<s>
Real-time	B-General_Concept
computing	I-General_Concept
(	O
RTC	O
)	O
is	O
the	O
computer	B-General_Concept
science	I-General_Concept
term	O
for	O
hardware	B-Architecture
and	O
software	B-Application
systems	O
subject	O
to	O
a	O
"	O
real-time	B-General_Concept
constraint	O
"	O
,	O
for	O
example	O
from	O
event	B-Operating_System
to	O
system	O
response	O
.	O
</s>
<s>
Real-time	B-General_Concept
programs	O
must	O
guarantee	O
response	O
within	O
specified	O
time	O
constraints	O
,	O
often	O
referred	O
to	O
as	O
"	O
deadlines	O
"	O
.	O
</s>
<s>
Real-time	B-General_Concept
responses	O
are	O
often	O
understood	O
to	O
be	O
in	O
the	O
order	O
of	O
milliseconds	O
,	O
and	O
sometimes	O
microseconds	O
.	O
</s>
<s>
Real-time	B-General_Concept
processing	O
fails	O
if	O
not	O
completed	O
within	O
a	O
specified	O
deadline	O
relative	O
to	O
an	O
event	B-Operating_System
;	O
deadlines	O
must	O
always	O
be	O
met	O
,	O
regardless	O
of	O
system	B-Operating_System
load	I-Operating_System
.	O
</s>
<s>
A	O
real-time	B-General_Concept
system	I-General_Concept
has	O
been	O
described	O
as	O
one	O
which	O
"	O
controls	O
an	O
environment	O
by	O
receiving	O
data	O
,	O
processing	O
them	O
,	O
and	O
returning	O
the	O
results	O
sufficiently	O
quickly	O
to	O
affect	O
the	O
environment	O
at	O
that	O
time	O
"	O
.	O
</s>
<s>
The	O
term	O
"	O
real-time	B-General_Concept
"	O
is	O
also	O
used	O
in	O
simulation	B-Application
to	O
mean	O
that	O
the	O
simulation	B-Application
's	O
clock	O
runs	O
at	O
the	O
same	O
speed	O
as	O
a	O
real	O
clock	O
,	O
and	O
in	O
process	O
control	O
and	O
enterprise	B-Architecture
systems	I-Architecture
to	O
mean	O
"	O
without	O
significant	O
delay	B-Protocol
"	O
.	O
</s>
<s>
Real-time	B-General_Concept
software	I-General_Concept
may	O
use	O
one	O
or	O
more	O
of	O
the	O
following	O
:	O
synchronous	B-Language
programming	I-Language
languages	I-Language
,	O
real-time	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
(	O
RTOSes	O
)	O
,	O
and	O
real-time	B-General_Concept
networks	I-General_Concept
,	O
each	O
of	O
which	O
provide	O
essential	O
frameworks	O
on	O
which	O
to	O
build	O
a	O
real-time	B-General_Concept
software	I-General_Concept
application	O
.	O
</s>
<s>
Systems	O
used	O
for	O
many	O
safety-critical	B-Application
applications	O
must	O
be	O
real-time	B-General_Concept
,	O
such	O
as	O
for	O
control	O
of	O
fly-by-wire	O
aircraft	O
,	O
or	O
anti-lock	O
brakes	O
,	O
both	O
of	O
which	O
demand	O
immediate	O
and	O
accurate	O
mechanical	O
response	O
.	O
</s>
<s>
The	O
term	O
real-time	B-General_Concept
derives	O
from	O
its	O
use	O
in	O
early	O
simulation	B-Application
,	O
in	O
which	O
a	O
real-world	O
process	O
is	O
simulated	O
at	O
a	O
rate	O
that	O
matched	O
that	O
of	O
the	O
real	O
process	O
(	O
now	O
called	O
real-time	B-General_Concept
simulation	B-Application
to	O
avoid	O
ambiguity	O
)	O
.	O
</s>
<s>
Analog	O
computers	O
,	O
most	O
