<s>
A	O
computer	O
is	O
a	O
machine	O
that	O
can	O
be	O
programmed	B-General_Concept
to	O
carry	B-General_Concept
out	I-General_Concept
sequences	O
of	O
arithmetic	O
or	O
logical	O
operations	O
(	O
computation	O
)	O
automatically	O
.	O
</s>
<s>
Modern	O
digital	B-Device
electronic	I-Device
computers	I-Device
can	O
perform	O
generic	O
sets	O
of	O
operations	O
known	O
as	O
programs	B-Application
.	O
</s>
<s>
These	O
programs	B-Application
enable	O
computers	O
to	O
perform	O
a	O
wide	O
range	O
of	O
tasks	O
.	O
</s>
<s>
A	O
computer	O
system	O
is	O
a	O
nominally	O
complete	O
computer	O
that	O
includes	O
the	O
hardware	B-Architecture
,	O
operating	B-General_Concept
system	I-General_Concept
(	O
main	O
software	B-Application
)	O
,	O
and	O
peripheral	O
equipment	O
needed	O
and	O
used	O
for	O
full	O
operation	O
.	O
</s>
<s>
This	O
term	O
may	O
also	O
refer	O
to	O
a	O
group	O
of	O
computers	O
that	O
are	O
linked	O
and	O
function	O
together	O
,	O
such	O
as	O
a	O
computer	B-Architecture
network	I-Architecture
or	O
computer	B-Architecture
cluster	I-Architecture
.	O
</s>
<s>
A	O
broad	O
range	O
of	O
industrial	B-Architecture
and	O
consumer	O
products	O
use	O
computers	O
as	O
control	O
systems	O
.	O
</s>
<s>
Simple	O
special-purpose	O
devices	O
like	O
microwave	O
ovens	O
and	O
remote	B-Protocol
controls	I-Protocol
are	O
included	O
,	O
as	O
are	O
factory	O
devices	O
like	O
industrial	B-Architecture
robots	O
and	O
computer-aided	B-Application
design	I-Application
,	O
as	O
well	O
as	O
general-purpose	O
devices	O
like	O
personal	B-Device
computers	I-Device
and	O
mobile	B-Application
devices	I-Application
like	O
smartphones	B-Application
.	O
</s>
<s>
Simple	O
manual	O
instruments	O
like	O
the	O
abacus	B-Application
have	O
aided	O
people	O
in	O
doing	O
calculations	O
since	O
ancient	O
times	O
.	O
</s>
<s>
Early	O
in	O
the	O
Industrial	B-Architecture
Revolution	O
,	O
some	O
mechanical	O
devices	O
were	O
built	O
to	O
automate	O
long	O
,	O
tedious	O
tasks	O
,	O
such	O
as	O
guiding	O
patterns	O
for	O
looms	B-Language
.	O
</s>
<s>
The	O
first	O
digital	B-General_Concept
electronic	O
calculating	O
machines	O
were	O
developed	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
The	O
first	O
semiconductor	O
transistors	B-Application
in	O
the	O
late	O
1940s	O
were	O
followed	O
by	O
the	O
silicon-based	O
MOSFET	B-Architecture
(	O
MOS	B-Architecture
transistor	I-Architecture
)	O
and	O
monolithic	O
integrated	O
circuit	O
chip	O
technologies	O
in	O
the	O
late	O
1950s	O
,	O
leading	O
to	O
the	O
microprocessor	B-Architecture
and	O
the	O
microcomputer	B-Architecture
revolution	O
in	O
the	O
1970s	O
.	O
</s>
<s>
The	O
speed	O
,	O
power	O
and	O
versatility	O
of	O
computers	O
have	O
been	O
increasing	O
dramatically	O
ever	O
since	O
then	O
,	O
with	O
transistor	B-Application
counts	O
increasing	O
at	O
a	O
rapid	O
pace	O
(	O
as	O
predicted	O
by	O
Moore	O
's	O
law	O
)	O
,	O
leading	O
to	O
the	O
Digital	B-General_Concept
Revolution	O
during	O
the	O
late	O
20th	O
to	O
early	O
21st	O
centuries	O
.	O
</s>
<s>
Conventionally	O
,	O
a	O
modern	O
computer	O
consists	O
of	O
at	O
least	O
one	O
processing	O
element	O
,	O
typically	O
a	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	B-Device
)	O
in	O
the	O
form	O
of	O
a	O
microprocessor	B-Architecture
,	O
along	O
with	O
some	O
type	O
of	O
computer	B-General_Concept
memory	I-General_Concept
,	O
typically	O
semiconductor	B-Architecture
memory	I-Architecture
chips	O
.	O
</s>
<s>
The	O
processing	O
element	O
carries	O
out	O
arithmetic	O
and	O
logical	O
operations	O
,	O
and	O
a	O
sequencing	O
and	O
control	B-General_Concept
unit	I-General_Concept
can	O
change	O
the	O
order	O
of	O
operations	O
in	O
response	O
to	O
stored	O
information	O
.	O
</s>
<s>
Peripheral	O
devices	O
include	O
input	O
devices	O
(	O
keyboards	B-Device
,	O
mice	O
,	O
joystick	B-Device
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
output	O
devices	O
(	O
monitor	B-Device
screens	O
,	O
printers	O
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
and	O
input/output	B-General_Concept
devices	I-General_Concept
that	O
perform	O
both	O
functions	O
(	O
e.g.	O
,	O
the	O
2000s-era	O
touchscreen	B-Device
)	O
.	O
</s>
<s>
According	O
to	O
the	B-Application
Oxford	I-Application
English	I-Application
Dictionary	I-Application
,	O
the	O
first	O
known	O
use	O
of	O
computer	O
was	O
in	O
a	O
1613	O
book	O
called	O
The	O
Yong	O
Mans	O
Gleanings	O
by	O
the	O
English	O
writer	O
Richard	O
Brathwait	O
:	O
"	O
I	O
haue	O
read	O
the	O
truest	O
computer	O
of	O
Times	O
,	O
and	O
the	O
best	O
Arithmetician	O
that	O
euer	O
breathed	O
,	O
and	O
he	O
reduceth	O
thy	O
dayes	O
into	O
a	O
short	O
number.	O
"	O
</s>
<s>
The	O
Online	O
Etymology	O
Dictionary	O
indicates	O
that	O
the	O
"	O
modern	O
use	O
"	O
of	O
the	O
term	O
,	O
to	O
mean	O
'	O
programmable	B-General_Concept
digital	B-Device
electronic	I-Device
computer	I-Device
 '	O
dates	O
from	O
"	O
1945	O
under	O
this	O
name	O
;	O
[	O
in	O
a ]	O
theoretical	O
 [ sense ] 	O
from	O
1937	O
,	O
as	O
Turing	B-Architecture
machine	I-Architecture
"	O
.	O
</s>
<s>
Devices	O
have	O
been	O
used	O
to	O
aid	O
computation	O
for	O
thousands	O
of	O
years	O
,	O
mostly	O
using	O
one-to-one	B-Algorithm
correspondence	I-Algorithm
with	O
fingers	O
.	O
</s>
<s>
The	O
abacus	B-Application
was	O
initially	O
used	O
for	O
arithmetic	O
tasks	O
.	O
</s>
<s>
The	O
Roman	O
abacus	B-Application
was	O
developed	O
from	O
devices	O
used	O
in	O
Babylonia	O
as	O
early	O
as	O
2400	O
BC	O
.	O
</s>
<s>
An	O
astrolabe	O
incorporating	O
a	O
mechanical	O
calendar	B-Application
computer	O
and	O
gear-wheels	O
was	O
invented	O
by	O
Abi	O
Bakr	O
of	O
Isfahan	O
,	O
Persia	O
in	O
1235	O
.	O
</s>
<s>
Abū	O
Rayhān	O
al-Bīrūnī	O
invented	O
the	O
first	O
mechanical	O
geared	O
lunisolar	O
calendar	B-Application
astrolabe	O
,	O
an	O
early	O
fixed-wired	O
knowledge	O
processing	O
machine	O
with	O
a	O
gear	O
train	O
and	O
gear-wheels	O
,	O
.	O
</s>
<s>
The	O
sector	O
,	O
a	O
calculating	O
instrument	O
used	O
for	O
solving	O
problems	O
in	O
proportion	O
,	O
trigonometry	O
,	O
multiplication	O
and	O
division	O
,	O
and	O
for	O
various	O
functions	O
,	O
such	O
as	O
squares	O
and	O
cube	O
roots	O
,	O
was	O
developed	O
in	O
the	O
late	O
16th	O
century	O
and	O
found	O
application	B-Application
in	O
gunnery	O
,	O
surveying	O
and	O
navigation	O
.	O
</s>
<s>
Slide	O
rules	O
with	O
special	O
scales	O
are	O
still	O
used	O
for	O
quick	O
performance	O
of	O
routine	O
calculations	O
,	O
such	O
as	O
the	O
E6B	B-Device
circular	O
slide	O
rule	O
used	O
for	O
time	O
and	O
distance	O
calculations	O
on	O
light	O
aircraft	O
.	O
</s>
<s>
In	O
effect	O
,	O
it	O
could	O
be	O
mechanically	O
"	O
programmed	B-General_Concept
"	O
to	O
read	O
instructions	O
.	O
</s>
<s>
Along	O
with	O
two	O
other	O
complex	O
machines	O
,	O
the	O
doll	O
is	O
at	O
the	O
Musée	O
d'Art	O
et	O
d'Histoire	O
of	O
Neuchâtel	O
,	O
Switzerland	B-Protocol
,	O
and	O
still	O
operates	O
.	O
</s>
<s>
In	O
1831	O
–	O
1835	O
,	O
mathematician	O
and	O
engineer	O
Giovanni	O
Plana	O
devised	O
a	O
Perpetual	O
Calendar	B-Application
machine	O
,	O
which	O
,	O
through	O
a	O
system	O
of	O
pulleys	O
and	O
cylinders	O
and	O
over	O
,	O
could	O
predict	O
the	O
perpetual	O
calendar	B-Application
for	O
every	O
year	O
from	O
AD	O
0	O
(	O
that	O
is	O
,	O
1	O
BC	O
)	O
to	O
AD	O
4000	O
,	O
keeping	O
track	O
of	O
leap	O
years	O
and	O
varying	O
day	O
length	O
.	O
</s>
<s>
The	O
differential	B-Device
analyser	I-Device
,	O
a	O
mechanical	O
analog	O
computer	O
designed	O
to	O
solve	O
differential	O
equations	O
by	O
integration	O
,	O
used	O
wheel-and-disc	O
mechanisms	O
to	O
perform	O
the	O
integration	O
.	O
</s>
<s>
In	O
1876	O
,	O
Sir	O
William	O
Thomson	O
had	O
already	O
discussed	O
the	O
possible	O
construction	O
of	O
such	O
calculators	B-Application
,	O
but	O
he	O
had	O
been	O
stymied	O
by	O
the	O
limited	O
output	O
torque	O
of	O
the	O
ball-and-disk	B-Device
integrators	I-Device
.	O
</s>
<s>
In	O
a	O
differential	B-Device
analyzer	I-Device
,	O
the	O
output	O
of	O
one	O
integrator	O
drove	O
the	O
input	O
of	O
the	O
next	O
integrator	O
,	O
or	O
a	O
graphing	O
output	O
.	O
</s>
<s>
Starting	O
in	O
the	O
1920s	O
,	O
Vannevar	O
Bush	O
and	O
others	O
developed	O
mechanical	O
differential	B-Device
analyzers	I-Device
.	O
</s>
<s>
Charles	O
Babbage	O
,	O
an	O
English	O
mechanical	O
engineer	O
and	O
polymath	O
,	O
originated	O
the	O
concept	O
of	O
a	O
programmable	B-General_Concept
computer	O
.	O
</s>
<s>
Considered	O
the	O
"	O
father	O
of	O
the	O
computer	O
"	O
,	O
he	O
conceptualized	O
and	O
invented	O
the	O
first	O
mechanical	B-Device
computer	I-Device
in	O
the	O
early	O
19th	O
century	O
.	O
</s>
<s>
After	O
working	O
on	O
his	O
revolutionary	O
difference	O
engine	O
,	O
designed	O
to	O
