Wikipedia article on Nibble

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You can access an ordered font table for octet code page 866 by toggling the table of contents. A nibble is crucial in computer science as a four-bit aggregation. It is also referred to as a half-byte or tetrade. In a networking or telecommunication context, it is known as a semi-octet, quadbit, or quartet. A nibble has a total of 16 (24) possible values and can be represented using a single hexadecimal digit (0–F), also known as a hex digit.

A byte, also known as an octet, is made up of two hexadecimal digits ranging from 00 to FF. It is common practice to display a byte as two nibbles. A set of 256-byte values can be represented as a 16x16 table, which provides easily comprehensible hexadecimal codes for each value.

Early microprocessors, pocket calculators, and pocket computers utilized four-bit computer architectures with groups of four bits as their fundamental unit. Some microcontrollers still use them. These 4-bit groups were occasionally referred to as characters instead of nibbles.

The word nibble comes from its representation of "half a byte," with byte being a homophone of the English word bite. In 1958, while conversing with a programmer at Los Alamos Scientific Laboratory, David B. Benson playfully coined the term to represent a unit of storage required to hold a binary-coded decimal (BCD) decimal digit. The word nybble, spelled with a "y," originated from editorials in Kilobaud and Byte in the early 1980s to be consistent with the spelling of byte. Another recorded use of the term nybble was in 1977 by Citibank's consumer-banking technology group, which used the basic informational unit of "NABBLE" in their pre-ISO 8583 standard for transactional messages between cash machines and their data centers.

When discussing an IBM mainframe, the term "nibble" refers to the amount of memory used to store a digit of a number in packed decimal format (BCD). This method enhances computing speed and facilitates debugging. Essentially, an 8-bit byte is divided in half and each nibble is employed to store one decimal digit. The final (rightmost) nibble is reserved for the sign. Hence, a variable with a capacity of up to nine digits will be "packed" into five bytes. Debugging is made simpler because the numbers are legible in a hex dump where two hexadecimal numbers represent the value of a byte since 16×16 = 28. For instance, a five-byte BCD value of 31 41 59 26 5C represents a decimal value of +314159265.

In history, there are instances where nybble denoted a group of bits greater than 4. For example, in the Apple II microcomputer line, software was utilized to implement much of the disk drive control and group-coded recording. Recording data on a disk was achieved by converting 256-byte pages into sets of 5-bit (later, 6-bit) nibbles, and loading disk data required the opposite. Furthermore, 1982 documents for the Integrated Woz Machine consistently referred to an "8 bit nibble." The term byte formerly had the same ambiguity and meant a collection of bits but not necessarily 8. Consequently, bytes and octets, or nibbles and quartets (or quadbits), are now distinguished. Nowadays, the terms byte and nibble almost exclusively refer to 8-bit and 4-bit collections, respectively, and are only seldom used to indicate other sizes.

"Low and high nibbles" pertains to the division of a byte into two nibbles - a lower nibble and an upper nibble. They are often discussed in relation to bitwise operations, such as the right shift, left shift, and logical operations.

The concepts of low and high nibble refer to the nibbles that respectively contain the more and less significant bits within a byte. When bits within a byte are represented graphically, the leftmost bit is usually the most significant bit or MSB, similar to how the digit at the left of a decimal number is the most significant. In this visualization, the high nibble is formed by the four bits on the left, and the low nibble by the four bits on the right end of the byte. For instance, the binary representation of ninety-seven as 0110 0001 would have 0110 as the high nibble and 0001 as the low nibble, which when converted to hexadecimal representation equals 6 and 1 respectively. The total value is derived by multiplying the high-nibble value by 16 and adding it to the low-nibble value.

To extract a nibble from a byte, you would need to perform a bitwise logical AND operation and adjust it with a bit shift as needed, depending on whether you want the high or low nibble. In C programming, for example, the HI_NIBBLE and LO_NIBBLE macros are used to extract the high and low nibbles respectively. These macros require that the input is of integral data type and only the least-significant byte is used in the operation. For Common Lisp, the functions hi-nibble and lo-nibble are utilized instead, which extract the high and low nibbles using the ldb function with a byte specifier.

