Early microprocessors of the decade of the 70's used to only have one register, (Jiffy Mel and Christians are soooo poor... sooo poor, that they only have one God!), and it was the coolest register of them all man, it was the only register that could hold an operand and receive a result.

Most modern processors can use more than one general purpose register to play the role of the accumulator. Thus the accumulator is not anymore a very special register. Still there are always some instructions which use a unique register to store the result, this would the accumulator. Data transfers from/to memory used to require the involvement of the accumulator. Not so any more. Yes, now more than one register can receive incoming data from a memory location. Ah, the sweet scent of technology.