<s>
In	O
computing	O
,	O
a	O
parallel	B-Device
port	I-Device
is	O
a	O
type	O
of	O
interface	B-Application
found	O
on	O
early	O
computers	O
(	O
personal	B-Device
and	O
otherwise	O
)	O
for	O
connecting	O
peripherals	O
.	O
</s>
<s>
The	O
name	O
refers	O
to	O
the	O
way	O
the	O
data	O
is	O
sent	O
;	O
parallel	B-Device
ports	I-Device
send	O
multiple	O
bits	O
of	O
data	O
at	O
once	O
(	O
parallel	O
communication	O
)	O
,	O
as	O
opposed	O
to	O
serial	B-Protocol
communication	I-Protocol
,	O
in	O
which	O
bits	O
are	O
sent	O
one	O
at	O
a	O
time	O
.	O
</s>
<s>
To	O
do	O
this	O
,	O
parallel	B-Device
ports	I-Device
require	O
multiple	O
data	O
lines	O
in	O
their	O
cables	O
and	O
port	B-Protocol
connectors	O
and	O
tend	O
to	O
be	O
larger	O
than	O
contemporary	O
serial	B-Protocol
ports	I-Protocol
,	O
which	O
only	O
require	O
one	O
data	O
line	O
.	O
</s>
<s>
There	O
are	O
many	O
types	O
of	O
parallel	B-Device
ports	I-Device
,	O
but	O
the	O
term	O
has	O
become	O
most	O
closely	O
associated	O
with	O
the	O
printer	B-Device
port	I-Device
or	O
Centronics	B-Device
port	I-Device
found	O
on	O
most	O
personal	B-Device
computers	I-Device
from	O
the	O
1970s	O
through	O
the	O
2000s	O
.	O
</s>
<s>
It	O
was	O
an	O
industry	O
de	O
facto	O
standard	O
for	O
many	O
years	O
,	O
and	O
was	O
finally	O
standardized	O
as	O
IEEE	B-Device
1284	I-Device
in	O
the	O
late	O
1990s	O
,	O
which	O
defined	O
the	O
Enhanced	B-Device
Parallel	I-Device
Port	I-Device
(	O
EPP	O
)	O
and	O
Extended	O
Capability	O
Port	B-Protocol
(	O
ECP	O
)	O
bi-directional	O
versions	O
.	O
</s>
<s>
Today	O
,	O
the	O
parallel	B-Device
port	I-Device
interface	B-Application
is	O
virtually	O
non-existent	O
in	O
new	O
computers	O
because	O
of	O
the	O
rise	O
of	O
Universal	B-Protocol
Serial	I-Protocol
Bus	I-Protocol
(	O
USB	B-Protocol
)	O
devices	O
,	O
along	O
with	O
network	B-Application
printing	I-Application
using	O
Ethernet	O
and	O
Wi-Fi	O
connected	O
printers	O
.	O
</s>
<s>
The	O
parallel	B-Device
port	I-Device
interface	B-Application
was	O
originally	O
known	O
as	O
the	O
Parallel	O
Printer	O
Adapter	O
on	O
IBM	O
PC-compatible	O
computers	O
.	O
</s>
<s>
It	O
was	O
primarily	O
designed	O
to	O
operate	O
printers	O
that	O
used	O
IBM	O
's	O
eight-bit	O
extended	B-Protocol
ASCII	I-Protocol
character	B-General_Concept
set	I-General_Concept
to	O
print	O
text	O
,	O
but	O
could	O
also	O
be	O
used	O
to	O
adapt	O
other	O
peripherals	O
.	O
</s>
<s>
An	O
Wang	O
,	O
Robert	O
Howard	O
and	O
Prentice	O
Robinson	O
began	O
development	O
of	O
a	O
low-cost	O
printer	O
at	O
Centronics	O
,	O
a	O
subsidiary	O
of	O
Wang	O
Laboratories	O
that	O
produced	O
specialty	O
computer	B-General_Concept
terminals	I-General_Concept
.	O
</s>
<s>
The	O
printer	O
used	O
the	O
dot	O
matrix	O
printing	O
principle	O
,	O
with	O
a	O
print	O
head	O
consisting	O
of	O
a	O
vertical	O
row	O
of	O
seven	O
metal	O
pins	O
connected	O
to	O
solenoids	B-Algorithm
.	O
</s>
<s>
When	O
power	O
was	O
applied	O
to	O
the	O
solenoids	B-Algorithm
,	O
the	O
pin	O
was	O
pushed	O
forward	O
to	O
strike	O
the	O
paper	O
and	O
leave	O
a	O
dot	O
.	O
</s>
<s>
To	O
make	O
