24-bit computing explained

Notable 24-bit machines include the CDC 924 – a 24-bit version of the CDC 1604, CDC lower 3000 series, SDS 930 and SDS 940, the ICT 1900 series, the Elliott 4100 series, and the Datacraft minicomputers/Harris H series.[1]

The term SWORD is sometimes used to describe a 24-bit data type with the S prefix referring to sesqui.

The range of unsigned integers that can be represented in 24 bits is 0 to 16,777,215 (in hexadecimal). The range of signed integers that can be represented in 24 bits is −8,388,608 to 8,388,607.

Usage

The IBM System/360, announced in 1964, was a popular computer system with 24-bit addressing and 32-bit general registers and arithmetic. The early 1980s saw the first popular personal computers, including the IBM PC/AT with an Intel 80286 processor using 24-bit addressing and 16-bit general registers and arithmetic, and the Apple Macintosh 128K with a Motorola 68000 processor featuring 24-bit addressing and 32-bit registers.

The eZ80 is a microprocessor and microcontroller family, with 24-bit registers and therefore 24-bit linear addressing, that is binary compatible with the 8/16-bit Z80.

The 65816 is a microprocessor and microcontroller family with 16-bit registers and 24-bit bank switched addressing. It is binary compatible with the 8-bit 6502.[2]

Several fixed-point digital signal processors have a 24-bit data bus, selected as the basic word length because it gave the system a reasonable precision for the processing audio (sound). In particular, the Motorola 56000 series has three parallel 24-bit data buses, one connected to each memory space: program memory, data memory X, and data memory Y.[3]

Engineering Research Associates (later merged into UNIVAC) designed a series of 24-bit drum memory machines including the Atlas, its commercial version the UNIVAC 1101, the ATHENA computer, the UNIVAC 1824 guidance computer, etc. Those designers selected a 24-bit word length because the Earth is roughly 40 million feet in diameter, and an intercontinental ballistic missile guidance computer needs to do the Earth-centered inertial navigation calculations to an accuracy of a few feet.[4]

OpenCL has a built-in intrinsic for multiplication (mul24) with two 24-bit integers, returning a 32-bit result. It is typically much faster than a 32-bit multiplication.[5]

See also

Notes and References

  1. Web site: Real Machines with 24-bit and 48-bit words . 2011-02-11 . Savard . John. https://web.archive.org/web/20110107183451/http://quadibloc.com/comp/cp0303.htm. 7 January 2011 . live.
  2. Brett Tabke . A 6502 Programmer's Introduction to the 65816 . Commodore World magazine . 16 . 1996.
  3. Web site: 24-BIT. DIGITAL SIGNAL PROCESSOR. FAMILY.
  4. Web site: UNIVAC 24-bit computer genealogy.
  5. Web site: integerFunctions(3) Manual Page . www.khronos.org.