<s>
In	O
a	O
computer	O
's	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
,	O
the	O
accumulator	B-General_Concept
is	O
a	O
register	B-General_Concept
in	O
which	O
intermediate	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
results	O
are	O
stored	O
.	O
</s>
<s>
Without	O
a	O
register	B-General_Concept
like	O
an	O
accumulator	B-General_Concept
,	O
it	O
would	O
be	O
necessary	O
to	O
write	O
the	O
result	O
of	O
each	O
calculation	O
(	O
addition	O
,	O
multiplication	O
,	O
shift	O
,	O
etc	O
.	O
)	O
</s>
<s>
Access	O
to	O
main	O
memory	O
is	O
slower	O
than	O
access	O
to	O
a	O
register	B-General_Concept
like	O
an	O
accumulator	B-General_Concept
because	O
the	O
technology	O
used	O
for	O
the	O
large	O
main	O
memory	O
is	O
slower	O
(	O
but	O
cheaper	O
)	O
than	O
that	O
used	O
for	O
a	O
register	B-General_Concept
.	O
</s>
<s>
Early	O
electronic	O
computer	O
systems	O
were	O
often	O
split	O
into	O
two	O
groups	O
,	O
those	O
with	O
accumulators	B-General_Concept
and	O
those	O
without	O
.	O
</s>
<s>
Modern	O
computer	O
systems	O
often	O
have	O
multiple	O
general-purpose	O
registers	O
that	O
can	O
operate	O
as	O
accumulators	B-General_Concept
,	O
and	O
the	O
term	O
is	O
no	O
longer	O
as	O
common	O
as	O
it	O
once	O
was	O
.	O
</s>
<s>
However	O
,	O
to	O
simplify	O
their	O
design	O
,	O
a	O
number	O
of	O
special-purpose	O
processors	O
still	O
use	O
a	O
single	O
accumulator	B-General_Concept
.	O
</s>
<s>
In	O
early	O
computers	O
,	O
the	O
number	O
of	O
hours	O
would	O
likely	O
be	O
held	O
on	O
a	O
punch	B-Architecture
card	I-Architecture
and	O
the	O
pay	O
rate	O
in	O
some	O
other	O
form	O
of	O
memory	O
,	O
perhaps	O
a	O
magnetic	B-General_Concept
drum	I-General_Concept
.	O
</s>
<s>
Accumulators	B-General_Concept
dramatically	O
improve	O
performance	O
in	O
systems	O
like	O
these	O
by	O
providing	O
a	O
scratchpad	O
area	O
where	O
the	O
results	O
of	O
one	O
operation	O
can	O
be	O
fed	O
to	O
the	O
next	O
one	O
for	O
little	O
or	O
no	O
performance	O
penalty	O
.	O
</s>
<s>
In	O
the	O
example	O
above	O
,	O
the	O
basic	O
weekly	O
pay	O
would	O
be	O
calculated	O
and	O
placed	O
in	O
the	O
accumulator	B-General_Concept
,	O
which	O
could	O
then	O
immediately	O
be	O
used	O
by	O
the	O
income	O
tax	O
calculation	O
.	O
</s>
<s>
An	O
accumulator	B-General_Concept
machine	I-General_Concept
,	O
also	O
called	O
a	O
1-operand	O
machine	O
,	O
or	O
a	O
CPU	O
with	O
accumulator-based	B-General_Concept
architecture	I-General_Concept
,	O
is	O
a	O
kind	O
of	O
CPU	O
where	O
,	O
although	O
it	O
may	O
have	O
several	O
registers	O
,	O
the	O
CPU	O
mostly	O
stores	O
the	O
results	O
of	O
calculations	O
in	O
one	O
special	O
register	B-General_Concept
,	O
typically	O
called	O
"	O
the	O
accumulator	B-General_Concept
"	O
.	O
</s>
<s>
Almost	O
all	O
computers	O
were	O