a	O
complete	O
character	O
glyph	B-Application
,	O
the	O
print	O
head	O
would	O
receive	O
power	O
to	O
specified	O
pins	O
to	O
create	O
a	O
single	O
vertical	O
pattern	O
,	O
then	O
the	O
print	O
head	O
would	O
move	O
to	O
the	O
right	O
by	O
a	O
small	O
amount	O
,	O
and	O
the	O
process	O
repeated	O
.	O
</s>
<s>
On	O
their	O
original	O
design	O
,	O
a	O
typical	O
glyph	B-Application
was	O
printed	O
as	O
a	O
matrix	O
seven	O
high	O
and	O
five	O
wide	O
,	O
while	O
the	O
"	O
A	O
"	O
models	O
used	O
a	O
print	O
head	O
with	O
9	O
pins	O
and	O
formed	O
glyphs	B-Application
that	O
were	O
9	O
by	O
7	O
.	O
</s>
<s>
This	O
left	O
the	O
problem	O
of	O
sending	O
the	O
ASCII	B-Protocol
data	O
to	O
the	O
printer	O
.	O
</s>
<s>
While	O
a	O
serial	B-Protocol
port	I-Protocol
does	O
so	O
with	O
the	O
minimum	O
of	O
pins	O
and	O
wires	O
,	O
it	O
requires	O
the	O
device	O
to	O
buffer	B-General_Concept
up	O
the	O
data	O
as	O
it	O
arrives	O
bit	O
by	O
bit	O
and	O
turn	O
it	O
back	O
into	O
multi-bit	O
values	O
.	O
</s>
<s>
A	O
parallel	B-Device
port	I-Device
makes	O
this	O
simpler	O
;	O
the	O
entire	O
ASCII	B-Protocol
value	I-Protocol
is	O
presented	O
on	O
the	O
pins	O
in	O
complete	O
form	O
.	O
</s>
<s>
Wang	O
happened	O
to	O
have	O
a	O
surplus	O
stock	O
of	O
20,000	O
Amphenol	O
36-pin	O
micro	B-Protocol
ribbon	I-Protocol
connectors	I-Protocol
that	O
were	O
originally	O
used	O
for	O
one	O
of	O
their	O
early	O
calculators	O
.	O
</s>
<s>
The	O
interface	B-Application
only	O
required	O
21	O
of	O
these	O
pins	O
,	O
the	O
rest	O
were	O
grounded	O
or	O
not	O
connected	O
.	O
</s>
<s>
The	O
connector	O
has	O
become	O
so	O
closely	O
associated	O
with	O
Centronics	O
that	O
it	O
is	O
now	O
popularly	O
known	O
as	O
the	O
"	O
Centronics	B-Device
connector	I-Device
"	O
.	O
</s>
<s>
The	O
host	O
sent	O
ASCII	B-Protocol
characters	I-Protocol
to	O
the	O
printer	O
using	O
seven	O
of	O
eight	O
data	O
pins	O
,	O
pulling	O
them	O
high	O
to	O
+5V	O
to	O
represent	O
a	O
1	O
.	O
</s>
<s>
The	O
printer	O
side	O
of	O
the	O
interface	B-Application
quickly	O
became	O
an	O
industry	O
de	O
facto	O
standard	O
,	O
but	O
manufacturers	O
used	O
various	O
connectors	O
on	O
the	O
system	O
side	O
,	O
so	O
a	O
variety	O
of	O
cables	O
were	O
required	O
.	O
</s>
<s>
For	O
example	O
,	O
NCR	O
used	O
the	O
36-pin	O
micro	B-Protocol
ribbon	I-Protocol
connector	I-Protocol
on	O
both	O
ends	O
of	O
the	O
connection	O
,	O
early	O
VAX	B-Device
systems	O
used	O
a	O
DC-37	B-Protocol
connector	O
,	O
Texas	O
Instruments	O
used	O
a	O
25-pin	O
card	O
edge	O
connector	O
and	O
Data	O
General	O
used	O
a	O
50-pin	O
micro	B-Protocol
ribbon	I-Protocol
connector	I-Protocol
.	O
</s>
<s>
When	O
IBM	O
implemented	O
the	O
parallel	B-Device
interface	I-Device
on	O
the	O
IBM	B-Device
PC	I-Device
,	O
they	O
used	O
the	O
DB-25F	B-Protocol
connector	O
at	O
the	O
PC-end	O
of	O
the	O
interface	B-Application
,	O
creating	O
the	O
now	O
familiar	O
parallel	O
cable	O
with	O
a	O
DB25M	B-Protocol
at	O
one	O
end	O
and	O
a	O
36-pin	O
micro	B-Protocol
ribbon	I-Protocol
connector	I-Protocol
at	O
the	O
other	O
.	O
</s>
<s>
In	O
theory	O
