<s>
A	O
computer	B-Application
program	I-Application
is	O
a	O
sequence	O
or	O
set	O
of	O
instructions	O
in	O
a	O
programming	O
language	O
for	O
a	O
computer	O
to	O
execute	B-General_Concept
.	O
</s>
<s>
Computer	B-Application
programs	I-Application
are	O
one	O
component	O
of	O
software	O
,	O
which	O
also	O
includes	O
documentation	O
and	O
other	O
intangible	O
components	O
.	O
</s>
<s>
A	O
computer	B-Application
program	I-Application
in	O
its	O
human-readable	O
form	O
is	O
called	O
source	O
code	O
.	O
</s>
<s>
Source	O
code	O
needs	O
another	O
computer	B-Application
program	I-Application
to	O
execute	B-General_Concept
because	O
computers	O
can	O
only	O
execute	B-General_Concept
their	O
native	O
machine	B-Language
instructions	I-Language
.	O
</s>
<s>
Therefore	O
,	O
source	O
code	O
may	O
be	O
translated	O
to	O
machine	B-Language
instructions	I-Language
using	O
the	O
language	O
's	O
compiler	B-Language
.	O
</s>
<s>
(	O
Assembly	B-Language
language	I-Language
programs	O
are	O
translated	O
using	O
an	O
assembler	B-Language
.	O
)	O
</s>
<s>
The	O
resulting	O
file	O
is	O
called	O
an	O
executable	B-Application
.	O
</s>
<s>
Alternatively	O
,	O
source	O
code	O
may	O
execute	B-General_Concept
within	O
the	O
language	O
's	O
interpreter	B-Application
.	O
</s>
<s>
If	O
the	O
executable	B-Application
is	O
requested	O
for	O
execution	O
,	O
then	O
the	O
operating	B-General_Concept
system	I-General_Concept
loads	B-Operating_System
it	O
into	O
memory	B-General_Concept
and	O
starts	O
a	O
process	B-Operating_System
.	O
</s>
<s>
The	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
will	O
soon	O
switch	B-Operating_System
to	O
this	O
process	B-Operating_System
so	O
it	O
can	O
fetch	B-General_Concept
,	I-General_Concept
decode	I-General_Concept
,	I-General_Concept
and	I-General_Concept
then	I-General_Concept
execute	I-General_Concept
each	O
machine	B-Language
instruction	I-Language
.	O
</s>
<s>
If	O
the	O
source	O
code	O
is	O
requested	O
for	O
execution	O
,	O
then	O
the	O
operating	B-General_Concept
system	I-General_Concept
loads	B-Operating_System
the	O
corresponding	O
interpreter	B-Application
into	O
memory	B-General_Concept
and	O
starts	O
a	O
process	B-Operating_System
.	O
</s>
<s>
The	O
interpreter	B-Application
then	O
loads	B-Operating_System
the	O
source	O
code	O
into	O
memory	B-General_Concept
to	O
translate	O
and	O
execute	B-General_Concept
each	O
statement	O
.	O
</s>
<s>
Running	O
the	O
source	O
code	O
is	O
slower	O
than	O
running	O
an	O
executable	B-Application
.	O
</s>
<s>
Moreover	O
,	O
the	O
interpreter	B-Application
must	O
be	O
installed	O
on	O
the	O
computer	O
.	O
</s>
<s>
program	O
is	O
used	O
to	O
illustrate	O
a	O
language	O
's	O
basic	B-Language
syntax	O
.	O
</s>
<s>
The	O
syntax	O
of	O
the	O
language	O
BASIC	B-Language
(	O
1964	O
)	O
was	O
intentionally	O
limited	O
to	O
make	O
the	O
language	O
easy	O
to	O
learn	O
.	O
</s>
<s>
Here	O
is	O
an	O
example	O
computer	B-Application
program	I-Application
,	O
in	O
Basic	B-Language
,	O
to	O
average	O
a	O
list	B-General_Concept
of	O
numbers	O
:	O
</s>
<s>
Once	O
the	O
mechanics	O
of	O
basic	B-Language
computer	B-General_Concept
programming	I-General_Concept
are	O
learned	O
,	O
more	O
sophisticated	O
and	O
powerful	O
languages	O
are	O
available	O
to	O
build	O
large	O
computer	O
systems	O
.	O
</s>
<s>
Improvements	O
in	O
software	O
development	O
are	O
the	O
result	O
of	O
improvements	O
in	O
computer	B-Architecture
hardware	I-Architecture
.	O
</s>
<s>
At	O
each	O
stage	O
in	O
hardware	B-General_Concept
's	O
history	O
,	O
the	O
task	O
of	O
computer	B-General_Concept
programming	I-General_Concept
changed	O
dramatically	O
.	O
</s>
<s>
In	O
1837	O
,	O
Charles	O
Babbage	O
was	O
inspired	O
by	O
Jacquard	O
's	O
loom	O
to	O
attempt	O
to	O
build	O
the	B-Device
Analytical	I-Device
Engine	I-Device
.	O
</s>
<s>
The	O
device	O
had	O
a	O
"	O
store	O
"	O
which	O
consisted	O
of	O
memory	B-General_Concept
to	O
hold	O
1,000	O
numbers	O
of	O
50	O
decimal	O
digits	O
each	O
.	O
</s>
<s>
Ada	B-General_Concept
Lovelace	I-General_Concept
worked	O
for	O
Charles	O
Babbage	O
to	O
create	O
a	O
description	O
of	O
the	B-Device
Analytical	I-Device
Engine	I-Device
(	O
1843	O
)	O
.	O
</s>
<s>
The	O
description	O
contained	O
Note	O
G	O
which	O
completely	O
detailed	O
a	O
method	B-Language
for	O
calculating	O
Bernoulli	O
numbers	O
using	O
the	B-Device
Analytical	I-Device
Engine	I-Device
.	O
</s>
<s>
This	O
note	O
is	O
recognized	O
by	O
some	O
historians	O
as	O
the	O
world	O
's	O
first	O
computer	B-Application
program	I-Application
.	O
</s>
<s>
It	O
is	O
a	O
finite-state	B-Architecture
machine	I-Architecture
that	O
has	O
an	O
infinitely	O
long	O
read/write	O
tape	O
.	O
</s>
<s>
All	O
present-day	O
computers	O
are	O
Turing	B-Algorithm
complete	I-Algorithm
.	O
</s>
<s>
The	O
Electronic	B-Device
Numerical	I-Device
Integrator	I-Device
And	I-Device
Computer	I-Device
(	O
ENIAC	B-Device
)	O
was	O
built	O
between	O
July	O
1943	O
and	O
Fall	O
1945	O
.	O
</s>
<s>
It	O
was	O
a	O
Turing	B-Algorithm
complete	I-Algorithm
,	O
general-purpose	O
computer	O
that	O
used	O
17,468	O
vacuum	O
tubes	O
to	O
create	O
the	O
circuits	O
.	O
</s>
<s>
It	O
had	O
20	O
base-10	O
accumulators	B-General_Concept
.	O
</s>
<s>
Programming	O
the	O
ENIAC	B-Device
took	O
up	O
to	O
two	O
months	O
.	O
</s>
<s>
Programming	O
the	O
ENIAC	B-Device
also	O
involved	O
setting	O
some	O
of	O
the	O
3,000	O
switches	O
.	O
</s>
<s>
Instead	O
of	O
plugging	O
in	O
cords	O
and	O
turning	O
switches	O
,	O
a	O
stored-program	O
computer	O
loads	B-Operating_System
its	O
instructions	O
into	O
memory	B-General_Concept
just	O
like	O
it	O
loads	B-Operating_System
its	O
data	O
into	O
memory	B-General_Concept
.	O
</s>
<s>
Presper	O
Eckert	O
and	O
John	O
Mauchly	O
built	O
the	O
ENIAC	B-Device
.	O
</s>
<s>
Later	O
,	O
in	O
September	O
1944	O
,	O
Dr.	O
John	O
von	O
Neumann	O
began	O
working	O
on	O
the	O
ENIAC	B-Device
project	O
.	O
</s>
<s>
On	O
June	O
30	O
,	O
1945	O
,	O
von	O
Neumann	O
published	O
the	O
First	O
Draft	O
of	O
a	O
Report	O
on	O
the	O
EDVAC	B-Device
which	O
equated	O
the	O
structures	O
of	O
the	O
computer	O
with	O
the	O
structures	O
of	O
the	O
human	O
brain	O
.	O
</s>
<s>
The	O
design	O
became	O
known	O
as	O
the	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
.	O
</s>
<s>
The	O
architecture	O
was	O
simultaneously	O
deployed	O
in	O
the	O
constructions	O
of	O
the	O
EDVAC	B-Device
and	O
EDSAC	B-Device
computers	O
in	O
1949	O
.	O
</s>
<s>
The	O
IBM	B-Application
System/360	I-Application
(	O
1964	O
)	O
was	O
a	O
family	O
of	O
computers	O
,	O
each	O
having	O
the	O
same	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
.	O
</s>
<s>
The	O
Model	B-Device
20	I-Device
was	O
the	O
smallest	O
and	O
least	O
expensive	O
.	O
</s>
<s>
Customers	O
could	O
upgrade	O
and	O
retain	O
the	O
same	O
application	B-Application
software	I-Application
.	O
</s>
<s>
The	O
Model	B-Device
195	I-Device
was	O
the	O
most	O
premium	O
.	O
</s>
<s>
Each	O
System/360	B-Application
model	O
featured	O
multiprogramming	O
—	O
having	O
multiple	O
processes	B-Operating_System
in	O
memory	B-General_Concept
at	O
once	O
.	O
</s>
<s>
When	O
one	O
process	B-Operating_System
was	O
waiting	O
for	O
input/output	B-General_Concept
,	O
another	O
could	O
compute	O
.	O
</s>
<s>
IBM	O
planned	O
for	O
each	O
model	O
to	O
be	O
programmed	O
using	O
PL/1	B-Language
.	O
</s>
<s>
A	O
committee	O
was	O
formed	O
that	O
included	O
COBOL	B-Application
,	O
Fortran	B-Application
and	O
ALGOL	B-Language
programmers	B-Application
.	O
</s>
<s>
The	O
purpose	O
was	O
to	O
develop	O
a	O
language	O
that	O
was	O
comprehensive	O
,	O
easy	O
to	O
use	O
,	O
extendible	O
,	O
and	O
would	O
replace	O
Cobol	B-Application
and	O
Fortran	B-Application
.	O
</s>
<s>
The	O
result	O
was	O
a	O
large	O
and	O
complex	O
language	O
that	O
took	O
a	O
long	O
time	O
to	O
compile	B-Language
.	O
</s>
<s>
The	O
computer	B-Application
program	I-Application
was	O
written	O
on	O
paper	O
for	O
reference	O
.	O
</s>
<s>
After	O
setting	O
the	O
configuration	O
,	O
an	O
execute	B-General_Concept
button	O
was	O
pressed	O
.	O
</s>
<s>
This	O
process	B-Operating_System
was	O
then	O
repeated	O
.	O
</s>
<s>
Computer	B-Application
programs	I-Application
also	O
were	O
automatically	O
inputted	O
via	O
paper	O
tape	O
,	O
punched	B-Architecture
cards	I-Architecture
or	O
magnetic-tape	B-Device
.	O
</s>
<s>
After	O
the	O
medium	O
was	O
loaded	O
,	O
the	O
starting	O
address	O
was	O
set	O
via	O
switches	O
,	O
and	O
the	O
execute	B-General_Concept
button	O
was	O
pressed	O
.	O
</s>
<s>
Robert	O
Noyce	O
,	O
co-founder	O
of	O
Fairchild	O
Semiconductor	O
(	O
1957	O
)	O
and	O
Intel	O
(	O
1968	O
)	O
,	O
achieved	O
a	O
technological	O
improvement	O
to	O
refine	O
the	O
production	B-Architecture
of	O
field-effect	O
transistors	O
(	O
1963	O
)	O
.	O
</s>
<s>
First	O
,	O
naturally	O
occurring	O
silicate	O
minerals	O
are	O
converted	O
into	O
polysilicon	O
rods	O
using	O
the	O
Siemens	O
process	B-Operating_System
.	O
</s>
<s>
The	O
Czochralski	O
process	B-Operating_System
then	O
converts	O
the	O
rods	O
into	O
a	O
monocrystalline	O
silicon	O
,	O
boule	B-Algorithm
crystal	I-Algorithm
