Accumulators are registers that can be used for arithmetic, logical, shift, rotate, or other similar operations. The first computers typically only had one accumulator. Many times there were related special purpose registers that contained the source data for an accumulator. Accumulators were replaced with data registers and general purpose registers. Accumulators reappeared in the first microprocessors.

* Intel 8086/80286: one word (16 bit) accumulator; named AX (high order byte of the AX register is named AH and low order byte of the AX register is named AL)
* Intel 80386: one doubleword (32 bit) accumulator; named EAX (low order word uses the same names as the accumulator on the Intel 8086 and 80286 [AX] and low order and high order bytes of the low order words of four of the registers use the same names as the accumulator on the Intel 8086 and 80286 [AH and AL])
* MIX: one accumulator; named A-register; five bytes plus sign