,	O
the	O
Centronics	B-Device
port	I-Device
could	O
transfer	O
data	O
as	O
rapidly	O
as	O
75,000	O
characters	O
per	O
second	O
.	O
</s>
<s>
This	O
was	O
far	O
faster	O
than	O
the	O
printer	O
,	O
which	O
averaged	O
about	O
160	O
characters	O
per	O
second	O
,	O
meaning	O
the	O
port	B-Protocol
spent	O
much	O
of	O
its	B-Application
time	O
idle	O
.	O
</s>
<s>
To	O
improve	O
performance	O
,	O
printers	O
began	O
incorporating	O
buffers	B-General_Concept
so	O
the	O
host	O
could	O
send	O
them	O
data	O
more	O
rapidly	O
,	O
in	O
bursts	O
.	O
</s>
<s>
Performance	O
was	O
further	O
improved	O
by	O
using	O
the	O
buffer	B-General_Concept
to	O
store	O
several	O
lines	O
and	O
then	O
printing	O
in	O
both	O
directions	O
,	O
eliminating	O
the	O
delay	O
while	O
the	O
print	O
head	O
returned	O
to	O
the	O
left	O
side	O
of	O
the	O
page	O
.	O
</s>
<s>
IBM	O
released	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
in	O
1981	O
and	O
included	O
a	O
variant	O
of	O
the	O
Centronics	B-Protocol
interface	I-Protocol
—	O
only	O
IBM	O
logo	O
printers	O
(	O
rebranded	O
from	O
Epson	O
)	O
could	O
be	O
used	O
with	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
IBM	O
standardized	O
the	O
parallel	O
cable	O
with	O
a	O
DB25F	B-Protocol
connector	O
on	O
the	O
PC	O
side	O
and	O
the	O
36-pin	O
Centronics	B-Device
connector	I-Device
on	O
the	O
printer	O
side	O
.	O
</s>
<s>
The	O
original	O
IBM	O
parallel	O
printer	O
adapter	O
for	O
the	O
IBM	B-Device
PC	I-Device
of	O
1981	O
was	O
designed	O
to	O
support	O
limited	O
bidirectionality	O
,	O
with	O
8	O
lines	O
of	O
data	O
output	O
and	O
4	O
lines	O
of	O
data	O
input	O
.	O
</s>
<s>
This	O
allowed	O
the	O
port	B-Protocol
to	O
be	O
used	O
for	O
other	O
purposes	O
,	O
not	O
just	O
output	O
to	O
a	O
printer	O
.	O
</s>
<s>
Years	O
later	O
,	O
in	O
1987	O
,	O
IBM	O
reintroduced	O
the	O
bidirectional	O
interface	B-Application
with	O
its	B-Application
IBM	B-Device
PS/2	I-Device
series	O
,	O
where	O
it	O
could	O
be	O
enabled	O
or	O
disabled	O
for	O
compatibility	O
with	O
applications	O
hardwired	O
not	O
to	O
expect	O
a	O
printer	B-Device
port	I-Device
to	O
be	O
bidirectional	O
.	O
</s>
<s>
These	O
often	O
supported	O
new	O
features	O
and	O
error	O
conditions	O
that	O
could	O
not	O
be	O
represented	O
on	O
the	O
existing	O
port	B-Protocol
's	O
relatively	O
few	O
status	O
pins	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
Bi-Tronics	O
system	O
,	O
introduced	O
by	O
HP	O
on	O
their	O
LaserJet	B-Device
4Si	I-Device
in	O
April	O
1993	O
.	O
</s>
<s>
The	O
introduction	O
of	O
new	O
devices	O
like	O
scanners	B-Application
and	O
multi-function	O
printers	O
demanded	O
much	O
more	O
performance	O
than	O
either	O
the	O
Bi-Tronics	O
or	O
IBM	O
style	O
backchannels	O
could	O
handle	O
.	O
</s>
<s>
The	O
Enhanced	B-Device
Parallel	I-Device
Port	I-Device
(	O
EPP	O
)	O
,	O
originally	O
defined	O
by	O
Zenith	O
Electronics	O
,	O
is	O
similar	O
to	O
IBM	O
's	O
byte	O
mode	O
in	O
concept	O
,	O
but	O
changes	O
details	O
of	O
the	O
handshaking	O
to	O
allow	O
up	O
to	O
2	O
MB/s	O
.	O
</s>
<s>
The	O
Extended	O
Capability	O
Port	B-Protocol
