<s>
In	O
telecommunication	O
and	O
data	O
transmission	O
,	O
serial	B-Protocol
communication	I-Protocol
is	O
the	O
process	O
of	O
sending	O
data	O
one	O
bit	O
at	O
a	O
time	O
,	O
sequentially	O
,	O
over	O
a	O
communication	O
channel	O
or	O
computer	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
Serial	B-Protocol
communication	I-Protocol
is	O
used	O
for	O
all	O
long-haul	O
communication	O
and	O
most	O
computer	B-Architecture
networks	I-Architecture
,	O
where	O
the	O
cost	O
of	O
cable	O
and	O
synchronization	O
difficulties	O
make	O
parallel	O
communication	O
impractical	O
.	O
</s>
<s>
Serial	O
computer	B-General_Concept
buses	I-General_Concept
are	O
becoming	O
more	O
common	O
even	O
at	O
shorter	O
distances	O
,	O
as	O
improved	O
signal	O
integrity	O
and	O
transmission	O
speeds	O
in	O
newer	O
serial	O
technologies	O
have	O
begun	O
to	O
outweigh	O
the	O
parallel	O
bus	O
's	O
advantage	O
of	O
simplicity	O
(	O
no	O
need	O
for	O
serializer	B-Protocol
and	O
deserializer	O
,	O
or	O
SerDes	O
)	O
and	O
to	O
outstrip	O
its	O
disadvantages	O
(	O
clock	O
skew	O
,	O
interconnect	B-General_Concept
density	O
)	O
.	O
</s>
<s>
The	O
migration	O
from	O
PCI	B-Protocol
to	O
PCI	B-Protocol
Express	O
is	O
an	O
example	O
.	O
</s>
<s>
Many	O
serial	B-Protocol
communication	I-Protocol
systems	O
were	O
originally	O
designed	O
to	O
transfer	O
data	O
over	O
relatively	O
large	O
distances	O
through	O
some	O
sort	O
of	O
data	B-Protocol
cable	I-Protocol
.	O
</s>
<s>
The	O
cables	O
that	O
carry	O
this	O
data	O
(	O
other	O
than	O
"	O
the	O
"	O
serial	O
cable	O
)	O
and	O
the	O
computer	B-Protocol
ports	I-Protocol
they	O
plug	O
into	O
are	O
usually	O
referred	O
to	O
with	O
a	O
more	O
specific	O
name	O
,	O
to	O
reduce	O
confusion	O
.	O
</s>
<s>
Keyboard	O
and	O
mouse	O
cables	O
and	O
ports	O
are	O
almost	O
invariably	O
serial	O
—	O
such	O
as	O
PS/2	B-Protocol
port	I-Protocol
,	O
Apple	B-Device
Desktop	I-Device
Bus	I-Device
and	O
USB	B-Protocol
.	O
</s>
<s>
The	O
cables	O
that	O
carry	O
digital	O
video	O
are	O
also	O
mostly	O
serial	O
—	O
such	O
as	O
coax	O
cable	O
plugged	O
into	O
a	O
HD-SDI	B-Protocol
port	O
,	O
a	O
webcam	B-Protocol
plugged	O
into	O
a	O
USB	B-Protocol
port	I-Protocol
or	O
FireWire	B-Protocol
port	I-Protocol
,	O
Ethernet	B-Protocol
cable	I-Protocol
connecting	O
an	O
IP	B-Algorithm
camera	I-Algorithm
to	O
a	O
Power	B-Device
over	I-Device
Ethernet	I-Device
port	O
,	O
FPD-Link	B-Protocol
,	O
digital	O
telephone	O
lines	O
(	O
ex	O
.	O
</s>
<s>
ISDN	B-Protocol
)	O
,	O
etc	O
.	O
</s>
<s>
Other	O
such	O
cables	O
and	O
ports	O
,	O
transmitting	O
data	O
one	O
bit	O
at	O
a	O
time	O
,	O
include	O
Serial	O
ATA	O
,	O
Serial	O
SCSI	O
,	O
Ethernet	B-Protocol
cable	I-Protocol
plugged	O
into	O
Ethernet	O
ports	O
,	O
the	O
Display	O
Data	O
Channel	O
using	O
previously	O
reserved	O
pins	O
of	O
the	O
VGA	B-Protocol
connector	I-Protocol
or	O
the	O
DVI	B-Protocol
port	I-Protocol
or	O
the	O
HDMI	B-Protocol
port	O
.	O
</s>
<s>
Some	O
examples	O
of	O
such	O
low-cost	O
serial	O
buses	O
include	O
RS-232	O
,	O
SPI	B-Architecture
,	O
I²C	O
,	O
UNI/O	O
,	O
1-Wire	O
and	O
PCI	B-Protocol
Express	O
.	O
</s>
<s>
A	O
parallel	O
link	O
transmits	O
several	O
streams	O
of	O
data	O
simultaneously	O
along	O
multiple	O
channels	O
(	O
e.g.	O
,	O
wires	O
,	O
printed	O
circuit	O
tracks	O
,	O
or	O
optical	O
fibers	O
)	O
;	O
whereas	O
,	O
a	O
serial	B-Protocol
link	I-Protocol
transmits	O
only	O
a	O
single	O
stream	O
of	O
data	O
.	O
</s>
<s>
Although	O
a	O
serial	B-Protocol
link	I-Protocol
may	O
seem	O
inferior	O
to	O
a	O
parallel	O
one	O
,	O
since	O
it	O
can	B-Protocol
transmit	O
less	O
data	O
per	O
clock	O
cycle	O
,	O
it	O
is	O
often	O
the	O
case	O
that	O
serial	B-Protocol
links	I-Protocol
can	B-Protocol
be	O
clocked	O
considerably	O
faster	O
than	O
parallel	O
links	O
in	O
order	O
to	O
achieve	O
a	O
higher	O
data	O
rate	O
.	O
</s>
<s>
Clock	O
skew	O
between	O
different	O
channels	O
is	O
not	O
an	O
issue	O
(	O
for	O
unclocked	O
asynchronous	O
serial	B-Protocol
communication	I-Protocol
links	O
)	O
.	O
</s>
<s>
can	B-Protocol
be	O
focused	O
on	O
a	O
single	O
link	O
.	O
</s>
<s>
Many	O
ICs	O
have	O
serial	B-Protocol
interfaces	I-Protocol
,	O
as	O
opposed	O
to	O
parallel	O
ones	O
,	O
so	O
that	O
they	O
have	O
fewer	O
pins	O
and	O
are	O
therefore	O
less	O
expensive	O
.	O
</s>