.	O
</s>
<s>
The	O
crystal	O
is	O
then	O
thinly	O
sliced	O
to	O
form	O
a	O
wafer	B-Architecture
substrate	B-Architecture
.	O
</s>
<s>
The	O
planar	B-Algorithm
process	I-Algorithm
of	O
photolithography	B-Algorithm
then	O
integrates	O
unipolar	O
transistors	O
,	O
capacitors	O
,	O
diodes	O
,	O
and	O
resistors	O
onto	O
the	O
wafer	B-Architecture
to	O
build	O
a	O
matrix	B-General_Concept
of	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	O
)	O
transistors	O
.	O
</s>
<s>
The	O
MOS	B-Architecture
transistor	I-Architecture
is	O
the	O
primary	O
component	O
in	O
integrated	O
circuit	O
chips	O
.	O
</s>
<s>
During	O
the	O
1960s	O
,	O
controlling	O
the	O
electrical	O
flow	O
migrated	O
to	O
programming	O
a	O
matrix	B-General_Concept
of	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
.	O
</s>
<s>
The	O
matrix	B-General_Concept
resembled	O
a	O
two-dimensional	O
array	O
of	O
fuses	O
.	O
</s>
<s>
The	O
process	B-Operating_System
to	O
embed	O
instructions	O
onto	O
the	O
matrix	B-General_Concept
was	O
to	O
burn	O
out	O
the	O
unneeded	O
connections	O
.	O
</s>
<s>
There	O
were	O
so	O
many	O
connections	O
,	O
firmware	B-Application
programmers	B-Application
wrote	O
a	O
computer	B-Application
program	I-Application
on	O
another	O
chip	O
to	O
oversee	O
the	O
burning	O
.	O
</s>
<s>
The	O
technology	O
became	O
known	O
as	O
Programmable	B-General_Concept
ROM	I-General_Concept
.	O
</s>
<s>
In	O
1971	O
,	O
Intel	O
installed	O
the	O
computer	B-Application
program	I-Application
onto	O
the	O
chip	O
and	O
named	O
it	O
the	O
Intel	B-General_Concept
4004	I-General_Concept
microprocessor	B-Architecture
.	O
</s>
<s>
The	O
terms	O
microprocessor	B-Architecture
and	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	B-Device
)	O
are	O
now	O
used	O
interchangeably	O
.	O
</s>
<s>
However	O
,	O
CPUs	B-Device
predate	O
microprocessors	B-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
the	O
IBM	B-Application
System/360	I-Application
(	O
1964	O
)	O
had	O
a	O
CPU	B-Device
made	O
from	O
circuit	B-Algorithm
boards	I-Algorithm
containing	I-Algorithm
discrete	I-Algorithm
components	I-Algorithm
on	I-Algorithm
ceramic	I-Algorithm
substrates	I-Algorithm
.	O
</s>
<s>
The	O
Intel	B-General_Concept
4004	I-General_Concept
(	O
1971	O
)	O
was	O
a	O
4-bit	O
microprocessor	B-Architecture
designed	O
to	O
run	O
the	O
Busicom	O
calculator	O
.	O
</s>
<s>
Five	O
months	O
after	O
its	O
release	O
,	O
Intel	O
released	O
the	O
Intel	B-General_Concept
8008	I-General_Concept
,	O
an	O
8-bit	O
microprocessor	B-Architecture
.	O
</s>
<s>
Bill	O
Pentz	O
led	O
a	O
team	O
at	O
Sacramento	O
State	O
to	O
build	O
the	O
first	O
microcomputer	B-Architecture
using	O
the	O
Intel	B-General_Concept
8008	I-General_Concept
:	O
the	O
Sac	O
State	O
8008	B-General_Concept
(	O
1972	O
)	O
.	O
</s>
<s>
The	O
computer	O
supported	O
a	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
to	O
run	O
a	O
Memorex	O
,	O
3-megabyte	O
,	O
hard	B-Device
disk	I-Device
drive	I-Device
.	O
</s>
<s>
The	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
was	O
programmed	O
using	O
IBM	O
's	O
Basic	B-Device
Assembly	I-Device
Language	I-Device
(	O
BAL	O
)	O
.	O
</s>
<s>
The	O
medical	O
records	O
application	O
was	O
programmed	O
using	O
a	O
BASIC	B-Language
interpreter	B-Application
.	O
</s>
<s>
Nonetheless	O
,	O
the	O
project	O
contributed	O
to	O
the	O
development	O
of	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
(	O
1974	O
)	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
In	O
1978	O
,	O
the	O
modern	O
software	B-Application
development	I-Application
environment	I-Application
began	O
when	O
Intel	O
upgraded	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
to	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
.	O
</s>
<s>
Intel	O
simplified	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
to	O
manufacture	O
the	O
cheaper	O
Intel	B-Device
8088	I-Device
.	O
</s>
<s>
IBM	O
embraced	O
the	O
Intel	B-Device
8088	I-Device
when	O
they	O
entered	O
the	O
personal	B-Device
computer	I-Device
market	O
(	O
1981	O
)	O
.	O
</s>
<s>
As	O
consumer	O
demand	O
for	O
personal	B-Device
computers	I-Device
increased	O
,	O
so	O
did	O
Intel	O
's	O
microprocessor	B-Architecture
development	O
.	O
</s>
<s>
The	O
succession	O
of	O
development	O
is	O
known	O
as	O
the	O
x86	B-Operating_System
series	I-Operating_System
.	O
</s>
<s>
The	O
x86	B-Language
assembly	I-Language
language	I-Language
is	O
a	O
family	O
of	O
backward-compatible	B-General_Concept
machine	B-Language
instructions	I-Language
.	O
</s>
<s>
Machine	B-Language
instructions	I-Language
created	O
in	O
earlier	O
microprocessors	B-Architecture
were	O
retained	O
throughout	O
microprocessor	B-Architecture
upgrades	O
.	O
</s>
<s>
This	O
enabled	O
consumers	O
to	O
purchase	O
new	O
computers	O
without	O
having	O
to	O
purchase	O
new	O
application	B-Application
software	I-Application
.	O
</s>
<s>
Memory	B-General_Concept
instructions	O
to	O
set	O
and	O
access	O
numbers	O
and	O
strings	O
in	O
random-access	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Integer	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
instructions	O
to	O
perform	O
the	O
primary	O
arithmetic	O
operations	B-Language
on	O
integers	O
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
ALU	O
instructions	O
to	O
perform	O
the	O
primary	O
arithmetic	O
operations	B-Language
on	O
real	O
numbers	O
.	O
</s>
<s>
Call	B-General_Concept
stack	I-General_Concept
instructions	O
to	O
push	O
and	O
pop	O
words	O
needed	O
to	O
allocate	B-Language
memory	B-General_Concept
and	O
interface	B-Application
with	O
functions	O
.	O
</s>
<s>
Single	B-Device
instruction	I-Device
,	I-Device
multiple	I-Device
data	I-Device
(	O
SIMD	B-Device
)	O
instructions	O
to	O
increase	O
speed	O
when	O
multiple	O
processors	O
are	O
available	O
to	O
perform	O
the	O
same	O
algorithm	O
on	O
an	O
array	B-Data_Structure
of	I-Data_Structure
data	I-Data_Structure
.	O
</s>
<s>
VLSI	O
circuits	O
enabled	O
the	O
programming	B-Application
environment	I-Application
to	O
advance	O
from	O
a	O
computer	B-General_Concept
terminal	I-General_Concept
(	O
until	O
the	O
1990s	O
)	O
to	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
computer	O
.	O
</s>
<s>
Computer	B-General_Concept
terminals	I-General_Concept
limited	O
programmers	B-Application
to	O
a	O
single	O
shell	B-Operating_System
running	O
in	O
a	O
command-line	B-Application
environment	I-Application
.	O
</s>
<s>
During	O
the	O
1970s	O
,	O
full-screen	O
source	O
code	O
editing	O
became	O
possible	O
through	O
a	O
text-based	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
procedural	B-Application
languages	I-Application
,	O
functional	B-Language
languages	I-Language
,	O
and	O
logical	B-Language
languages	I-Language
.	O
</s>
<s>
different	O
levels	O
of	O
data	B-Application
abstraction	I-Application
.	O
</s>
<s>
different	O
levels	O
of	O
class	B-Application
hierarchy	I-Application
.	O
</s>
<s>
different	O
levels	O
of	O
input	O
datatypes	O
,	O
as	O
in	O
container	B-Application
types	I-Application
and	O
generic	B-Language
programming	I-Language
.	O
</s>
<s>
A	O
programming	O
language	O
is	O
a	O
set	O
of	O
keywords	O
,	O
symbols	O
,	O
identifiers	O
,	O
and	O
rules	O
by	O
which	O
programmers	B-Application
can	O
communicate	O
instructions	O
to	O
the	O
computer	O
.	O
</s>
<s>
Symbols	O
are	O
characters	O
to	O
form	O
operations	B-Language
,	O
assignments	O
,	O
control	O
flow	O
,	O
and	O
delimiters	B-Algorithm
.	O
</s>
<s>
Identifiers	O
are	O
words	O
created	O
by	O
programmers	B-Application
to	O
form	O
constants	O
,	O
variable	O
names	O
,	O
structure	O
names	O
,	O
and	O
function	O
names	O
.	O
</s>
<s>
The	O
evolution	O
of	O
programming	O
language	O
began	O
when	O
the	O
EDSAC	B-Device
(	O
1949	O
)	O
used	O
the	O
first	O
stored	O
computer	B-Application
program	I-Application
in	O
its	O
von	B-Architecture
Neumann	I-Architecture
architecture	I-Architecture
.	O
</s>
<s>
Programming	O
the	O
EDSAC	B-Device
was	O
in	O
the	O
first	O
generation	O
of	O
programming	O
language	O
.	O
</s>
<s>
The	O
first	O
generation	O
of	O
programming	O
language	O
is	O
machine	B-Language
language	I-Language
.	O
</s>
<s>
Machine	B-Language
language	I-Language
requires	O
the	O
programmer	B-Application
to	O
enter	O
instructions	O
using	O
instruction	O
numbers	O
called	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
For	O
example	O
,	O
the	O
ADD	O
operation	O
on	O
the	O
PDP-11	B-Device
has	O
instruction	O
number	O
24576	O
.	O
</s>
<s>
The	O
second	O
generation	O
of	O
programming	O
language	O
is	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
Assembly	B-Language
language	I-Language
allows	O
the	O
programmer	B-Application
to	O
use	O
mnemonic	O
instructions	O
instead	O
of	O
remembering	O
instruction	O
numbers	O
.	O
</s>
<s>
An	O
assembler	B-Language
translates	O
each	O
assembly	B-Language
language	I-Language
mnemonic	O
into	O
its	O
machine	B-Language
language	I-Language
number	O
.	O
</s>
<s>
For	O
example	O
,	O
on	O
the	O
PDP-11	B-Device
,	O
the	O
operation	O
24576	O
can	O
be	O
referenced	O
as	O
ADD	O
in	O
the	O
source	O
code	O
.	O
</s>
<s>
The	O
four	O
basic	B-Language
arithmetic	O
