One instruction may have several fields, which identify the logical operation, and may also include source and destination addresses and constant values. This is the MIPS "Add Immediate" instruction, which allows selection of source and destination registers and inclusion of a small constant.
Walther WSR-16 mechanical calculator. The row of digit-wheels in the carriage (at the front), is the Accumulator.
Front panel of an IBM 701 computer with lights displaying the accumulator and other registers

The characteristic which distinguishes one register as being the accumulator of a computer architecture is that the accumulator (if the architecture were to have one) would be used as an implicit operand for arithmetic instructions.

- Accumulator (computing)

1-operand (one-address machines), so called accumulator machines, include early computers and many small microcontrollers: most instructions specify a single right operand (that is, constant, a register, or a memory location), with the implicit accumulator as the left operand (and the destination if there is one):, ,.

- Instruction set architecture
One instruction may have several fields, which identify the logical operation, and may also include source and destination addresses and constant values. This is the MIPS "Add Immediate" instruction, which allows selection of source and destination registers and inclusion of a small constant.

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Processor register

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Quickly accessible location available to a computer's processor.

Quickly accessible location available to a computer's processor.

The term normally refers only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set.

Data registers can hold numeric data values such as integer and, in some architectures, floating-point values, as well as characters, small bit arrays and other data. In some older and low-end CPUs, a special data register, known as the accumulator, is used implicitly for many operations.