often	O
,	O
were	O
capable	O
of	O
simulating	O
at	O
a	O
much	O
faster	O
pace	O
than	O
real-time	B-General_Concept
,	O
a	O
situation	O
that	O
could	O
be	O
just	O
as	O
dangerous	O
as	O
a	O
slow	O
simulation	B-Application
if	O
it	O
were	O
not	O
also	O
recognized	O
and	O
accounted	O
for	O
.	O
</s>
<s>
Minicomputers	O
,	O
particularly	O
in	O
the	O
1970s	O
onwards	O
,	O
when	O
built	O
into	O
dedicated	O
embedded	B-Architecture
systems	I-Architecture
such	O
as	O
DOG	O
(	O
Digital	O
on-screen	O
graphic	O
)	O
scanners	O
,	O
increased	O
the	O
need	O
for	O
low-latency	O
priority-driven	O
responses	O
to	O
important	O
interactions	O
with	O
incoming	O
data	O
and	O
so	O
operating	O
systems	O
such	O
as	O
Data	O
General	O
's	O
RDOS	O
(	O
Real-Time	B-General_Concept
Disk	O
Operating	O
System	O
)	O
and	O
RTOS	B-Operating_System
with	O
background	B-Operating_System
and	I-Operating_System
foreground	I-Operating_System
scheduling	I-Operating_System
as	O
well	O
as	O
Digital	O
Equipment	O
Corporation	O
's	O
RT-11	B-Operating_System
date	O
from	O
this	O
era	O
.	O
</s>
<s>
Real-time	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
would	O
also	O
be	O
used	O
for	O
time-sharing	B-General_Concept
multiuser	O
duties	O
.	O
</s>
<s>
For	O
example	O
,	O
Data	B-Language
General	I-Language
Business	I-Language
Basic	I-Language
could	O
run	O
in	O
the	O
foreground	O
or	O
background	O
of	O
RDOS	O
and	O
would	O
introduce	O
additional	O
elements	O
to	O
the	O
scheduling	O
algorithm	O
to	O
make	O
it	O
more	O
appropriate	O
for	O
people	O
interacting	O
via	O
dumb	O
terminals	O
.	O
</s>
<s>
Once	O
when	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
(	O
used	O
in	O
the	O
Commodore	O
64	O
and	O
Apple	B-Device
II	I-Device
)	O
,	O
and	O
later	O
when	O
the	O
Motorola	B-Device
68000	I-Device
(	O
used	O
in	O
the	O
Macintosh	B-Device
,	O
Atari	B-Device
ST	I-Device
,	O
and	O
Amiga	B-Device
)	O
were	O
popular	O
,	O
anybody	O
could	O
use	O
their	O
home	O
computer	O
as	O
a	O
real-time	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
possibility	O
to	O
deactivate	O
other	O
interrupts	O
allowed	O
for	O
hard-coded	O
loops	O
with	O
defined	O
timing	O
,	O
and	O
the	O
low	O
interrupt	B-General_Concept
latency	I-General_Concept
allowed	O
the	O
implementation	O
of	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
giving	O
the	O
user	O
interface	O
and	O
the	O
disk	O
drives	O
lower	O
priority	O
than	O
the	O
real-time	B-General_Concept
thread	O
.	O
</s>
<s>
Compared	O
to	O
these	O
the	O
programmable	B-Architecture
interrupt	I-Architecture
controller	I-Architecture
of	O
the	O
Intel	O
CPUs	O
(	O
8086	O
..	O
80586	O
)	O
generates	O
a	O
very	O
large	O
latency	O
and	O
the	O
Windows	O
operating	O
system	O
is	O
neither	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
nor	O
does	O
it	O
allow	O
a	O
program	O
to	O
take	O
over	O
the	O
CPU	O
completely	O
and	O
use	O
its	O
own	O