operations	B-Language
have	O
assembly	B-Language
instructions	O
like	O
ADD	O
,	O
SUB	O
,	O
MUL	O
,	O
and	O
DIV	O
.	O
</s>
<s>
Computers	O
also	O
have	O
instructions	O
like	O
DW	O
(	O
Define	O
Word	O
)	O
to	O
reserve	O
memory	B-General_Concept
cells	O
.	O
</s>
<s>
Then	O
the	O
MOV	O
instruction	O
can	O
copy	O
integers	O
between	O
registers	B-General_Concept
and	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
basic	B-Language
structure	O
of	O
an	O
assembly	B-Language
language	I-Language
statement	O
is	O
a	O
label	O
,	O
operation	O
,	O
operand	O
,	O
and	O
comment	O
.	O
</s>
<s>
Labels	O
allow	O
the	O
programmer	B-Application
to	O
work	O
with	O
variable	O
names	O
.	O
</s>
<s>
The	O
assembler	B-Language
will	O
later	O
translate	O
labels	O
into	O
physical	O
memory	B-General_Concept
addresses	B-General_Concept
.	O
</s>
<s>
Operations	B-Language
allow	O
the	O
programmer	B-Application
to	O
work	O
with	O
mnemonics	O
.	O
</s>
<s>
The	O
assembler	B-Language
will	O
later	O
translate	O
mnemonics	O
into	O
instruction	O
numbers	O
.	O
</s>
<s>
Operands	O
tell	O
the	O
assembler	B-Language
which	O
data	O
the	O
operation	O
will	O
process	B-Operating_System
.	O
</s>
<s>
Comments	O
allow	O
the	O
programmer	B-Application
to	O
articulate	O
a	O
narrative	O
because	O
the	O
instructions	O
alone	O
are	O
vague	O
.	O
</s>
<s>
The	O
key	O
characteristic	O
of	O
an	O
assembly	B-Language
language	I-Language
program	O
is	O
it	O
forms	O
a	O
one-to-one	O
mapping	O
to	O
its	O
corresponding	O
machine	B-Language
language	I-Language
target	O
.	O
</s>
<s>
The	O
third	O
generation	O
of	O
programming	O
language	O
uses	O
compilers	B-Language
and	O
interpreters	B-Application
to	O
execute	B-General_Concept
computer	B-Application
programs	I-Application
.	O
</s>
<s>
The	O
distinguishing	O
feature	O
of	O
a	O
third	O
generation	O
language	O
is	O
its	O
independence	O
from	O
particular	O
hardware	B-General_Concept
.	O
</s>
<s>
Early	O
languages	O
include	O
Fortran	B-Application
(	O
1958	O
)	O
,	O
COBOL	B-Application
(	O
1959	O
)	O
,	O
ALGOL	B-Language
(	O
1960	O
)	O
,	O
and	O
BASIC	B-Language
(	O
1964	O
)	O
.	O
</s>
<s>
In	O
1973	O
,	O
the	O
C	B-Language
programming	I-Language
language	I-Language
emerged	O
as	O
a	O
high-level	B-Language
language	I-Language
that	O
produced	O
efficient	O
machine	B-Language
language	I-Language
instructions	O
.	O
</s>
<s>
Whereas	O
third-generation	O
languages	O
historically	O
generated	O
many	O
machine	B-Language
instructions	I-Language
for	O
each	O
statement	O
,	O
C	B-Language
has	O
statements	O
that	O
may	O
generate	O
a	O
single	O
machine	B-Language
instruction	I-Language
.	O
</s>
<s>
Moreover	O
,	O
an	O
optimizing	B-Application
compiler	I-Application
might	O
overrule	O
the	O
programmer	B-Application
and	O
produce	O
fewer	O
machine	B-Language
instructions	I-Language
than	O
statements	O
.	O
</s>
<s>
Today	O
,	O
an	O
entire	O
paradigm	O
of	O
languages	O
fill	O
the	O
imperative	B-Application
,	O
third	O
generation	O
spectrum	O
.	O
</s>
<s>
The	O
fourth	B-Language
generation	I-Language
of	I-Language
programming	I-Language
language	I-Language
emphasizes	O
what	O
output	O
results	O
are	O
desired	O
,	O
rather	O
than	O
how	O
programming	O
statements	O
should	O
be	O
constructed	O
.	O
</s>
<s>
Declarative	B-Language
languages	I-Language
attempt	O
to	O
limit	O
side	O
effects	O
and	O
allow	O
programmers	B-Application
to	O
write	O
code	O
with	O
relatively	O
few	O
errors	O
.	O
</s>
<s>
One	O
popular	O
fourth	B-Language
generation	I-Language
language	I-Language
is	O
called	O
Structured	B-Language
Query	I-Language
Language	I-Language
(	O
SQL	B-Language
)	O
.	O
</s>
<s>
Database	O
developers	B-Application
no	O
longer	O
need	O
to	O
process	B-Operating_System
each	O
database	O
record	O
one	O
at	O
a	O
time	O
.	O
</s>
<s>
Imperative	B-Application
languages	I-Application
specify	O
a	O
sequential	O
algorithm	O
using	O
declarations	O
,	O
expressions	O
,	O
and	O
statements	O
:	O
</s>
<s>
A	O
declaration	O
introduces	O
a	O
variable	O
name	O
to	O
the	O
computer	B-Application
program	I-Application
and	O
assigns	O
it	O
to	O
a	O
datatype	O
–	O
for	O
example	O
:	O
var	O
x	O
:	O
integer	O
;	O
</s>
<s>
FORTRAN	B-Application
(	O
1958	O
)	O
was	O
unveiled	O
as	O
"	O
The	O
IBM	O
Mathematical	O
FORmula	O
TRANslating	O
system.	O
"	O
</s>
<s>
arrays	B-Data_Structure
.	O
</s>
<s>
However	O
,	O
non-IBM	O
vendors	O
also	O
wrote	O
Fortran	B-Application
compilers	B-Language
,	O
but	O
with	O
a	O
syntax	O
that	O
would	O
likely	O
fail	O
IBM	O
's	O
compiler	B-Language
.	O
</s>
<s>
The	O
American	O
National	O
Standards	O
Institute	O
(	O
ANSI	O
)	O
developed	O
the	O
first	O
Fortran	B-Application
standard	O
in	O
1966	O
.	O
</s>
<s>
In	O
1978	O
,	O
Fortran	B-Application
77	O
became	O
the	O
standard	O
until	O
1991	O
.	O
</s>
<s>
Fortran	B-Application
90	O
supports	O
:	O
</s>
<s>
pointers	O
to	O
arrays	B-Data_Structure
.	O
</s>
<s>
COBOL	B-Application
(	O
1959	O
)	O
stands	O
for	O
"	O
COmmon	O
Business	O
Oriented	O
Language.	O
"	O
</s>
<s>
Fortran	B-Application
manipulated	O
symbols	O
.	O
</s>
<s>
The	O
US	O
Department	O
of	O
Defense	O
influenced	O
COBOL	B-Application
's	O
development	O
,	O
with	O
Grace	O
Hopper	O
being	O
a	O
major	O
contributor	O
.	O
</s>
<s>
COBOL	B-Application
's	O
development	O
was	O
tightly	O
controlled	O
,	O
so	O
dialects	O
did	O
n't	O
emerge	O
to	O
require	O
ANSI	O
standards	O
.	O
</s>
<s>
The	O
1990s	O
version	O
did	O
make	O
consequential	O
changes	O
,	O
like	O
object-oriented	B-Language
programming	I-Language
.	O
</s>
<s>
ALGOL	B-Language
(	O
1960	O
)	O
stands	O
for	O
"	O
ALGOrithmic	O
Language.	O
"	O
</s>
<s>
Algol	B-Language
was	O
first	O
to	O
define	O
its	O
syntax	O
using	O
the	O
Backus	O
–	O
Naur	O
form	O
.	O
</s>
<s>
This	O
led	O
to	O
syntax-directed	B-Application
compilers	B-Language
.	O
</s>
<s>
arrays	B-Data_Structure
with	O
variable	O
bounds	O
.	O
</s>
<s>
"	B-Language
for	I-Language
"	I-Language
loops	I-Language
.	O
</s>
<s>
Algol	B-Language
's	O
direct	O
descendants	O
include	O
Pascal	B-Application
,	O
Modula-2	B-Language
,	O
Ada	B-Language
,	O
Delphi	B-Language
and	O
Oberon	B-Language
on	O
one	O
branch	O
.	O
</s>
<s>
On	O
another	O
branch	O
the	O
descendants	O
include	O
C	B-Language
,	O
C++	B-Language
and	O
Java	B-Language
.	O
</s>
<s>
BASIC	B-Language
(	O
1964	O
)	O
stands	O
for	O
"	O
Beginner	O
's	O
All-Purpose	O
Symbolic	O
Instruction	O
Code.	O
"	O
</s>
<s>
If	O
a	O
student	O
did	O
n't	O
go	O
on	O
to	O
a	O
more	O
powerful	O
language	O
,	O
the	O
student	O
would	O
still	O
remember	O
Basic	B-Language
.	O
</s>
<s>
A	O
Basic	B-Language
interpreter	B-Application
was	O
installed	O
in	O
the	O
microcomputers	B-Architecture
manufactured	O
in	O
the	O
late	O
1970s	O
.	O
</s>
<s>
As	O
the	O
microcomputer	B-Architecture
industry	O
grew	O
,	O
so	O
did	O
the	O
language	O
.	O
</s>
<s>
Basic	B-Language
pioneered	O
the	O
interactive	B-Application
session	I-Application
.	O
</s>
<s>
It	O
offered	O
operating	B-General_Concept
system	I-General_Concept
commands	O
within	O
its	O
environment	O
:	O
</s>
<s>
The	O
'	O
list	B-General_Concept
 '	O
command	O
displayed	O
the	O
program	O
.	O
</s>
<s>
However	O
,	O
the	O
Basic	B-Language
syntax	O
was	O
too	O
simple	O
for	O
large	O
programs	O
.	O
</s>
<s>
Recent	O
dialects	O
added	O
structure	O
and	O
object-oriented	B-Language
extensions	O
.	O
</s>
<s>
Microsoft	O
's	O
Visual	B-Language
Basic	I-Language
is	O
still	O
widely	O
used	O
and	O
produces	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
C	B-Language
programming	I-Language
language	I-Language
(	O
1973	O
)	O
got	O
its	O
name	O
because	O
the	O
language	O
BCPL	B-Language
was	O
replaced	O
with	O
B	B-Language
,	O
and	O
AT&T	O
Bell	O
Labs	O
called	O
the	O
next	O
version	O
"	O
C.	O
"	O
Its	O
purpose	O
was	O
to	O
write	O
the	O
UNIX	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
C	B-Language
is	O
a	O
relatively	O
small	O
language	O
,	O
making	O
it	O
easy	O
to	O
write	O
compilers	B-Language
.	O
</s>
<s>
Its	O
growth	O
mirrored	O
the	O
hardware	B-General_Concept
growth	O
in	O
the	O
1980s	O
.	O
</s>
<s>
Its	O
growth	O
also	O
was	O
because	O
it	O
has	O
the	O
facilities	O
of	O
assembly	B-Language
language	I-Language
,	O
but	O
uses	O
a	O
high-level	B-Language
syntax	I-Language
.	O
</s>
<s>
inline	B-Language
assembler	I-Language
.	O
</s>
<s>
bit	O
operations	B-Language
.	O
</s>
<s>
freely	O
combining	O
complex	O
operators	B-Language
.	O
</s>
<s>
C	B-Language
allows	O
the	O
programmer	B-Application
to	O
control	O
which	O
region	O
of	O
memory	B-General_Concept
data	O
is	O
to	O
be	O
stored	O
.	O
</s>
<s>
The	O
stack	B-General_Concept
is	O
automatically	O
used	O
for	O
the	O
standard	O
variable	O
declarations	O
.	O
</s>
<s>
Heap	B-Application
memory	B-General_Concept
is	O
returned	O
to	O
a	O
pointer	O
variable	O
from	O
the	O
malloc( )	O
function	O
.	O
</s>
<s>
It	O
's	O
where	O
machine	B-Language
instructions	I-Language
are	O
stored	O
.	O
)	O
</s>
<s>
The	O
global	O
and	O
static	O
data	O
region	O
is	O
technically	O
two	O
regions	B-General_Concept
.	O
</s>
<s>
One	O
region	O
is	O
called	O
the	O
initialized	O
data	B-General_Concept
segment	I-General_Concept
,	O
where	O