aid	O
in	O
navigational	O
calculations	O
,	O
in	O
1833	O
he	O
realized	O
that	O
a	O
much	O
more	O
general	O
design	O
,	O
an	O
Analytical	B-Device
Engine	I-Device
,	O
was	O
possible	O
.	O
</s>
<s>
The	O
input	O
of	O
programs	B-Application
and	O
data	B-General_Concept
was	O
to	O
be	O
provided	O
to	O
the	O
machine	O
via	O
punched	B-Architecture
cards	I-Architecture
,	O
a	O
method	O
being	O
used	O
at	O
the	O
time	O
to	O
direct	O
mechanical	O
looms	B-Language
such	O
as	O
the	O
Jacquard	O
loom	B-Language
.	O
</s>
<s>
The	O
Engine	O
incorporated	O
an	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
,	O
control	O
flow	O
in	O
the	O
form	O
of	O
conditional	B-Language
branching	I-Language
and	O
loops	O
,	O
and	O
integrated	O
memory	B-General_Concept
,	O
making	O
it	O
the	O
first	O
design	O
for	O
a	O
general-purpose	O
computer	O
that	O
could	O
be	O
described	O
in	O
modern	O
terms	O
as	O
Turing-complete	O
.	O
</s>
<s>
Babbage	O
's	O
failure	O
to	O
complete	O
the	B-Device
analytical	I-Device
engine	I-Device
can	O
be	O
chiefly	O
attributed	O
to	O
political	O
and	O
financial	O
difficulties	O
as	O
well	O
as	O
his	O
desire	O
to	O
develop	O
an	O
increasingly	O
sophisticated	O
computer	O
and	O
to	O
move	O
ahead	O
faster	O
than	O
anyone	O
else	O
could	O
follow	O
.	O
</s>
<s>
Nevertheless	O
,	O
his	O
son	O
,	O
Henry	O
Babbage	O
,	O
completed	O
a	O
simplified	O
version	O
of	O
the	B-Device
analytical	I-Device
engine	I-Device
's	O
computing	O
unit	O
(	O
the	O
mill	O
)	O
in	O
1888	O
.	O
</s>
<s>
However	O
,	O
these	O
were	O
not	O
programmable	B-General_Concept
and	O
generally	O
lacked	O
the	O
versatility	O
and	O
accuracy	O
of	O
modern	O
digital	B-General_Concept
computers	O
.	O
</s>
<s>
The	O
differential	B-Device
analyser	I-Device
,	O
a	O
mechanical	O
analog	O
computer	O
designed	O
to	O
solve	O
differential	O
equations	O
by	O
integration	O
using	O
wheel-and-disc	O
mechanisms	O
,	O
was	O
conceptualized	O
in	O
1876	O
by	O
James	O
Thomson	O
,	O
the	O
elder	O
brother	O
of	O
the	O
more	O
famous	O
Sir	O
William	O
Thomson	O
.	O
</s>
<s>
The	O
art	O
of	O
mechanical	O
analog	O
computing	O
reached	O
its	O
zenith	O
with	O
the	O
differential	B-Device
analyzer	I-Device
,	O
built	O
by	O
H	O
.	O
L	O
.	O
Hazen	O
and	O
Vannevar	O
Bush	O
at	O
MIT	O
starting	O
in	O
1927	O
.	O
</s>
<s>
By	O
the	O
1950s	O
,	O
the	O
success	O
of	O
digital	B-Device
electronic	I-Device
computers	I-Device
had	O
spelled	O
the	O
end	O
for	O
most	O
analog	O
computing	O
machines	O
,	O
but	O
analog	O
computers	O
remained	O
in	O
use	O
during	O
the	O
1950s	O
in	O
some	O
specialized	O
applications	O
such	O
as	O
education	O
(	O
slide	O
rule	O
)	O
and	O
aircraft	O
(	O
control	O
systems	O
)	O
.	O
</s>
<s>
This	O
was	O
the	O
Torpedo	B-Device
Data	I-Device
Computer	I-Device
,	O
which	O
used	O
trigonometry	O
to	O
solve	O
the	O
problem	O
of	O
firing	O
a	O
torpedo	O
at	O
a	O
moving	O
target	O
.	O
</s>
<s>
Early	O
digital	B-General_Concept
computers	O
were	O
electromechanical	O
;	O
electric	O
switches	O
drove	O
mechanical	O
relays	O
to	O
perform	O
the	O
calculation	O
.	O
</s>
<s>
The	O
Z2	B-Device
,	O
created	O
by	O
German	O
engineer	O
Konrad	O
Zuse	O
in	O
1939	O
in	O
Berlin	O
,	O
was	O
one	O
of	O
the	O
earliest	O
examples	O
of	O
an	O
electromechanical	O
relay	O
computer	O
.	O
</s>
<s>
In	O
1941	O
,	O
Zuse	O
followed	O
his	O
earlier	O
machine	O
up	O
with	O
the	O
Z3	B-Device
,	O
the	O
world	O
's	O
first	O
working	O
electromechanical	O
programmable	B-General_Concept
,	O
fully	O
automatic	O
digital	B-General_Concept
computer	O
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
built	O
with	O
2000	O
relays	O
,	O
implementing	O
a	O
22	O
bit	O
word	O
length	O
that	O
operated	O
at	O
a	O
clock	O
frequency	O
of	O
about	O
5	O
–	O
10	O
Hz	O
.	O
</s>
<s>
Program	B-Application
code	O
was	O
supplied	O
on	O
punched	O
film	B-Language
while	O
data	B-General_Concept
could	O
be	O
stored	O
in	O
64	O
words	O
of	O
memory	B-General_Concept
or	O
supplied	O
from	O
the	O
keyboard	B-Device
.	O
</s>
<s>
It	O
was	O
quite	O
similar	O
to	O
modern	O
machines	O
in	O
some	O
respects	O
,	O
pioneering	O
numerous	O
advances	O
such	O
as	O
floating-point	B-Algorithm
numbers	I-Algorithm
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
not	O
itself	O
a	O
universal	B-Architecture
computer	I-Architecture
but	O
could	O
be	O
extended	O
to	O
be	O
Turing	B-Algorithm
complete	I-Algorithm
.	O
</s>
<s>
Zuse	O
's	O
next	O
computer	O
,	O
the	O
Z4	B-Device
,	O
became	O
the	O
world	O
's	O
first	O
commercial	O
computer	O
;	O
after	O
initial	O
delay	O
due	O
to	O
the	O
Second	O
World	O
War	O
,	O
it	O
was	O
completed	O
in	O
1950	O
and	O
delivered	O
to	O
the	O
ETH	O
Zurich	O
.	O
</s>
<s>
Purely	O
electronic	O
circuit	O
elements	O
soon	O
replaced	O
their	O
mechanical	O
and	O
electromechanical	O
equivalents	O
,	O
at	O
the	O
same	O
time	O
that	O
digital	B-General_Concept
calculation	O
replaced	O
analog	O
.	O
</s>
<s>
Experimental	O
equipment	O
that	O
he	O
built	O
in	O
1934	O
went	O
into	O
operation	O
five	O
years	O
later	O
,	O
converting	O
a	O
portion	O
of	O
the	O
telephone	O
exchange	O
network	O
into	O
an	O
electronic	O
data	B-General_Concept
processing	O
system	O
,	O
using	O
thousands	O
of	O
vacuum	O
tubes	O
.	O
</s>
<s>
In	O
the	O
US	O
,	O
John	O
Vincent	O
Atanasoff	O
and	O
Clifford	O
E	O
.	O
Berry	O
of	O
Iowa	O
State	O
University	O
developed	O
and	O
tested	O
the	B-Device
Atanasoff	I-Device
–	I-Device
Berry	I-Device
Computer	I-Device
(	O
ABC	O
)	O
in	O
1942	O
,	O
the	O
first	O
"	O
automatic	O
electronic	B-Device
digital	I-Device
computer	I-Device
"	O
.	O
</s>
<s>
This	O
design	O
was	O
also	O
all-electronic	O
and	O
used	O
about	O
300	O
vacuum	O
tubes	O
,	O
with	O
capacitors	O
fixed	O
in	O
a	O
mechanically	O
rotating	O
drum	O
for	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
German	O
encryption	O
machine	O
,	O
Enigma	O
,	O
was	O
first	O
attacked	O
with	O
the	O
help	O
of	O
the	O
electro-mechanical	O
bombes	B-Device
which	O
were	O
often	O
run	O
by	O
women	O
.	O
</s>
<s>
To	O
crack	O
the	O
more	O
sophisticated	O
German	O
Lorenz	O
SZ	O
40/42	O
machine	O
,	O
used	O
for	O
high-level	O
Army	O
communications	O
,	O
Max	O
Newman	O
and	O
his	O
colleagues	O
commissioned	O
Flowers	O
to	O
build	O
the	O
Colossus	B-Device
.	O
</s>
<s>
He	O
spent	O
eleven	O
months	O
from	O
early	O
February	O
1943	O
designing	O
and	O
building	O
the	O
first	O
Colossus	B-Device
.	O
</s>
<s>
After	O
a	O
functional	O
test	O
in	O
December	O
1943	O
,	O
Colossus	B-Device
was	O
shipped	O
to	O
Bletchley	O
Park	O
,	O
where	O
it	O
was	O
delivered	O
on	O
18	O
January	O
1944	O
and	O
attacked	O
its	O
first	O
message	O
on	O
5	O
February	O
.	O
</s>
<s>
Colossus	B-Device
was	O
the	O
world	O
's	O
first	O
electronic	O
digital	B-General_Concept
programmable	B-General_Concept
computer	O
.	O
</s>
<s>
It	O
had	O
paper-tape	O
input	O
and	O
was	O
capable	O
of	O
being	O
configured	O
to	O
perform	O
a	O
variety	O
of	O
boolean	O
logical	O
operations	O
on	O
its	O
data	B-General_Concept
,	O
but	O
it	O
was	O
not	O
Turing-complete	O
.	O
</s>
<s>
Colossus	B-Device
Mark	I-Device
I	I-Device
contained	O
1,500	O
thermionic	O
valves	O
(	O
tubes	O
)	O
,	O
but	O
Mark	O
II	O
with	O
2,400	O
valves	O
,	O
was	O
both	O
five	O
times	O
faster	O
and	O
simpler	O
to	O
operate	O
than	O
Mark	O
I	O
,	O
greatly	O
speeding	O
the	O
decoding	O
process	O
.	O
</s>
<s>
The	O
ENIAC	B-Device
(	O
Electronic	B-Device
Numerical	I-Device
Integrator	I-Device
and	I-Device
Computer	I-Device
)	O
was	O
the	O
first	O
electronic	O
programmable	B-General_Concept
computer	O
built	O
in	O
the	O
U.S.	O
</s>
<s>
Although	O
the	O
ENIAC	B-Device
was	O
similar	O
to	O
the	O
Colossus	B-Device
,	O
it	O
was	O
much	O
faster	O
,	O
more	O
flexible	O
,	O
and	O
it	O
was	O
Turing-complete	O
.	O
</s>
<s>
Like	O
the	O
Colossus	B-Device
,	O
a	O
"	O
program	B-Application
"	O
on	O
the	O
ENIAC	B-Device
was	O
defined	O
by	O
the	O
states	O
of	O
its	O
patch	O
cables	O
and	O
switches	O
,	O
a	O
far	O
cry	O
from	O
the	O
stored	O
program	B-Application
electronic	O
machines	O
that	O
came	O
later	O
.	O
</s>
<s>
Once	O
a	O
program	B-Application
was	O
written	O
,	O
it	O
had	O
to	O
be	O
mechanically	O
set	O
into	O
the	O
machine	O
with	O
manual	O
resetting	O
of	O
plugs	O
and	O
switches	O
.	O
</s>
<s>
The	O
programmers	B-Application
of	O
the	O
ENIAC	B-Device
were	O
six	O
women	O
,	O
often	O
known	O
collectively	O
as	O
the	O
"	O
ENIAC	B-Device
girls	O
"	O
.	O
</s>
<s>
It	O
combined	O
the	O
high	O
speed	O
of	O
electronics	O
with	O
the	O
ability	O
to	O
be	O
programmed	B-General_Concept
for	O
many	O
complex	O
problems	O
.	O
</s>
<s>
High	O
speed	O
memory	B-General_Concept
was	O
limited	O
to	O
20	O
words	O
(	O
about	O
80	O
bytes	B-Application
)	O
.	O
</s>
<s>
Built	O
under	O
the	O
direction	O
of	O
John	O