(	O
ECP	O
)	O
is	O
essentially	O
an	O
entirely	O
new	O
port	B-Protocol
in	O
the	O
same	O
physical	O
housing	O
that	O
also	O
adds	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
based	O
on	O
ISA	B-Architecture
and	O
run-length	B-Algorithm
encoding	I-Algorithm
to	O
compress	O
the	O
data	O
,	O
which	O
is	O
especially	O
useful	O
when	O
transferring	O
simple	O
images	O
like	O
faxes	O
or	O
black-and-white	O
scanned	B-Application
images	I-Application
.	O
</s>
<s>
All	O
of	O
these	O
enhancements	O
are	O
collected	O
as	O
part	O
of	O
the	O
IEEE	B-Device
1284	I-Device
standard	O
.	O
</s>
<s>
The	O
first	O
release	O
in	O
1994	O
included	O
original	O
Centronics	O
mode	O
(	O
"	O
compatibility	O
mode	O
"	O
)	O
,	O
nibble	O
and	O
byte	O
modes	O
,	O
as	O
well	O
as	O
a	O
change	O
to	O
the	O
handshaking	O
that	O
was	O
already	O
widely	O
used	O
;	O
the	O
original	O
Centronics	O
implementation	O
called	O
for	O
the	O
BUSY	O
lead	O
to	O
toggle	O
with	O
each	O
change	O
on	O
any	O
line	O
of	O
data	O
(	O
busy-by-line	O
)	O
,	O
whereas	O
IEEE	B-Device
1284	I-Device
calls	O
for	O
BUSY	O
to	O
toggle	O
with	O
each	O
received	O
character	O
(	O
busy-by-character	O
)	O
.	O
</s>
<s>
In	O
2000	O
,	O
the	O
EPP	O
and	O
ECP	O
modes	O
were	O
moved	O
into	O
the	O
standard	O
,	O
as	O
well	O
as	O
several	O
connector	O
and	O
cable	O
styles	O
,	O
and	O
a	O
method	O
for	O
daisy	B-Application
chaining	I-Application
up	O
to	O
eight	O
devices	O
from	O
a	O
single	O
port	B-Protocol
.	O
</s>
<s>
Some	O
host	O
systems	O
or	O
print	B-Application
servers	I-Application
may	O
use	O
a	O
strobe	O
signal	O
with	O
a	O
relatively	O
low	O
voltage	O
output	O
or	O
a	O
fast	O
toggle	O
.	O
</s>
<s>
Dataproducts	O
introduced	O
a	O
very	O
different	O
implementation	O
of	O
the	O
parallel	B-Device
interface	I-Device
for	O
their	O
printers	O
.	O
</s>
<s>
It	O
used	O
a	O
DC-37	B-Protocol
connector	O
on	O
the	O
host	O
side	O
and	O
a	O
50	O
pin	O
connector	O
on	O
the	O
printer	O
side	O
—	O
either	O
a	O
DD-50	B-Protocol
(	O
sometimes	O
incorrectly	O
referred	O
to	O
as	O
a	O
"	O
DB50	O
"	O
)	O
or	O
the	O
block	O
shaped	O
M-50	O
connector	O
;	O
the	O
M-50	O
was	O
also	O
referred	O
to	O
as	O
Winchester	O
.	O
</s>
<s>
The	O
Dataproducts	O
interface	B-Application
was	O
found	O
on	O
many	O
mainframe	O
systems	O
up	O
through	O
the	O
1990s	O
,	O
and	O
many	O
printer	O
manufacturers	O
offered	O
the	O
Dataproducts	O
interface	B-Application
as	O
an	O
option	O
.	O
</s>
<s>
A	O
wide	O
variety	O
of	O
devices	O
were	O
eventually	O
designed	O
to	O
operate	O
on	O
a	O
parallel	B-Device
port	I-Device
.	O
</s>
<s>
However	O
,	O
some	O
devices	O
such	O
as	O
Zip	B-Operating_System
drives	I-Operating_System
were	O
able	O
to	O
operate	O
in	O
bi-directional	O
mode	O
.	O
</s>
<s>
Before	O
the	O
advent	O
of	O
USB	B-Protocol
,	O
the	O
parallel	B-Device
interface	I-Device
was	O
adapted	O
to	O
access	O
a	O
number	O
of	O
peripheral	O
devices	O
other	O
than	O
printers	O
.	O
</s>
<s>
One	O
early	O
use	O
of	O
the	O
parallel	B-Device
port	I-Device
was	O
for	O
dongles	B-Device
used	O
as	O
hardware	O
keys	O
which	O
were	O