scheduler	O
,	O
without	O
using	O
native	O
machine	O
language	O
and	O
thus	O
surpassing	O
all	O
interrupting	O
Windows	O
code	O
.	O
</s>
<s>
However	O
,	O
several	O
coding	O
libraries	O
exist	O
which	O
offer	O
real	O
time	O
capabilities	O
in	O
a	O
high	O
level	O
language	O
on	O
a	O
variety	O
of	O
operating	O
systems	O
,	O
for	O
example	O
Java	B-Language
Real	I-Language
Time	I-Language
.	O
</s>
<s>
The	O
Motorola	B-Device
68000	I-Device
and	O
subsequent	O
family	O
members	O
(	O
68010	O
,	O
68020	O
etc	O
.	O
)	O
</s>
<s>
This	O
application	O
area	O
is	O
one	O
in	O
which	O
real-time	B-General_Concept
control	I-General_Concept
offers	O
genuine	O
advantages	O
in	O
terms	O
of	O
process	O
performance	O
and	O
safety	O
.	O
</s>
<s>
A	O
system	O
is	O
said	O
to	O
be	O
real-time	B-General_Concept
if	O
the	O
total	O
correctness	O
of	O
an	O
operation	O
depends	O
not	O
only	O
upon	O
its	O
logical	O
correctness	O
,	O
but	O
also	O
upon	O
the	O
time	O
in	O
which	O
it	O
is	O
performed	O
.	O
</s>
<s>
Real-time	B-General_Concept
systems	I-General_Concept
,	O
as	O
well	O
as	O
their	O
deadlines	O
,	O
are	O
classified	O
by	O
the	O
consequence	O
of	O
missing	O
a	O
deadline	O
:	O
</s>
<s>
Thus	O
,	O
the	O
goal	O
of	O
a	O
hard	O
real-time	B-General_Concept
system	I-General_Concept
is	O
to	O
ensure	O
that	O
all	O
deadlines	O
are	O
met	O
,	O
but	O
for	O
soft	O
real-time	B-General_Concept
systems	I-General_Concept
the	O
goal	O
becomes	O
meeting	O
a	O
certain	O
subset	O
of	O
deadlines	O
in	O
order	O
to	O
optimize	O
some	O
application-specific	O
criteria	O
.	O
</s>
<s>
Hard	O
real-time	B-General_Concept
systems	I-General_Concept
are	O
used	O
when	O
it	O
is	O
imperative	O
that	O
an	O
event	B-Operating_System
be	O
reacted	O
to	O
within	O
a	O
strict	O
deadline	O
.	O
</s>
<s>
Some	O
examples	O
of	O
hard	O
real-time	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
A	O
car	O
engine	O
control	O
system	O
is	O
a	O
hard	O
real-time	B-General_Concept
system	I-General_Concept
because	O
a	O
delayed	O
signal	O
may	O
cause	O
engine	O
failure	O
or	O
damage	O
.	O
</s>
<s>
Medical	O
systems	O
such	O
as	O
heart	B-Device
pacemakers	I-Device
.	O
</s>
<s>
Even	O
though	O
a	O
pacemaker	B-Device
's	O
task	O
is	O
simple	O
,	O
because	O
of	O
the	O
potential	O
risk	O
to	O
human	O
life	O
,	O
medical	O
systems	O
like	O
these	O
are	O
typically	O
required	O
to	O
undergo	O
thorough	O
testing	O
and	O
certification	O
,	O
which	O
in	O
turn	O
requires	O
hard	O
real-time	B-General_Concept
computing	I-General_Concept
in	O
order	O
to	O
offer	O
provable	O
guarantees	O
that	O
a	O
failure	O
is	O
unlikely	O
or	O
impossible	O
.	O
</s>
<s>
Hard	O
real-time	B-General_Concept
systems	I-General_Concept
are	O
typically	O
found	O
interacting	O
at	O
a	O
low	O
level	O
with	O
physical	O
hardware	B-Architecture
,	O
in	O
embedded	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
Early	O
video	O
game	O
systems	O
