In computer architecture, 48-bit

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

s can represent 281,474,976,710,656 (2⁴⁸ or 2.814749767×10¹⁴) discrete values. This allows an unsigned binary integer range of 0 through 281,474,976,710,655 (2⁴⁸ − 1) or a signed

two's complement Two's complement is the most common method of representing signed (positive, negative, and zero) integers on computers, and more generally, fixed point binary values. Two's complement uses the binary digit with the ''greatest'' value as the ''s ...

range of −140,737,488,355,328 (−2⁴⁷) through 140,737,488,355,327 (2⁴⁷ − 1). A 48-bit

memory address In computing, a memory address is a reference to a specific memory location in memory used by both software and hardware. These addresses are fixed-length sequences of digits, typically displayed and handled as unsigned integers. This numeric ...

can directly address every byte of 256

terabyte 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 un ...

s of storage. 48-bit can refer to any other

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

unit that consumes 48 bits (6

octets 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 compos ...

) in width. Examples include 48-bit CPU and ALU

architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...

s that are based on

register Register or registration may refer to: Arts, entertainment, and media Music * Register (music), the relative "height" or range of a note, melody, part, instrument, etc. * ''Register'', a 2017 album by Travis Miller * Registration (organ), ...

address bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

es, or data buses of that size.

Word size

Computers with 48-bit words include the AN/FSQ-32,

CDC The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency under the Department of Health and Human Services (HHS), and is headquartered in Atlanta, ...

1604/ upper-3000 series, BESM-6,

Ferranti Ferranti International PLC or simply Ferranti was a UK-based electrical engineering and equipment firm that operated for over a century, from 1885 until its bankruptcy in 1993. At its peak, Ferranti was a significant player in power grid system ...

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

Philco Philco (an acronym for Philadelphia Battery Company) is an American electronics industry, electronics manufacturer headquartered in Philadelphia. Philco was a pioneer in battery, radio, and television production. In 1961, the company was purchase ...

TRANSAC S-2000 and

Burroughs large systems The Burroughs Large Systems Group produced a family of large 48-bit computing, 48-bit mainframe computer, mainframes using stack machine instruction sets with dense Syllable (computing), syllables.E.g., 12-bit syllables for B5000, 8-bit syllables f ...

. The Honeywell DATAmatic 1000, H-800, the MANIAC II, the MANIAC III, the

Brookhaven National Laboratory Brookhaven National Laboratory (BNL) is a United States Department of Energy national laboratories, United States Department of Energy national laboratory located in Upton, New York, a hamlet of the Brookhaven, New York, Town of Brookhaven. It w ...

Merlin, the Philco CXPQ, the Ferranti Orion, the Telefunken Rechner TR 440, the ICT 1301, and many other early transistor-based and vacuum tube computers"In search of 48 bit computers"
used 48-bit words.

Addressing

The IBM System/38, and the

IBM AS/400 The IBM AS/400 (Application System/400) is a family of midrange computers from IBM announced in June 1988 and released in August 1988. It was the successor to the System/36 and System/38 platforms, and ran the OS/400 operating system. Lower-cost b ...

in its CISC variants, use 48-bit addresses. The address size used in

logical block addressing Logical block addressing (LBA) is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disk drives. LBA is a particularly simple linear addressin ...

was increased to 48 bits with the introduction of ATA-6. The

Ext4 ext4 (fourth extended filesystem) is a journaling file system for Linux, developed as the successor to ext3. ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for ...

file system physically limits the file block count to 48 bits. The minimal implementation of the

x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit extension of the x86 instruction set architecture, instruction set. It was announced in 1999 and first available in the AMD Opteron family in 2003. It introduces two new ope ...

architecture provides 48-bit addressing encoded into 64 bits; future versions of the architecture can expand this without breaking properly written applications. The media access control address (

MAC address A MAC address (short for medium access control address or media access control address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use i ...

) of a

network interface controller A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter and physical network interface) is a computer hardware component that connects a computer to a computer network. Early network interface ...

uses a 48-bit address space.

Images

In digital images, 48 bits per pixel, or 16 bits per each color channel (red, green and blue), is used for accurate processing. For the human eye, it is almost impossible to see any difference between such an image and a 24-bit image, but the existence of more shades of each of the three primary colors (65,536 as opposed to 256) means that more operations can be performed on the image without risk of noticeable banding or

posterization Posterization or posterisation of an image is the conversion of a continuous gradation of tone to several regions of fewer tones, causing abrupt changes from one tone to another. This was originally done with photographic processes to create ...

Notes

References

{{CPU technologies Data unit