supplied	O
with	O
application	O
software	O
as	O
a	O
form	O
of	O
software	O
copy	O
protection	O
.	O
</s>
<s>
Other	O
uses	O
included	O
optical	O
disc	O
drives	O
such	O
as	O
CD	O
readers	O
and	O
writers	O
,	O
Zip	B-Operating_System
drives	I-Operating_System
,	O
scanners	B-Application
,	O
tape	O
drives	O
,	O
external	B-Application
modems	I-Application
,	O
gamepads	B-Device
,	O
and	O
joysticks	B-Device
.	O
</s>
<s>
Some	O
of	O
the	O
earliest	O
portable	O
MP3	O
players	O
required	O
a	O
parallel	B-Device
port	I-Device
connection	O
for	O
transferring	O
songs	O
to	O
the	O
device	O
.	O
</s>
<s>
Adapters	O
were	O
available	O
to	O
run	O
SCSI	B-Architecture
devices	O
via	O
parallel	O
.	O
</s>
<s>
Other	O
devices	O
such	O
as	O
EPROM	B-General_Concept
programmers	I-General_Concept
and	O
hardware	O
controllers	O
could	O
be	O
connected	O
via	O
the	O
parallel	B-Device
port	I-Device
.	O
</s>
<s>
If	O
no	O
printer	B-Device
port	I-Device
is	O
present	O
at	O
0x3BC	O
,	O
the	O
second	O
port	B-Protocol
in	O
the	O
row	O
(	O
0x378	O
)	O
becomes	O
logical	O
parallel	B-Device
port	I-Device
1	O
and	O
0x278	O
becomes	O
logical	O
parallel	B-Device
port	I-Device
2	O
for	O
the	O
BIOS	O
.	O
</s>
<s>
Sometimes	O
,	O
printer	B-Device
ports	I-Device
are	O
jumpered	O
to	O
share	O
an	O
interrupt	B-Application
despite	O
having	O
their	O
own	O
IO	O
addresses	O
(	O
i.e.	O
</s>
<s>
only	O
one	O
can	O
be	O
used	O
interrupt-driven	O
at	O
a	O
time	O
)	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
the	O
BIOS	O
supports	O
a	O
fourth	O
printer	B-Device
port	I-Device
as	O
well	O
,	O
but	O
the	O
base	B-General_Concept
address	I-General_Concept
for	O
it	O
differs	O
significantly	O
between	O
vendors	O
.	O
</s>
<s>
Since	O
the	O
reserved	O
entry	O
for	O
a	O
fourth	O
logical	O
printer	B-Device
port	I-Device
in	O
the	O
BIOS	O
Data	O
Area	O
(	O
BDA	O
)	O
is	O
shared	O
with	O
other	O
uses	O
on	O
PS/2	B-Device
machines	O
and	O
with	O
S3	O
compatible	O
graphics	O
cards	O
,	O
it	O
typically	O
requires	O
special	O
drivers	O
in	O
most	O
environments	O
.	O
</s>
<s>
Under	O
DR-DOS	B-Application
7.02	O
the	O
BIOS	O
port	B-Protocol
assignments	O
can	O
be	O
changed	O
and	O
overridden	O
using	O
the	O
LPT1	B-Device
,	O
LPT2	B-Device
,	O
LPT3	B-Device
(	O
and	O
optionally	O
LPT4	B-Device
)	O
CONFIG.SYS	B-Device
directives	O
.	O
</s>
<s>
DOS-based	O
systems	O
make	O
the	O
logical	O
parallel	B-Device
ports	I-Device
detected	O
by	O
the	O
BIOS	O
available	O
under	O
device	B-Application
names	I-Application
such	O
as	O
LPT1	B-Device
,	O
LPT2	B-Device
or	O
LPT3	B-Device
(	O
corresponding	O
with	O
logical	O
parallel	B-Device
port	I-Device
1	O
,	O
2	O
,	O
and	O
3	O
,	O
respectively	O
)	O
.	O
</s>
<s>
These	O
names	O
derive	O
from	O
terms	O
like	O
Line	O
Print	O
Terminal	O
,	O
Local	O
Print	O
Terminal	O
(	O
both	O
abbreviated	O
as	O
LPT	B-Device
)	O
,	O
or	O
Line	O
Printer	O
.	O
</s>
<s>
A	O
similar	O
naming	O
convention	O
was	O
used	O
on	O
ITS	B-Application
,	O
DEC	O
systems	O
,	O
as	O
well	O
as	O
in	O
CP/M	B-Application
and	O
86-DOS	B-Operating_System
(	O
LST	O
)	O
.	O
</s>
<s>
In	O
DOS	B-Device