such	O
as	O
the	O
Atari	B-General_Concept
2600	I-General_Concept
and	O
Cinematronics	O
vector	O
graphics	O
had	O
hard	O
real-time	B-General_Concept
requirements	O
because	O
of	O
the	O
nature	O
of	O
the	O
graphics	O
and	O
timing	O
hardware	B-Architecture
.	O
</s>
<s>
Softmodems	B-Device
replace	O
a	O
hardware	B-Architecture
modem	O
with	O
software	B-Application
running	O
on	O
a	O
computer	O
's	O
CPU	O
.	O
</s>
<s>
The	B-Application
software	I-Application
must	O
run	O
every	O
few	O
milliseconds	O
to	O
generate	O
the	O
next	O
audio	O
data	O
to	O
be	O
output	O
.	O
</s>
<s>
Many	O
types	O
of	O
printers	O
have	O
hard	O
real-time	B-General_Concept
requirements	O
,	O
such	O
as	O
inkjets	O
(	O
the	O
ink	O
must	O
be	O
deposited	O
at	O
the	O
correct	O
time	O
as	O
the	O
printhead	O
crosses	O
the	O
page	O
)	O
,	O
laser	O
printers	O
(	O
the	O
laser	O
must	O
be	O
activated	O
at	O
the	O
right	O
time	O
as	O
the	O
beam	O
scans	O
across	O
the	O
rotating	O
drum	O
)	O
,	O
and	O
dot	O
matrix	O
and	O
various	O
types	O
of	O
line	O
printers	O
(	O
the	O
impact	O
mechanism	O
must	O
be	O
activated	O
at	O
the	O
right	O
time	O
as	O
the	O
print	O
mechanism	O
comes	O
into	O
alignment	O
with	O
the	O
desired	O
output	O
)	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
multitasking	B-Operating_System
systems	O
the	O
scheduling	O
policy	O
is	O
normally	O
priority	O
driven	O
(	O
pre-emptive	O
schedulers	O
)	O
.	O
</s>
<s>
In	O
some	O
situations	O
,	O
these	O
can	O
guarantee	O
hard	O
real-time	B-General_Concept
performance	O
(	O
for	O
instance	O
if	O
the	O
set	O
of	O
tasks	O
and	O
their	O
priorities	O
is	O
known	O
in	O
advance	O
)	O
.	O
</s>
<s>
There	O
are	O
other	O
hard	O
real-time	B-General_Concept
schedulers	O
such	O
as	O
rate-monotonic	B-Operating_System
which	O
is	O
not	O
common	O
in	O
general-purpose	O
systems	O
,	O
as	O
it	O
requires	O
additional	O
information	O
in	O
order	O
to	O
schedule	O
a	O
task	O
:	O
namely	O
a	O
bound	O
or	O
worst-case	O
estimate	O
for	O
how	O
long	O
the	O
task	O
must	O
execute	O
.	O
</s>
<s>
Specific	O
algorithms	O
for	O
scheduling	O
such	O
hard	O
real-time	B-General_Concept
tasks	O
exist	O
,	O
such	O
as	O
earliest	B-Operating_System
deadline	I-Operating_System
first	I-Operating_System
,	O
which	O
,	O
ignoring	O
the	O
overhead	O
of	O
context	B-Operating_System
switching	I-Operating_System
,	O
is	O
sufficient	O
for	O
system	B-Operating_System
loads	I-Operating_System
of	O
less	O
than	O
100%	O
.	O
</s>
<s>
New	O
overlay	O
scheduling	O
systems	O
,	O
such	O
as	O
an	O
adaptive	B-Operating_System
partition	I-Operating_System
scheduler	I-Operating_System
assist	O
in	O
managing	O
large	O
systems	O
with	O
a	O
mixture	O
of	O
hard	O
real-time	B-General_Concept
and	O
non	O
real-time	B-General_Concept
applications	I-General_Concept
.	O
</s>
<s>
Firm	O
real-time	B-General_Concept
systems	I-General_Concept
are	O
more	O
nebulously	O
defined	O