Mauchly	O
and	O
J	O
.	O
Presper	O
Eckert	O
at	O
the	O
University	O
of	O
Pennsylvania	O
,	O
ENIAC	B-Device
's	O
development	O
and	O
construction	O
lasted	O
from	O
1943	O
to	O
full	O
operation	O
at	O
the	O
end	O
of	O
1945	O
.	O
</s>
<s>
Turing	O
proposed	O
a	O
simple	O
device	O
that	O
he	O
called	O
"	O
Universal	B-Architecture
Computing	I-Architecture
machine	I-Architecture
"	O
and	O
that	O
is	O
now	O
known	O
as	O
a	O
universal	O
Turing	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
He	O
proved	O
that	O
such	O
a	O
machine	O
is	O
capable	O
of	O
computing	O
anything	O
that	O
is	O
computable	O
by	O
executing	O
instructions	O
(	O
program	B-Application
)	O
stored	O
on	O
tape	O
,	O
allowing	O
the	O
machine	O
to	O
be	O
programmable	B-General_Concept
.	O
</s>
<s>
The	O
fundamental	O
concept	O
of	O
Turing	O
's	O
design	O
is	O
the	O
stored	O
program	B-Application
,	O
where	O
all	O
the	O
instructions	O
for	O
computing	O
are	O
stored	O
in	O
memory	B-General_Concept
.	O
</s>
<s>
Turing	B-Architecture
machines	I-Architecture
are	O
to	O
this	O
day	O
a	O
central	O
object	O
of	O
study	O
in	O
theory	O
of	O
computation	O
.	O
</s>
<s>
Except	O
for	O
the	O
limitations	O
imposed	O
by	O
their	O
finite	O
memory	B-General_Concept
stores	O
,	O
modern	O
computers	O
are	O
said	O
to	O
be	O
Turing-complete	O
,	O
which	O
is	O
to	O
say	O
,	O
they	O
have	O
algorithm	O
execution	O
capability	O
equivalent	O
to	O
a	O
universal	O
Turing	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Early	O
computing	O
machines	O
had	O
fixed	O
programs	B-Application
.	O
</s>
<s>
With	O
the	O
proposal	O
of	O
the	O
stored-program	O
computer	O
this	O
changed	O
.	O
</s>
<s>
A	O
stored-program	O
computer	O
includes	O
by	O
design	O
an	O
instruction	B-General_Concept
set	I-General_Concept
and	O
can	O
store	O
in	O
memory	B-General_Concept
a	O
set	O
of	O
instructions	O
(	O
a	O
program	B-Application
)	O
that	O
details	O
the	O
computation	O
.	O
</s>
<s>
The	O
theoretical	O
basis	O
for	O
the	O
stored-program	O
computer	O
was	O
laid	O
out	O
by	O
Alan	O
Turing	O
in	O
his	O
1936	O
paper	O
.	O
</s>
<s>
In	O
1945	O
,	O
Turing	O
joined	O
the	O
National	O
Physical	O
Laboratory	O
and	O
began	O
work	O
on	O
developing	O
an	O
electronic	O
stored-program	O
digital	B-General_Concept
computer	O
.	O
</s>
<s>
His	O
1945	O
report	O
"	O
Proposed	O
Electronic	O
Calculator	B-Application
"	O
was	O
the	O
first	O
specification	O
for	O
such	O
a	O
device	O
.	O
</s>
<s>
John	O
von	O
Neumann	O
at	O
the	O
University	O
of	O
Pennsylvania	O
also	O
circulated	O
his	O
First	O
Draft	O
of	O
a	O
Report	O
on	O
the	O
EDVAC	B-Device
in	O
1945	O
.	O
</s>
<s>
The	O
Manchester	B-Device
Baby	I-Device
was	O
the	O
world	O
's	O
first	O
stored-program	O
computer	O
.	O
</s>
<s>
It	O
was	O
built	O
at	O
the	O
University	O
of	O
Manchester	O
in	O
England	O
by	O
Frederic	O
C	B-Language
.	O
Williams	O
,	O
Tom	O
Kilburn	O
and	O
Geoff	O
Tootill	O
,	O
and	O
ran	O
its	O
first	O
program	B-Application
on	O
21	O
June	O
1948	O
.	O
</s>
<s>
It	O
was	O
designed	O
as	O
a	O
testbed	O
for	O
the	O
Williams	B-General_Concept
tube	I-General_Concept
,	O
the	O
first	O
random-access	B-Architecture
digital	B-General_Concept
storage	O
device	O
.	O
</s>
<s>
As	O
soon	O
as	O
the	O
Baby	O
had	O
demonstrated	O
the	O
feasibility	O
of	O
its	O
design	O
,	O
a	O
project	O
began	O
at	O
the	O
university	O
to	O
develop	O
it	O
into	O
a	O
practically	O
useful	O
computer	O
,	O
the	O
Manchester	B-Device
Mark	I-Device
1	I-Device
.	O
</s>
<s>
The	O
Mark	O
1	O
in	O
turn	O
quickly	O
became	O
the	O
prototype	O
for	O
the	O
Ferranti	B-Device
Mark	I-Device
1	I-Device
,	O
the	O
world	O
's	O
first	O
commercially	O
available	O
general-purpose	O
computer	O
.	O
</s>
<s>
Lyons	O
's	O
LEO	B-Device
I	I-Device
computer	O
,	O
modelled	O
closely	O
on	O
the	O
Cambridge	O
EDSAC	B-Device
of	O
1949	O
,	O
became	O
operational	O
in	O
April	O
1951	O
and	O
ran	O
the	O
world	O
's	O
first	O
routine	O
office	O
computer	O
job	B-General_Concept
.	O
</s>
<s>
Grace	O
Hopper	O
was	O
the	O
first	O
to	O
develop	O
a	O
compiler	B-Language
for	O
a	O
programming	O
language	O
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
field-effect	O
transistor	B-Application
was	O
proposed	O
by	O
Julius	O
Edgar	O
Lilienfeld	O
in	O
1925	O
.	O
</s>
<s>
John	O
Bardeen	O
and	O
Walter	O
Brattain	O
,	O
while	O
working	O
under	O
William	O
Shockley	O
at	O
Bell	O
Labs	O
,	O
built	O
the	O
first	O
working	O
transistor	B-Application
,	O
the	O
point-contact	O
transistor	B-Application
,	O
in	O
1947	O
,	O
which	O
was	O
followed	O
by	O
Shockley	O
's	O
bipolar	O
junction	O
transistor	B-Application
in	O
1948	O
.	O
</s>
<s>
From	O
1955	O
onwards	O
,	O
transistors	B-Application
replaced	O
vacuum	O
tubes	O
in	O
computer	B-General_Concept
designs	I-General_Concept
,	O
giving	O
rise	O
to	O
the	O
"	O
second	O
generation	O
"	O
of	O
computers	O
.	O
</s>
<s>
Compared	O
to	O
vacuum	O
tubes	O
,	O
transistors	B-Application
have	O
many	O
advantages	O
:	O
they	O
are	O
smaller	O
,	O
and	O
require	O
less	O
power	O
than	O
vacuum	O
tubes	O
,	O
so	O
give	O
off	O
less	O
heat	O
.	O
</s>
<s>
Junction	O
transistors	B-Application
were	O
much	O
more	O
reliable	O
than	O
vacuum	O
tubes	O
and	O
had	O
longer	O
,	O
indefinite	O
,	O
service	O
life	O
.	O
</s>
<s>
Transistorized	B-Device
computers	I-Device
could	O
contain	O
tens	O
of	O
thousands	O
of	O
binary	O
logic	O
circuits	O
in	O
a	O
relatively	O
compact	O
space	O
.	O
</s>
<s>
However	O
,	O
early	O
junction	O
transistors	B-Application
were	O
relatively	O
bulky	O
devices	O
that	O
were	O
difficult	O
to	O
manufacture	O
on	O
a	O
mass-production	O
basis	O
,	O
which	O
limited	O
them	O
to	O
a	O
number	O
of	O
specialised	O
applications	O
.	O
</s>
<s>
At	O
the	O
University	O
of	O
Manchester	O
,	O
a	O
team	O
under	O
the	O
leadership	O
of	O
Tom	O
Kilburn	O
designed	O
and	O
built	O
a	O
machine	O
using	O
the	O
newly	O
developed	O
transistors	B-Application
instead	O
of	O
valves	O
.	O
</s>
<s>
Their	O
first	O
transistorised	B-Device
computer	I-Device
and	O
the	O
first	O
in	O
the	O
world	O
,	O
was	O
operational	O
by	O
1953	O
,	O
and	O
a	O
second	O
version	O
was	O
completed	O
there	O
in	O
April	O
1955	O
.	O
</s>
<s>
However	O
,	O
the	O
machine	O
did	O
make	O
use	O
of	O
valves	O
to	O
generate	O
its	O
125kHz	O
clock	O
waveforms	O
and	O
in	O
the	O
circuitry	O
to	O
read	O
and	O
write	O
on	O
its	O
magnetic	B-General_Concept
drum	I-General_Concept
memory	I-General_Concept
,	O
so	O
it	O
was	O
not	O
the	O
first	O
completely	O
transistorized	B-Device
computer	I-Device
.	O
</s>
<s>
That	O
distinction	O
goes	O
to	O
the	O
Harwell	B-Device
CADET	I-Device
of	O
1955	O
,	O
built	O
by	O
the	O
electronics	O
division	O
of	O
the	O
Atomic	O
Energy	O
Research	O
Establishment	O
at	O
Harwell	O
.	O
</s>
<s>
The	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
silicon	I-Architecture
field-effect	I-Architecture
transistor	I-Architecture
(	O
MOSFET	B-Architecture
)	O
,	O
also	O
known	O
as	O
the	O
MOS	B-Architecture
transistor	I-Architecture
,	O
was	O
invented	O
by	O
Mohamed	O
M	O
.	O
Atalla	O
and	O
Dawon	O
Kahng	O
at	O
Bell	O
Labs	O
in	O
1959	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
truly	O
compact	O
transistor	B-Application
that	O
could	O
be	O
miniaturised	O
and	O
mass-produced	O
for	O
a	O
wide	O
range	O
of	O
uses	O
.	O
</s>
<s>
With	O
its	O
high	O
scalability	O
,	O
and	O
much	O
lower	O
power	O
consumption	O
and	O
higher	O
density	O
than	O
bipolar	O
junction	O
transistors	B-Application
,	O
the	O
MOSFET	B-Architecture
made	O
it	O
possible	O
to	O
build	O
high-density	O
integrated	O
circuits	O
.	O
</s>
<s>
In	O
addition	O
to	O
data	B-General_Concept
processing	O
,	O
it	O
also	O
enabled	O
the	O
practical	O
use	O
of	O
MOS	B-Architecture
transistors	I-Architecture
as	O
memory	B-Algorithm
cell	I-Algorithm
storage	O
elements	O
,	O
leading	O
to	O
the	O
development	O
of	O
MOS	B-Architecture
semiconductor	B-Architecture
memory	I-Architecture
,	O
which	O
replaced	O
earlier	O
magnetic-core	O
memory	B-General_Concept
in	O
computers	O
.	O
</s>
<s>
The	O
MOSFET	B-Architecture
led	O
to	O
the	O
microcomputer	B-Architecture
revolution	O
,	O
and	O
became	O
the	O
driving	O
force	O
behind	O
the	O
computer	O
revolution	O
.	O
</s>
<s>
The	O
MOSFET	B-Architecture
is	O
the	O
most	O
widely	O
used	O
transistor	B-Application
in	O
computers	O
,	O
and	O
is	O
the	O
fundamental	O
building	O
block	O
of	O
digital	B-General_Concept
electronics	O
.	O
</s>
<s>
Dummer	O
presented	O
the	O
first	O
public	O
description	O
of	O
an	O
integrated	O
circuit	O
at	O
the	O
Symposium	O
on	O
Progress	O
in	O
Quality	O
Electronic	O
Components	O
in	O
Washington	O
,	O
D.C.	O
on	O
7	O
May	O
1952	O
.	O
</s>
<s>
In	O
his	O
patent	O
application	B-Application
of	O
6	O
February	O
1959	O
,	O
Kilby	O
described	O
