<s>
COM	B-Architecture
(	O
communication	O
port	O
)	O
is	O
the	O
original	O
,	O
yet	O
still	O
common	O
,	O
name	O
of	O
the	O
serial	B-Protocol
port	I-Protocol
interface	O
on	O
PC-compatible	O
computers	O
.	O
</s>
<s>
It	O
can	O
refer	O
not	O
only	O
to	O
physical	O
ports	O
,	O
but	O
also	O
to	O
emulated	O
ports	O
,	O
such	O
as	O
ports	O
created	O
by	O
Bluetooth	B-Protocol
or	O
USB	B-Device
adapters	I-Device
.	O
</s>
<s>
The	O
name	O
for	O
the	O
COM	B-Protocol
port	I-Protocol
started	O
with	O
the	O
original	O
IBM	O
PC	O
.	O
</s>
<s>
IBM	O
had	O
called	O
the	O
four	O
well-defined	O
communication	O
RS-232	O
ports	O
the	O
"	O
COM	B-Architecture
"	O
ports	O
,	O
starting	O
from	O
COM1	B-Architecture
through	O
COM4	O
.	O
</s>
<s>
In	O
BASICA	O
and	O
PC	O
DOS	O
you	O
can	O
open	O
these	O
ports	O
as	O
"	O
COM1	B-Architecture
:	O
"	O
through	O
"	O
COM4	O
:	O
"	O
,	O
and	O
all	O
PC	O
compatibles	O
using	O
MSDOS	O
used	O
the	O
same	O
denotation	O
.	O
</s>
<s>
Most	O
PC-compatible	O
computers	O
in	O
the	O
1980s	O
and	O
1990s	O
had	O
one	O
or	O
two	O
COM	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
By	O
2007	O
,	O
most	O
computers	O
shipped	O
with	O
only	O
one	O
or	O
no	O
physical	O
COM	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
Today	O
few	O
consumer-grade	O
PC-compatible	O
computers	O
include	O
COM	B-Protocol
ports	I-Protocol
,	O
though	O
some	O
of	O
them	O
do	O
still	O
include	O
a	O
COM	B-Architecture
header	B-Protocol
on	O
the	O
motherboard	O
.	O
</s>
<s>
After	O
the	O
RS-232	O
COM	B-Protocol
port	I-Protocol
was	O
removed	O
from	O
most	O
consumer-grade	O
computers	O
,	O
an	O
external	O
USB-to-UART	O
serial	O
adapter	O
cable	O
was	O
used	O
to	O
compensate	O
for	O
the	O
loss	O
.	O
</s>
<s>
The	O
COM	B-Protocol
ports	I-Protocol
are	O
interfaced	O
by	O
an	O
integrated	O
circuit	O
such	O
as	O
16550	B-Device
UART	I-Device
.	O
</s>
<s>
This	O
IC	O
has	O
seven	O
internal	O
8-bit	O
registers	B-General_Concept
which	O
hold	O
information	O
and	O
configuration	O
data	O
about	O
which	O
data	O
is	O
to	O
be	O
sent	O
or	O
was	O
received	O
,	O
the	O
baud	O
rate	O
,	O
interrupt	O
configuration	O
and	O
more	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
COM1	B-Architecture
,	O
these	O
registers	B-General_Concept
can	O
be	O
accessed	O
by	O
writing	O
to	O
or	O
reading	O
from	O
the	O
I/O	O
addresses	O
0x3F8	B-Architecture
to	O
0x3FF	O
.	O
</s>
<s>
If	O
the	O
CPU	O
,	O
for	O
example	O
,	O
wants	O
to	O
send	O
information	O
out	O
on	O
COM1	B-Architecture
,	O
it	O
writes	O
to	O
I/O	B-Architecture
port	I-Architecture
0x3F8	B-Architecture
,	O
as	O
this	O
I/O	B-Architecture
port	I-Architecture
is	O
"	O
connected	O
"	O
to	O
the	O
UART	O
IC	O
register	O
which	O
holds	O
the	O
information	O
that	O
is	O
to	O
be	O
sent	O
out	O
.	O
</s>
<s>
The	O
COM	B-Protocol
ports	I-Protocol
in	O
PC-compatible	O
computers	O
are	O
typically	O
defined	O
as	O
:	O
</s>
