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Consequently, all early computers had a serial ALU that operated on one data bit at a time although they often presented a wider word size to programmers. The first computer to have multiple parallel discrete single-bit ALU circuits was the 1951 Whirlwind I, which employed sixteen such "math units" to enable it to operate on 16-bit words.
Computer hardware and software standards are technical standards instituted for compatibility and interoperability between software, systems, platforms and devices. Hardware [ edit ]
An arithmetic logic unit (ALU) capable of adding and subtracting 8-bit 2's complement integers from registers A and B. This module also has a flags register with two possible flags (Z and C). Z stands for "zero," and is activated if the ALU outputs zero. C stands for "carry," and is activated if the ALU produces a carry-out bit.
It provides many of the functions found in simple, commercially available CPUs. The most complex element of the CPU is the arithmetic logic unit (ALU) which provides the computational functionality of the computer. The ALU is a combinational logic device having two 16-bit input operands and a single 16-bit output.
The carry flag is set according to this addition, and subtract with carry computes a+not(b)+C, while subtract without carry acts as if the carry bit were set. The result is that the carry bit is set if a≥b, and clear if a<b. The System/360, [3] ARM, POWER/PowerPC, 6502, MSP430, COP8, Am29000, i960, and 88000 processors use this convention.
In theoretical computer science, a circuit is a model of computation in which input values proceed through a sequence of gates, each of which computes a function. Circuits of this kind provide a generalization of Boolean circuits and a mathematical model for digital logic circuits.
In computing, an opcode (abbreviated from operation code) [1] [2] is an enumerated value that specifies the operation to be performed. Opcodes are employed in hardware devices such as arithmetic logic units (ALUs), central processing units (CPUs), and software instruction sets.
A common example is the Data General Nova, which was a 16-bit design that performed 16-bit math as a series of four 4-bit operations. 4-bits was the word size of a widely available single-chip ALU and thus allowed for inexpensive implementation. Using the definition being applied to the 68000, the Nova would be a 4-bit computer, or 4/16.