<s>
The	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
—	O
also	O
known	O
as	O
the	O
von	B-Architecture
Neumann	I-Architecture
model	I-Architecture
or	O
Princeton	B-Architecture
architecture	I-Architecture
—	O
is	O
a	O
computer	B-General_Concept
architecture	I-General_Concept
based	O
on	O
a	O
1945	O
description	O
by	O
John	O
von	O
Neumann	O
,	O
and	O
by	O
others	O
,	O
in	O
the	O
First	O
Draft	O
of	O
a	O
Report	O
on	O
the	O
EDVAC	B-Device
.	O
</s>
<s>
The	O
term	O
"	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
"	O
has	O
evolved	O
to	O
refer	O
to	O
any	O
stored-program	O
computer	O
in	O
which	O
an	O
instruction	O
fetch	O
and	O
a	O
data	B-General_Concept
operation	O
cannot	O
occur	O
at	O
the	O
same	O
time	O
(	O
since	O
they	O
share	O
a	O
common	O
bus	B-General_Concept
)	O
.	O
</s>
<s>
The	O
design	O
of	O
a	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
machine	O
is	O
simpler	O
than	O
in	O
a	O
Harvard	B-Architecture
architecture	I-Architecture
machine	O
—	O
which	O
is	O
also	O
a	O
stored-program	O
system	O
,	O
yet	O
has	O
one	O
dedicated	O
set	O
of	O
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
for	O
reading	O
and	O
writing	O
to	O
memory	B-General_Concept
,	O
and	O
another	O
set	O
of	O
address	O
and	O
data	B-General_Concept
buses	I-General_Concept
to	O
fetch	O
instructions	B-General_Concept
.	O
</s>
<s>
A	O
stored-program	O
computer	O
uses	O
the	O
same	O
underlying	O
mechanism	O
to	O
encode	O
both	O
program	B-Application
instructions	I-Application
and	O
data	B-General_Concept
as	O
opposed	O
to	O
designs	O
which	O
use	O
a	O
mechanism	O
such	O
as	O
discrete	O
plugboard	O
wiring	O
or	O
fixed	O
control	O
circuitry	O
for	O
instruction	O
implementation	O
.	O
</s>
<s>
Stored-program	O
computers	O
were	O
an	O
advancement	O
over	O
the	O
manually	O
reconfigured	O
or	O
fixed	O
function	O
computers	O
of	O
the	O
1940s	O
,	O
such	O
as	O
the	O
Colossus	B-Device
and	O
the	O
ENIAC	B-Device
.	O
</s>
<s>
These	O
were	O
programmed	O
by	O
setting	O
switches	O
and	O
inserting	O
patch	B-Device
cables	I-Device
to	O
route	O
data	B-General_Concept
and	O
control	O
signals	O
between	O
various	O
functional	O
units	O
.	O
</s>
<s>
The	O
vast	O
majority	O
of	O
modern	O
computers	O
use	O
the	O
same	O
hardware	O
mechanism	O
to	O
encode	O
and	O
store	O
both	O
data	B-General_Concept
and	O
program	B-Application
instructions	I-Application
,	O
but	O
have	O
caches	B-General_Concept
between	O
the	O
CPU	O
and	O
memory	B-General_Concept
,	O
and	O
,	O
for	O
the	O
caches	B-General_Concept
closest	O
to	O
the	O
CPU	O
,	O
have	O
separate	O
caches	B-General_Concept
for	O
instructions	B-General_Concept
and	O
data	B-General_Concept
,	O
so	O
that	O
most	O
instruction	O
and	O
data	B-General_Concept
fetches	O
use	O
separate	O
buses	O
(	O
split	O
cache	B-General_Concept
architecture	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
desk	O
calculator	B-Application
(	O
in	O
principle	O
)	O
is	O
a	O
fixed	O
program	B-Application
computer	O