,	O
and	O
some	O
classifications	O
do	O
not	O
include	O
them	O
,	O
distinguishing	O
only	O
hard	O
and	O
soft	O
real-time	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Some	O
examples	O
of	O
firm	O
real-time	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
The	O
assembly	O
line	O
machine	O
described	O
earlier	O
as	O
hard	O
real-time	B-General_Concept
could	O
instead	O
be	O
considered	O
firm	O
real-time	B-General_Concept
.	O
</s>
<s>
Soft	O
real-time	B-General_Concept
systems	I-General_Concept
are	O
typically	O
used	O
to	O
solve	O
issues	O
of	O
concurrent	B-Operating_System
access	O
and	O
the	O
need	O
to	O
keep	O
a	O
number	O
of	O
connected	O
systems	O
up-to-date	O
through	O
changing	O
situations	O
.	O
</s>
<s>
Some	O
examples	O
of	O
soft	O
real-time	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
Software	B-Application
that	O
maintains	O
and	O
updates	O
the	O
flight	O
plans	O
for	O
commercial	O
airliners	O
.	O
</s>
<s>
Live	O
audio-video	O
systems	O
are	O
also	O
usually	O
soft	O
real-time	B-General_Concept
.	O
</s>
<s>
Similarly	O
,	O
video	O
games	O
are	O
often	O
soft	O
real-time	B-General_Concept
,	O
particularly	O
as	O
they	O
try	O
to	O
meet	O
a	O
target	O
frame	O
rate	O
.	O
</s>
<s>
If	O
the	O
deadline	O
is	O
missed	O
,	O
the	O
game	O
can	O
continue	O
at	O
a	O
lower	O
frame	O
rate	O
;	O
depending	O
on	O
the	O
game	O
,	O
this	O
may	O
only	O
affect	O
its	O
graphics	O
(	O
while	O
the	O
gameplay	O
continues	O
at	O
normal	O
speed	O
)	O
,	O
or	O
the	O
gameplay	O
itself	O
may	O
be	O
slowed	O
down	O
(	O
which	O
was	O
common	O
on	O
older	O
third	B-Application
-	I-Application
and	O
fourth-generation	B-Application
consoles	I-Application
)	O
.	O
</s>
<s>
In	O
a	O
real-time	B-General_Concept
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
(	O
DSP	O
)	O
process	O
,	O
the	O
analyzed	O
(	O
input	O
)	O
and	O
generated	O
(	O
output	O
)	O
samples	O
can	O
be	O
processed	O
(	O
or	O
generated	O
)	O
continuously	O
in	O
the	O
time	O
it	O
takes	O
to	O
input	O
and	O
output	O
the	O
same	O
set	O
of	O
samples	O
independent	O
of	O
the	O
processing	O
delay	B-Protocol
.	O
</s>
<s>
It	O
means	O
that	O
the	O
processing	O
delay	B-Protocol
must	O
be	O
bounded	O
even	O
if	O
the	O
processing	O
continues	O
for	O
an	O
unlimited	O
time	O
.	O
</s>
<s>
This	O
is	O
the	O
criterion	O
whether	O
the	O
samples	O
are	O
grouped	O
together	O
in	O
large	O
segments	O
and	O
processed	O
as	O
blocks	O
or	O
are	O
processed	O
individually	O
and	O
whether	O
there	O
are	O
long	O
,	O
short	O
,	O
or	O
non-existent	O
input	B-General_Concept
and	I-General_Concept
output	I-General_Concept
buffers	I-General_Concept
.	O
</s>
<s>
Consider	O
an	O
audio	B-Algorithm
DSP	I-Algorithm
example	O
;	O
if	O
a	O
process	O
requires	O
2.01	O
seconds	O
to	O
analyze	O
,	O
synthesize	O
,	O
or	O
process	O
2.00	O
seconds	O
of	O
sound	O
,	O
it	O
is	O
not	O
real-time	B-General_Concept
.	O
</s>
