Accumulator (computing) - History of The Computer Accumulator

History of The Computer Accumulator

Historical convention dedicates a register to "the accumulator", an "arithmetic organ" that literally accumulates its number during a sequence of arithmetic operations:

"The first part of our arithmetic organ ... should be a parallel storage organ which can receive a number and add it to the one already in it, which is also able to clear its contents and which can store what it contains. We will call such an organ an Accumulator. It is quite conventional in principle in past and present computing machines of the most varied types, e.g. desk multipliers, standard IBM counters, more modern relay machines, the ENIAC" (Goldstine and von Neumann, 1946; p. 98 in Bell and Newell 1971).

Just a few of the instructions are, for example (with some modern interpretation):

• Clear accumulator and add number from memory location X
• Clear accumulator and subtract number from memory location X
• Add number copied from memory location X to the contents of the accumulator
• Subtract number copied from memory location X from the contents of the accumulator
• Clear accumulator and shift contents of register into accumulator

No convention exists regarding the names for operations from registers to accumulator and from accumulator to registers. Tradition (e.g. Donald Knuth's (1973) hypothetical MIX computer), for example, uses two instructions called load accumulator from register/memory (e.g. "LDA r") and store accumulator to register/memory (e.g. "STA r"). Knuth's model has many other instructions as well.