In computer architecture, 24-bit integers, memory addresses, or other data units are those that are 24 bits (3 octets) wide. Also, 24-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.

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, and the Datacraft minicomputers/Harris H series.[1]

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]

The range of unsigned integers that can be represented in 24 bits is 0 to 16,777,215 (FFFFFF16 in hexadecimal). The range of signed integers that can be represented in 24 bits is −8,388,608 to 8,388,607.

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]

1 2 4 8 12 16 18 24 26 31 32 36 48 60 64 128 256 512
8 16 32 64
Binary floating-point precision
16 32 40 64 80 128 256
×½ ×1 ×2 ×4 ×8
Decimal floating-point precision
32 64 128

See also

  • Catena, a term used for a 24-bit unit of data on the Bull Gamma 60 computer


  1. ^ Savard, John. "Real Machines with 24-bit and 48-bit words". Archived from the original on 7 January 2011. Retrieved 2011-02-11.
  2. ^ Brett Tabke. "A 6502 Programmer's Introduction to the 65816". Commodore World magazine, Issue #16. 1996.
  4. ^ "UNIVAC 24-bit computer genealogy"

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