<s>
However	O
,	O
if	O
it	O
takes	O
1.99	O
seconds	O
,	O
it	O
is	O
or	O
can	O
be	O
made	O
into	O
a	O
real-time	B-General_Concept
DSP	O
process	O
.	O
</s>
<s>
If	O
the	O
line	O
asymptotically	O
grows	O
longer	O
and	O
longer	O
without	O
bound	O
,	O
the	O
checkout	O
process	O
is	O
not	O
real-time	B-General_Concept
.	O
</s>
<s>
If	O
the	O
length	O
of	O
the	O
line	O
is	O
bounded	O
,	O
customers	O
are	O
being	O
"	O
processed	O
"	O
and	O
output	O
as	O
rapidly	O
,	O
on	O
average	O
,	O
as	O
they	O
are	O
being	O
inputted	O
then	O
that	O
process	O
is	O
real-time	B-General_Concept
.	O
</s>
<s>
The	O
grocer	O
might	O
go	O
out	O
of	O
business	O
or	O
must	O
at	O
least	O
lose	O
business	O
if	O
they	O
cannot	O
make	O
their	O
checkout	O
process	O
real-time	B-General_Concept
;	O
thus	O
,	O
it	O
is	O
fundamentally	O
important	O
that	O
this	O
process	O
is	O
real-time	B-General_Concept
.	O
</s>
<s>
A	O
signal	O
processing	O
algorithm	O
that	O
cannot	O
keep	O
up	O
with	O
the	O
flow	O
of	O
input	O
data	O
with	O
output	O
falling	O
farther	O
and	O
farther	O
behind	O
the	O
input	O
,	O
is	O
not	O
real-time	B-General_Concept
.	O
</s>
<s>
But	O
if	O
the	O
delay	B-Protocol
of	O
the	O
output	O
(	O
relative	O
to	O
the	O
input	O
)	O
is	O
bounded	O
regarding	O
a	O
process	O
that	O
operates	O
over	O
an	O
unlimited	O
time	O
,	O
then	O
that	O
signal	O
processing	O
algorithm	O
is	O
real-time	B-General_Concept
,	O
even	O
if	O
the	O
throughput	O
delay	B-Protocol
may	O
be	O
very	O
long	O
.	O
</s>
<s>
Real-time	B-General_Concept
signal	O
processing	O
is	O
necessary	O
,	O
but	O
not	O
sufficient	O
in	O
and	O
of	O
itself	O
,	O
for	O
live	O
signal	O
processing	O
such	O
as	O
what	O
is	O
required	O
in	O
live	O
event	B-Operating_System
support	O
.	O
</s>
<s>
Live	O
audio	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
requires	O
both	O
real-time	B-General_Concept
operation	O
and	O
a	O
sufficient	O
limit	O
to	O
throughput	O
delay	B-Protocol
so	O
as	O
to	O
be	O
tolerable	O
to	O
performers	O
using	O
stage	O
monitors	O
or	O
in-ear	B-Device
monitors	I-Device
and	O
not	O
noticeable	O
as	O
lip	B-Protocol
sync	I-Protocol
error	I-Protocol
by	O
the	O
audience	O
also	O
directly	O
watching	O
the	O
performers	O
.	O
</s>
<s>
Tolerable	O
limits	O
to	O
latency	O
for	O
live	O
,	O
real-time	B-General_Concept
processing	O
is	O
a	O
subject	O
of	O
investigation	O
and	O
debate	O
but	O
is	O
estimated	O
to	O
be	O
between	O
6	O
and	O
20	O
milliseconds	O
.	O
</s>
<s>
Real-time	B-General_Concept
bidirectional	O
telecommunications	O
delays	O
of	O
less	O
than	O
300	O
ms	O
(	O
"	O
round	O
trip	O
"	O
or	O
twice	O
the	O
unidirectional	O
delay	B-Protocol
)	O
are	O
considered	O
"	O
acceptable	O
"	O
to	O
avoid	O
undesired	O
"	O
talk-over	O
"	O
in	O
conversation	O
.	O
</s>
<s>
Real-time	B-General_Concept
computing	I-General_Concept
is	O
sometimes	O
misunderstood	O
to	O
be	O
high-performance	B-Architecture