his	O
new	O
device	O
as	O
"	O
a	O
body	O
of	O
semiconductor	O
material	O
...	O
wherein	O
all	O
the	O
components	O
of	O
the	O
electronic	O
circuit	O
are	O
completely	O
integrated	O
"	O
.	O
</s>
<s>
Noyce	O
's	O
monolithic	O
IC	O
was	O
fabricated	B-Architecture
using	O
the	O
planar	B-Algorithm
process	I-Algorithm
,	O
developed	O
by	O
his	O
colleague	O
Jean	O
Hoerni	O
in	O
early	O
1959	O
.	O
</s>
<s>
In	O
turn	O
,	O
the	O
planar	B-Algorithm
process	I-Algorithm
was	O
based	O
on	O
Mohamed	O
M	O
.	O
Atalla	O
's	O
work	O
on	O
semiconductor	O
surface	O
passivation	O
by	O
silicon	O
dioxide	O
in	O
the	O
late	O
1950s	O
.	O
</s>
<s>
Modern	O
monolithic	O
ICs	O
are	O
predominantly	O
MOS	B-Architecture
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
)	O
integrated	O
circuits	O
,	O
built	O
from	O
MOSFETs	B-Architecture
(	O
MOS	B-Architecture
transistors	I-Architecture
)	O
.	O
</s>
<s>
The	O
earliest	O
experimental	O
MOS	B-Architecture
IC	O
to	O
be	O
fabricated	B-Architecture
was	O
a	O
16-transistor	O
chip	O
built	O
by	O
Fred	O
Heiman	O
and	O
Steven	O
Hofstein	O
at	O
RCA	O
in	O
1962	O
.	O
</s>
<s>
General	O
Microelectronics	O
later	O
introduced	O
the	O
first	O
commercial	O
MOS	B-Architecture
IC	O
in	O
1964	O
,	O
developed	O
by	O
Robert	O
Norman	O
.	O
</s>
<s>
Following	O
the	O
development	O
of	O
the	O
self-aligned	O
gate	B-Algorithm
(	O
silicon-gate	O
)	O
MOS	B-Architecture
transistor	I-Architecture
by	O
Robert	O
Kerwin	O
,	O
Donald	O
Klein	O
and	O
John	O
Sarace	O
at	O
Bell	O
Labs	O
in	O
1967	O
,	O
the	O
first	O
silicon-gate	O
MOS	B-Architecture
IC	O
with	O
self-aligned	O
gates	O
was	O
developed	O
by	O
Federico	O
Faggin	O
at	O
Fairchild	O
Semiconductor	O
in	O
1968	O
.	O
</s>
<s>
The	O
MOSFET	B-Architecture
has	O
since	O
become	O
the	O
most	O
critical	O
device	O
component	O
in	O
modern	O
ICs	O
.	O
</s>
<s>
The	O
development	O
of	O
the	O
MOS	B-Architecture
integrated	O
circuit	O
led	O
to	O
the	O
invention	O
of	O
the	O
microprocessor	B-Architecture
,	O
and	O
heralded	O
an	O
explosion	O
in	O
the	O
commercial	O
and	O
personal	O
use	O
of	O
computers	O
.	O
</s>
<s>
While	O
the	O
subject	O
of	O
exactly	O
which	O
device	O
was	O
the	O
first	O
microprocessor	B-Architecture
is	O
contentious	O
,	O
partly	O
due	O
to	O
lack	O
of	O
agreement	O
on	O
the	O
exact	O
definition	O
of	O
the	O
term	O
"	O
microprocessor	B-Architecture
"	O
,	O
it	O
is	O
largely	O
undisputed	O
that	O
the	O
first	O
single-chip	O
microprocessor	B-Architecture
was	O
the	O
Intel	B-General_Concept
4004	I-General_Concept
,	O
designed	O
and	O
realized	O
by	O
Federico	O
Faggin	O
with	O
his	O
silicon-gate	O
MOS	B-Architecture
IC	O
technology	O
,	O
along	O
with	O
Ted	O
Hoff	O
,	O
Masatoshi	O
Shima	O
and	O
Stanley	O
Mazor	O
at	O
Intel	O
.	O
</s>
<s>
In	O
the	O
early	O
1970s	O
,	O
MOS	B-Architecture
IC	O
technology	O
enabled	O
the	O
integration	O
of	O
more	O
than	O
10,000	O
transistors	B-Application
on	O
a	O
single	O
chip	O
.	O
</s>
<s>
System	B-Architecture
on	I-Architecture
a	I-Architecture
Chip	I-Architecture
(	O
SoCs	O
)	O
are	O
complete	O
computers	O
on	O
a	O
microchip	O
(	O
or	O
chip	O
)	O
the	O
size	O
of	O
a	O
coin	O
.	O
</s>
<s>
They	O
may	O
or	O
may	O
not	O
have	O
integrated	O
RAM	B-Architecture
and	O
flash	B-Device
memory	I-Device
.	O
</s>
<s>
If	O
not	O
integrated	O
,	O
the	O
RAM	B-Architecture
is	O
usually	O
placed	O
directly	O
above	O
(	O
known	O
as	O
Package	B-Algorithm
on	I-Algorithm
package	I-Algorithm
)	O
or	O
below	O
(	O
on	O
the	O
opposite	O
side	O
of	O
the	O
circuit	O
board	O
)	O
the	O
SoC	O
,	O
and	O
the	O
flash	B-Device
memory	I-Device
is	O
usually	O
placed	O
right	O
next	O
to	O
the	O
SoC	O
,	O
this	O
all	O
done	O
to	O
improve	O
data	B-General_Concept
transfer	O
speeds	O
,	O
as	O
the	O
data	B-General_Concept
signals	O
do	O
n't	O
have	O
to	O
travel	O
long	O
distances	O
.	O
</s>
<s>
Since	O
ENIAC	B-Device
in	O
1945	O
,	O
computers	O
have	O
advanced	O
enormously	O
,	O
with	O
modern	O
SoCs	O
(	O
Such	O
as	O
the	O
Snapdragon	O
865	O
)	O
being	O
the	O
size	O
of	O
a	O
coin	O
while	O
also	O
being	O
hundreds	O
of	O
thousands	O
of	O
times	O
more	O
powerful	O
than	O
ENIAC	B-Device
,	O
integrating	O
billions	O
of	O
transistors	B-Application
,	O
and	O
consuming	O
only	O
a	O
few	O
watts	O
of	O
power	O
.	O
</s>
<s>
The	O
first	O
mobile	B-Device
computers	I-Device
were	O
heavy	O
and	O
ran	O
from	O
mains	O
power	O
.	O
</s>
<s>
The	O
IBM	B-Device
5100	I-Device
was	O
an	O
early	O
example	O
.	O
</s>
<s>
Later	O
portables	O
such	O
as	O
the	O
Osborne	B-Device
1	I-Device
and	O
Compaq	B-Device
Portable	I-Device
were	O
considerably	O
lighter	O
but	O
still	O
needed	O
to	O
be	O
plugged	O
in	O
.	O
</s>
<s>
The	O
first	O
laptops	B-Device
,	O
such	O
as	O
the	O
Grid	O
Compass	O
,	O
removed	O
this	O
requirement	O
by	O
incorporating	O
batteries	O
–	O
and	O
with	O
the	O
continued	O
miniaturization	O
of	O
computing	O
resources	O
and	O
advancements	O
in	O
portable	O
battery	O
life	O
,	O
portable	B-Device
computers	I-Device
grew	O
in	O
popularity	O
in	O
the	O
2000s	O
.	O
</s>
<s>
These	O
smartphones	B-Application
and	O
tablets	B-Device
run	O
on	O
a	O
variety	O
of	O
operating	B-General_Concept
systems	I-General_Concept
and	O
recently	O
became	O
the	O
dominant	O
computing	O
device	O
on	O
the	O
market	O
.	O
</s>
<s>
These	O
are	O
powered	O
by	O
System	B-Architecture
on	I-Architecture
a	I-Architecture
Chip	I-Architecture
(	O
SoCs	O
)	O
,	O
which	O
are	O
complete	O
computers	O
on	O
a	O
microchip	O
the	O
size	O
of	O
a	O
coin	O
.	O
</s>
<s>
Mobile	B-Device
computers	I-Device
:	O
</s>
<s>
The	O
term	O
hardware	B-Architecture
covers	O
all	O
of	O
those	O
parts	O
of	O
a	O
computer	O
that	O
are	O
tangible	O
physical	O
objects	O
.	O
</s>
<s>
Circuits	O
,	O
computer	O
chips	O
,	O
graphic	B-Device
cards	I-Device
,	O
sound	B-Device
cards	I-Device
,	O
memory	B-General_Concept
(	O
RAM	B-Architecture
)	O
,	O
motherboard	O
,	O
displays	O
,	O
power	O
supplies	O
,	O
cables	O
,	O
keyboards	B-Device
,	O
printers	O
and	O
"	O
mice	O
"	O
input	O
devices	O
are	O
all	O
hardware	B-Architecture
.	O
</s>
<s>
A	O
general-purpose	O
computer	O
has	O
four	O
main	O
components	O
:	O
the	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
,	O
the	O
control	B-General_Concept
unit	I-General_Concept
,	O
the	O
memory	B-General_Concept
,	O
and	O
the	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
devices	O
(	O
collectively	O
termed	O
I/O	B-General_Concept
)	O
.	O
</s>
<s>
These	O
parts	O
are	O
interconnected	O
by	O
buses	B-General_Concept
,	O
often	O
made	O
of	O
groups	O
of	O
wires	O
.	O
</s>
<s>
Inside	O
each	O
of	O
these	O
parts	O
are	O
thousands	O
to	O
trillions	O
of	O
small	O
electrical	O
circuits	O
which	O
can	O
be	O
turned	O
off	O
or	O
on	O
by	O
means	O
of	O
an	O
electronic	B-Application
switch	I-Application
.	O
</s>
<s>
When	O
unprocessed	O
data	B-General_Concept
is	O
sent	O
to	O
the	O
computer	O
with	O
the	O
help	O
of	O
input	O
devices	O
,	O
the	O
data	B-General_Concept
is	O
processed	O
and	O
sent	O
to	O
output	O
devices	O
.	O
</s>
<s>
The	O
act	O
of	O
processing	O
is	O
mainly	O
regulated	O
by	O
the	O
CPU	B-Device
.	O
</s>
<s>
The	O
control	B-General_Concept
unit	I-General_Concept
(	O
often	O
called	O
a	O
control	O
system	O
or	O
central	O
controller	O
)	O
manages	O
the	O
computer	O
's	O
various	O
components	O
;	O
it	O
reads	O
and	O
interprets	O
(	O
decodes	O
)	O
the	O
program	B-Application
instructions	O
,	O
transforming	O
them	O
into	O
control	O
signals	O
that	O
activate	O
other	O
parts	O
of	O
the	O
computer	O
.	O
</s>
<s>
A	O
key	O
component	O
common	O
to	O
all	O
CPUs	B-Device
is	O
the	O
program	B-General_Concept
counter	I-General_Concept
,	O
a	O
special	O
memory	B-Algorithm
cell	I-Algorithm
(	O
a	O
register	B-General_Concept
)	O
that	O
keeps	O
track	O
of	O
which	O
location	O
in	O
memory	B-General_Concept
the	O
next	B-General_Concept
instruction	I-General_Concept
is	O
to	O
be	O
read	O
from	O
.	O
</s>
<s>
The	O
control	O
system	O
's	O
function	O
is	O
as	O
follows	O
—	O
this	O
is	O
a	O
simplified	O
description	O
,	O
and	O
some	O
of	O
these	O
steps	O
may	O
be	O
performed	O
concurrently	O
or	O
in	O
a	O
different	O
order	O
depending	O
on	O
the	O
type	O
of	O
CPU	B-Device
:	O
</s>
<s>
Read	O
the	O
code	O
for	O
the	O
next	B-General_Concept
instruction	I-General_Concept
from	O
the	O
cell	O
indicated	O
by	O
the	O
program	B-General_Concept
counter	I-General_Concept
.	O
</s>
<s>
Increment	O
the	O
program	B-General_Concept
counter	I-General_Concept
so	O
it	O
points	O
to	O
the	O
next	B-General_Concept
instruction	I-General_Concept
.	O
</s>
<s>
Read	O
whatever	O
data	B-General_Concept
the	O
instruction	O
requires	O
from	O
cells	O
in	O
memory	B-General_Concept
(	O
or	O
perhaps	O
from	O
an	O
input	O
device	O
)	O
.	O
</s>
<s>
The	O
location	O
of	O
this	O
required	O