accumulator	B-General_Concept
machines	I-General_Concept
with	O
only	O
the	O
high-performance	O
"	O
supercomputers	B-Architecture
"	O
having	O
multiple	O
registers	O
.	O
</s>
<s>
Then	O
as	O
mainframe	B-Architecture
systems	O
gave	O
way	O
to	O
microcomputers	B-Architecture
,	O
accumulator	B-General_Concept
architectures	O
were	O
again	O
popular	O
with	O
the	O
MOS	B-General_Concept
6502	I-General_Concept
being	O
a	O
notable	O
example	O
.	O
</s>
<s>
Many	O
8-bit	O
microcontrollers	B-Architecture
that	O
are	O
still	O
popular	O
as	O
of	O
2014	O
,	O
such	O
as	O
the	O
PICmicro	B-Architecture
and	O
8051	B-Architecture
,	O
are	O
accumulator-based	O
machines	O
.	O
</s>
<s>
The	O
additional	O
operands	O
specify	O
which	O
one	O
of	O
many	O
general	O
purpose	O
registers	O
(	O
also	O
called	O
"	O
general	O
purpose	O
accumulators	B-General_Concept
"	O
)	O
are	O
used	O
as	O
the	O
source	O
and	O
destination	O
for	O
calculations	O
.	O
</s>
<s>
These	O
CPUs	O
are	O
not	O
considered	O
"	O
accumulator	B-General_Concept
machines	I-General_Concept
"	O
.	O
</s>
<s>
The	O
characteristic	O
which	O
distinguishes	O
one	O
register	B-General_Concept
as	O
being	O
the	O
accumulator	B-General_Concept
of	O
a	O
computer	B-General_Concept
architecture	I-General_Concept
is	O
that	O
the	O
accumulator	B-General_Concept
(	O
if	O
the	O
architecture	O
were	O
to	O
have	O
one	O
)	O
would	O
be	O
used	O
as	O
an	O
implicit	O
operand	O
for	O
arithmetic	O
instructions	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
CPU	O
might	O
have	O
an	O
instruction	O
like	O
:	O
ADD	O
memaddress	B-General_Concept
that	O
adds	O
the	O
value	O
read	O
from	O
memory	B-General_Concept
location	I-General_Concept
memaddress	B-General_Concept
to	O
the	O
value	O
in	O
the	O
accumulator	B-General_Concept
,	O
placing	O
the	O
result	O
back	O
in	O
the	O
accumulator	B-General_Concept
.	O
</s>
<s>
The	O
accumulator	B-General_Concept
is	O
not	O
identified	O
in	O
the	O
instruction	O
by	O
a	O
register	B-General_Concept
number	O
;	O
it	O
is	O
implicit	O
in	O
the	O
instruction	O
and	O
no	O
other	O
register	B-General_Concept
can	O
be	O
specified	O
in	O
the	O
instruction	O
.	O
</s>
<s>
Some	O
architectures	O
use	O
a	O
particular	O
register	B-General_Concept
as	O
an	O
accumulator	B-General_Concept
in	O
some	O
instructions	O
,	O
but	O
other	O
instructions	O
use	O
register	B-General_Concept
numbers	O
for	O
explicit	O
operand	O
specification	O
.	O
</s>
<s>
Any	O
system	O
that	O
uses	O
a	O
single	O
"	O
memory	O
"	O
to	O
store	O
the	O
result	O
of	O
multiple	O
operations	O
can	O
be	O
considered	O
an	O
accumulator	B-General_Concept
.	O
</s>
<s>
J	O
.	O
Presper	O
Eckert	O
refers	O
to	O
even	O
the	O
earliest	O
adding	O
machines	O
of	O
Gottfried	O
Leibniz	O
and	O
Blaise	O
Pascal	O
as	O
accumulator-based	O
systems	O
.	O
