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(In the examples that follow, a, b, and c are (direct or calculated) addresses referring to memory cells, while reg1 and so on refer to machine registers.) C = A+B 0-operand (zero-address machines), so called stack machines: All arithmetic operations take place using the top one or two positions on the stack: [9] push a, push b, add, pop c.
Instructions included an address for the operand. For instance, an ADD address instruction would cause the CPU to retrieve the number in memory found at that address and then add it to the value already in the accumulator. This very simple example ISA has a "one-address format" because each instruction includes the address of the data. [4]
Another example is the x86 family, of which processors of three different word lengths (16-bit, later 32- and 64-bit) have been released, while word continues to designate a 16-bit quantity. As software is routinely ported from one word-length to the next, some APIs and documentation define or refer to an older (and thus shorter) word-length ...
The number of operands is one of the factors that may give an indication about the performance of the instruction set. A three-operand architecture (2-in, 1-out) will allow A := B + C to be computed in one instruction ADD B, C, A A two-operand architecture (1-in, 1-in-and-out) will allow A := A + B to be computed in one instruction ADD B, A
Microsoft Word is a word processing program developed by Microsoft.It was first released on October 25, 1983, [12] under the name Multi-Tool Word for Xenix systems. [13] [14] [15] Subsequent versions were later written for several other platforms including: IBM PCs running DOS (1983), Apple Macintosh running the Classic Mac OS (1985), AT&T UNIX PC (1985), Atari ST (1988), OS/2 (1989 ...
Some instruction sets have nearly uniform fields for opcode and operand specifiers, whereas others (e.g., x86 architecture) have a less uniform, variable-length structure. [10] [11] Instruction sets can be extended through the use of opcode prefixes which add a subset of new instructions made up of existing opcodes following reserved byte ...
The resulting instruction set has real-world limitations; for instance, it can only perform two-operand math of the form A = A + B, whereas most processors of the era used the three-operand format, A = B + C. By removing one operand, four bits are removed from the instruction (there are 16 registers, needing 4 bits), although this is at the ...
Double words are used by the MUL, DIV, and ASHC instructions. Other 32-bit data are supported as extensions to the basic architecture: floating point in the FPU Instruction Set or long data in the Commercial Instruction Set are stored in more than one format, including an unusual middle-endian format [2] [3] sometimes referred to as "PDP-endian."