data	B-General_Concept
is	O
typically	O
stored	O
within	O
the	O
instruction	B-Language
code	I-Language
.	O
</s>
<s>
Provide	O
the	O
necessary	O
data	B-General_Concept
to	O
an	O
ALU	O
or	O
register	B-General_Concept
.	O
</s>
<s>
If	O
the	O
instruction	O
requires	O
an	O
ALU	O
or	O
specialized	O
hardware	B-Architecture
to	O
complete	O
,	O
instruct	O
the	O
hardware	B-Architecture
to	O
perform	O
the	O
requested	O
operation	O
.	O
</s>
<s>
Write	O
the	O
result	O
from	O
the	O
ALU	O
back	O
to	O
a	O
memory	B-General_Concept
location	O
or	O
to	O
a	O
register	B-General_Concept
or	O
perhaps	O
an	O
output	O
device	O
.	O
</s>
<s>
Since	O
the	O
program	B-General_Concept
counter	I-General_Concept
is	O
(	O
conceptually	O
)	O
just	O
another	O
set	O
of	O
memory	B-Algorithm
cells	I-Algorithm
,	O
it	O
can	O
be	O
changed	O
by	O
calculations	O
done	O
in	O
the	O
ALU	O
.	O
</s>
<s>
Adding	O
100	O
to	O
the	O
program	B-General_Concept
counter	I-General_Concept
would	O
cause	O
the	O
next	B-General_Concept
instruction	I-General_Concept
to	O
be	O
read	O
from	O
a	O
place	O
100	O
locations	O
further	O
down	O
the	O
program	B-Application
.	O
</s>
<s>
Instructions	O
that	O
modify	O
the	O
program	B-General_Concept
counter	I-General_Concept
are	O
often	O
known	O
as	O
"	O
jumps	O
"	O
and	O
allow	O
for	O
loops	O
(	O
instructions	O
that	O
are	O
repeated	O
by	O
the	O
computer	O
)	O
and	O
often	O
conditional	B-Language
instruction	O
execution	O
(	O
both	O
examples	O
of	O
control	O
flow	O
)	O
.	O
</s>
<s>
The	O
sequence	O
of	O
operations	O
that	O
the	O
control	B-General_Concept
unit	I-General_Concept
goes	O
through	O
to	O
process	O
an	O
instruction	O
is	O
in	O
itself	O
like	O
a	O
short	O
computer	B-Application
program	I-Application
,	O
and	O
indeed	O
,	O
in	O
some	O
more	O
complex	O
CPU	B-Device
designs	O
,	O
there	O
is	O
another	O
yet	O
smaller	O
computer	O
called	O
a	O
microsequencer	B-General_Concept
,	O
which	O
runs	O
a	O
microcode	B-Device
program	B-Application
that	O
causes	O
all	O
of	O
these	O
events	O
to	O
happen	O
.	O
</s>
<s>
The	O
control	B-General_Concept
unit	I-General_Concept
,	O
ALU	O
,	O
and	O
registers	B-General_Concept
are	O
collectively	O
known	O
as	O
a	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	B-Device
)	O
.	O
</s>
<s>
Early	O
CPUs	B-Device
were	O
composed	O
of	O
many	O
separate	O
components	O
.	O
</s>
<s>
Since	O
the	O
1970s	O
,	O
CPUs	B-Device
have	O
typically	O
been	O
constructed	O
on	O
a	O
single	O
MOS	B-Architecture
integrated	O
circuit	O
chip	O
called	O
a	O
microprocessor	B-Architecture
.	O
</s>
<s>
Some	O
can	O
operate	O
only	O
on	O
whole	O
numbers	O
(	O
integers	O
)	O
while	O
others	O
use	O
floating	B-Algorithm
point	I-Algorithm
to	O
represent	O
real	O
numbers	O
,	O
albeit	O
with	O
limited	O
precision	O
.	O
</s>
<s>
However	O
,	O
any	O
computer	O
that	O
is	O
capable	O
of	O
performing	O
just	O
the	O
simplest	O
operations	O
can	O
be	O
programmed	B-General_Concept
to	O
break	O
down	O
the	O
more	O
complex	O
operations	O
into	O
simple	O
steps	O
that	O
it	O
can	O
perform	O
.	O
</s>
<s>
Therefore	O
,	O
any	O
computer	O
can	O
be	O
programmed	B-General_Concept
to	O
perform	O
any	O
arithmetic	O
operation	O
—	O
although	O
it	O
will	O
take	O
more	O
time	O
to	O
do	O
so	O
if	O
its	O
ALU	O
does	O
not	O
directly	O
support	O
the	O
operation	O
.	O
</s>
<s>
These	O
can	O
be	O
useful	O
for	O
creating	O
complicated	O
conditional	B-Language
statements	I-Language
and	O
processing	O
Boolean	O
logic	O
.	O
</s>
<s>
Superscalar	B-General_Concept
computers	O
may	O
contain	O
multiple	O
ALUs	O
,	O
allowing	O
them	O
to	O
process	O
several	O
instructions	O
simultaneously	O
.	O
</s>
<s>
Graphics	B-Architecture
processors	I-Architecture
and	O
computers	O
with	O
SIMD	B-Device
and	O
MIMD	B-Operating_System
features	O
often	O
contain	O
ALUs	O
that	O
can	O
perform	O
arithmetic	O
on	O
vectors	O
and	O
matrices	B-Architecture
.	O
</s>
<s>
A	O
computer	O
's	O
memory	B-General_Concept
can	O
be	O
viewed	O
as	O
a	O
list	O
of	O
cells	O
into	O
which	O
numbers	O
can	O
be	O
placed	O
or	O
read	O
.	O
</s>
<s>
The	O
information	O
stored	O
in	O
memory	B-General_Concept
may	O
represent	O
practically	O
anything	O
.	O
</s>
<s>
Letters	O
,	O
numbers	O
,	O
even	O
computer	O
instructions	O
can	O
be	O
placed	O
into	O
memory	B-General_Concept
with	O
equal	O
ease	O
.	O
</s>
<s>
Since	O
the	O
CPU	B-Device
does	O
not	O
differentiate	O
between	O
different	O
types	O
of	O
information	O
,	O
it	O
is	O
the	B-Application
software	I-Application
's	O
responsibility	O
to	O
give	O
significance	O
to	O
what	O
the	O
memory	B-General_Concept
sees	O
as	O
nothing	O
but	O
a	O
series	O
of	O
numbers	O
.	O
</s>
<s>
In	O
almost	O
all	O
modern	O
computers	O
,	O
each	O
memory	B-Algorithm
cell	I-Algorithm
is	O
set	O
up	O
to	O
store	O
binary	O
numbers	O
in	O
groups	O
of	O
eight	O
bits	O
(	O
called	O
a	O
byte	B-Application
)	O
.	O
</s>
<s>
Each	O
byte	B-Application
is	O
able	O
to	O
represent	O
256	O
different	O
numbers	O
(	O
28	O
=	O
256	O
)	O
;	O
either	O
from	O
0	O
to	O
255	O
or	O
−128	O
to	O
+127	O
.	O
</s>
<s>
To	O
store	O
larger	O
numbers	O
,	O
several	O
consecutive	O
bytes	B-Application
may	O
be	O
used	O
(	O
typically	O
,	O
two	O
,	O
four	O
or	O
eight	O
)	O
.	O
</s>
<s>
When	O
negative	O
numbers	O
are	O
required	O
,	O
they	O
are	O
usually	O
stored	O
in	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
notation	I-General_Concept
.	O
</s>
<s>
A	O
computer	O
can	O
store	O
any	O
kind	O
of	O
information	O
in	O
memory	B-General_Concept
if	O
it	O
can	O
be	O
represented	O
numerically	O
.	O
</s>
<s>
Modern	O
computers	O
have	O
billions	O
or	O
even	O
trillions	O
of	O
bytes	B-Application
of	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
CPU	B-Device
contains	O
a	O
special	O
set	O
of	O
memory	B-Algorithm
cells	I-Algorithm
called	O
registers	B-General_Concept
that	O
can	O
be	O
read	O
and	O
written	O
to	O
much	O
more	O
rapidly	O
than	O
the	O
main	O
memory	B-General_Concept
area	O
.	O
</s>
<s>
There	O
are	O
typically	O
between	O
two	O
and	O
one	O
hundred	O
registers	B-General_Concept
depending	O
on	O
the	O
type	O
of	O
CPU	B-Device
.	O
</s>
<s>
Registers	B-General_Concept
are	O
used	O
for	O
the	O
most	O
frequently	O
needed	O
data	B-General_Concept
items	O
to	O
avoid	O
having	O
to	O
access	O
main	O
memory	B-General_Concept
every	O
time	O
data	B-General_Concept
is	O
needed	O
.	O
</s>
<s>
As	O
data	B-General_Concept
is	O
constantly	O
being	O
worked	O
on	O
,	O
reducing	O
the	O
need	O
to	O
access	O
main	O
memory	B-General_Concept
(	O
which	O
is	O
often	O
slow	O
compared	O
to	O
the	O
ALU	O
and	O
control	B-General_Concept
units	I-General_Concept
)	O
greatly	O
increases	O
the	O
computer	O
's	O
speed	O
.	O
</s>
<s>
Computer	O
main	O
memory	B-General_Concept
comes	O
in	O
two	O
principal	O
varieties	O
:	O
</s>
<s>
RAM	B-Architecture
can	O
be	O
read	O
and	O
written	O
to	O
anytime	O
the	O
CPU	B-Device
commands	O
it	O
,	O
but	O
ROM	B-Device
is	O
preloaded	O
with	O
data	B-General_Concept
and	O
software	B-Application
that	O
never	O
changes	O
,	O
therefore	O
the	O
CPU	B-Device
can	O
only	O
read	O
from	O
it	O
.	O
</s>
<s>
ROM	B-Device
is	O
typically	O
used	O
to	O
store	O
the	O
computer	O
's	O
initial	O
start-up	O
instructions	O
.	O
</s>
<s>
In	O
general	O
,	O
the	O
contents	O
of	O
RAM	B-Architecture
are	O
erased	O
when	O
the	O
power	O
to	O
the	O
computer	O
is	O
turned	O
off	O
,	O
but	O
ROM	B-Device
retains	O
its	O
data	B-General_Concept
indefinitely	O
.	O
</s>
<s>
In	O
a	O
PC	B-Device
,	O
the	O
ROM	B-Device
contains	O
a	O
specialized	O
program	B-Application
called	O
the	O
BIOS	B-Operating_System
that	O
orchestrates	O
loading	O
the	O
computer	O
's	O
operating	B-General_Concept
system	I-General_Concept
from	O
the	O
hard	B-Device
disk	I-Device
drive	I-Device
into	O
RAM	B-Architecture
whenever	O
the	O
computer	O
is	O
turned	O
on	O
or	O
reset	O
.	O
</s>
<s>
In	O
embedded	B-Architecture
computers	I-Architecture
,	O
which	O
frequently	O
do	O
not	O
have	O
disk	O
drives	O
,	O
all	O
of	O
the	O
required	O
software	B-Application
may	O
be	O
stored	O
in	O
ROM	B-Device
.	O
</s>
<s>
Software	B-Application
stored	O
in	O
ROM	B-Device
is	O
often	O
called	O
firmware	B-Application
,	O
because	O
it	O
is	O
notionally	O
more	O
like	O
hardware	B-Architecture
than	O
software	B-Application
.	I-Application
</s>
<s>
Flash	B-Device
memory	I-Device
blurs	O
the	O
distinction	O
between	O
ROM	B-Device
and	O
RAM	B-Architecture
,	O
as	O
it	O
retains	O
its	O
data	B-General_Concept
when	O
turned	O
off	O
but	O
is	O
also	O
rewritable	O
.	O
</s>
<s>
It	O
is	O
typically	O
much	O
slower	O
than	O
conventional	O
ROM	B-Device
and	O
RAM	B-Architecture
however	O
,	O
so	O
its	O
use	O
is	O
restricted	O
to	O
applications	O
where	O
high	O
speed	O
is	O
unnecessary	O
.	O
</s>
<s>
In	O
more	O