computing	I-Architecture
,	O
but	O
this	O
is	O
not	O
an	O
accurate	O
classification	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
massive	O
supercomputer	B-Architecture
executing	O
a	O
scientific	O
simulation	B-Application
may	O
offer	O
impressive	O
performance	O
,	O
yet	O
it	O
is	O
not	O
executing	O
a	O
real-time	B-General_Concept
computation	O
.	O
</s>
<s>
Conversely	O
,	O
once	O
the	O
hardware	B-Architecture
and	O
software	B-Application
for	O
an	O
anti-lock	O
braking	O
system	O
have	O
been	O
designed	O
to	O
meet	O
its	O
required	O
deadlines	O
,	O
no	O
further	O
performance	O
gains	O
are	O
obligatory	O
or	O
even	O
useful	O
.	O
</s>
<s>
Hence	O
,	O
such	O
a	O
network	O
server	O
would	O
not	O
be	O
considered	O
a	O
real-time	B-General_Concept
system	I-General_Concept
:	O
temporal	O
failures	O
(	O
delays	O
,	O
time-outs	O
,	O
etc	O
.	O
)	O
</s>
<s>
In	O
a	O
real-time	B-General_Concept
system	I-General_Concept
,	O
such	O
as	O
the	O
FTSE	O
100	O
Index	O
,	O
a	O
slow-down	O
beyond	O
limits	O
would	O
often	O
be	O
considered	O
catastrophic	O
in	O
its	O
application	O
context	O
.	O
</s>
<s>
The	O
most	O
important	O
requirement	O
of	O
a	O
real-time	B-General_Concept
system	I-General_Concept
is	O
consistent	O
output	O
,	O
not	O
high	O
throughput	O
.	O
</s>
<s>
Some	O
kinds	O
of	O
software	B-Application
,	O
such	O
as	O
many	O
chess-playing	B-Application
programs	I-Application
,	O
can	O
fall	O
into	O
either	O
category	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
chess	B-Application
program	O
designed	O
to	O
play	O
in	O
a	O
tournament	O
with	O
a	O
clock	O
will	O
need	O
to	O
decide	O
on	O
a	O
move	O
before	O
a	O
certain	O
deadline	O
or	O
lose	O
the	O
game	O
,	O
and	O
is	O
therefore	O
a	O
real-time	B-General_Concept
computation	O
,	O
but	O
a	O
chess	B-Application
program	O
that	O
is	O
allowed	O
to	O
run	O
indefinitely	O
before	O
moving	O
is	O
not	O
.	O
</s>
<s>
In	O
both	O
of	O
these	O
cases	O
,	O
however	O
,	O
high	O
performance	O
is	O
desirable	O
:	O
the	O
more	O
work	O
a	O
tournament	O
chess	B-Application
program	O
can	O
do	O
in	O
the	O
allotted	O
time	O
,	O
the	O
better	O
its	O
moves	O
will	O
be	O
,	O
and	O
the	O
faster	O
an	O
unconstrained	O
chess	B-Application
program	O
runs	O
,	O
the	O
sooner	O
it	O
will	O
be	O
able	O
to	O
move	O
.	O
</s>
<s>
This	O
example	O
also	O
illustrates	O
the	O
essential	O
difference	O
between	O
real-time	B-General_Concept
computations	O
and	O
other	O
computations	O
:	O
if	O
the	O
tournament	O
chess	B-Application
program	O
does	O
not	O
make	O
a	O
decision	O
about	O
its	O
next	O
move	O
in	O
its	O
allotted	O
time	O
it	O
loses	O
the	O
game	O
—	O
i.e.	O
,	O
it	O
fails	O
as	O
a	O
real-time	B-General_Concept
computation	O
—	O
while	O
in	O
the	O
other	O
scenario	O
,	O
meeting	O
the	O
deadline	O
is	O
assumed	O
not	O
to	O
be	O
necessary	O
.	O
</s>
<s>
High-performance	O
is	O
indicative	O
of	O
the	O
amount	O