variables	O
declared	O
with	O
default	O
values	O
are	O
stored	O
.	O
</s>
<s>
The	O
other	O
region	O
is	O
called	O
the	O
block	B-General_Concept
started	I-General_Concept
by	I-General_Concept
segment	I-General_Concept
,	O
where	O
variables	O
declared	O
without	O
default	O
values	O
are	O
stored	O
.	O
</s>
<s>
Variables	O
stored	O
in	O
the	O
global	O
and	O
static	O
data	O
region	O
have	O
their	O
addresses	B-General_Concept
set	O
at	O
compile-time	B-Application
.	O
</s>
<s>
They	O
retain	O
their	O
values	O
throughout	O
the	O
life	O
of	O
the	O
process	B-Operating_System
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
variable	O
declarations	O
inside	O
of	O
main( )	O
,	O
other	O
functions	O
,	O
or	O
within	O
{	O
}	O
block	O
delimiters	B-Algorithm
are	O
local	O
variables	O
.	O
</s>
<s>
They	O
provide	O
an	O
interface	B-Application
to	O
the	O
function	O
.	O
</s>
<s>
The	O
stack	B-General_Concept
region	O
is	O
a	O
contiguous	O
block	O
of	O
memory	B-General_Concept
located	O
near	O
the	O
top	O
memory	B-General_Concept
address	I-General_Concept
.	O
</s>
<s>
Variables	O
placed	O
in	O
the	O
stack	B-General_Concept
are	O
populated	O
from	O
top	O
to	O
bottom	O
.	O
</s>
<s>
A	O
stack	B-General_Concept
pointer	O
is	O
a	O
special-purpose	O
register	B-General_Concept
that	O
keeps	O
track	O
of	O
the	O
last	O
memory	B-General_Concept
address	I-General_Concept
populated	O
.	O
</s>
<s>
Variables	O
are	O
placed	O
into	O
the	O
stack	B-General_Concept
via	O
the	O
assembly	B-Language
language	I-Language
PUSH	O
instruction	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
addresses	B-General_Concept
of	O
these	O
variables	O
are	O
set	O
during	O
runtime	B-Library
.	O
</s>
<s>
The	O
method	B-Language
for	O
stack	B-General_Concept
variables	O
to	O
lose	O
their	O
scope	B-Language
is	O
via	O
the	O
POP	O
instruction	O
.	O
</s>
<s>
Local	O
variables	O
declared	O
without	O
the	O
static	O
prefix	O
,	O
including	O
formal	O
parameter	O
variables	O
,	O
are	O
called	O
automatic	O
variables	O
and	O
are	O
stored	O
in	O
the	O
stack	B-General_Concept
.	O
</s>
<s>
They	O
are	O
visible	O
inside	O
the	O
function	O
or	O
block	O
and	O
lose	O
their	O
scope	B-Language
upon	O
exiting	O
the	O
function	O
or	O
block	O
.	O
</s>
<s>
The	O
heap	B-Application
region	O
is	O
located	O
below	O
the	O
stack	B-General_Concept
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
manages	O
the	O
heap	B-Application
using	O
a	O
heap	B-Application
pointer	O
and	O
a	O
list	B-General_Concept
of	O
allocated	O
memory	B-General_Concept
blocks	O
.	O
</s>
<s>
Like	O
the	O
stack	B-General_Concept
,	O
the	O
addresses	B-General_Concept
of	O
heap	B-Application
variables	O
are	O
set	O
during	O
runtime	B-Library
.	O
</s>
<s>
An	O
out	B-General_Concept
of	I-General_Concept
memory	I-General_Concept
error	O
occurs	O
when	O
the	O
heap	B-Application
pointer	O
and	O
the	O
stack	B-General_Concept
pointer	O
meet	O
.	O
</s>
<s>
C	B-Language
provides	O
the	O
malloc( )	O
library	O
function	O
to	O
allocate	B-Language
heap	B-Application
memory	B-General_Concept
.	O
</s>
<s>
Populating	O
the	O
heap	B-Application
with	O
data	O
is	O
an	O
additional	O
copy	O
function	O
.	O
</s>
<s>
Variables	O
stored	O
in	O
the	O
heap	B-Application
are	O
economically	O
passed	O
to	O
functions	O
using	O
pointers	O
.	O
</s>
<s>
Without	O
pointers	O
,	O
the	O
entire	O
block	O
of	O
data	O
would	O
have	O
to	O
be	O
passed	O
to	O
the	O
function	O
via	O
the	O
stack	B-General_Concept
.	O
</s>
<s>
In	O
the	O
1970s	O
,	O
software	B-General_Concept
engineers	I-General_Concept
needed	O
language	O
support	O
to	O
break	O
large	O
projects	O
down	O
into	O
modules	B-Architecture
.	O
</s>
<s>
One	O
obvious	O
feature	O
was	O
to	O
decompose	O
large	O
projects	O
physically	O
into	O
separate	O
files	B-Operating_System
.	O
</s>
<s>
At	O
the	O
time	O
,	O
languages	O
supported	O
concrete	O
(	O
scalar	O
)	O
datatypes	O
like	O
integer	O
numbers	O
,	O
floating-point	B-Algorithm
numbers	I-Algorithm
,	O
and	O
strings	O
of	O
characters	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
list	B-General_Concept
of	O
integers	O
could	O
be	O
called	O
integer_list	O
.	O
</s>
<s>
In	O
object-oriented	B-Language
jargon	O
,	O
abstract	O
datatypes	O
are	O
called	O
classes	O
.	O
</s>
<s>
However	O
,	O
a	O
class	O
is	O
only	O
a	O
definition	O
;	O
no	O
memory	B-General_Concept
is	O
allocated	O
.	O
</s>
<s>
When	O
memory	B-General_Concept
is	O
allocated	O
to	O
a	O
class	O
and	O
bound	O
to	O
a	O
identifier	O
,	O
it	O
's	O
called	O
an	O
object	O
.	O
</s>
<s>
Object-oriented	B-Language
imperative	I-Language
languages	I-Language
developed	O
by	O
combining	O
the	O
need	O
for	O
classes	O
and	O
the	O
need	O
for	O
safe	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
A	O
function	O
,	O
in	O
an	O
object-oriented	B-Language
language	I-Language
,	O
is	O
assigned	O
to	O
a	O
class	O
.	O
</s>
<s>
An	O
assigned	O
function	O
is	O
then	O
referred	O
to	O
as	O
a	O
method	B-Language
,	O
member	O
function	O
,	O
or	O
operation	O
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
is	O
executing	O
operations	B-Language
on	O
objects	O
.	O
</s>
<s>
Object-oriented	B-Language
languages	I-Language
support	O
a	O
syntax	O
to	O
model	O
subset/superset	O
relationships	O
.	O
</s>
<s>
Object-oriented	B-Language
languages	I-Language
model	O
subset/superset	O
relationships	O
using	O
inheritance	B-Language
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
became	O
the	O
dominant	O
language	O
paradigm	O
by	O
the	O
late	O
1990s	O
.	O
</s>
<s>
C++	B-Language
(	O
1985	O
)	O
was	O
originally	O
called	O
"	O
C	B-Language
with	O
Classes.	O
"	O
</s>
<s>
It	O
was	O
designed	O
to	O
expand	O
C	B-Language
's	I-Language
capabilities	O
by	O
adding	O
the	O
object-oriented	B-Language
facilities	O
of	O
the	O
language	O
Simula	B-Language
.	O
</s>
<s>
An	O
object-oriented	B-Language
module	B-Architecture
is	O
composed	O
of	O
two	O
files	B-Operating_System
.	O
</s>
<s>
The	O
definitions	O
file	O
is	O
called	O
the	O
header	B-Language
file	I-Language
.	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
header	B-Language
file	I-Language
for	O
the	O
GRADE	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
A	O
module	B-Architecture
's	O
other	O
file	O
is	O
the	O
source	O
file	O
.	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
source	O
file	O
for	O
the	O
GRADE	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
header	B-Language
file	I-Language
for	O
the	O
PERSON	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
source	O
file	O
for	O
the	O
PERSON	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
header	B-Language
file	I-Language
for	O
the	O
STUDENT	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C++	B-Language
source	O
file	O
for	O
the	O
STUDENT	O
class	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
makefile	O
to	O
compile	B-Language
everything	O
:	O
</s>
<s>
Imperative	B-Application
languages	I-Application
have	O
one	O
major	O
criticism	O
:	O
assigning	O
an	O
expression	O
to	O
a	O
non-local	O
variable	O
may	O
produce	O
an	O
unintended	O
side	O
effect	O
.	O
</s>
<s>
Declarative	B-Language
languages	I-Language
generally	O
omit	O
the	O
assignment	O
statement	O
and	O
the	O
control	O
flow	O
.	O
</s>
<s>
Two	O
broad	O
categories	O
of	O
declarative	B-Language
languages	I-Language
are	O
functional	B-Language
languages	I-Language
and	O
logical	B-Language
languages	I-Language
.	O
</s>
<s>
The	O
principle	O
behind	O
a	O
functional	B-Language
language	I-Language
is	O
to	O
use	O
lambda	B-Language
calculus	I-Language
as	O
a	O
guide	O
for	O
a	O
well	O
defined	O
semantic	B-Application
.	O
</s>
<s>
A	O
functional	B-Language
language	I-Language
compiler	B-Language
will	O
not	O
store	O
this	O
value	O
in	O
a	O
variable	O
.	O
</s>
<s>
Instead	O
,	O
it	O
will	O
push	O
the	O
value	O
onto	O
the	O
computer	O
's	O
stack	B-General_Concept
before	O
setting	O
the	O
program	B-General_Concept
counter	I-General_Concept
back	O
to	O
the	O
calling	O
function	O
.	O
</s>
<s>
The	O
calling	O
function	O
will	O
then	O
pop	O
the	O
value	O
from	O
the	O
stack	B-General_Concept
.	O
</s>
<s>
Imperative	B-Application
languages	I-Application
do	O
support	O
functions	O
.	O
</s>
<s>
Therefore	O
,	O
functional	B-Language
programming	I-Language
can	O
be	O
achieved	O
in	O
an	O
imperative	B-Application
language	I-Application
,	O
if	O
the	O
programmer	B-Application
uses	O
discipline	O
.	O
</s>
<s>
However	O
,	O
a	O
functional	B-Language
language	I-Language
will	O
force	O
this	O
discipline	O
onto	O
the	O
programmer	B-Application
through	O
its	O
syntax	O
.	O
</s>
<s>
Functional	B-Language
languages	I-Language
have	O
a	O
syntax	O
tailored	O
to	O
emphasize	O
the	O
what	O
.	O
</s>
<s>
A	O
functional	B-Language
program	I-Language
is	O
developed	O
with	O
a	O
set	O
of	O
primitive	O
functions	O
followed	O
by	O
a	O
single	O
driver	O
function	O
.	O
</s>
<s>
Consider	O
the	O
snippet	B-Application
:	O
</s>
<s>
return	O
max( a	O
,	O
max(b,c )	O
)	O
-	O
min( a	O
,	O
min(b,c )	O
)	O
;	O
</s>
<s>
Functional	B-Language
languages	I-Language
are	O
used	O
in	O
computer	B-General_Concept
science	I-General_Concept
research	O
to	O