.	O
</s>
<s>
It	O
can	O
do	O
basic	O
mathematics	O
,	O
but	O
it	O
cannot	O
run	O
a	O
word	B-General_Concept
processor	I-General_Concept
or	O
games	O
.	O
</s>
<s>
Changing	O
the	O
program	B-Application
of	O
a	O
fixed-program	O
machine	O
requires	O
rewiring	O
,	O
restructuring	O
,	O
or	O
redesigning	O
the	O
machine	O
.	O
</s>
<s>
"	O
Reprogramming	O
"	O
–	O
when	O
possible	O
at	O
all	O
–	O
was	O
a	O
laborious	O
process	O
that	O
started	O
with	O
flowcharts	B-Language
and	O
paper	O
notes	O
,	O
followed	O
by	O
detailed	O
engineering	O
designs	O
,	O
and	O
then	O
the	O
often-arduous	O
process	O
of	O
physically	O
rewiring	O
and	O
rebuilding	O
the	O
machine	O
.	O
</s>
<s>
It	O
could	O
take	O
three	O
weeks	O
to	O
set	O
up	O
and	O
debug	O
a	O
program	B-Application
on	O
ENIAC	B-Device
.	O
</s>
<s>
With	O
the	O
proposal	O
of	O
the	O
stored-program	O
computer	O
,	O
this	O
changed	O
.	O
</s>
<s>
A	O
stored-program	O
computer	O
includes	O
,	O
by	O
design	O
,	O
an	O
instruction	B-General_Concept
set	I-General_Concept
,	O
and	O
can	O
store	O
in	O
memory	B-General_Concept
a	O
set	O
of	O
instructions	B-General_Concept
(	O
a	O
program	B-Application
)	O
that	O
details	O
the	O
computation	O
.	O
</s>
<s>
A	O
stored-program	O
design	O
also	O
allows	O
for	O
self-modifying	B-Application
code	I-Application
.	O
</s>
<s>
One	O
early	O
motivation	O
for	O
such	O
a	O
facility	O
was	O
the	O
need	O
for	O
a	O
program	B-Application
to	O
increment	O
or	O
otherwise	O
modify	O
the	O
address	O
portion	O
of	O
instructions	B-General_Concept
,	O
which	O
operators	O
had	O
to	O
do	O
manually	O
in	O
early	O
designs	O
.	O
</s>
<s>
This	O
became	O
less	O
important	O
when	O
index	B-General_Concept
registers	I-General_Concept
and	O
indirect	B-Language
addressing	I-Language
became	O
usual	O
features	O
of	O
machine	O
architecture	O
.	O
</s>
<s>
Another	O
use	O
was	O
to	O
embed	O
frequently	O
used	O
data	B-General_Concept
in	O
the	O
instruction	O
stream	O
using	O
immediate	B-Language
addressing	I-Language
.	O
</s>
<s>
Self-modifying	B-Application
code	I-Application
has	O
largely	O
fallen	O
out	O
of	O
favor	O
,	O
since	O
it	O
is	O
usually	O
hard	O
to	O
understand	O
and	O
debug	O
,	O
as	O
well	O
as	O
being	O
inefficient	O
under	O
modern	O
processor	O
pipelining	B-General_Concept
and	O
caching	O
schemes	O
.	O
</s>
<s>
On	O
a	O
large	O
scale	O
,	O
the	O
ability	O
to	O
treat	O
instructions	B-General_Concept
as	O
data	B-General_Concept
is	O
what	O
makes	O
assemblers	O
,	O
compilers	B-Language
,	O
linkers	B-Application
,	O
loaders	B-Operating_System
,	O
and	O
other	O
automated	O
programming	O
tools	O
possible	O
.	O
</s>
<s>
This	O
has	O
made	O
a	O
sophisticated	O
self-hosting	O
computing	O
ecosystem	O
flourish	O
around	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
machines	O
.	O
</s>
<s>
Some	O
high	O
level	O
languages	O
leverage	O
the	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
by	O
providing	O
an	O
abstract	O
,	O
machine-independent	O
way	O
to	O