of	O
processing	O
that	O
is	O
performed	O
in	O
a	O
given	O
amount	O
of	O
time	O
,	O
whereas	O
real-time	B-General_Concept
is	O
the	O
ability	O
to	O
get	O
done	O
with	O
the	O
processing	O
to	O
yield	O
a	O
useful	O
output	O
in	O
the	O
available	O
time	O
.	O
</s>
<s>
The	O
term	O
"	O
near	O
real-time	B-General_Concept
"	O
or	O
"	O
nearly	O
real-time	B-General_Concept
"	O
(	O
NRT	O
)	O
,	O
in	O
telecommunications	O
and	O
computing	O
,	O
refers	O
to	O
the	O
time	O
delay	B-Protocol
introduced	O
,	O
by	O
automated	O
data	B-General_Concept
processing	I-General_Concept
or	O
network	O
transmission	O
,	O
between	O
the	O
occurrence	O
of	O
an	O
event	B-Operating_System
and	O
the	O
use	O
of	O
the	O
processed	B-General_Concept
data	I-General_Concept
,	O
such	O
as	O
for	O
display	O
or	O
feedback	O
and	O
control	O
purposes	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
near-real-time	B-General_Concept
display	O
depicts	O
an	O
event	B-Operating_System
or	O
situation	O
as	O
it	O
existed	O
at	O
the	O
current	O
time	O
minus	O
the	O
processing	O
time	O
,	O
as	O
nearly	O
the	O
time	O
of	O
the	O
live	O
event	B-Operating_System
.	O
</s>
<s>
In	O
many	O
cases	O
,	O
processing	O
described	O
as	O
"	O
real-time	B-General_Concept
"	O
would	O
be	O
more	O
accurately	O
described	O
as	O
"	O
near	O
real-time	B-General_Concept
"	O
.	O
</s>
<s>
Near	O
real-time	B-General_Concept
also	O
refers	O
to	O
delayed	O
real-time	B-General_Concept
transmission	O
of	O
voice	O
and	O
video	O
.	O
</s>
<s>
It	O
allows	O
playing	O
video	O
images	O
,	O
in	O
approximately	O
real-time	B-General_Concept
,	O
without	O
having	O
to	O
wait	O
for	O
an	O
entire	O
large	O
video	O
file	O
to	O
download	O
.	O
</s>
<s>
Incompatible	O
databases	O
can	O
export/import	O
to	O
common	O
flat	O
files	O
that	O
the	O
other	O
database	O
can	O
import/export	O
on	O
a	O
scheduled	O
basis	O
so	O
that	O
they	O
can	O
sync/share	O
common	O
data	O
in	O
"	O
near	O
real-time	B-General_Concept
"	O
with	O
each	O
other	O
.	O
</s>
<s>
The	O
distinction	O
between	O
"	O
near	O
real-time	B-General_Concept
"	O
and	O
"	O
real-time	B-General_Concept
"	O
varies	O
,	O
and	O
the	O
delay	B-Protocol
is	O
dependent	O
on	O
the	O
type	O
and	O
speed	O
of	O
the	O
transmission	O
.	O
</s>
<s>
The	O
delay	B-Protocol
in	O
near	O
real-time	B-General_Concept
is	O
typically	O
in	O
a	O
range	O
of	O
1-10	O
seconds	O
.	O
</s>
<s>
Several	O
methods	O
exist	O
to	O
aid	O
the	O
design	O
of	O
real-time	B-General_Concept
systems	I-General_Concept
,	O
an	O
example	O
of	O
which	O
is	O
MASCOT	O
,	O
an	O
old	O
but	O
very	O
successful	O
method	O
which	O
represents	O
the	O
concurrent	B-Operating_System
structure	O
of	O
the	O
system	O
.	O
</s>
<s>
Other	O
examples	O
are	O
HOOD	B-Language
,	O
Real-Time	B-General_Concept
UML	O
,	O
AADL	B-Architecture
,	O
the	O
Ravenscar	B-Language
profile	I-Language
,	O
and	O
Real-Time	B-Language
Java	I-Language
.	O
</s>
