24-bit computing

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.

"24-bit" redirects here. For other uses, see 24-bit (disambiguation).
Computer architecture bit widths
Bit
Application
Binary floating-point precision
  • 16
  • 32
  • 40
  • 64
  • 80
  • 128
  • 256
Decimal floating-point precision

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 (FFFFFF16 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]

gollark: I blatantly stole it from helloboi.
gollark: I may be referred to as car/cdr if desired.
gollark: The problem with spaces is that you can’t actually see them. So you can’t be sure they’re correct. Also they aren’t actually there anyway - they are the absence of code. “Anti-code” if you will. Too many developers format their code “to make it more maintainable” (like that’s actually a thing), but they’re really just filling the document with spaces. And it’s impossible to know how spaces will effect your code, because if you can’t see them, then you can’t read them. Real code wizards know to just write one long line and pack it in tight. What’s that you say? You wrote 600 lines of code today? Well I wrote one, and it took all week, but it’s the best. And when I hand this project over to you next month I’ll have solved world peace in just 14 lines and you will be so lucky to have my code on your screen <ninja chop>.
gollark: Remove the call stack and do trampolining or something?
gollark: Yes, I think this is possible.

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

References
  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 (1996). "A 6502 Programmer's Introduction to the 65816". Commodore World magazine. No. 16.
  3. "24-BIT. DIGITAL SIGNAL PROCESSOR. FAMILY" (PDF).
  4. "UNIVAC 24-bit computer genealogy".
  5. "integerFunctions(3) Manual Page". www.khronos.org.
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