explore	O
new	O
language	O
features	O
.	O
</s>
<s>
Moreover	O
,	O
their	O
lack	O
of	O
side-effects	O
have	O
made	O
them	O
popular	O
in	O
parallel	B-Operating_System
programming	I-Operating_System
and	O
concurrent	B-Architecture
programming	I-Architecture
.	O
</s>
<s>
However	O
,	O
application	B-Application
developers	I-Application
prefer	O
the	O
object-oriented	B-Language
features	I-Language
of	O
imperative	B-Application
languages	I-Application
.	O
</s>
<s>
Lisp	B-Language
(	O
1958	O
)	O
stands	O
for	O
"	O
LISt	B-General_Concept
Processor.	O
"	O
</s>
<s>
It	O
is	O
tailored	O
to	O
process	B-Operating_System
lists	O
.	O
</s>
<s>
In	O
memory	B-General_Concept
,	O
a	O
tree	B-Application
data	I-Application
structure	I-Application
is	O
built	O
.	O
</s>
<s>
The	O
following	O
is	O
a	O
list	B-General_Concept
of	O
three	O
elements	O
.	O
</s>
<s>
Lisp	B-Language
has	O
functions	O
to	O
extract	O
and	O
reconstruct	O
elements	O
.	O
</s>
<s>
The	O
function	O
head( )	O
returns	O
a	O
list	B-General_Concept
containing	O
the	O
first	O
element	O
in	O
the	O
list	B-General_Concept
.	O
</s>
<s>
The	O
function	O
tail( )	O
returns	O
a	O
list	B-General_Concept
containing	O
everything	O
but	O
the	O
first	O
element	O
.	O
</s>
<s>
The	O
function	O
cons( )	O
returns	O
a	O
list	B-General_Concept
that	O
is	O
the	O
concatenation	O
of	O
other	O
lists	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
following	O
expression	O
will	O
return	O
the	O
list	B-General_Concept
x	O
:	O
</s>
<s>
One	O
drawback	O
of	O
Lisp	B-Language
is	O
when	O
many	O
functions	O
are	O
nested	O
,	O
the	O
parentheses	O
may	O
look	O
confusing	O
.	O
</s>
<s>
Modern	O
Lisp	B-Language
environments	B-Application
help	O
ensure	O
parenthesis	O
match	O
.	O
</s>
<s>
As	O
an	O
aside	O
,	O
Lisp	B-Language
does	O
support	O
the	O
imperative	B-Application
language	I-Application
operations	B-Language
of	O
the	O
assignment	O
statement	O
and	O
goto	O
loops	O
.	O
</s>
<s>
Also	O
,	O
Lisp	B-Language
is	O
not	O
concerned	O
with	O
the	O
datatype	O
of	O
the	O
elements	O
at	O
compile	B-Application
time	I-Application
.	O
</s>
<s>
Instead	O
,	O
it	O
assigns	O
(	O
and	O
may	O
reassign	O
)	O
the	O
datatypes	O
at	B-Library
runtime	I-Library
.	O
</s>
<s>
Assigning	O
the	O
datatype	O
at	B-Library
runtime	I-Library
is	O
called	O
dynamic	O
binding	O
.	O
</s>
<s>
Whereas	O
dynamic	O
binding	O
increases	O
the	O
language	O
's	O
flexibility	O
,	O
programming	O
errors	O
may	O
linger	O
until	O
late	O
in	O
the	O
software	O
development	O
process	B-Operating_System
.	O
</s>
<s>
Writing	O
large	O
,	O
reliable	O
,	O
and	O
readable	O
Lisp	B-Language
programs	O
requires	O
forethought	O
.	O
</s>
<s>
If	O
properly	O
planned	O
,	O
the	O
program	O
may	O
be	O
much	O
shorter	O
than	O
an	O
equivalent	O
imperative	B-Application
language	I-Application
program	O
.	O
</s>
<s>
Lisp	B-Language
is	O
widely	O
used	O
in	O
artificial	B-Application
intelligence	I-Application
.	I-Application
</s>
<s>
However	O
,	O
its	O
usage	O
has	O
been	O
accepted	O
only	O
because	O
it	O
has	O
imperative	B-Application
language	I-Application
operations	B-Language
,	O
making	O
unintended	O
side-effects	O
possible	O
.	O
</s>
<s>
ML	B-Language
(	O
1973	O
)	O
stands	O
for	O
"	O
Meta	O
Language.	O
"	O
</s>
<s>
ML	B-Language
checks	O
to	O
make	O
sure	O
only	O
data	O
of	O
the	O
same	O
type	O
are	O
compared	O
with	O
one	O
another	O
.	O
</s>
<s>
ML	B-Language
is	O
not	O
parenthesis-eccentric	O
like	O
Lisp	B-Language
.	O
</s>
<s>
Like	O
Lisp	B-Language
,	O
ML	B-Language
is	O
tailored	O
to	O
process	B-Operating_System
lists	O
.	O
</s>
<s>
Unlike	O
Lisp	B-Language
,	O
each	O
element	O
is	O
the	O
same	O
datatype	O
.	O
</s>
<s>
Moreover	O
,	O
ML	B-Language
assigns	O
the	O
datatype	O
of	O
an	O
element	O
at	O
compile-time	B-Application
.	O
</s>
<s>
Assigning	O
the	O
datatype	O
at	O
compile-time	B-Application
is	O
called	O
static	O
binding	O
.	O
</s>
<s>
Static	O
binding	O
increases	O
reliability	O
because	O
the	O
compiler	B-Language
checks	O
the	O
context	O
of	O
variables	O
before	O
they	O
are	O
used	O
.	O
</s>
<s>
Prolog	B-Language
(	O
1972	O
)	O
stands	O
for	O
"	O
PROgramming	O
in	O
LOgic.	O
"	O
</s>
<s>
It	O
was	O
designed	O
to	O
process	B-Operating_System
natural	O
languages	O
.	O
</s>
<s>
The	O
building	O
blocks	O
of	O
a	O
Prolog	B-Language
program	O
are	O
objects	O
and	O
their	O
relationships	O
to	O
other	O
objects	O
.	O
</s>
<s>
Prolog	B-Language
's	O
usage	O
has	O
expanded	O
to	O
become	O
a	O
goal-oriented	O
language	O
.	O
</s>
<s>
In	O
a	O
goal-oriented	O
application	O
,	O
the	O
goal	O
is	O
defined	O
by	O
providing	O
a	O
list	B-General_Concept
of	O
subgoals	O
.	O
</s>
<s>
Then	O
each	O
subgoal	O
is	O
defined	O
by	O
further	O
providing	O
a	O
list	B-General_Concept
of	O
its	O
subgoals	O
,	O
etc	O
.	O
</s>
<s>
If	O
a	O
path	O
of	O
subgoals	O
fails	O
to	O
find	O
a	O
solution	O
,	O
then	O
that	O
subgoal	O
is	O
backtracked	B-Algorithm
and	O
another	O
path	O
is	O
systematically	O
attempted	O
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
is	O
a	O
programming	O
method	B-Language
to	O
execute	B-General_Concept
operations	B-Language
(	O
functions	O
)	O
on	O
objects	O
.	O
</s>
<s>
The	O
basic	B-Language
idea	O
is	O
to	O
group	O
the	O
characteristics	O
of	O
a	O
phenomenon	O
into	O
an	O
object	O
container	B-Application
and	O
give	O
the	O
container	B-Application
a	O
name	O
.	O
</s>
<s>
The	O
operations	B-Language
on	O
the	O
phenomenon	O
are	O
also	O
grouped	O
into	O
the	O
container	B-Application
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
developed	O
by	O
combining	O
the	O
need	O
for	O
containers	B-Application
and	O
the	O
need	O
for	O
safe	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
This	O
programming	O
method	B-Language
need	O
not	O
be	O
confined	O
to	O
an	O
object-oriented	B-Language
language	I-Language
.	O
</s>
<s>
In	O
an	O
object-oriented	B-Language
language	I-Language
,	O
an	O
object	O
container	B-Application
is	O
called	O
a	O
class	O
.	O
</s>
<s>
In	O
a	O
non-object-oriented	O
language	O
,	O
a	O
data	B-General_Concept
structure	I-General_Concept
(	O
which	O
is	O
also	O
known	O
as	O
a	O
record	O
)	O
may	O
become	O
an	O
object	O
container	B-Application
.	O
</s>
<s>
To	O
turn	O
a	O
data	B-General_Concept
structure	I-General_Concept
into	O
an	O
object	O
container	B-Application
,	O
operations	B-Language
need	O
to	O
be	O
written	O
specifically	O
for	O
the	O
structure	O
.	O
</s>
<s>
However	O
,	O
inheritance	B-Language
will	O
be	O
missing	O
.	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
header	B-Language
file	I-Language
for	O
the	O
GRADE	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
The	O
grade_new( )	O
function	O
performs	O
the	O
same	O
algorithm	O
as	O
the	O
C++	B-Language
constructor	O
operation	O
.	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
source	O
file	O
for	O
the	O
GRADE	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
In	O
the	O
constructor	O
,	O
the	O
function	O
calloc( )	O
is	O
used	O
instead	O
of	O
malloc( )	O
because	O
each	O
memory	B-General_Concept
cell	O
will	O
be	O
set	O
to	O
zero	O
.	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
header	B-Language
file	I-Language
for	O
the	O
PERSON	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
source	O
file	O
for	O
the	O
PERSON	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
header	B-Language
file	I-Language
for	O
the	O
STUDENT	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
C	B-Language
programming	I-Language
language	I-Language
source	O
file	O
for	O
the	O
STUDENT	O
abstract	O
datatype	O
in	O
a	O
simple	O
school	O
application	O
:	O
</s>
<s>
Here	O
is	O
a	O
makefile	O
to	O
compile	B-Language
everything	O
:	O
</s>
<s>
The	O
formal	O
strategy	O
to	O
build	O
object-oriented	B-Language
objects	O
is	O
to	O
:	O
</s>
<s>
The	O
syntax	O
of	O
a	O
programming	O
language	O
is	O
a	O
list	B-General_Concept
of	O
production	B-Architecture
rules	O
which	O
govern	O
its	O
form	O
.	O
</s>
<s>
Complementing	O
the	O
syntax	O
of	O
a	O
language	O
are	O
its	O
semantics	B-Application
.	O
</s>
<s>
The	O
semantics	B-Application
describe	O
the	O
meanings	O
attached	O
to	O
various	O
syntactic	O
constructs	O
.	O
</s>
<s>
A	O
syntactic	O
construct	O
may	O
need	O
a	O
semantic	B-Application
description	O
because	O
a	O
form	O
may	O
have	O
an	O
invalid	O
interpretation	O
.	O
</s>
<s>
The	O
syntax	O
of	O
a	O
language	O
is	O
formally	O
described	O
by	O
listing	O
the	O
production	B-Architecture
rules	O
.	O
</s>
<s>
Whereas	O
the	O
syntax	O
of	O
a	O
natural	O
language	O
is	O
extremely	O
complicated	O
,	O
a	O
subset	O
of	O
the	O
English	O
language	O
can	O
have	O
this	O
production	B-Architecture
rule	O
listing	O
:	O
</s>
<s>
From	O
this	O
production	B-Architecture
rule	O
listing	O
,	O
complete	O
sentences	O
may	O
be	O
formed	O
using	O
a	O
series	O
of	O
replacements	O
.	O
</s>
<s>
The	O
process	B-Operating_System
is	O
to	O
replace	O
non-terminals	O
with	O
either	O
a	O
valid	O
non-terminal	O
or	O
a	O
valid	O
terminal	O
.	O
</s>
<s>
The	O
replacement	O
process	B-Operating_System
repeats	O
until	O
only	O
terminals	O
remain	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