,	O
the	O
parallel	O
printers	O
could	O
be	O
accessed	O
directly	O
on	O
the	O
command	B-Application
line	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	O
command	O
"	O
TYPE	O
C:\AUTOEXEC.BAT	O
>	O
LPT1	B-Device
:	O
"	O
would	O
redirect	O
the	O
contents	O
of	O
the	O
AUTOEXEC.BAT	O
file	O
to	O
the	O
printer	B-Device
port	I-Device
.	O
</s>
<s>
A	O
PRN	B-Device
device	O
was	O
also	O
available	O
as	O
an	O
alias	O
for	O
LPT1	B-Device
.	O
</s>
<s>
Some	O
operating	O
systems	O
(	O
like	O
Multiuser	B-Operating_System
DOS	I-Operating_System
)	O
allow	O
to	O
change	O
this	O
fixed	O
assignment	O
by	O
different	O
means	O
.	O
</s>
<s>
Some	O
DOS	B-Device
versions	O
use	O
resident	O
driver	O
extensions	O
provided	O
by	O
MODE	O
,	O
or	O
users	O
can	O
change	O
the	O
mapping	O
internally	O
via	O
a	O
CONFIG.SYS	B-Device
PRN	B-Device
=	O
n	O
directive	O
(	O
as	O
under	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
)	O
.	O
</s>
<s>
DR-DOS	B-Application
7.02	O
also	O
provides	O
optional	O
built-in	O
support	O
for	O
LPT4	B-Device
if	O
the	O
underlying	O
BIOS	O
supports	O
it	O
.	O
</s>
<s>
PRN	B-Device
,	O
along	O
with	O
CON	O
,	O
AUX	O
and	O
a	O
few	O
others	O
are	O
invalid	O
file	O
and	O
directory	O
names	O
in	O
DOS	B-Device
and	O
Windows	B-Application
,	O
even	O
in	O
Windows	B-Application
XP	I-Application
.	O
</s>
<s>
There	O
is	O
even	O
an	O
MS-DOS	B-Application
device	O
in	O
path	O
name	O
vulnerability	O
in	O
Windows	B-Application
95	I-Application
and	O
98	B-Device
,	O
which	O
causes	O
the	O
computer	O
to	O
crash	O
if	O
the	O
user	O
types	O
"	O
C:\CON\CON	O
 "	O
,	O
"	O
C:\PRN\PRN	O
 "	O
or	O
"	O
C:\AUX\AUX	O
 "	O
in	O
the	O
Windows	B-Application
Explorer	O
address	O
bar	O
.	O
</s>
<s>
Microsoft	O
has	O
released	O
a	O
patch	O
to	O
fix	O
this	O
bug	O
,	O
but	O
newly	O
installed	O
Windows	B-Application
95	I-Application
and	O
98	B-Device
operating	O
systems	O
will	O
still	O
have	O
the	O
bug	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
still	O
refers	O
to	O
the	O
ports	O
in	O
this	O
manner	O
in	O
many	O
cases	O
,	O
though	O
this	O
is	O
often	O
fairly	O
hidden	O
.	O
</s>
<s>
In	O
SCO	B-Operating_System
UNIX	I-Operating_System
and	O
Linux	B-Application
,	O
the	O
first	O
parallel	B-Device
port	I-Device
is	O
available	O
via	O
the	O
filesystem	O
as	O
/dev/lp0	O
.	O
</s>
<s>
Linux	B-Application
IDE	O
devices	O
can	O
use	O
a	O
paride	O
(	O
parallel	B-Device
port	I-Device
IDE	O
)	O
driver	O
.	O
</s>
<s>
For	O
consumers	O
,	O
USB	B-Protocol
and	O
computer	B-Architecture
networks	I-Architecture
have	O
replaced	O
the	O
parallel	B-Device
printer	I-Device
port	I-Device
,	O
for	O
connections	O
both	O
to	O
printers	O
and	O
to	O
other	O
devices	O
.	O
</s>
<s>
Many	O
manufacturers	O
of	O
personal	B-Device
computers	I-Device
and	O
laptops	O
consider	O
parallel	O
to	O
be	O
a	O
legacy	B-Device
port	I-Device
and	O
no	O
longer	O
include	O
the	O
parallel	B-Device
interface	I-Device
.	O
</s>
<s>
Smaller	O
machines	O
have	O
less	O
room	O
for	O
large	O
parallel	B-Device
port	I-Device
connectors	O
.	O
</s>
<s>
USB-to-parallel	O
adapters	O
are	O
available	O