manipulate	O
executable	B-Application
code	I-Application
at	O
runtime	O
(	O
e.g.	O
,	O
LISP	B-Language
)	O
,	O
or	O
by	O
using	O
runtime	O
information	O
to	O
tune	O
just-in-time	O
compilation	B-Language
(	O
e.g.	O
</s>
<s>
languages	O
hosted	O
on	O
the	O
Java	B-Language
virtual	I-Language
machine	I-Language
,	O
or	O
languages	O
embedded	O
in	O
web	B-Application
browsers	I-Application
)	O
.	O
</s>
<s>
On	O
a	O
smaller	O
scale	O
,	O
some	O
repetitive	O
operations	O
such	O
as	O
BITBLT	B-Algorithm
or	O
pixel	B-Language
and	I-Language
vertex	I-Language
shaders	I-Language
can	O
be	O
accelerated	O
on	O
general	O
purpose	O
processors	O
with	O
just-in-time	O
compilation	B-Language
techniques	O
.	O
</s>
<s>
This	O
is	O
one	O
use	O
of	O
self-modifying	B-Application
code	I-Application
that	O
has	O
remained	O
popular	O
.	O
</s>
<s>
In	O
it	O
he	O
described	O
a	O
hypothetical	O
machine	O
he	O
called	O
a	O
universal	B-Architecture
computing	I-Architecture
machine	I-Architecture
,	O
now	O
known	O
as	O
the	O
"	O
Universal	O
Turing	B-Architecture
machine	I-Architecture
"	O
.	O
</s>
<s>
The	O
hypothetical	O
machine	O
had	O
an	O
infinite	O
store	O
(	O
memory	B-General_Concept
in	O
today	O
's	O
terminology	O
)	O
that	O
contained	O
both	O
instructions	B-General_Concept
and	O
data	B-General_Concept
.	O
</s>
<s>
In	O
1936	O
,	O
Konrad	O
Zuse	O
also	O
anticipated	O
,	O
in	O
two	O
patent	O
applications	O
,	O
that	O
machine	O
instructions	B-General_Concept
could	O
be	O
stored	O
in	O
the	O
same	O
storage	O
used	O
for	O
data	B-General_Concept
.	O
</s>
<s>
Independently	O
,	O
J	O
.	O
Presper	O
Eckert	O
and	O
John	O
Mauchly	O
,	O
who	O
were	O
developing	O
the	O
ENIAC	B-Device
at	O
the	O
Moore	O
School	O
of	O
Electrical	O
Engineering	O
of	O
the	O
University	O
of	O
Pennsylvania	O
,	O
wrote	O
about	O
the	O
stored-program	O
concept	O
in	O
December	O
1943	O
.	O
</s>
<s>
In	O
planning	O
a	O
new	O
machine	O
,	O
EDVAC	B-Device
,	O
Eckert	O
wrote	O
in	O
January	O
1944	O
that	O
they	O
would	O
store	O
data	B-General_Concept
and	O
programs	O
in	O
a	O
new	O
addressable	O
memory	B-General_Concept
device	I-General_Concept
,	O
a	O
mercury	O
metal	O
delay-line	O
memory	B-General_Concept
.	O
</s>
<s>
This	O
was	O
the	O
first	O
time	O
the	O
construction	O
of	O
a	O
practical	O
stored-program	O
machine	O
was	O
proposed	O
.	O
</s>
<s>
It	O
required	O
huge	O
amounts	O
of	O
calculation	O
,	O
and	O
thus	O
drew	O
him	O
to	O
the	O
ENIAC	B-Device
project	O
,	O
during	O
the	O
summer	O
of	O
1944	O
.	O
</s>
<s>
There	O
he	O
joined	O
the	O
ongoing	O
discussions	O
on	O
the	O
design	O
of	O
this	O
stored-program	O
computer	O
,	O
the	O
EDVAC	B-Device
.	O
</s>
<s>
As	O
part	O
of	O
that	O
group	O
,	O
he	O
wrote	O
up	O
a	O
description	O
titled	O
First	O
Draft	O
of	O
a	O
Report	O
on	O
the	O
EDVAC	B-Device
based	O
on	O
the	O
work	O
of	O
Eckert	O
and	O
Mauchly	O
.	O
</s>
<s>
The	O
paper	O
was	O
read	O
by	O
dozens	O
of	O
von	O
Neumann	O
's	O
colleagues	O
in	O
America	O
and	O
Europe	O
,	O