semantic	B-Application
is	O
necessary	O
to	O
correctly	O
describe	O
the	O
meaning	O
of	O
an	O
eat	O
activity	O
.	O
</s>
<s>
One	O
production	B-Architecture
rule	O
listing	O
method	B-Language
is	O
called	O
the	O
Backus	O
–	O
Naur	O
form	O
(	O
BNF	O
)	O
.	O
</s>
<s>
Using	O
BNF	O
,	O
a	O
subset	O
of	O
the	O
English	O
language	O
can	O
have	O
this	O
production	B-Architecture
rule	O
listing	O
:	O
</s>
<s>
Using	O
BNF	O
,	O
a	O
signed-integer	O
has	O
the	O
production	B-Architecture
rule	O
listing	O
:	O
</s>
<s>
Notice	O
the	O
recursive	O
production	B-Architecture
rule	O
:	O
</s>
<s>
Therefore	O
,	O
a	O
semantic	B-Application
is	O
necessary	O
to	O
describe	O
a	O
limitation	O
of	O
the	O
number	O
of	O
digits	O
.	O
</s>
<s>
Notice	O
the	O
leading	O
zero	O
possibility	O
in	O
the	O
production	B-Architecture
rules	O
:	O
</s>
<s>
Therefore	O
,	O
a	O
semantic	B-Application
is	O
necessary	O
to	O
describe	O
that	O
leading	O
zeros	O
need	O
to	O
be	O
ignored	O
.	O
</s>
<s>
Two	O
formal	O
methods	O
are	O
available	O
to	O
describe	O
semantics	B-Application
.	O
</s>
<s>
They	O
are	O
denotational	B-Application
semantics	I-Application
and	O
axiomatic	O
semantics	B-Application
.	O
</s>
<s>
Software	B-General_Concept
engineering	I-General_Concept
is	O
a	O
variety	O
of	O
techniques	O
to	O
produce	O
quality	O
software	O
.	O
</s>
<s>
Computer	B-General_Concept
programming	I-General_Concept
is	O
the	O
process	B-Operating_System
of	O
writing	O
or	O
editing	O
source	O
code	O
.	O
</s>
<s>
In	O
a	O
formal	O
environment	O
,	O
a	O
systems	O
analyst	O
will	O
gather	O
information	O
from	O
managers	O
about	O
all	O
the	O
organization	O
's	O
processes	B-Operating_System
to	O
automate	O
.	O
</s>
<s>
Hardware	B-General_Concept
costs	O
.	O
</s>
<s>
Applying	O
a	O
systems	B-General_Concept
development	I-General_Concept
process	I-General_Concept
will	O
mitigate	O
the	O
axiom	O
:	O
the	O
later	O
in	O
the	O
process	B-Operating_System
an	O
error	O
is	O
detected	O
,	O
the	O
more	O
expensive	O
it	O
is	O
to	O
correct	O
.	O
</s>
<s>
The	O
waterfall	O
model	O
is	O
an	O
implementation	O
of	O
a	O
systems	B-General_Concept
development	I-General_Concept
process	I-General_Concept
.	O
</s>
<s>
As	O
the	O
waterfall	O
label	O
implies	O
,	O
the	O
basic	B-Language
phases	O
overlap	O
each	O
other	O
:	O
</s>
<s>
A	O
computer	B-Application
programmer	I-Application
is	O
a	O
specialist	O
responsible	O
for	O
writing	O
or	O
modifying	O
the	O
source	O
code	O
to	O
implement	O
the	O
detailed	O
plan	O
.	O
</s>
<s>
A	O
programming	O
team	O
is	O
likely	O
to	O
be	O
needed	O
because	O
most	O
systems	O
are	O
too	O
large	O
to	O
be	O
completed	O
by	O
a	O
single	O
programmer	B-Application
.	O
</s>
<s>
However	O
,	O
adding	O
programmers	B-Application
to	O
a	O
project	O
may	O
not	O
shorten	O
the	O
completion	O
time	O
.	O
</s>
<s>
To	O
be	O
effective	O
,	O
program	O
modules	B-Architecture
need	O
to	O
be	O
defined	O
and	O
distributed	O
to	O
team	O
members	O
.	O
</s>
<s>
Computer	B-Application
programmers	I-Application
may	O
be	O
programming-in-the-small	O
:	O
programming	O
within	O
a	O
single	O
module	B-Architecture
.	O
</s>
<s>
Chances	O
are	O
a	O
module	B-Architecture
will	O
execute	B-General_Concept
modules	B-Architecture
located	O
in	O
other	O
source	O
code	O
files	B-Operating_System
.	O
</s>
<s>
Therefore	O
,	O
computer	B-Application
programmers	I-Application
may	O
be	O
programming-in-the-large	O
:	O
programming	O
modules	B-Architecture
so	O
they	O
will	O
effectively	O
couple	O
with	O
each	O
other	O
.	O
</s>
<s>
Programming-in-the-large	O
includes	O
contributing	O
to	O
the	O
application	B-General_Concept
programming	I-General_Concept
interface	I-General_Concept
(	O
API	B-General_Concept
)	O
.	O
</s>
<s>
Modular	B-Architecture
programming	I-Architecture
is	O
a	O
technique	O
to	O
refine	O
imperative	B-Application
language	I-Application
programs	O
.	O
</s>
<s>
Refined	O
programs	O
may	O
reduce	O
the	O
software	O
size	O
,	O
separate	O
responsibilities	O
,	O
and	O
thereby	O
mitigate	O
software	B-General_Concept
aging	I-General_Concept
.	O
</s>
<s>
A	O
program	O
module	B-Architecture
is	O
a	O
sequence	O
of	O
statements	O
that	O
are	O
bounded	O
within	O
a	O
block	O
and	O
together	O
identified	O
by	O
a	O
name	O
.	O
</s>
<s>
Modules	B-Architecture
have	O
a	O
function	O
,	O
context	O
,	O
and	O
logic	O
:	O
</s>
<s>
The	O
function	O
of	O
a	O
module	B-Architecture
is	O
what	O
it	O
does	O
.	O
</s>
<s>
The	O
context	O
of	O
a	O
module	B-Architecture
are	O
the	O
elements	O
being	O
performed	O
upon	O
.	O
</s>
<s>
The	O
logic	O
of	O
a	O
module	B-Architecture
is	O
how	O
it	O
performs	O
the	O
function	O
.	O
</s>
<s>
The	O
module	B-Architecture
's	O
name	O
should	O
be	O
derived	O
first	O
by	O
its	O
function	O
,	O
then	O
by	O
its	O
context	O
.	O
</s>
<s>
For	O
example	O
,	O
function	O
compute_square_root( x )	O
or	O
function	O
compute_square_root_integer( 	O
i	O
:	O
integer	O
)	O
are	O
appropriate	O
module	B-Architecture
names	O
.	O
</s>
<s>
The	O
degree	O
of	O
interaction	O
within	O
a	O
module	B-Architecture
is	O
its	O
level	O
of	O
cohesion	O
.	O
</s>
<s>
Cohesion	O
is	O
a	O
judgment	O
of	O
the	O
relationship	O
between	O
a	O
module	B-Architecture
's	O
name	O
and	O
its	O
function	O
.	O
</s>
<s>
The	O
degree	O
of	O
interaction	O
between	O
modules	B-Architecture
is	O
the	O
level	O
of	O
coupling	B-Application
.	O
</s>
<s>
Coupling	B-Application
is	O
a	O
judgement	O
of	O
the	O
relationship	O
between	O
a	O
module	B-Architecture
's	O
context	O
and	O
the	O
elements	O
being	O
performed	O
upon	O
.	O
</s>
<s>
Coincidental	O
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
coincidental	O
cohesion	O
if	O
it	O
performs	O
multiple	O
functions	O
,	O
and	O
the	O
functions	O
are	O
completely	O
unrelated	O
.	O
</s>
<s>
For	O
example	O
,	O
"	O
Every	O
module	B-Architecture
will	O
have	O
between	O
35	O
and	O
50	O
executable	B-Application
statements.	O
"	O
</s>
<s>
Logical	O
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
logical	O
cohesion	O
if	O
it	O
has	O
available	O
a	O
series	O
of	O
functions	O
,	O
but	O
only	O
one	O
of	O
them	O
is	O
executed	O
.	O
</s>
<s>
For	O
example	O
,	O
function	O
perform_arithmetic( perform_addition, a, b )	O
.	O
</s>
<s>
Temporal	O
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
temporal	O
cohesion	O
if	O
it	O
performs	O
functions	O
related	O
to	O
time	O
.	O
</s>
<s>
Procedural	B-Application
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
procedural	B-Application
cohesion	O
if	O
it	O
performs	O
multiple	O
loosely	O
related	O
functions	O
.	O
</s>
<s>
Communicational	O
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
communicational	O
cohesion	O
if	O
it	O
performs	O
multiple	O
closely	O
related	O
functions	O
.	O
</s>
<s>
Informational	O
Cohesion	O
:	O
A	O
module	B-Architecture
has	O
informational	O
cohesion	O
if	O
it	O
performs	O
multiple	O
functions	O
,	O
but	O
each	O
function	O
has	O
its	O
own	O
entry	O
and	O
exit	O
points	O
.	O
</s>
<s>
Moreover	O
,	O
the	O
functions	O
share	O
the	O
same	O
data	B-General_Concept
structure	I-General_Concept
.	O
</s>
<s>
Object-oriented	B-Language
classes	O
work	O
at	O
this	O
level	O
.	O
</s>
<s>
Functional	O
Cohesion	O
:	O
a	O
module	B-Architecture
has	O
functional	O
cohesion	O
if	O
it	O
achieves	O
a	O
single	O
goal	O
working	O
only	O
on	O
local	O
variables	O
.	O
</s>
<s>
The	O
levels	O
of	O
coupling	B-Application
from	O
worst	O
to	O
best	O
are	O
:	O
</s>
<s>
Content	O
Coupling	B-Application
:	O
A	O
module	B-Architecture
has	O
content	O
coupling	B-Application
if	O
it	O
modifies	O
a	O
local	O
variable	O
of	O
another	O
function	O
.	O
</s>
<s>
COBOL	B-Application
used	O
to	O
do	O
this	O
with	O
the	O
alter	O
verb	O
.	O
</s>
<s>
Common	O
Coupling	B-Application
:	O
A	O
module	B-Architecture
has	O
common	O
coupling	B-Application
if	O
it	O
modifies	O
a	O
global	O
variable	O
.	O
</s>
<s>
Control	O
Coupling	B-Application
:	O
A	O
module	B-Architecture
has	O
control	O
coupling	B-Application
if	O
another	O
module	B-Architecture
can	O
modify	O
its	O
control	O
flow	O
.	O
</s>
<s>
For	O
example	O
,	O
perform_arithmetic( perform_addition, a, b )	O
.	O
</s>
<s>
Stamp	O
Coupling	B-Application
:	O
A	O
module	B-Architecture
has	O
stamp	O
coupling	B-Application
if	O
an	O
element	O
of	O
a	O
data	B-General_Concept
structure	I-General_Concept
passed	O
as	O
a	O
parameter	O
is	O
modified	O
.	O
</s>
<s>
Object-oriented	B-Language
classes	O
work	O
at	O
this	O
level	O
.	O
</s>
<s>
Data	O
Coupling	B-Application
:	O
A	O
module	B-Architecture
has	O
data	O
coupling	B-Application
if	O
all	O
of	O
its	O
input	O
parameters	O
are	O
needed	O
and	O
none	O
of	O
them	O
are	O
modified	O
.	O
</s>
<s>
Data	O
flow	O
analysis	O
is	O
a	O
design	O
method	B-Language
used	O
to	O
achieve	O
modules	B-Architecture
of	O
functional	O
cohesion	O
and	O
data	O
coupling	B-Application
.	O
</s>
<s>
The	O
input	O
to	O
the	O
method	B-Language
is	O
a	O
data-flow	B-Application
diagram	I-Application
.	O
</s>
<s>
A	O
data-flow	B-Application
diagram	I-Application
is	O
a	O
set	O
of	O
ovals	O
representing	O
modules	B-Architecture
.	O
</s>
<s>
Each	O
module	B-Architecture
's	O
name	O
is	O