</s>
<s>
Percy	O
Ludgate	O
was	O
the	O
first	O
to	O
conceive	O
a	O
multiplier-accumulator	O
(	O
MAC	O
)	O
in	O
his	O
Analytical	O
Machine	O
of	O
1909	O
.	O
</s>
<s>
Historical	O
convention	O
dedicates	O
a	O
register	B-General_Concept
to	O
"	O
the	O
accumulator	B-General_Concept
"	O
,	O
an	O
"	O
arithmetic	O
organ	O
"	O
that	O
literally	O
accumulates	O
its	O
number	O
during	O
a	O
sequence	O
of	O
arithmetic	O
operations	O
:	O
</s>
<s>
We	O
will	O
call	O
such	O
an	O
organ	O
an	O
Accumulator	B-General_Concept
.	O
</s>
<s>
desk	O
multipliers	O
,	O
standard	O
IBM	O
counters	O
,	O
more	O
modern	O
relay	O
machines	O
,	O
the	O
ENIAC	B-Device
"	O
(	O
Goldstine	O
and	O
von	O
Neumann	O
,	O
1946	O
;	O
p	O
.	O
98	O
in	O
Bell	O
and	O
Newell	O
1971	O
)	O
.	O
</s>
<s>
No	O
convention	O
exists	O
regarding	O
the	O
names	O
for	O
operations	O
from	O
registers	O
to	O
accumulator	B-General_Concept
and	O
from	O
accumulator	B-General_Concept
to	O
registers	O
.	O
</s>
<s>
Donald	O
Knuth	O
's	O
(	O
1973	O
)	O
hypothetical	O
MIX	O
computer	O
)	O
,	O
for	O
example	O
,	O
uses	O
two	O
instructions	O
called	O
load	O
accumulator	B-General_Concept
from	O
register/memory	O
(	O
e.g.	O
</s>
<s>
"	O
LDA	O
r	O
"	O
)	O
and	O
store	O
accumulator	B-General_Concept
to	O
register/memory	O
(	O
e.g.	O
</s>
<s>
The	O
1945	O
configuration	O
of	O
ENIAC	B-Device
had	O
20	O
accumulators	B-General_Concept
,	O
which	O
could	O
operate	O
in	O
parallel	O
.	O
</s>
<s>
Most	O
of	O
IBM	O
's	O
early	O
binary	O
"	O
scientific	O
"	O
computers	O
,	O
beginning	O
with	O
the	O
vacuum	O
tube	O
IBM	B-Device
701	I-Device
in	O
1952	O
,	O
used	O
a	O
single	O
36-bit	O
accumulator	B-General_Concept
,	O
along	O
with	O
a	O
separate	O
multiplier/quotient	O
register	B-General_Concept
to	O
handle	O
operations	O
with	O
longer	O
results	O
.	O
</s>
<s>
The	O
IBM	B-Device
650	I-Device
,	O
a	O
decimal	O
machine	O
,	O
had	O
one	O
10	O
digit	O
distributor	O
and	O
two	O
ten-digit	O
accumulators	B-General_Concept
;	O
the	O
IBM	B-Device
7070	I-Device
,	O
a	O
later	O
,	O
transistorized	O
decimal	O
machine	O
had	O
three	O
accumulators	B-General_Concept
.	O
</s>
<s>
The	O
IBM	B-Application
System/360	I-Application
,	O
and	O
Digital	O
Equipment	O
Corporation	O
's	O
PDP-6	B-Device
,	O
had	O
16	O
general	O
purpose	O
registers	O
,	O
although	O
the	O
PDP-6	B-Device
and	O
its	O
successor	O
,	O
the	O
PDP-10	B-Device
,	O
call	O
them	O
accumulators	B-General_Concept
.	O
</s>
<s>
The	O
12-bit	O
PDP-8	B-Device
was	O
one	O
of	O
the	O
first	O
minicomputers	O
to	O
use	O
accumulators	B-General_Concept
,	O
and	O
inspired	O
many	O
later	O
machines	O
.	O
</s>
<s>
The	O
PDP-8	B-Device
had	O
but	O
one	O
accumulator	B-General_Concept
.	O
</s>
<s>
The	O
HP	B-Device
2100	I-Device
and	O
Data	B-Device
General	I-Device
Nova	I-Device
had	O