and	O
influenced	O
the	O
next	O
round	O
of	O
computer	B-General_Concept
designs	I-General_Concept
.	O
</s>
<s>
Jack	O
Copeland	O
considers	O
that	O
it	O
is	O
"	O
historically	O
inappropriate	O
to	O
refer	O
to	O
electronic	O
stored-program	O
digital	O
computers	O
as	O
'	O
von	O
Neumann	O
machines	O
.	O
</s>
<s>
At	O
the	O
time	O
that	O
the	O
"	O
First	O
Draft	O
"	O
report	O
was	O
circulated	O
,	O
Turing	O
was	O
producing	O
a	O
report	O
entitled	O
Proposed	O
Electronic	O
Calculator	B-Application
.	O
</s>
<s>
It	O
described	O
in	O
engineering	O
and	O
programming	O
detail	O
,	O
his	O
idea	O
of	O
a	O
machine	O
he	O
called	O
the	O
Automatic	B-Device
Computing	I-Device
Engine	I-Device
(	O
ACE	B-Device
)	O
.	O
</s>
<s>
Although	O
Turing	O
knew	O
from	O
his	O
wartime	O
experience	O
at	O
Bletchley	O
Park	O
that	O
what	O
he	O
proposed	O
was	O
feasible	O
,	O
the	O
secrecy	O
surrounding	O
Colossus	B-Device
,	O
that	O
was	O
subsequently	O
maintained	O
for	O
several	O
decades	O
,	O
prevented	O
him	O
from	O
saying	O
so	O
.	O
</s>
<s>
Various	O
successful	O
implementations	O
of	O
the	O
ACE	B-Device
design	O
were	O
produced	O
.	O
</s>
<s>
Both	O
von	O
Neumann	O
's	O
and	O
Turing	O
's	O
papers	O
described	O
stored-program	O
computers	O
,	O
but	O
von	O
Neumann	O
's	O
earlier	O
paper	O
achieved	O
greater	O
circulation	O
and	O
the	O
computer	B-General_Concept
architecture	I-General_Concept
it	O
outlined	O
became	O
known	O
as	O
the	O
"	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
"	O
.	O
</s>
<s>
(	O
electronic	B-Device
discrete	I-Device
variable	I-Device
automatic	I-Device
computer	I-Device
)	O
.	O
</s>
<s>
(	O
electronic	O
delay-storage	O
automatic	O
calculator	B-Application
)	O
in	O
Cambridge	O
(	O
see	O
page	O
130	O
)	O
.	O
</s>
<s>
In	O
1947	O
,	O
Burks	O
,	O
Goldstine	O
and	O
von	O
Neumann	O
published	O
another	O
report	O
that	O
outlined	O
the	O
design	O
of	O
another	O
type	O
of	O
machine	O
(	O
a	O
parallel	B-Operating_System
machine	I-Operating_System
this	O
time	O
)	O
that	O
would	O
be	O
exceedingly	O
fast	O
,	O
capable	O
perhaps	O
of	O
20,000	O
operations	O
per	O
second	O
.	O
</s>
<s>
They	O
pointed	O
out	O
that	O
the	O
outstanding	O
problem	O
in	O
constructing	O
such	O
a	O
machine	O
was	O
the	O
development	O
of	O
suitable	O
memory	B-General_Concept
with	O
instantaneously	O
accessible	O
contents	O
.	O
</s>
<s>
These	O
tubes	O
were	O
expensive	O
and	O
difficult	O
to	O
make	O
,	O
so	O
von	O
Neumann	O
subsequently	O
decided	O
to	O
build	O
a	O
machine	O
based	O
on	O
the	O
Williams	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
This	O
machine	O
—	O
completed	O
in	O
June	O
,	O
1952	O
in	O
Princeton	O
—	O
has	O
become	O
popularly	O
known	O
as	O
the	O
Maniac	B-Device
.	O
</s>
<s>
In	O
the	O
same	O
book	O
,	O
the	O
first	O
two	O
paragraphs	O
of	O
a	O
chapter	O
on	O
ACE	B-Device
read	O
as	O
follows	O
:	O
</s>
<s>
The	O
equipment	O
so	O
far	O
erected	O
at	O
the	O
Laboratory	O
is	O
only	O
the	O
pilot	O
model	O
of	O
a	O
much	O
