ''high nibble'' are used to denote the nibbles containing, respectively, the less significant bits and the more significant bits within a byte. In graphical representations of bits within a byte, the leftmost bit could represent the most significant bit (
MSB), corresponding to ordinary decimal notation in which the digit at the left of a number is the most significant. In such illustrations the four bits on the left end of the byte form the high nibble, and the remaining four bits form the low nibble.
For example,
the high nibble is (), and the low nibble is (). The total value is ().
Extracting a nibble from a byte
A nibble can be extracted from a byte by doing a
bitwise logical AND operation and optionally a
bit shift depending on if the high or low nibble is to be extracted.
In
C:
#define HI_NIBBLE(b) (((b) >> 4) & 0x0F)
#define LO_NIBBLE(b) ((b) & 0x0F)
where
b
must be a variable or constant of an
integral data type, and only the least-significant byte of
b
is used.
For example,
HI_NIBBLE(0xAB)0xA
and
LO_NIBBLE(0xAB)0xB
.
In
Common Lisp:
(defun hi-nibble (b)
(ldb (byte 4 4) b))
(defun lo-nibble (b)
(ldb (byte 4 0) b))
See also
*
Binary numeral system
A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typically "0" ( zero) and "1" (one).
The base-2 numeral system is a positional notati ...
*
Syllable (computing)
*
Word
A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...
References
External links
*
{{Computer Storage Volumes
Computing terminology
Data unit
Units of information
Articles with example C code