The IV/70, was introduced by
Four-Phase Systems in 1971. The IV/70 has an integer word size of 24 bits.
Byte addressing is not supported directly but bytes are handled by instructions that pack three bytes per word. The IV/70 CPU is a 9-chip
LSI microprocessor based on three
AL4 8-bit slice register/ALUs. 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. Some late-1980s Apple computers such as the
Macintosh SE/30 and
Macintosh IIx retained some 24-bit code in their
ROMs despite being advertised as 32-bit computers. As a result, these computers require the installation of the
MODE32 memory manager to address more than 8Mb of RAM. The
ARM1, supported 24-bit memory address, as it can access 16MiB memory. The
eZ80 is a microprocessor and microcontroller family, with 24-bit registers and 24-bit linear addressing. It is
binary compatible with the
8/16-bit
Z80. Although eZ80 supports 24-bit adds, subtracts, and moves, most ALU operations are limited to 8-bit. 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. 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.
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.
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. == See also ==