larger	O
installation	O
which	O
will	O
be	O
known	O
as	O
the	O
Automatic	B-Device
Computing	I-Device
Engine	I-Device
,	O
but	O
although	O
comparatively	O
small	O
in	O
bulk	O
and	O
containing	O
only	O
about	O
800	O
thermionic	O
valves	O
,	O
as	O
can	O
be	O
judged	O
from	O
Plates	O
XII	O
,	O
XIII	O
and	O
XIV	O
,	O
it	O
is	O
an	O
extremely	O
rapid	O
and	O
versatile	O
calculating	O
machine	O
.	O
</s>
<s>
Among	O
these	O
various	O
computers	O
,	O
only	O
ILLIAC	B-Device
and	O
ORDVAC	B-Device
had	O
compatible	O
instruction	B-General_Concept
sets	I-General_Concept
.	O
</s>
<s>
ARC2	B-Device
(	O
Birkbeck	O
,	O
University	O
of	O
London	O
)	O
officially	O
came	O
online	O
on	O
May	O
12	O
,	O
1948	O
.	O
</s>
<s>
Manchester	B-Device
Baby	I-Device
(	O
Victoria	O
University	O
of	O
Manchester	O
,	O
England	O
)	O
made	O
its	O
first	O
successful	O
run	O
of	O
a	O
stored	O
program	B-Application
on	O
June	O
21	O
,	O
1948	O
.	O
</s>
<s>
Some	O
dates	O
are	O
for	O
first	O
running	O
a	O
test	O
program	B-Application
,	O
some	O
dates	O
are	O
the	O
first	O
time	O
the	O
computer	O
was	O
demonstrated	O
or	O
completed	O
,	O
and	O
some	O
dates	O
are	O
for	O
the	O
first	O
delivery	O
or	O
installation	O
.	O
</s>
<s>
The	O
IBM	B-Device
SSEC	I-Device
had	O
the	O
ability	O
to	O
treat	O
instructions	B-General_Concept
as	O
data	B-General_Concept
,	O
and	O
was	O
publicly	O
demonstrated	O
on	O
January	O
27	O
,	O
1948	O
.	O
</s>
<s>
In	O
practice	O
,	O
instructions	B-General_Concept
were	O
read	O
from	O
paper	O
tape	O
due	O
to	O
its	O
limited	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
ARC2	B-Device
developed	O
by	O
Andrew	O
Booth	O
and	O
Kathleen	O
Booth	O
at	O
Birkbeck	O
,	O
University	O
of	O
London	O
officially	O
came	O
online	O
on	O
May	O
12	O
,	O
1948	O
.	O
</s>
<s>
It	O
featured	O
the	O
first	O
rotating	B-General_Concept
drum	I-General_Concept
storage	I-General_Concept
device	I-General_Concept
.	O
</s>
<s>
The	O
Manchester	B-Device
Baby	I-Device
was	O
the	O
first	O
fully	O
electronic	O
computer	O
to	O
run	O
a	O
stored	O
program	B-Application
.	O
</s>
<s>
It	O
ran	O
a	O
factoring	O
program	B-Application
for	O
52	O
minutes	O
on	O
June	O
21	O
,	O
1948	O
,	O
after	O
running	O
a	O
simple	O
division	O
program	B-Application
and	O
a	O
program	B-Application
to	O
show	O
that	O
two	O
numbers	O
were	O
relatively	O
prime	O
.	O
</s>
<s>
The	O
ENIAC	B-Device
was	O
modified	O
to	O
run	O
as	O
a	O
primitive	O
read-only	O
stored-program	O
computer	O
(	O
using	O
the	O
Function	O
Tables	O
for	O
program	B-Application
ROM	B-Device
)	O
and	O
was	O
demonstrated	O
as	O
such	O
on	O
September	O
16	O
,	O
1948	O
,	O
running	O
a	O
program	B-Application
by	O
Adele	O
Goldstine	O
for	O
von	O
Neumann	O
.	O
</s>
<s>
The	O
BINAC	B-Device
ran	O
some	O
test	O
programs	O
in	O
February	O
,	O
March	O
,	O
and	O
April	O
1949	O
,	O
although	O
was	O
not	O
completed	O
until	O
September	O
1949	O
.	O
</s>
<s>
The	O
Manchester	B-Device
Mark	I-Device
1	I-Device
developed	O
from	O
the	O