sophisticated	O
computers	O
there	O
may	O
be	O
one	O
or	O
more	O
RAM	B-Architecture
cache	B-General_Concept
memories	I-General_Concept
,	O
which	O
are	O
slower	O
than	O
registers	B-General_Concept
but	O
faster	O
than	O
main	O
memory	B-General_Concept
.	O
</s>
<s>
Generally	O
computers	O
with	O
this	O
sort	O
of	O
cache	O
are	O
designed	O
to	O
move	O
frequently	O
needed	O
data	B-General_Concept
into	O
the	O
cache	O
automatically	O
,	O
often	O
without	O
the	O
need	O
for	O
any	O
intervention	O
on	O
the	O
programmer	B-Application
's	O
part	O
.	O
</s>
<s>
I/O	B-General_Concept
is	O
the	O
means	O
by	O
which	O
a	O
computer	O
exchanges	O
information	O
with	O
the	O
outside	O
world	O
.	O
</s>
<s>
On	O
a	O
typical	O
personal	B-Device
computer	I-Device
,	O
peripherals	O
include	O
input	O
devices	O
like	O
the	O
keyboard	B-Device
and	O
mouse	B-Device
,	O
and	O
output	O
devices	O
such	O
as	O
the	O
display	B-Device
and	O
printer	O
.	O
</s>
<s>
Hard	B-Device
disk	I-Device
drives	I-Device
,	O
floppy	B-Device
disk	I-Device
drives	I-Device
and	O
optical	B-Device
disc	I-Device
drives	O
serve	O
as	O
both	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
devices	O
.	O
</s>
<s>
Computer	B-Architecture
networking	I-Architecture
is	O
another	O
form	O
of	O
I/O	B-General_Concept
.	O
</s>
<s>
I/O	B-General_Concept
devices	I-General_Concept
are	O
often	O
complex	O
computers	O
in	O
their	O
own	O
right	O
,	O
with	O
their	O
own	O
CPU	B-Device
and	O
memory	B-General_Concept
.	O
</s>
<s>
A	O
graphics	B-Architecture
processing	I-Architecture
unit	I-Architecture
might	O
contain	O
fifty	O
or	O
more	O
tiny	O
computers	O
that	O
perform	O
the	O
calculations	O
necessary	O
to	O
display	B-Device
3D	O
graphics	O
.	O
</s>
<s>
Modern	O
desktop	B-Device
computers	I-Device
contain	O
many	O
smaller	O
computers	O
that	O
assist	O
the	O
main	O
CPU	B-Device
in	O
performing	O
I/O	B-General_Concept
.	O
</s>
<s>
A	O
2016-era	O
flat	O
screen	O
display	B-Device
contains	O
its	O
own	O
computer	O
circuitry	O
.	O
</s>
<s>
While	O
a	O
computer	O
may	O
be	O
viewed	O
as	O
running	O
one	O
gigantic	O
program	B-Application
stored	O
in	O
its	O
main	O
memory	B-General_Concept
,	O
in	O
some	O
systems	O
it	O
is	O
necessary	O
to	O
give	O
the	O
appearance	O
of	O
running	O
several	O
programs	B-Application
simultaneously	O
.	O
</s>
<s>
having	O
the	O
computer	O
switch	O
rapidly	O
between	O
running	O
each	O
program	B-Application
in	O
turn	O
.	O
</s>
<s>
One	O
means	O
by	O
which	O
this	O
is	O
done	O
is	O
with	O
a	O
special	O
signal	O
called	O
an	O
interrupt	B-Application
,	O
which	O
can	O
periodically	O
cause	O
the	O
computer	O
to	O
stop	O
executing	O
instructions	O
where	O
it	O
was	O
and	O
do	O
something	O
else	O
instead	O
.	O
</s>
<s>
By	O
remembering	O
where	O
it	O
was	O
executing	O
prior	O
to	O
the	O
interrupt	B-Application
,	O
the	O
computer	O
can	O
return	O
to	O
that	O
task	O
later	O
.	O
</s>
<s>
If	O
several	O
programs	B-Application
are	O
running	O
"	O
at	O
the	O
same	O
time	O
"	O
.	O
</s>
<s>
then	O
the	O
interrupt	B-Application
generator	O
might	O
be	O
causing	O
several	O
hundred	O
interrupts	B-Application
per	O
second	O
,	O
causing	O
a	O
program	B-Application
switch	O
each	O
time	O
.	O
</s>
<s>
Since	O
modern	O
computers	O
typically	O
execute	O
instructions	O
several	O
orders	O
of	O
magnitude	O
faster	O
than	O
human	O
perception	O
,	O
it	O
may	O
appear	O
that	O
many	O
programs	B-Application
are	O
running	O
at	O
the	O
same	O
time	O
even	O
though	O
only	O
one	O
is	O
ever	O
executing	O
in	O
any	O
given	O
instant	O
.	O
</s>
<s>
This	O
method	O
of	O
multitasking	O
is	O
sometimes	O
termed	O
"	O
time-sharing	O
"	O
since	O
each	O
program	B-Application
is	O
allocated	O
a	O
"	O
slice	O
"	O
of	O
time	O
in	O
turn	O
.	O
</s>
<s>
Seemingly	O
,	O
multitasking	O
would	O
cause	O
a	O
computer	O
that	O
is	O
switching	O
between	O
several	O
programs	B-Application
to	O
run	O
more	O
slowly	O
,	O
in	O
direct	O
proportion	O
to	O
the	O
number	O
of	O
programs	B-Application
it	O
is	O
running	O
,	O
but	O
most	O
programs	B-Application
spend	O
much	O
of	O
their	O
time	O
waiting	O
for	O
slow	O
input/output	B-General_Concept
devices	I-General_Concept
to	O
complete	O
their	O
tasks	O
.	O
</s>
<s>
If	O
a	O
program	B-Application
is	O
waiting	O
for	O
the	O
user	O
to	O
click	O
on	O
the	O
mouse	B-Device
or	O
press	O
a	O
key	O
on	O
the	O
keyboard	B-Device
,	O
then	O
it	O
will	O
not	O
take	O
a	O
"	O
time	O
slice	O
"	O
until	O
the	O
event	O
it	O
is	O
waiting	O
for	O
has	O
occurred	O
.	O
</s>
<s>
This	O
frees	O
up	O
time	O
for	O
other	O
programs	B-Application
to	O
execute	O
so	O
that	O
many	O
programs	B-Application
may	O
be	O
run	O
simultaneously	O
without	O
unacceptable	O
speed	O
loss	O
.	O
</s>
<s>
Some	O
computers	O
are	O
designed	O
to	O
distribute	O
their	O
work	O
across	O
several	O
CPUs	B-Device
in	O
a	O
multiprocessing	O
configuration	O
,	O
a	O
technique	O
once	O
employed	O
in	O
only	O
large	O
and	O
powerful	O
machines	O
such	O
as	O
supercomputers	B-Architecture
,	O
mainframe	B-Architecture
computers	I-Architecture
and	O
servers	B-Application
.	O
</s>
<s>
Multiprocessor	O
and	O
multi-core	B-Architecture
(	O
multiple	O
CPUs	B-Device
on	O
a	O
single	O
integrated	O
circuit	O
)	O
personal	O
and	O
laptop	B-Device
computers	I-Device
are	O
now	O
widely	O
available	O
,	O
and	O
are	O
being	O
increasingly	O
used	O
in	O
lower-end	O
markets	O
as	O
a	O
result	O
.	O
</s>
<s>
Supercomputers	B-Architecture
in	O
particular	O
often	O
have	O
highly	O
unique	O
architectures	O
that	O
differ	O
significantly	O
from	O
the	O
basic	O
stored-program	B-Architecture
architecture	I-Architecture
and	O
from	O
general-purpose	O
computers	O
.	O
</s>
<s>
They	O
often	O
feature	O
thousands	O
of	O
CPUs	B-Device
,	O
customized	O
high-speed	O
interconnects	B-General_Concept
,	O
and	O
specialized	O
computing	B-Architecture
hardware	I-Architecture
.	O
</s>
<s>
Such	O
designs	O
tend	O
to	O
be	O
useful	O
for	O
only	O
specialized	O
tasks	O
due	O
to	O
the	O
large	O
scale	O
of	O
program	B-Application
organization	O
required	O
to	O
use	O
most	O
of	O
the	O
available	O
resources	O
at	O
once	O
.	O
</s>
<s>
Supercomputers	B-Architecture
usually	O
see	O
usage	O
in	O
large-scale	O
simulation	B-Application
,	O
graphics	O
rendering	O
,	O
and	O
cryptography	O
applications	O
,	O
as	O
well	O
as	O
with	O
other	O
so-called	O
"	O
embarrassingly	B-Operating_System
parallel	I-Operating_System
"	O
tasks	O
.	O
</s>
<s>
Software	B-Application
refers	O
to	O
parts	O
of	O
the	O
computer	O
which	O
do	O
not	O
have	O
a	O
material	O
form	O
,	O
such	O
as	O
programs	B-Application
,	O
data	B-General_Concept
,	O
protocols	O
,	O
etc	O
.	O
</s>
<s>
Software	B-Application
is	O
that	O
part	O
of	O
a	O
computer	O
system	O
that	O
consists	O
of	O
encoded	O
information	O
or	O
computer	O
instructions	O
,	O
in	O
contrast	O
to	O
the	O
physical	O
hardware	B-Architecture
from	O
which	O
the	O
system	O
is	O
built	O
.	O
</s>
<s>
Computer	B-Application
software	I-Application
includes	O
computer	B-Application
programs	I-Application
,	O
libraries	B-Library
and	O
related	O
non-executable	O
data	B-General_Concept
,	O
such	O
as	O
online	O
documentation	O
or	O
digital	B-General_Concept
media	O
.	O
</s>
<s>
It	O
is	O
often	O
divided	O
into	O
system	B-Application
software	I-Application
and	O
application	B-Application
software	I-Application
Computer	B-Architecture
hardware	I-Architecture
and	O
software	B-Application
require	O
each	O
other	O
and	O
neither	O
can	O
be	O
realistically	O
used	O
on	O
its	O
own	O
.	O
</s>
<s>
When	O
software	B-Application
is	O
stored	O
in	O
hardware	B-Architecture
that	O
cannot	O
easily	O
be	O
modified	O
,	O
such	O
as	O
with	O
BIOS	B-Operating_System
ROM	I-Operating_System
in	O
an	O
IBM	O
PC	B-Device
compatible	O
computer	O
,	O
it	O
is	O
sometimes	O
called	O
"	O
firmware	B-Application
"	O
.	O
</s>
<s>
The	O
defining	O
feature	O
of	O
modern	O
computers	O
which	O
distinguishes	O
them	O
from	O
all	O
other	O
machines	O
is	O
that	O
they	O
can	O
be	O
programmed	B-General_Concept
.	O
</s>
<s>
That	O
is	O
to	O
say	O
that	O
some	O
type	O
of	O
instructions	O
(	O
the	O
program	B-Application
)	O
can	O
be	O
given	O
to	O
the	O
computer	O
,	O
and	O
it	O
will	O
process	O
them	O
.	O
</s>
<s>
Modern	O
computers	O
based	O
on	O
the	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
often	O
have	O
machine	B-Language
code	I-Language
in	O
the	O
form	O
of	O
an	O
imperative	B-Application
programming	I-Application
language	I-Application
.	O
</s>
<s>
In	O
practical	O
terms	O
,	O
a	O
computer	B-Application
program	I-Application
may	O
be	O
just	O
a	O
few	O
instructions	O
or	O
extend	O
to	O
many	O
millions	O
of	O
instructions	O
,	O
as	O
do	O
the	O
programs	B-Application
for	O
word	B-General_Concept
processors	I-General_Concept
and	O
web	B-Application
