that the architecture under discussion is quite old. The term in
full is almost never used of microprocessor registers, for example,
though symbolic names for arithmetic registers beginning in `A'
derive from historical use of the term `accumulator' (and not,
actually, from `arithmetic'). Confusingly, though, an `A'
register name prefix may also stand for `address', as for
example on the Motorola 680x0 family. 2. A register being used for
arithmetic or logic (as opposed to addressing or a loop index),
especially one being used to accumulate a sum or count of many
items. This use is in context of a particular routine or stretch
of code. "The FOOBAZ routine uses A3 as an accumulator."
3. One's in-basket (esp. among old-timers who might use sense 1).
"You want this reviewed? Sure, just put it in the accumulator."
(See {stack}.)

:ACK: /ak/ /interj./ 1. [from the ASCII mnemonic for 0000110]
Acknowledge. Used to register one's presence (compare mainstream
*Yo!*). An appropriate response to {ping} or {ENQ}.
2. [from the comic strip "Bloom County"] An exclamation of
surprised disgust, esp. in "Ack pffft!" Semi-humorous.
Generally this sense is not spelled in caps (ACK) and is
distinguished by a following exclamation point. 3. Used to
politely interrupt someone to tell them you understand their point
(see {NAK}). Thus, for example, you might cut off an overly
long explanation with "Ack. Ack. Ack. I get it now".

There is also a usage "ACK?" (from sense 1) meaning "Are you
there?", often used in email when earlier mail has produced no
reply, or during a lull in {talk mode} to see if the person has
gone away (the standard humorous response is of course {NAK}