Baby	O
project	O
.	O
</s>
<s>
The	O
EDSAC	B-Device
ran	O
its	O
first	O
program	B-Application
on	O
May	O
6	O
,	O
1949	O
.	O
</s>
<s>
The	O
EDVAC	B-Device
was	O
delivered	O
in	O
August	O
1949	O
,	O
but	O
it	O
had	O
problems	O
that	O
kept	O
it	O
from	O
being	O
put	O
into	O
regular	O
operation	O
until	O
1951	O
.	O
</s>
<s>
The	O
CSIR	B-Device
Mk	I-Device
I	I-Device
ran	O
its	O
first	O
program	B-Application
in	O
November	O
1949	O
.	O
</s>
<s>
The	O
SEAC	B-Device
was	O
demonstrated	O
in	O
April	O
1950	O
.	O
</s>
<s>
The	O
Pilot	B-Device
ACE	I-Device
ran	O
its	O
first	O
program	B-Application
on	O
May	O
10	O
,	O
1950	O
,	O
and	O
was	O
demonstrated	O
in	O
December	O
1950	O
.	O
</s>
<s>
The	O
SWAC	B-Device
was	O
completed	O
in	O
July	O
1950	O
.	O
</s>
<s>
The	O
Whirlwind	B-Device
was	O
completed	O
in	O
December	O
1950	O
and	O
was	O
in	O
actual	O
use	O
in	O
April	O
1951	O
.	O
</s>
<s>
The	O
first	O
ERA	B-Device
Atlas	I-Device
(	O
later	O
the	O
commercial	O
ERA	O
1101/UNIVAC	O
1101	O
)	O
was	O
installed	O
in	O
December	O
1950	O
.	O
</s>
<s>
For	O
example	O
,	O
memory-mapped	B-Architecture
I/O	I-Architecture
lets	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
devices	O
be	O
treated	O
the	O
same	O
as	O
memory	B-General_Concept
.	O
</s>
<s>
A	O
single	O
system	B-Architecture
bus	I-Architecture
could	O
be	O
used	O
to	O
provide	O
a	O
modular	O
system	O
with	O
lower	O
cost	O
.	O
</s>
<s>
In	O
subsequent	O
decades	O
,	O
simple	O
microcontrollers	B-Architecture
would	O
sometimes	O
omit	O
features	O
of	O
the	O
model	O
to	O
lower	O
cost	O
and	O
size	O
.	O
</s>
<s>
The	O
shared	O
bus	B-General_Concept
between	O
the	O
program	B-Device
memory	I-Device
and	O
data	B-General_Concept
memory	B-General_Concept
leads	O
to	O
the	O
von	O
Neumann	O
bottleneck	O
,	O
the	O
limited	O
throughput	O
(	O
data	B-General_Concept
transfer	O
rate	O
)	O
between	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
and	O
memory	B-General_Concept
compared	O
to	O
the	O
amount	O
of	O
memory	B-General_Concept
.	O
</s>
<s>
Because	O
the	O
single	O
bus	B-General_Concept
can	O
only	O
access	O
one	O
of	O
the	O
two	O
classes	O
of	O
memory	B-General_Concept
at	O
a	O
time	O
,	O
throughput	O
is	O
lower	O
than	O
the	O
rate	O
at	O
which	O
the	O
CPU	O
can	O
work	O
.	O
</s>
<s>
This	O
seriously	O
limits	O
the	O
effective	O
processing	O
speed	O
when	O
the	O
CPU	O
is	O
required	O
to	O
perform	O
minimal	O
processing	O
on	O
large	O
amounts	O
of	O
data	B-General_Concept
.	O
</s>
<s>
The	O
CPU	O
is	O
continually	O
forced	B-Device
to	I-Device
wait	I-Device
for	O
needed	O
data	B-General_Concept
to	O
move	O
to	O
or	O
from	O
memory	B-General_Concept
.	O
</s>
<s>
Since	O
CPU	O
speed	O
and	O
memory	B-General_Concept
size	O
have	O
increased	O
much	O
faster	O
than	O
the	O
throughput	O
between	O
them	O
,	O
the	O
bottleneck	O
has	O
become	O
more	O
of	O
a	O
problem	O
,	O
a	O
problem	O
whose	O
severity	O
increases	O
with	O
every	O
new	O
generation	O
of	O
CPU	O
.	O
</s>
<s>
Not	O
only	O
