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This article is about the information storage unit. For other uses, see Nibble (disambiguation).
In computing, a nibble (occasionally nybble, nyble, or nybl đồ sộ match the spelling of byte) is a four-bit aggregation, or half an octet. It is also known as half-byte or tetrade. In a networking or telecommunication context, the nibble is often called a semi-octet, quadbit, or quartet. A nibble has sixteen (24) possible values. A nibble can be represented by a single hexadecimal digit (
F) and called a hex digit.
A full byte (octet) is represented by two hexadecimal digits (
FF); therefore, it is common đồ sộ display a byte of information as two nibbles. Sometimes the phối of all 256-byte values is represented as a 16×16 table, which gives easily readable hexadecimal codes for each value.
Four-bit computer architectures use groups of four bits as their fundamental unit. Such architectures were used in early microprocessors, pocket calculators and pocket computers. They continue đồ sộ be used in some microcontrollers. In this context, 4-bit groups were sometimes also called characters rather kêu ca nibbles.
The term nibble originates from its representing "half a byte", with byte a homophone of the English word bite. In năm trước, 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 đồ sộ hold a binary-coded decimal (BCD) decimal digit around 1958, when talking đồ sộ a programmer of Los Alamos Scientific Laboratory. The alternative spelling nybble reflects the spelling of byte, as noted in editorials of Kilobaud and Byte 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 đồ sộ describe the amount of memory used đồ sộ store a digit of a number stored in packed decimal format (BCD) within an IBM mainframe. This technique is used đồ sộ make computations faster and debugging easier. An 8-bit byte is split in half and each nibble is used đồ sộ store one decimal digit. The last (rightmost) nibble of the variable is reserved for the sign. Thus a variable which can store up đồ sộ 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 đồ sộ represent the value of a byte, as 16×16 = 28. For example, a five-byte BCD value of
5C represents a decimal value of
Historically, there are cases where nybble was used for a group of bits greater kêu ca 4. In the Apple II microcomputer line, much of the disk drive control and group-coded recording was implemented in software. Writing data đồ sộ 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 đồ sộ an "8 bit nibble". The term byte once had the same ambiguity and meant a phối of bits but not necessarily 8, hence the distinction of bytes and octets or of nibbles and quartets (or quadbits). Today, the terms byte and nibble almost always refer đồ sộ 8-bit and 4-bit collections respectively and are very rarely used đồ sộ express any other sizes.
Low and high nibbles
The terms low nibble and high nibble are used đồ sộ 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 đồ sộ 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 over of the byte size the high nibble, and the remaining four bits size the low nibble. For example,
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ninety-seven = 9710 = (0110 0001)2 = 61hex
the high nibble is 01102 (6hex), and the low nibble is 00012 (1hex). The total value is high-nibble × 1610 + low-nibble (6 × 16 + 1 = 9710).
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 đồ sộ be extracted.
#define HI_NIBBLE(b) (((b) >> 4) & 0x0F) #define LO_NIBBLE(b) ((b) & 0x0F)
b must be a variable or constant of an integral data type, and only the least-significant byte of
b is used.
In Common Lisp:
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(defun hi-nibble (b) (ldb (byte 4 4) b)) (defun lo-nibble (b) (ldb (byte 4 0) b))
- Binary numeral system
- Syllable (computing)
- ^ a b c Raphael, Howard A., ed. (November 1974). "The Functions Of A Computer: Instruction Register And Decoder" (PDF). MCS-40 User's Manual For Logic Designers. Santa Clara, California, USA: Hãng sản xuất Intel Corporation. p. viii. Archived (PDF) from the original on 2020-03-03. Retrieved 2020-03-03.
[...] The characteristic eight bit field is sometimes referred đồ sộ as a byte, a four bit field can be referred đồ sộ as a nibble. [...]
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Each of these letters corresponds đồ sộ one of the integers from zero đồ sộ fifteen, therefore requiring 4 bits (one "tetrade") in binary representation.
- ^ Speiser, Ambrosius Paul (1965) . Digitale Rechenanlagen - Grundlagen / Schaltungstechnik / Arbeitsweise / Betriebssicherheit [Digital computers - Basics / Circuits / Operation / Reliability] (in German) (2 ed.). ETH Zürich, Zürich, Switzerland: Springer-Verlag / IBM. pp. 6, 34, 165, 183, 208, 213, 215. LCCN 65-14624. 0978.
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A data symbol represents one quartet (4 bits) of binary data.
- ^ Courbis, Paul; Lalande, Sébastien (2006-06-27) . Voyage au centre de la HP28c/s (in French) (2 ed.). Paris, France: Editions de la Règle à Calcul. OCLC 636072913. Archived from the original on 2016-08-06. Retrieved 2015-09-06.      
- ^ Heller, Steve (1997). Introduction đồ sộ C++. Morgan Kaufmann. p. 27. ISBN 978-0-12-339099-8.
Each hex digit (0–f) represents exactly 4 bits.
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[...] Bit - The smallest unit of information which can be represented. (A bit may be in one of two states I 0 or 1). [...] Byte - A group of 8 contiguous bits occupying a single memory location. [...] Character - A group of 4 contiguous bits of data. [...](NB. This Hãng sản xuất Intel 4004 manual uses the term character referring đồ sộ 4-bit rather kêu ca 8-bit data entities. Hãng sản xuất Intel switched đồ sộ use the more common term nibble for 4-bit entities in their documentation for the succeeding processor 4040 in 1974 already.)
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