displayed	O
inside	O
its	O
oval	O
.	O
</s>
<s>
Modules	B-Architecture
may	O
be	O
at	O
the	O
executable	B-Application
level	O
or	O
the	O
function	O
level	O
.	O
</s>
<s>
The	O
diagram	O
also	O
has	O
arrows	O
connecting	O
modules	B-Architecture
to	O
each	O
other	O
.	O
</s>
<s>
Arrows	O
pointing	O
into	O
modules	B-Architecture
represent	O
a	O
set	O
of	O
inputs	O
.	O
</s>
<s>
Each	O
module	B-Architecture
should	O
have	O
only	O
one	O
arrow	O
pointing	O
out	O
from	O
it	O
to	O
represent	O
its	O
single	O
output	O
object	O
.	O
</s>
<s>
A	O
daisy	B-Application
chain	I-Application
of	O
ovals	O
will	O
convey	O
an	O
entire	O
algorithm	O
.	O
</s>
<s>
The	O
input	O
modules	B-Architecture
should	O
start	O
the	O
diagram	O
.	O
</s>
<s>
The	O
input	O
modules	B-Architecture
should	O
connect	O
to	O
the	O
transform	O
modules	B-Architecture
.	O
</s>
<s>
The	O
transform	O
modules	B-Architecture
should	O
connect	O
to	O
the	O
output	O
modules	B-Architecture
.	O
</s>
<s>
Computer	B-Application
programs	I-Application
may	O
be	O
categorized	O
along	O
functional	O
lines	O
.	O
</s>
<s>
The	O
main	O
functional	O
categories	O
are	O
application	B-Application
software	I-Application
and	O
system	B-Application
software	I-Application
.	O
</s>
<s>
System	B-Application
software	I-Application
includes	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
which	O
couples	O
computer	B-Architecture
hardware	I-Architecture
with	O
application	B-Application
software	I-Application
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
to	O
provide	O
an	O
environment	O
where	O
application	B-Application
software	I-Application
executes	O
in	O
a	O
convenient	O
and	O
efficient	O
manner	O
.	O
</s>
<s>
Both	O
application	B-Application
software	I-Application
and	O
system	B-Application
software	I-Application
execute	B-General_Concept
utility	B-Application
programs	I-Application
.	O
</s>
<s>
At	O
the	O
hardware	B-General_Concept
level	O
,	O
a	O
microcode	B-Device
program	I-Device
controls	O
the	O
circuits	O
throughout	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
.	O
</s>
<s>
Application	B-Application
software	I-Application
is	O
the	O
key	O
to	O
unlocking	O
the	O
potential	O
of	O
the	O
computer	O
system	O
.	O
</s>
<s>
Enterprise	B-Application
application	I-Application
software	I-Application
bundles	O
accounting	O
,	O
personnel	O
,	O
customer	O
,	O
and	O
vendor	O
applications	O
.	O
</s>
<s>
Enterprise	B-Application
applications	I-Application
may	O
be	O
developed	O
in-house	O
as	O
a	O
one-of-a-kind	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
Purchased	O
software	O
may	O
be	O
modified	O
to	O
provide	O
custom	B-Application
software	I-Application
.	O
</s>
<s>
Outsourced	O
software	O
development	O
may	O
be	O
from	O
the	O
original	O
software	O
vendor	O
or	O
a	O
third-party	O
developer	B-Application
.	O
</s>
<s>
Management	O
may	O
also	O
be	O
involved	O
in	O
the	O
development	O
process	B-Operating_System
and	O
offer	O
a	O
level	O
of	O
control	O
.	O
</s>
<s>
A	O
merger	O
or	O
acquisition	O
may	O
necessitate	O
enterprise	B-Application
software	I-Application
changes	O
.	O
</s>
<s>
The	O
potential	O
advantages	O
of	O
off-the-shelf	O
software	O
are	O
upfront	O
costs	O
are	O
identifiable	O
,	O
the	O
basic	B-Language
needs	O
should	O
be	O
fulfilled	O
,	O
and	O
its	O
performance	O
and	O
reliability	O
have	O
a	O
track	O
record	O
.	O
</s>
<s>
The	O
potential	O
disadvantages	O
of	O
off-the-shelf	O
software	O
are	O
it	O
may	O
have	O
unnecessary	O
features	O
that	O
confuse	O
end	O
users	O
,	O
it	O
may	O
lack	O
features	O
the	O
enterprise	O
needs	O
,	O
and	O
the	O
data	O
flow	O
may	O
not	O
match	O
the	O
enterprise	O
's	O
work	O
processes	B-Operating_System
.	O
</s>
<s>
One	O
approach	O
to	O
economically	O
obtaining	O
a	O
customized	O
enterprise	B-Application
application	I-Application
is	O
through	O
an	O
application	O
service	O
provider	O
.	O
</s>
<s>
Specialty	O
companies	O
provide	O
hardware	B-General_Concept
,	O
custom	B-Application
software	I-Application
,	O
and	O
end-user	O
support	O
.	O
</s>
<s>
An	O
operating	B-General_Concept
system	I-General_Concept
is	O
the	O
low-level	O
software	O
that	O
supports	O
a	O
computer	O
's	O
basic	B-Language
functions	O
,	O
such	O
as	O
scheduling	O
processes	B-Operating_System
and	O
controlling	O
peripherals	O
.	O
</s>
<s>
In	O
the	O
1950s	O
,	O
the	O
programmer	B-Application
,	O
who	O
was	O
also	O
the	O
operator	O
,	O
would	O
write	O
a	O
program	O
and	O
run	O
it	O
.	O
</s>
<s>
The	O
programmer	B-Application
then	O
looked	O
at	O
the	O
console	O
lights	O
and	O
fiddled	O
with	O
the	O
console	O
switches	O
.	O
</s>
<s>
If	O
less	O
fortunate	O
,	O
a	O
memory	B-General_Concept
printout	O
was	O
made	O
for	O
further	O
study	O
.	O
</s>
<s>
In	O
the	O
1960s	O
,	O
programmers	B-Application
reduced	O
the	O
amount	O
of	O
wasted	O
time	O
by	O
automating	O
the	O
operator	O
's	O
job	O
.	O
</s>
<s>
A	O
program	O
called	O
an	O
operating	B-General_Concept
system	I-General_Concept
was	O
kept	O
in	O
the	O
computer	O
at	O
all	O
times	O
.	O
</s>
<s>
The	O
term	O
operating	B-General_Concept
system	I-General_Concept
may	O
refer	O
to	O
two	O
levels	O
of	O
software	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
may	O
refer	O
to	O
the	O
kernel	B-Operating_System
program	I-Operating_System
that	O
manages	O
the	O
processes	B-Operating_System
,	O
memory	B-General_Concept
,	O
and	O
devices	O
.	O
</s>
<s>
More	O
broadly	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
may	O
refer	O
to	O
the	O
entire	O
package	O
of	O
the	O
central	O
software	O
.	O
</s>
<s>
The	O
package	O
includes	O
a	O
kernel	B-Operating_System
program	I-Operating_System
,	O
command-line	B-Application
interpreter	I-Application
,	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
utility	B-Application
programs	I-Application
,	O
and	O
editor	B-Application
.	O
</s>
<s>
The	O
kernel	B-Operating_System
's	O
main	O
purpose	O
is	O
to	O
manage	O
the	O
limited	O
resources	O
of	O
a	O
computer	O
:	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
perform	O
process	B-Operating_System
scheduling	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
creates	O
a	O
process	B-Operating_System
control	I-Operating_System
block	I-Operating_System
when	O
a	O
program	O
is	O
selected	O
for	O
execution	O
.	O
</s>
<s>
However	O
,	O
an	O
executing	O
program	O
gets	O
exclusive	O
access	O
to	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
only	O
for	O
a	O
time	O
slice	B-Architecture
.	O
</s>
<s>
To	O
provide	O
each	O
user	O
with	O
the	O
appearance	B-General_Concept
of	I-General_Concept
continuous	I-General_Concept
access	I-General_Concept
,	O
the	O
kernel	B-Operating_System
quickly	O
preempts	B-Operating_System
each	O
process	B-Operating_System
control	I-Operating_System
block	I-Operating_System
to	O
execute	B-General_Concept
another	O
one	O
.	O
</s>
<s>
The	O
goal	O
for	O
system	B-Application
developers	I-Application
is	O
to	O
minimize	O
dispatch	O
latency	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
perform	O
memory	B-General_Concept
management	I-General_Concept
.	O
</s>
<s>
When	O
the	O
kernel	B-Operating_System
initially	O
loads	B-Operating_System
an	O
executable	B-Application
into	O
memory	B-General_Concept
,	O
it	O
divides	O
the	O
address	O
space	O
logically	O
into	O
regions	B-General_Concept
.	O
</s>
<s>
The	O
kernel	B-Operating_System
maintains	O
a	O
master-region	O
table	O
and	O
many	O
per-process-region	O
(	O
pregion	O
)	O
tables	O
—	O
one	O
for	O
each	O
running	O
process	B-Operating_System
.	O
</s>
<s>
These	O
tables	O
constitute	O
the	O
virtual	B-General_Concept
address	I-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
master-pregion	O
table	O
is	O
used	O
to	O
determine	O
where	O
its	O
contents	O
are	O
located	O
in	O
physical	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
pregion	O
tables	O
allow	O
each	O
process	B-Operating_System
to	O
have	O
its	O
own	O
program	O
(	O
text	O
)	O
pregion	O
,	O
data	O
pregion	O
,	O
and	O
stack	B-General_Concept
pregion	O
.	O
</s>
<s>
The	O
program	O
pregion	O
stores	O
machine	B-Language
instructions	I-Language
.	O
</s>
<s>
Since	O
machine	B-Language
instructions	I-Language
do	O
n't	O
change	O
,	O
the	O
program	O
pregion	O
may	O
be	O
shared	O
by	O
many	O
processes	B-Operating_System
of	O
the	O
same	O
executable	B-Application
.	O
</s>
<s>
To	O
save	O
time	O
and	O
memory	B-General_Concept
,	O
the	O
kernel	B-Operating_System
may	O
load	O
only	O
blocks	O
of	O
execution	O
instructions	O
from	O
the	O
disk	O
drive	O
,	O
not	O
the	O
entire	O
execution	O
file	O
completely	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
is	O
responsible	O
for	O
translating	O
virtual	O
addresses	B-General_Concept
into	O
physical	O
addresses	B-General_Concept
.	O
</s>
<s>
The	O
kernel	B-Operating_System
may	O
request	O
data	O
from	O
the	O
memory	B-General_Concept
controller	I-General_Concept
and	O
,	O
instead	O
,	O
receive	O
a	O
page	B-General_Concept
fault	I-General_Concept
.	O
</s>
<s>
If	O
so	O
,	O
the	O
kernel	B-Operating_System
accesses	O
the	O
memory	B-General_Concept
management	I-General_Concept
unit	I-General_Concept
to	O
populate	O
the	O