is	O
this	O
tube	O
a	O
literal	O
bottleneck	O
for	O
the	O
data	B-General_Concept
traffic	O
of	O
a	O
problem	O
,	O
but	O
,	O
more	O
importantly	O
,	O
it	O
is	O
an	O
intellectual	O
bottleneck	O
that	O
has	O
kept	O
us	O
tied	O
to	O
word-at-a-time	O
thinking	O
instead	O
of	O
encouraging	O
us	O
to	O
think	O
in	O
terms	O
of	O
the	O
larger	O
conceptual	O
units	O
of	O
the	O
task	O
at	O
hand	O
.	O
</s>
<s>
Thus	O
programming	O
is	O
basically	O
planning	O
and	O
detailing	O
the	O
enormous	O
traffic	O
of	O
words	O
through	O
the	O
von	O
Neumann	O
bottleneck	O
,	O
and	O
much	O
of	O
that	O
traffic	O
concerns	O
not	O
significant	O
data	B-General_Concept
itself	O
,	O
but	O
where	O
to	O
find	O
it	O
.	O
</s>
<s>
The	O
problem	O
can	O
also	O
be	O
sidestepped	O
somewhat	O
by	O
using	O
parallel	B-Operating_System
computing	I-Operating_System
,	O
using	O
for	O
example	O
the	O
non-uniform	B-Operating_System
memory	I-Operating_System
access	I-Operating_System
(	O
NUMA	O
)	O
architecture	O
—	O
this	O
approach	O
is	O
commonly	O
employed	O
by	O
supercomputers	B-Architecture
.	O
</s>
<s>
Modern	O
functional	B-Language
programming	I-Language
and	O
object-oriented	B-Language
programming	I-Language
are	O
much	O
less	O
geared	O
towards	O
"	O
pushing	O
vast	O
numbers	O
of	O
words	O
back	O
and	O
forth	O
"	O
than	O
earlier	O
languages	O
like	O
FORTRAN	B-Application
were	O
,	O
but	O
internally	O
,	O
that	O
is	O
still	O
what	O
computers	O
spend	O
much	O
of	O
their	O
time	O
doing	O
,	O
even	O
highly	O
parallel	O
supercomputers	B-Architecture
.	O
</s>
<s>
As	O
of	O
1996	O
,	O
a	O
database	O
benchmark	O
study	O
found	O
that	O
three	O
out	O
of	O
four	O
CPU	O
cycles	O
were	O
spent	O
waiting	O
for	O
memory	B-General_Concept
.	O
</s>
<s>
Researchers	O
expect	O
that	O
increasing	O
the	O
number	O
of	O
simultaneous	O
instruction	O
streams	O
with	O
multithreading	B-General_Concept
or	O
single-chip	O
multiprocessing	B-Operating_System
will	O
make	O
this	O
bottleneck	O
even	O
worse	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
multi-core	B-Architecture
processors	I-Architecture
,	O
additional	O
overhead	O
is	O
required	O
to	O
maintain	O
cache	B-General_Concept
coherence	I-General_Concept
between	O
processors	O
and	O
threads	O
.	O
</s>
<s>
Aside	O
from	O
the	O
von	O
Neumann	O
bottleneck	O
,	O
program	B-Application
modifications	O
can	O
be	O
quite	O
harmful	O
,	O
either	O
by	O
accident	O
or	O
design	O
.	O
</s>
<s>
In	O
some	O
simple	O
stored-program	O
computer	B-General_Concept
designs	I-General_Concept
,	O
a	O
malfunctioning	O
program	B-Application
can	O
damage	O
itself	O
,	O
other	O
programs	O
,	O
or	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
possibly	O
leading	O
to	O
a	O
computer	B-General_Concept
crash	I-General_Concept
.	O
</s>
<s>
Memory	B-General_Concept
protection	I-General_Concept
and	O
other	O
forms	O
of	O
access	O
control	O
can	O
usually	O
protect	O
against	O
both	O
accidental	O
and	O
malicious	O
program	B-Application
changes	O
.	O
</s>
