Editing Accumulator (computing) (section)

== Notable accumulator-based computers ==
[[File:IBM 701console.jpg|thumb|Front panel of an [[IBM 701]] computer with lights displaying the accumulator and other registers]]
The 1945 configuration of [[ENIAC]] had 20 accumulators, which could operate in parallel.<ref name="ENIAC">{{cite book |last1=Haigh |first1=Thomas |first2=Mark |last2=Priestley |first3=Crispin |last3=Ropefir  |title=ENIAC in Action: Making and Remaking the Modern Computer |year= 2016 |publisher=MIT Press |isbn=9780262334419}}</ref>{{rp|46}}  Each one could store an eight decimal digit number and add to it (or subtract from it) a number it received.<ref name="ENIAC" />{{rp|33}} Most of IBM's early binary "scientific" computers, beginning with the vacuum tube [[IBM 701]] in 1952, used a single [[36-bit computing|36-bit]] accumulator, along with a separate multiplier/quotient register to handle operations with longer results. The [[IBM 650]], a decimal machine, had one 10 digit distributor and two ten-digit accumulators; the [[IBM 7070]], a later, transistorized decimal machine had three accumulators.  The [[IBM System/360]], and [[Digital Equipment Corporation]]'s [[PDP-6]], had 16 general-purpose registers, although the PDP-6 and its successor, the [[PDP-10]], call them accumulators.

The [[12-bit computing|12-bit]] [[PDP-8]] was one of the first minicomputers to use accumulators, and inspired many later machines.<ref>{{citation |publisher=[[Digital Equipment Corporation]] |location=[[Maynard, Massachusetts]] |date=1961 |url=http://bitsavers.trailing-edge.com/pdf/dec/pdp1/F15B_PDP1_Handbook_1961.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://bitsavers.trailing-edge.com/pdf/dec/pdp1/F15B_PDP1_Handbook_1961.pdf |archive-date=2022-10-09 |url-status=live |title=Programmed Data Processor-1 Manual |page=7: PDP-1 system block diagram |access-date=2014-07-03}}</ref> The PDP-8 had but one accumulator. The [[HP 2100]] and [[Data General Nova]] had 2 and 4 accumulators. The Nova was created when this follow-on to the PDP-8 was rejected in favor of what would become the [[PDP-11]]. The Nova provided four accumulators, AC0-AC3, although AC2 and AC3 could also be used to provide offset addresses, tending towards more generality of usage for the registers. The PDP-11 had 8 general-purpose registers, along the lines of the System/360 and PDP-10; most later CISC and RISC machines provided multiple general-purpose registers.
 
Early [[4-bit computing|4-bit]] and 8-bit microprocessors such as the [[Intel 4004|4004]], [[Intel 8008|8008]] and numerous others, typically had single accumulators. The [[Intel 8051|8051]] microcontroller has two, a primary accumulator and a secondary accumulator, where the second is used by instructions only when multiplying (MUL AB) or dividing (DIV AB); the former splits the [[16-bit computing|16-bit]] result between the two 8-bit accumulators, whereas the latter stores the quotient on the primary accumulator A and the remainder in the secondary accumulator B. As a direct descendant of the 8008, the [[Intel 8080|8080]], and the [[Intel 8086|8086]], the modern ubiquitous [[x86|Intel x86]] processors still uses the primary accumulator EAX and the secondary accumulator EDX for multiplication and division of large numbers. For instance, MUL ECX will multiply the [[32-bit computing|32-bit]] registers ECX and EAX and split the [[64-bit computing|64-bit]] result between EAX and EDX. However, MUL and DIV are special cases; other arithmetic-logical instructions (ADD, SUB, CMP, AND, OR, XOR, TEST) may specify any of the eight registers EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI as the accumulator (i.e. left operand and destination).  This is also supported for multiply if the upper half of the result is not required.  x86 is thus a fairly general register architecture, despite being based on an accumulator model.<ref>{{cite book |last= Irvine |first= Kip R. |title= Assembly Language for Intel-Based Computers |year= 2007 |edition= 5th  |publisher=Pearson Prentice Hall |isbn=978-0-13-238310-3 |pages=633, 622}}</ref>  The 64-bit extension of x86, [[x86-64]], has been further generalized to 16 instead of 8 general registers.