2	O
and	O
4	O
accumulators	B-General_Concept
.	O
</s>
<s>
The	O
Nova	O
was	O
created	O
when	O
this	O
follow-on	O
to	O
the	O
PDP-8	B-Device
was	O
rejected	O
in	O
favor	O
of	O
what	O
would	O
become	O
the	O
PDP-11	B-Device
.	O
</s>
<s>
The	O
Nova	O
provided	O
four	O
accumulators	B-General_Concept
,	O
AC0-AC3	O
,	O
although	O
AC2	O
and	O
AC3	O
could	O
also	O
be	O
used	O
to	O
provide	O
offset	O
addresses	O
,	O
tending	O
towards	O
more	O
generality	O
of	O
usage	O
for	O
the	O
registers	O
.	O
</s>
<s>
The	O
PDP-11	B-Device
had	O
8	O
general	O
purpose	O
registers	O
,	O
along	O
the	O
lines	O
of	O
the	O
System/360	B-Application
and	O
PDP-10	B-Device
;	O
most	O
later	O
CISC	O
and	O
RISC	O
machines	O
provided	O
multiple	O
general	O
purpose	O
registers	O
.	O
</s>
<s>
Early	O
4-bit	O
and	O
8-bit	O
microprocessors	O
such	O
as	O
the	O
4004	B-General_Concept
,	O
8008	B-General_Concept
and	O
numerous	O
others	O
,	O
typically	O
had	O
single	O
accumulators	B-General_Concept
.	O
</s>
<s>
The	O
8051	B-Architecture
microcontroller	B-Architecture
has	O
two	O
,	O
a	O
primary	O
accumulator	B-General_Concept
and	O
a	O
secondary	O
accumulator	B-General_Concept
,	O
where	O
the	O
second	O
is	O
used	O
by	O
instructions	O
only	O
when	O
multiplying	O
(	O
MUL	O
AB	O
)	O
or	O
dividing	O
(	O
DIV	O
AB	O
)	O
;	O
the	O
former	O
splits	O
the	O
16-bit	O
result	O
between	O
the	O
two	O
8-bit	O
accumulators	B-General_Concept
,	O
whereas	O
the	O
latter	O
stores	O
the	O
quotient	O
on	O
the	O
primary	O
accumulator	B-General_Concept
A	O
and	O
the	O
remainder	O
in	O
the	O
secondary	O
accumulator	B-General_Concept
B	O
.	O
</s>
<s>
As	O
a	O
direct	O
descendant	O
of	O
the	O
8008	B-General_Concept
,	O
the	O
8080	B-General_Concept
,	O
and	O
the	O
8086	B-General_Concept
,	O
the	O
modern	O
ubiquitous	O
Intel	B-Operating_System
x86	I-Operating_System
processors	O
still	O
uses	O
the	O
primary	O
accumulator	B-General_Concept
EAX	O
and	O
the	O
secondary	O
accumulator	B-General_Concept
EDX	O
for	O
multiplication	O
and	O
division	O
of	O
large	O
numbers	O
.	O
</s>
<s>
However	O
,	O
MUL	O
and	O
DIV	O
are	O
special	O
cases	O
;	O
other	O
arithmetic-logical	O
instructions	O
(	O
ADD	O
,	O
SUB	O
,	O
CMP	O
,	O
AND	O
,	O
OR	O
,	O
XOR	O
,	O
TEST	O
)	O
may	O
specify	O
any	O
of	O
the	O
eight	O
registers	O
EAX	O
,	O
ECX	O
,	O
EDX	O
,	O
EBX	O
,	O
ESP	O
,	O
EBP	O
,	O
ESI	O
,	O
EDI	O
as	O
the	O
accumulator	B-General_Concept
(	O
i.e.	O
</s>
<s>
x86	B-Operating_System
is	O
thus	O
a	O
fairly	O
general	O
register	B-General_Concept
architecture	O
,	O
despite	O
being	O
based	O
on	O
an	O
accumulator	B-General_Concept
model	O
.	O
</s>
<s>
The	O
64-bit	O
extension	O
of	O
x86	B-Operating_System
,	O
x86-64	B-Device
,	O
has	O
been	O
further	O
generalized	O
to	O
16	O
instead	O
of	O
8	O
general	O
registers	O
.	O
</s>