that	O
can	O
make	O
parallel-only	O
printers	O
work	O
with	O
USB-only	O
systems	O
.	O
</s>
<s>
There	O
are	O
PCI	O
(	O
and	O
PCI-express	O
)	O
cards	O
that	O
provide	O
parallel	B-Device
ports	I-Device
.	O
</s>
<s>
There	O
are	O
also	O
some	O
print	B-Application
servers	I-Application
that	O
provide	O
an	O
interface	B-Application
to	O
parallel	B-Device
ports	I-Device
through	O
a	O
network	O
.	O
</s>
<s>
USB-to-EPP	O
chips	O
can	O
also	O
allow	O
other	O
non-printer	O
devices	O
to	O
continue	O
to	O
work	O
on	O
modern	O
computers	O
without	O
a	O
parallel	B-Device
port	I-Device
.	O
</s>
<s>
For	O
electronics	O
hobbyists	O
the	O
parallel	B-Device
port	I-Device
is	O
still	O
often	O
the	O
easiest	O
way	O
to	O
connect	O
to	O
an	O
external	O
circuit	O
board	O
.	O
</s>
<s>
It	O
is	O
faster	O
than	O
the	O
other	O
common	O
legacy	B-Device
port	I-Device
(	O
serial	B-Protocol
port	I-Protocol
)	O
,	O
requires	O
no	O
serial-to-parallel	O
converter	O
,	O
and	O
requires	O
far	O
less	O
interface	B-Application
logic	O
and	O
software	O
than	O
a	O
USB	B-Protocol
target	O
interface	B-Application
.	O
</s>
<s>
However	O
,	O
Microsoft	O
operating	O
systems	O
later	O
than	O
Windows	O
95/98	O
prevent	O
user	O
programs	O
from	O
directly	O
writing	O
to	O
or	O
reading	O
from	O
the	O
LPT	B-Device
without	O
additional	O
software	O
(	O
kernel	O
extensions	O
)	O
.	O
</s>
<s>
Current	O
CNC	O
Milling	O
Machines	O
also	O
often	O
make	O
use	O
of	O
the	O
parallel	B-Device
port	I-Device
to	O
directly	O
control	O
the	O
machine	O
's	O
motors	O
and	O
attachments	O
.	O
</s>
<s>
Traditionally	O
IBM	B-Device
PC	I-Device
systems	O
have	O
allocated	O
their	O
first	O
three	O
parallel	B-Device
ports	I-Device
according	O
to	O
the	O
configuration	O
in	O
the	O
table	O
below	O
(	O
if	O
all	O
three	O
printer	B-Device
ports	I-Device
exist	O
)	O
.	O
</s>
<s>
If	O
there	O
is	O
an	O
unused	O
slot	O
,	O
the	O
port	B-Protocol
addresses	O
of	O
the	O
others	O
are	O
moved	O
up	O
.	O
</s>
<s>
(	O
For	O
example	O
,	O
if	O
a	O
port	B-Protocol
at	O
0x3BC	O
does	O
not	O
exist	O
,	O
the	O
port	B-Protocol
at	O
0x378	O
will	O
then	O
become	O
the	O
first	O
logical	O
parallel	B-Device
port	I-Device
.	O
)	O
</s>
<s>
The	O
base	B-General_Concept
address	I-General_Concept
0x3BC	O
is	O
typically	O
supported	O
by	O
printer	B-Device
ports	I-Device
on	O
MDA	O
and	O
Hercules	O
display	O
adapters	O
,	O
whereas	O
printer	B-Device
ports	I-Device
provided	O
by	O
the	O
mainboard	O
chipset	O
or	O
add-on	O
cards	O
rarely	O
allow	O
to	O
be	O
configured	O
to	O
this	O
base	B-General_Concept
address	I-General_Concept
.	O
</s>
<s>
Therefore	O
,	O
in	O
absence	O
of	O
a	O
monochrome	O
display	O
adapter	O
,	O
a	O
common	O
assignment	O
for	O
the	O
first	O
logical	O
parallel	B-Device
port	I-Device
(	O
and	O
therefore	O
also	O
for	O
the	O
corresponding	O
LPT1	B-Device
DOS	B-Device
device	O
driver	O
)	O
today	O
is	O
0x378	O
,	O
even	O
though	O
the	O
default	O
is	O
still	O
0x3BC	O
(	O
and	O
would	O
be	O
selected	O
by	O
the	O
BIOS	O
if	O
it	O
detects	O
a	O
printer	B-Device
port	I-Device
at	O
this	O
address	O
)	O
.	O
</s>
<s>