Additional Resources[Edit]

Binary system of numeration

Computing Syllables

Computer Architecture Words


^ Source (a) (b) (c) Raphael, Howard A. (ed.) (1974, November). The Functions And Operations Of A Computer: Instruction Register And Decoder (PDF). MCS-40 User's Manual For Logic Designers, Intel Corporation. p. viii. Archived (PDF) from the original on 2020-03-03. Retrieved 2020-03-03. [...] The eight significant bit field is occasionally named a byte, although a field of four bits may be referred to as a nibble. [...]

^ Hall, Douglas V. (1980). Digital Systems And Microprocessors. McGraw-Hill. ISBN 0-07-025571-7.

^ Warren Jr., Henry S. (2013) [2002]. Hacker's Delight (2nd ed.). Addison Wesley - Pearson Education, Inc. ISBN 978-0-321-84268-8. 0-321-84268-5.

According to Eric S. Raymond in The New Hacker's Dictionary (MIT Press, 1996), each letter from A to F in hexadecimal notation corresponds to one of the integers from zero to fifteen, requiring four bits in binary representation. This information was first shared by John W. Carr in Introduction to the Use of Digital Computers, a report from the 1959 Summer Conference held at the Computation Center of the University of North Carolina at Chapel Hill, which was published in Frontier Research on Digital Computers. Ambrosius Paul Speiser's book Digitale Rechenanlagen - Grundlagen / Schaltungstechnik / Arbeitsweise / Betriebssicherheit (Digital Computers - Basics / Circuits / Operation / Reliability) (2 ed., Springer-Verlag / IBM, 1965) provides further details and technical specifications on digital computers. Finally, Josef Puzman and Boris Kubin discuss the history and evolution of public data networks in their book Public Data Networks: From Separate PDNs to the ISDN (Springer Science Business Media, 2012).

Ray Horak wrote a dictionary called Webster's New World Telecom Dictionary in 2007, which was published by John Wiley & Sons and has an ISBN of 978-0-470-22571-4. According to Ronald L. Brewster's book, Data Communications and Networks, Vol. III, which was published in 1994 as volume 31 of the IEE telecommunications series by the Institution of Electrical Engineers and has an ISBN of 978-0-85296-804-8, a data symbol can be used to represent one quartet (4 bits) of binary data. In addition, Paul Courbis and Sébastien Lalande's book, Voyage au centre de la HP28c/s, second edition, was published in 1989 and is available from Editions de la Règle à Calcul in Paris, France. The book is archived at OCLC 636072913 and can be downloaded as six PDF files from the webpage of the original publisher.

According to Steve Heller in Introduction to C (1997), each hexadecimal digit corresponds to exactly 4 binary bits (0-1). The MCS-4 Assembly Language Programming Manual from Intel Corporation (1973) defines the term "bit" as the smallest unit of information; the term "byte" refers to a group of 8 contiguous bits located in one memory location. In computing, a "character" refers to a group of 4 contiguous bits of data; notable is the fact that this Intel 4004 manual uses "character" for 4-bit rather than 8-bit data entities, opting instead to use "nibble" for 4-bit entities in their documentation for the succeeding 4040 processor in 1974. Moreover, according to Beneath Apple DOS (1981) by Don D. Worth and Pieter M. Lechner, "Quality Software," a book that describes the workings of Apple DOS and some of its basic architecture, has 4th printing, 1st edition.

In March 1985, Don D. Worth and Pieter M. Lechner released the book "Beneath Apple ProDOS - For Users of Apple II Plus, Apple IIe and Apple IIc Computers," which was published by Quality Software. This 1st edition was laid out in a 2nd printing format and carried an ISBN of 0-912985-05-4 and an LCCN of 84-61383. The book is still available through the archived version of the PDF format, which was accessed on March 21, 2017, through the link provided in the external links section below.

Also in the external links section, a link to the May 1981 issue of the "Apple Assembly Line" publication is provided. This publication is a reliable source of information on the topic of nibbles, along with other informative articles.

In 1989, Central Point Software, Inc. released Copy II Plus Version 9 - ProDOS/DOS Utilities - Data Recovery, File Management, Protected Software Backup. This version offered a range of data recovery and file management tools, along with the ability to backup protected software. This was made possible due to the integration of Woz Machine (IWM) Specifications, which are available in PDF format in the DigiBarn Computer Museum archives. Finally, the topic of binary arithmetic can be explored through an April 1997 article by Brent Baccala titled "Binary Arithmetic," which can be accessed through the archived version of "Connected: An Internet Encyclopedia."

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