browsers	I-Application
for	O
example	O
.	O
</s>
<s>
Large	O
computer	B-Application
programs	I-Application
consisting	O
of	O
several	O
million	O
instructions	O
may	O
take	O
teams	O
of	O
programmers	B-Application
years	O
to	O
write	O
,	O
and	O
due	O
to	O
the	O
complexity	O
of	O
the	O
task	O
almost	O
certainly	O
contain	O
errors	O
.	O
</s>
<s>
This	O
section	O
applies	O
to	O
most	O
common	O
RAM	B-Application
machine	I-Application
–	O
based	O
computers	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
computer	O
instructions	O
are	O
simple	O
:	O
add	O
one	O
number	O
to	O
another	O
,	O
move	O
some	O
data	B-General_Concept
from	O
one	O
location	O
to	O
another	O
,	O
send	O
a	O
message	O
to	O
some	O
external	O
device	O
,	O
etc	O
.	O
</s>
<s>
These	O
instructions	O
are	O
read	O
from	O
the	O
computer	O
's	O
memory	B-General_Concept
and	O
are	O
generally	O
carried	O
out	O
(	O
executed	B-General_Concept
)	O
in	O
the	O
order	O
they	O
were	O
given	O
.	O
</s>
<s>
However	O
,	O
there	O
are	O
usually	O
specialized	O
instructions	O
to	O
tell	O
the	O
computer	O
to	O
jump	O
ahead	O
or	O
backwards	O
to	O
some	O
other	O
place	O
in	O
the	O
program	B-Application
and	O
to	O
carry	O
on	O
executing	O
from	O
there	O
.	O
</s>
<s>
These	O
are	O
called	O
"	O
jump	O
"	O
instructions	O
(	O
or	O
branches	B-General_Concept
)	O
.	O
</s>
<s>
Furthermore	O
,	O
jump	O
instructions	O
may	O
be	O
made	O
to	O
happen	O
conditionally	B-Language
so	O
that	O
different	O
sequences	O
of	O
instructions	O
may	O
be	O
used	O
depending	O
on	O
the	O
result	O
of	O
some	O
previous	O
calculation	O
or	O
some	O
external	O
event	O
.	O
</s>
<s>
Program	B-Application
execution	O
might	O
be	O
likened	O
to	O
reading	O
a	O
book	O
.	O
</s>
<s>
Similarly	O
,	O
a	O
computer	O
may	O
sometimes	O
go	O
back	O
and	O
repeat	O
the	O
instructions	O
in	O
some	O
section	O
of	O
the	O
program	B-Application
over	O
and	O
over	O
again	O
until	O
some	O
internal	O
condition	O
is	O
met	O
.	O
</s>
<s>
This	O
is	O
called	O
the	O
flow	O
of	O
control	O
within	O
the	O
program	B-Application
and	O
it	O
is	O
what	O
allows	O
the	O
computer	O
to	O
perform	O
tasks	O
repeatedly	O
without	O
human	O
intervention	O
.	O
</s>
<s>
Comparatively	O
,	O
a	O
person	O
using	O
a	O
pocket	O
calculator	B-Application
can	O
perform	O
a	O
basic	O
arithmetic	O
operation	O
such	O
as	O
adding	O
two	O
numbers	O
with	O
just	O
a	O
few	O
button	O
presses	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
a	O
computer	O
may	O
be	O
programmed	B-General_Concept
to	O
do	O
this	O
with	O
just	O
a	O
few	O
simple	O
instructions	O
.	O
</s>
<s>
The	O
following	O
example	O
is	O
written	O
in	O
the	O
MIPS	B-Device
assembly	I-Device
language	I-Device
:	O
</s>
<s>
Once	O
told	O
to	O
run	O
this	O
program	B-Application
,	O
the	O
computer	O
will	O
perform	O
the	O
repetitive	O
addition	O
task	O
without	O
further	O
human	O
intervention	O
.	O
</s>
<s>
It	O
will	O
almost	O
never	O
make	O
a	O
mistake	O
and	O
a	O
modern	O
PC	B-Device
can	O
complete	O
the	O
task	O
in	O
a	O
fraction	O
of	O
a	O
second	O
.	O
</s>
<s>
In	O
most	O
computers	O
,	O
individual	O
instructions	O
are	O
stored	O
as	O
machine	B-Language
code	I-Language
with	O
each	O
instruction	O
being	O
given	O
a	O
unique	O
number	O
(	O
its	O
operation	B-Language
code	I-Language
or	O
opcode	B-Language
for	O
short	O
)	O
.	O
</s>
<s>
The	O
command	O
to	O
add	O
two	O
numbers	O
together	O
would	O
have	O
one	O
opcode	B-Language
;	O
the	O
command	O
to	O
multiply	O
them	O
would	O
have	O
a	O
different	O
opcode	B-Language
,	O
and	O
so	O
on	O
.	O
</s>
<s>
Since	O
the	O
computer	O
's	O
memory	B-General_Concept
is	O
able	O
to	O
store	O
numbers	O
,	O
it	O
can	O
also	O
store	O
the	O
instruction	B-Language
codes	I-Language
.	O
</s>
<s>
This	O
leads	O
to	O
the	O
important	O
fact	O
that	O
entire	O
programs	B-Application
(	O
which	O
are	O
just	O
lists	O
of	O
these	O
instructions	O
)	O
can	O
be	O
represented	O
as	O
lists	O
of	O
numbers	O
and	O
can	O
themselves	O
be	O
manipulated	O
inside	O
the	O
computer	O
in	O
the	O
same	O
way	O
as	O
numeric	B-Algorithm
data	B-General_Concept
.	O
</s>
<s>
The	O
fundamental	O
concept	O
of	O
storing	O
programs	B-Application
in	O
the	O
computer	O
's	O
memory	B-General_Concept
alongside	O
the	O
data	B-General_Concept
they	O
operate	O
on	O
is	O
the	O
crux	O
of	O
the	O
von	O
Neumann	O
,	O
or	O
stored	O
program	B-Application
,	O
architecture	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
a	O
computer	O
might	O
store	O
some	O
or	O
all	O
of	O
its	O
program	B-Application
in	O
memory	B-General_Concept
that	O
is	O
kept	O
separate	O
from	O
the	O
data	B-General_Concept
it	O
operates	O
on	O
.	O
</s>
<s>
This	O
is	O
called	O
the	O
Harvard	B-Architecture
architecture	I-Architecture
after	O
the	O
Harvard	B-Device
Mark	I-Device
I	I-Device
computer	O
.	O
</s>
<s>
Modern	O
von	B-Architecture
Neumann	I-Architecture
computers	I-Architecture
display	B-Device
some	O
traits	O
of	O
the	O
Harvard	B-Architecture
architecture	I-Architecture
in	O
their	O
designs	O
,	O
such	O
as	O
in	O
CPU	B-General_Concept
caches	I-General_Concept
.	O
</s>
<s>
While	O
it	O
is	O
possible	O
to	O
write	O
computer	B-Application
programs	I-Application
as	O
long	O
lists	O
of	O
numbers	O
(	O
machine	B-Language
language	I-Language
)	O
and	O
while	O
this	O
technique	O
was	O
used	O
with	O
many	O
early	O
computers	O
,	O
it	O
is	O
extremely	O
tedious	O
and	O
potentially	O
error-prone	O
to	O
do	O
so	O
in	O
practice	O
,	O
especially	O
for	O
complicated	O
programs	B-Application
.	O
</s>
<s>
These	O
mnemonics	O
are	O
collectively	O
known	O
as	O
a	O
computer	O
's	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
Converting	O
programs	B-Application
written	O
in	O
assembly	B-Language
language	I-Language
into	O
something	O
the	O
computer	O
can	O
actually	O
understand	O
(	O
machine	B-Language
language	I-Language
)	O
is	O
usually	O
done	O
by	O
a	O
computer	B-Application
program	I-Application
called	O
an	O
assembler	B-Language
.	O
</s>
<s>
Programming	O
languages	O
provide	O
various	O
ways	O
of	O
specifying	O
programs	B-Application
for	O
computers	O
to	O
run	O
.	O
</s>
<s>
They	O
are	O
generally	O
either	O
translated	O
into	O
machine	B-Language
code	I-Language
by	O
a	O
compiler	B-Language
or	O
an	O
assembler	B-Language
before	O
being	O
run	O
,	O
or	O
translated	O
directly	O
at	O
run	O
time	O
by	O
an	O
interpreter	B-Application
.	O
</s>
<s>
Sometimes	O
programs	B-Application
are	O
executed	B-General_Concept
by	O
a	O
hybrid	O
method	O
of	O
the	O
two	O
techniques	O
.	O
</s>
<s>
Machine	B-Language
languages	I-Language
and	O
the	O
assembly	B-Language
languages	I-Language
that	O
represent	O
them	O
(	O
collectively	O
termed	O
low-level	O
programming	O
languages	O
)	O
are	O
generally	O
unique	O
to	O
the	O
particular	O
architecture	O
of	O
a	O
computer	O
's	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	B-Device
)	O
.	O
</s>
<s>
For	O
instance	O
,	O
an	O
ARM	B-Architecture
architecture	I-Architecture
CPU	B-Device
(	O
such	O
as	O
may	O
be	O
found	O
in	O
a	O
smartphone	B-Application
or	O
a	O
hand-held	B-Application
videogame	I-Application
)	O
cannot	O
understand	O
the	O
machine	B-Language
language	I-Language
of	O
an	O
x86	B-Operating_System
CPU	B-Device
that	O
might	O
be	O
in	O
a	O
PC	B-Device
.	O
</s>
<s>
Historically	O
a	O
significant	O
number	O
of	O
other	O
cpu	B-Device
architectures	O
were	O
created	O
and	O
saw	O
extensive	O
use	O
,	O
notably	O
including	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
and	O
6510	O
in	O
addition	O
to	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
.	O
</s>
<s>
Although	O
considerably	O
easier	O
than	O
in	O
machine	B-Language
language	I-Language
,	O
writing	O
long	O
programs	B-Application
in	O
assembly	B-Language
language	I-Language
is	O
often	O
difficult	O
and	O
is	O
also	O
error	O
prone	O
.	O
</s>
<s>
Therefore	O
,	O
most	O
practical	O
programs	B-Application
are	O
written	O
in	O
more	O
abstract	O
high-level	B-Language
programming	I-Language
languages	I-Language
that	O
are	O
able	O
to	O
express	O
the	O
needs	O
of	O
the	O
programmer	B-Application
more	O
conveniently	O
(	O
and	O
thereby	O
help	O
reduce	O
programmer	B-Application
error	O
)	O
.	O
</s>
<s>
High	B-Language
level	I-Language
languages	I-Language
are	O
usually	O
"	O
compiled	B-Language
"	O
into	O
machine	B-Language
language	I-Language
(	O
or	O
sometimes	O
into	O
assembly	B-Language
language	I-Language
and	O
then	O
into	O
machine	B-Language
language	I-Language
)	O
using	O
another	O
computer	B-Application
program	I-Application
called	O
a	O
compiler	B-Language
.	O
</s>
<s>
High	B-Language
level	I-Language
languages	I-Language
are	O
less	O
related	O
to	O
the	O
workings	O
of	O
the	O
target	O
computer	O
than	O
assembly	B-Language
language	I-Language
,	O
and	O