The	O
IRQ	B-General_Concept
lines	O
are	O
typically	O
configurable	O
in	O
the	O
hardware	O
as	O
well	O
.	O
</s>
<s>
Assigning	O
the	O
same	O
interrupt	B-Application
to	O
more	O
than	O
one	O
printer	B-Device
port	I-Device
should	O
be	O
avoided	O
and	O
will	O
typically	O
cause	O
one	O
of	O
the	O
corresponding	O
ports	O
to	O
work	O
in	O
polled	O
mode	O
only	O
.	O
</s>
<s>
The	O
port	B-Protocol
addresses	O
assigned	O
to	O
slot	O
can	O
be	O
determined	O
by	O
reading	O
the	O
BIOS	O
Data	O
Area	O
(	O
BDA	O
)	O
at	O
0000h:0408h	O
.	O
</s>
<s>
Bit-to-pin	O
mapping	O
for	O
the	O
Standard	O
Parallel	B-Device
Port	I-Device
(	O
SPP	O
)	O
:	O
</s>
<s>
In	O
versions	O
of	O
Windows	B-Application
that	O
did	O
not	O
use	O
the	O
Windows	B-Device
NT	I-Device
kernel	O
(	O
as	O
well	O
as	O
DOS	B-Device
and	O
some	O
other	O
operating	O
systems	O
)	O
,	O
programs	O
could	O
access	O
the	O
parallel	B-Device
port	I-Device
with	O
simple	O
outportb( )	O
and	O
inportb( )	O
subroutine	O
commands	O
.	O
</s>
<s>
In	O
operating	O
systems	O
such	O
as	O
Windows	B-Device
NT	I-Device
and	O
Unix	B-Application
(	O
NetBSD	B-Device
,	O
FreeBSD	B-Operating_System
,	O
Solaris	B-Application
,	O
386BSD	B-Operating_System
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
the	O
microprocessor	O
is	O
operated	O
in	O
a	O
different	O
security	O
ring	O
,	O
and	O
access	O
to	O
the	O
parallel	B-Device
port	I-Device
is	O
prohibited	O
,	O
unless	O
using	O
the	O
required	O
driver	O
.	O
</s>
<s>
On	O
Linux	B-Application
,	O
inb( )	O
and	O
outb( )	O
can	O
be	O
used	O
when	O
a	O
process	O
is	O
run	O
as	O
root	O
and	O
an	O
ioperm( )	O
command	O
is	O
used	O
to	O
allow	O
access	O
to	O
its	B-Application
base	B-General_Concept
address	I-General_Concept
;	O
alternatively	O
,	O
ppdev	O
allows	O
shared	O
access	O
and	O
can	O
be	O
used	O
from	O
userspace	O
if	O
the	O
appropriate	O
permissions	O
are	O
set	O
.	O
</s>
<s>
The	O
cross-platform	O
library	O
for	O
parallel	B-Device
port	I-Device
access	O
,	O
libieee1284	O
,	O
also	O
is	O
available	O
on	O
many	O
Linux	B-Application
distributions	O
and	O
provides	O
an	O
abstract	O
interface	B-Application
to	O
the	O
parallel	B-Device
ports	I-Device
of	O
the	O
system	O
.	O
</s>
<s>
The	O
older	O
parallel	B-Device
printer	I-Device
ports	I-Device
had	O
an	O
8-bit	O
data	O
bus	O
and	O
four	O
pins	O
for	O
control	O
output	O
(	O
Strobe	O
,	O
Linefeed	O
,	O
Initialize	O
,	O
and	O
Select	O
In	O
)	O
,	O
and	O
five	O
more	O
for	O
control	O
input	O
(	O
ACK	O
,	O
Busy	O
,	O
Select	O
,	O
Error	O
,	O
and	O
Paper	O
Out	O
)	O
.	O
</s>
<s>
Its	B-Application
data	O
transfer	O
speed	O
is	O
at	O
150	O
kB/s	O
.	O
</s>
<s>
The	O
newer	O
EPPs	O
(	O
Enhanced	B-Device
Parallel	I-Device
Ports	I-Device
)	O
have	O
an	O
8-bit	O
data	O
bus	O
,	O
and	O
the	O
same	O
control	O
pins	O
as	O
the	O
normal	O
parallel	B-Device
printer	I-Device
port	I-Device
.	O
</s>
<s>
Pinouts	B-Application
for	O
parallel	B-Device
port	I-Device
connectors	O
are	O
:	O
</s>
<s>
Pin	O
25	O
on	O
the	O
DB25	B-Protocol
connector	O
might	O
not	O
be	O
connected	O
to	O
ground	O
on	O
modern	O
computers	O
.	O
</s>