physical	O
data	O
region	O
and	O
translate	O
the	O
address	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
allocates	O
memory	B-General_Concept
from	O
the	O
heap	B-Application
upon	O
request	O
by	O
a	O
process	B-Operating_System
.	O
</s>
<s>
When	O
the	O
process	B-Operating_System
is	O
finished	O
with	O
the	O
memory	B-General_Concept
,	O
the	O
process	B-Operating_System
may	O
request	O
for	O
it	O
to	O
be	O
freed	B-Application
.	O
</s>
<s>
If	O
the	O
process	B-Operating_System
exits	O
without	O
requesting	O
all	O
allocated	O
memory	B-General_Concept
to	O
be	O
freed	B-Application
,	O
then	O
the	O
kernel	B-Operating_System
performs	O
garbage	B-General_Concept
collection	I-General_Concept
to	O
free	O
the	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
kernel	B-Operating_System
also	O
ensures	O
that	O
a	O
process	B-Operating_System
only	O
accesses	O
its	O
own	O
memory	B-General_Concept
,	O
and	O
not	O
that	O
of	O
the	O
kernel	B-Operating_System
or	O
other	O
processes	B-Operating_System
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
perform	O
file	B-Application
system	I-Application
management	I-Application
.	O
</s>
<s>
The	O
kernel	B-Operating_System
has	O
instructions	O
to	O
create	O
,	O
retrieve	O
,	O
update	O
,	O
and	O
delete	O
files	B-Operating_System
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
perform	O
device	O
management	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
provides	O
programs	O
to	O
standardize	O
and	O
simplify	O
the	O
interface	B-Application
to	O
the	O
mouse	O
,	O
keyboard	O
,	O
disk	O
drives	O
,	O
printers	O
,	O
and	O
other	O
devices	O
.	O
</s>
<s>
Moreover	O
,	O
the	O
kernel	B-Operating_System
should	O
arbitrate	O
access	O
to	O
a	O
device	O
if	O
two	O
processes	B-Operating_System
request	O
it	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
perform	O
network	O
management	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
transmits	O
and	O
receives	O
packets	B-Protocol
on	O
behalf	O
of	O
processes	B-Operating_System
.	O
</s>
<s>
One	O
key	O
service	O
is	O
to	O
find	O
an	O
efficient	O
route	B-Protocol
to	O
the	O
target	O
system	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
provide	O
system	B-Operating_System
level	I-Operating_System
functions	I-Operating_System
for	O
programmers	B-Application
to	O
use	O
.	O
</s>
<s>
Programmers	B-Application
access	O
files	B-Operating_System
through	O
a	O
relatively	O
simple	O
interface	B-Application
that	O
in	O
turn	O
executes	O
a	O
relatively	O
complicated	O
low-level	O
I/O	B-General_Concept
interface	I-General_Concept
.	O
</s>
<s>
The	O
low-level	O
interface	B-Application
includes	O
file	O
creation	O
,	O
file	B-Application
descriptors	I-Application
,	O
file	O
seeking	O
,	O
physical	O
reading	O
,	O
and	O
physical	O
writing	O
.	O
</s>
<s>
Programmers	B-Application
create	O
processes	B-Operating_System
through	O
a	O
relatively	O
simple	O
interface	B-Application
that	O
in	O
turn	O
executes	O
a	O
relatively	O
complicated	O
low-level	O
interface	B-Application
.	O
</s>
<s>
Programmers	B-Application
perform	O
date/time	O
arithmetic	O
through	O
a	O
relatively	O
simple	O
interface	B-Application
that	O
in	O
turn	O
executes	O
a	O
relatively	O
complicated	O
low-level	O
time	O
interface	B-Application
.	O
</s>
<s>
The	O
kernel	B-Operating_System
program	I-Operating_System
should	O
provide	O
a	O
communication	B-Operating_System
channel	I-Operating_System
between	O
executing	O
processes	B-Operating_System
.	O
</s>
<s>
For	O
a	O
large	O
software	O
system	O
,	O
it	O
may	O
be	O
desirable	O
to	O
engineer	B-General_Concept
the	O
system	O
into	O
smaller	O
processes	B-Operating_System
.	O
</s>
<s>
Processes	B-Operating_System
may	O
communicate	O
with	O
one	O
another	O
by	O
sending	O
and	O
receiving	O
signals	B-Operating_System
.	O
</s>
<s>
Originally	O
,	O
operating	B-General_Concept
systems	I-General_Concept
were	O
programmed	O
in	O
assembly	B-Language
;	O
however	O
,	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
are	O
typically	O
written	O
in	O
higher-level	O
languages	O
like	O
C	B-Language
,	O
Objective-C	B-Language
,	O
and	O
Swift	B-Application
.	O
</s>
<s>
A	O
utility	B-Application
program	I-Application
is	O
designed	O
to	O
aid	O
system	O
administration	O
and	O
software	B-General_Concept
execution	I-General_Concept
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
execute	B-General_Concept
hardware	B-General_Concept
utility	B-Application
programs	I-Application
to	O
check	O
the	O
status	O
of	O
disk	O
drives	O
,	O
memory	B-General_Concept
,	O
speakers	O
,	O
and	O
printers	O
.	O
</s>
<s>
A	O
utility	B-Application
program	I-Application
may	O
optimize	O
the	O
placement	O
of	O
a	O
file	O
on	O
a	O
crowded	O
disk	O
.	O
</s>
<s>
System	O
utility	B-Application
programs	I-Application
monitor	O
hardware	B-General_Concept
and	O
network	O
performance	O
.	O
</s>
<s>
Utility	B-Application
programs	I-Application
include	O
compression	O
programs	O
so	O
data	O
files	B-Operating_System
are	O
stored	O
on	O
less	O
disk	O
space	O
.	O
</s>
<s>
Compressed	O
programs	O
also	O
save	O
time	O
when	O
data	O
files	B-Operating_System
are	O
transmitted	O
over	O
the	O
network	O
.	O
</s>
<s>
Utility	B-Application
programs	I-Application
can	O
sort	O
and	O
merge	O
data	O
sets	O
.	O
</s>
<s>
Utility	B-Application
programs	I-Application
detect	O
computer	O
viruses	O
.	O
</s>
<s>
A	O
microcode	B-Device
program	I-Device
is	O
the	O
bottom-level	O
interpreter	B-Application
that	O
controls	O
the	O
data	B-General_Concept
path	I-General_Concept
of	O
software-driven	O
computers	O
.	O
</s>
<s>
(	O
Advances	O
in	O
hardware	B-General_Concept
have	O
migrated	O
these	O
operations	B-Language
to	O
hardware	B-General_Concept
execution	O
circuits	O
.	O
)	O
</s>
<s>
Microcode	B-Device
instructions	O
allow	O
the	O
programmer	B-Application
to	O
more	O
easily	O
implement	O
the	O
digital	O
logic	O
level	O
—	O
the	O
computer	O
's	O
real	O
hardware	B-General_Concept
.	O
</s>
<s>
The	O
digital	O
logic	O
level	O
is	O
the	O
boundary	O
between	O
computer	B-General_Concept
science	I-General_Concept
and	O
computer	O
engineering	O
.	O
</s>
<s>
A	O
logic	O
gate	O
is	O
a	O
tiny	O
transistor	O
that	O
can	O
return	O
one	O
of	O
two	O
signals	B-Operating_System
:	O
on	O
or	O
off	O
.	O
</s>
<s>
Microcode	B-Device
instructions	O
are	O
mnemonics	O
programmers	B-Application
may	O
use	O
to	O
execute	B-General_Concept
digital	O
logic	O
functions	O
instead	O
of	O
forming	O
them	O
in	O
binary	O
algebra	O
.	O
</s>
<s>
They	O
are	O
stored	O
in	O
a	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
's	I-General_Concept
(	O
CPU	B-Device
)	O
control	B-General_Concept
store	I-General_Concept
.	O
</s>
<s>
These	O
hardware-level	O
instructions	O
move	O
data	O
throughout	O
the	O
data	B-General_Concept
path	I-General_Concept
.	O
</s>
<s>
The	O
micro-instruction	O
cycle	O
begins	O
when	O
the	O
microsequencer	B-General_Concept
uses	O
its	O
microprogram	B-Device
counter	O
to	O
fetch	O
the	O
next	O
machine	B-Language
instruction	I-Language
from	O
random-access	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
The	O
next	O
step	O
is	O
to	O
decode	O
the	O
machine	B-Language
instruction	I-Language
by	O
selecting	O
the	O
proper	O
output	O
line	O
to	O
the	O
hardware	B-General_Concept
module	B-Architecture
.	O
</s>
<s>
The	O
final	O
step	O
is	O
to	O
execute	B-General_Concept
the	O
instruction	O
using	O
the	O
hardware	B-General_Concept
module	B-Architecture
's	O
set	O
of	O
gates	O
.	O
</s>
<s>
Instructions	O
to	O
perform	O
arithmetic	O
are	O
passed	O
through	O
an	O
arithmetic	B-General_Concept
logic	I-General_Concept
unit	I-General_Concept
(	O
ALU	O
)	O
.	O
</s>
<s>
The	O
ALU	O
has	O
circuits	O
to	O
perform	O
elementary	O
operations	B-Language
to	O
add	O
,	O
shift	O
,	O
and	O
compare	O
integers	O
.	O
</s>
<s>
By	O
combining	O
and	O
looping	O
the	O
elementary	O
operations	B-Language
through	O
the	O
ALU	O
,	O
the	O
CPU	B-Device
performs	O
its	O
complex	O
arithmetic	O
.	O
</s>
<s>
Microcode	B-Device
instructions	O
move	O
data	O
between	O
the	O
CPU	B-Device
and	O
the	O
memory	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
Memory	B-General_Concept
controller	I-General_Concept
microcode	B-Device
instructions	O
manipulate	O
two	O
registers	B-General_Concept
.	O
</s>
<s>
The	O
memory	B-General_Concept
address	I-General_Concept
register	I-General_Concept
is	O
used	O
to	O
access	O
each	O
memory	B-General_Concept
cell	O
's	O
address	O
.	O
</s>
<s>
The	O
memory	B-General_Concept
data	I-General_Concept
register	I-General_Concept
is	O
used	O
to	O
set	O
and	O
read	O
each	O
cell	O
's	O
contents	O
.	O
</s>
<s>
Microcode	B-Device
instructions	O
move	O
data	O
between	O
the	O
CPU	B-Device
and	O
the	O
many	O
computer	B-General_Concept
buses	I-General_Concept
.	O
</s>
<s>
The	O
disk	B-General_Concept
controller	I-General_Concept
bus	I-General_Concept
writes	O
to	O
and	O
reads	O
from	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
Data	O
is	O
also	O
moved	O
between	O
the	O
CPU	B-Device
and	O
other	O
functional	O
units	O
via	O
the	O
peripheral	O
component	O
interconnect	B-General_Concept
express	O
bus	O
.	O
</s>