more	O
related	O
to	O
the	O
language	O
and	O
structure	O
of	O
the	O
problem(s )	O
to	O
be	O
solved	O
by	O
the	O
final	O
program	B-Application
.	O
</s>
<s>
It	O
is	O
therefore	O
often	O
possible	O
to	O
use	O
different	O
compilers	B-Language
to	O
translate	O
the	O
same	O
high	B-Language
level	I-Language
language	I-Language
program	B-Application
into	O
the	O
machine	B-Language
language	I-Language
of	O
many	O
different	O
types	O
of	O
computer	O
.	O
</s>
<s>
This	O
is	O
part	O
of	O
the	O
means	O
by	O
which	O
software	B-Application
like	O
video	O
games	O
may	O
be	O
made	O
available	O
for	O
different	O
computer	B-General_Concept
architectures	I-General_Concept
such	O
as	O
personal	B-Device
computers	I-Device
and	O
various	O
video	B-Device
game	I-Device
consoles	I-Device
.	O
</s>
<s>
Program	B-Application
design	O
of	O
small	O
programs	B-Application
is	O
relatively	O
simple	O
and	O
involves	O
the	O
analysis	O
of	O
the	O
problem	O
,	O
collection	O
of	O
inputs	O
,	O
using	O
the	O
programming	O
constructs	O
within	O
languages	O
,	O
devising	O
or	O
using	O
established	O
procedures	O
and	O
algorithms	O
,	O
providing	O
data	B-General_Concept
for	O
output	O
devices	O
and	O
solutions	O
to	O
the	O
problem	O
as	O
applicable	O
.	O
</s>
<s>
Large	O
programs	B-Application
involving	O
thousands	O
of	O
line	O
of	O
code	O
and	O
more	O
require	O
formal	O
software	B-Application
methodologies	O
.	O
</s>
<s>
The	O
task	O
of	O
developing	O
large	O
software	B-Application
systems	O
presents	O
a	O
significant	O
intellectual	O
challenge	O
.	O
</s>
<s>
Producing	O
software	B-Application
with	O
an	O
acceptably	O
high	O
reliability	O
within	O
a	O
predictable	O
schedule	O
and	O
budget	O
has	O
historically	O
been	O
difficult	O
;	O
the	O
academic	O
and	O
professional	O
discipline	O
of	O
software	B-General_Concept
engineering	I-General_Concept
concentrates	O
specifically	O
on	O
this	O
challenge	O
.	O
</s>
<s>
Errors	O
in	O
computer	B-Application
programs	I-Application
are	O
called	O
"	O
bugs	B-Error_Name
"	O
.	O
</s>
<s>
They	O
may	O
be	O
benign	O
and	O
not	O
affect	O
the	O
usefulness	O
of	O
the	O
program	B-Application
,	O
or	O
have	O
only	O
subtle	O
effects	O
.	O
</s>
<s>
However	O
,	O
in	O
some	O
cases	O
they	O
may	O
cause	O
the	O
program	B-Application
or	O
the	O
entire	O
system	O
to	O
"	O
hang	B-General_Concept
"	O
,	O
becoming	O
unresponsive	O
to	O
input	O
such	O
as	O
mouse	B-Device
clicks	O
or	O
keystrokes	O
,	O
to	O
completely	O
fail	O
,	O
or	O
to	O
crash	B-General_Concept
.	O
</s>
<s>
Otherwise	O
benign	O
bugs	B-Error_Name
may	O
sometimes	O
be	O
harnessed	O
for	O
malicious	O
intent	O
by	O
an	O
unscrupulous	O
user	O
writing	O
an	O
exploit	O
,	O
code	O
designed	O
to	O
take	O
advantage	O
of	O
a	O
bug	B-Error_Name
and	O
disrupt	O
a	O
computer	O
's	O
proper	O
execution	O
.	O
</s>
<s>
Bugs	B-Error_Name
are	O
usually	O
not	O
the	O
fault	O
of	O
the	O
computer	O
.	O
</s>
<s>
Since	O
computers	O
merely	O
execute	O
the	O
instructions	O
they	O
are	O
given	O
,	O
bugs	B-Error_Name
are	O
nearly	O
always	O
the	O
result	O
of	O
programmer	B-Application
error	O
or	O
an	O
oversight	O
made	O
in	O
the	O
program	B-Application
's	O
design	O
.	O
</s>
<s>
Admiral	O
Grace	O
Hopper	O
,	O
an	O
American	O
computer	O
scientist	O
and	O
developer	B-Application
of	O
the	O
first	O
compiler	B-Language
,	O
is	O
credited	O
for	O
having	O
first	O
used	O
the	O
term	O
"	O
bugs	B-Error_Name
"	O
in	O
computing	O
after	O
a	O
dead	O
moth	O
was	O
found	O
shorting	O
a	O
relay	O
in	O
the	O
Harvard	B-Device
Mark	I-Device
II	I-Device
computer	O
in	O
September	O
1947	O
.	O
</s>
<s>
The	O
U.S.	O
military	O
's	O
SAGE	B-Device
system	I-Device
was	O
the	O
first	O
large-scale	O
example	O
of	O
such	O
a	O
system	O
,	O
which	O
led	O
to	O
a	O
number	O
of	O
special-purpose	O
commercial	O
systems	O
such	O
as	O
Sabre	B-Application
.	O
</s>
<s>
The	O
effort	O
was	O
funded	O
by	O
ARPA	O
(	O
now	O
DARPA	O
)	O
,	O
and	O
the	O
computer	B-Architecture
network	I-Architecture
that	O
resulted	O
was	O
called	O
the	O
ARPANET	O
.	O
</s>
<s>
Computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
and	O
applications	O
were	O
modified	O
to	O
include	O
the	O
ability	O
to	O
define	O
and	O
access	O
the	O
resources	O
of	O
other	O
computers	O
on	O
the	O
network	O
,	O
such	O
as	O
peripheral	O
devices	O
,	O
stored	O
information	O
,	O
and	O
the	O
like	O
,	O
as	O
extensions	O
of	O
the	O
resources	O
of	O
an	O
individual	O
computer	O
.	O
</s>
<s>
Initially	O
these	O
facilities	O
were	O
available	O
primarily	O
to	O
people	O
working	O
in	O
high-tech	O
environments	O
,	O
but	O
in	O
the	O
1990s	O
the	O
spread	O
of	O
applications	O
like	O
e-mail	O
and	O
the	O
World	O
Wide	O
Web	O
,	O
combined	O
with	O
the	O
development	O
of	O
cheap	O
,	O
fast	O
networking	O
technologies	O
like	O
Ethernet	O
and	O
ADSL	O
saw	O
computer	B-Architecture
networking	I-Architecture
become	O
almost	O
ubiquitous	O
.	O
</s>
<s>
A	O
very	O
large	O
proportion	O
of	O
personal	B-Device
computers	I-Device
regularly	O
connect	O
to	O
the	O
Internet	O
to	O
communicate	O
and	O
receive	O
information	O
.	O
</s>
<s>
A	O
computer	O
does	O
not	O
need	O
to	O
be	O
electronic	O
,	O
nor	O
even	O
have	O
a	O
processor	B-General_Concept
,	O
nor	O
RAM	B-Architecture
,	O
nor	O
even	O
a	O
hard	B-Device
disk	I-Device
.	O
</s>
<s>
While	O
popular	O
usage	O
of	O
the	O
word	O
"	O
computer	O
"	O
is	O
synonymous	O
with	O
a	O
personal	O
electronic	O
computer	O
,	O
a	O
typical	O
modern	O
definition	O
of	O
a	O
computer	O
is	O
:	O
"	O
A	O
device	O
that	O
computes	O
,	O
especially	O
a	O
programmable	B-General_Concept
 [ usually ] 	O
electronic	O
machine	O
that	O
performs	O
high-speed	O
mathematical	O
or	O
logical	O
operations	O
or	O
that	O
assembles	O
,	O
stores	O
,	O
correlates	O
,	O
or	O
otherwise	O
processes	O
information.	O
"	O
</s>
<s>
There	O
is	O
active	O
research	O
to	O
make	O
computers	O
out	O
of	O
many	O
promising	O
new	O
types	O
of	O
technology	O
,	O
such	O
as	O
optical	O
computers	O
,	O
DNA	B-Application
computers	I-Application
,	O
neural	B-General_Concept
computers	I-General_Concept
,	O
and	O
quantum	B-Architecture
computers	I-Architecture
.	O
</s>
<s>
Most	O
computers	O
are	O
universal	O
,	O
and	O
are	O
able	O
to	O
calculate	O
any	O
computable	O
function	O
,	O
and	O
are	O
limited	O
only	O
by	O
their	O
memory	B-General_Concept
capacity	O
and	O
operating	O
speed	O
.	O
</s>
<s>
However	O
different	O
designs	O
of	O
computers	O
can	O
give	O
very	O
different	O
performance	O
for	O
particular	O
problems	O
;	O
for	O
example	O
quantum	B-Architecture
computers	I-Architecture
can	O
potentially	O
break	O
some	O
modern	O
encryption	O
algorithms	O
(	O
by	O
quantum	B-Algorithm
factoring	I-Algorithm
)	O
very	O
quickly	O
.	O
</s>
<s>
There	O
are	O
many	O
types	O
of	O
computer	B-General_Concept
architectures	I-General_Concept
:	O
</s>
<s>
Of	O
all	O
these	O
abstract	B-Application
machines	I-Application
,	O
a	O
quantum	B-Architecture
computer	I-Architecture
holds	O
the	O
most	O
promise	O
for	O
revolutionizing	O
computing	O
.	O
</s>
<s>
Logic	O
gates	O
are	O
a	O
common	O
abstraction	O
which	O
can	O
apply	O
to	O
most	O
of	O
the	O
above	O
digital	B-General_Concept
or	O
analog	O
paradigms	O
.	O
</s>
<s>
The	O
ability	O
to	O
store	O
and	O
execute	O
lists	O
of	O
instructions	O
called	O
programs	B-Application
makes	O
computers	O
extremely	O
versatile	O
,	O
distinguishing	O
them	O
from	O
calculators	B-Application
.	O
</s>
<s>
Therefore	O
,	O
any	O
type	O
of	O
computer	O
(	O
netbook	B-Device
,	O
supercomputer	B-Architecture
,	O
cellular	O
automaton	O
,	O
etc	O
.	O
)	O
</s>
<s>
is	O
able	O
to	O
perform	O
the	O
same	O
computational	O
tasks	O
,	O
given	O
enough	O
time	O
and	O
storage	B-General_Concept
capacity	I-General_Concept
.	O
</s>
<s>
A	O
computer	O
will	O
solve	O
problems	O
in	O
exactly	O
the	O
way	O
it	O
is	O
programmed	B-General_Concept
to	O
,	O
without	O
regard	O
to	O
efficiency	O
,	O
alternative	O
solutions	O
,	O
possible	O
shortcuts	O
,	O
or	O
possible	O
errors	O
in	O
the	O
code	O
.	O
</s>
<s>
Computer	B-Application
programs	I-Application
that	O
learn	O
and	O
adapt	O
are	O
part	O
of	O
the	O
emerging	O
field	O
of	O
artificial	B-Application
intelligence	I-Application
and	O
machine	O
learning	O
.	O
</s>
<s>
Artificial	B-Application
intelligence	I-Application
based	O
products	O
generally	O
fall	O
into	O
two	O
major	O
categories	O
:	O
rule-based	O
systems	O
and	O
pattern	O
recognition	O
systems	O
.	O
</s>
<s>
Pattern-based	O
systems	O
use	O
data	B-General_Concept
about	O
a	O
problem	O
to	O
generate	O
conclusions	O
.	O
</s>
<s>
Examples	O
of	O
pattern-based	O
systems	O
include	O
voice	B-Application
recognition	I-Application
,	O
font	O
recognition	O
,	O
translation	O
and	O
the	O
emerging	O
field	O
of	O
on-line	O
marketing	O
.	O
</s>
