<s>
The	O
term	O
Legacy	B-Device
Plug	I-Device
and	I-Device
Play	I-Device
,	O
also	O
shortened	O
to	O
Legacy	B-Device
PnP	I-Device
,	O
describes	O
a	O
series	O
of	O
specifications	O
and	O
Microsoft	B-Application
Windows	I-Application
features	O
geared	O
towards	O
operating	B-General_Concept
system	I-General_Concept
configuration	O
of	O
devices	O
,	O
and	O
some	O
device	O
IDs	O
are	O
assigned	O
by	O
UEFI	B-Device
Forum	I-Device
.	O
</s>
<s>
The	O
standards	O
were	O
primarily	O
aimed	O
at	O
the	O
IBM	B-Device
PC	I-Device
standard	O
bus	O
,	O
later	O
dubbed	O
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
(	O
ISA	O
)	O
.	O
</s>
<s>
Related	O
specifications	O
are	O
also	O
defined	O
for	O
the	O
common	O
external	O
or	O
specialist	O
buses	O
commonly	O
attached	O
via	O
ISA	O
at	O
the	O
time	O
of	O
development	O
,	O
including	O
RS-232	O
and	O
parallel	B-Device
port	I-Device
devices	O
.	O
</s>
<s>
As	O
a	O
Windows	O
feature	O
,	O
Plug	B-Device
and	I-Device
Play	I-Device
refers	O
to	O
operating	B-General_Concept
system	I-General_Concept
functionality	O
that	O
supports	O
connectivity	O
,	O
configuration	O
and	O
management	O
with	O
native	O
plug	B-Device
and	I-Device
play	I-Device
devices	O
.	O
</s>
<s>
Originally	O
considered	O
part	O
of	O
the	O
same	O
feature	O
set	O
as	O
the	O
specifications	O
,	O
Plug	B-Device
and	I-Device
Play	I-Device
in	O
this	O
context	O
refers	O
primarily	O
to	O
the	O
responsibilities	O
and	O
interfaces	O
associated	O
with	O
Windows	O
driver	O
development	O
.	O
</s>
<s>
Plug	B-Device
and	I-Device
Play	I-Device
allows	O
for	O
detection	O
of	O
devices	O
without	O
user	O
intervention	O
,	O
and	O
occasionally	O
for	O
minor	O
configuration	O
of	O
device	O
resources	O
,	O
such	O
as	O
I/O	B-Architecture
ports	I-Architecture
and	O
device	O
memory	O
maps	O
.	O
</s>
<s>
PnP	O
is	O
a	O
specific	O
set	O
of	O
standards	O
,	O
not	O
be	O
confused	O
with	O
the	O
generic	O
term	O
plug	B-Device
and	I-Device
play	I-Device
,	O
which	O
describes	O
any	O
hardware	O
specification	O
that	O
alleviates	O
the	O
need	O
for	O
user	O
configuration	O
of	O
device	O
resources	O
.	O
</s>
<s>
ACPI	B-Device
is	O
the	O
successor	O
to	O
Legacy	B-Device
Plug	I-Device
and	I-Device
Play	I-Device
.	O
</s>
<s>
The	O
Plug	B-Device
and	I-Device
Play	I-Device
standard	O
requires	O
configuration	O
of	O
devices	O
to	O
be	O
handled	O
by	O
the	O
PnP	O
BIOS	B-Operating_System
,	O
which	O
then	O
provides	O
details	O
of	O
resources	O
allocations	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
When	O
the	O
computer	O
is	O
first	O
turned	O
on	O
,	O
compatible	O
devices	O
are	O
identified	O
and	O
assigned	O
non-conflicting	O
IO	O
addresses	O
,	O
interrupt	B-General_Concept
request	I-General_Concept
numbers	O
and	O
DMA	O
channels	O
.	O
</s>
<s>
The	O
term	O
was	O
adopted	O
by	O
Microsoft	O
in	O
reference	O
to	O
their	O
Windows	B-Application
95	I-Application
product	O
.	O
</s>
<s>
Other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
AmigaOS	B-Application
Autoconfig	B-Device
and	O
the	O
Mac	B-Application
OS	I-Application
NuBus	B-Device
system	O
,	O
had	O
already	O
supported	O
such	O
features	O
for	O
some	O
time	O
(	O
under	O
various	O
names	O
,	O
or	O
no	O
name	O
)	O
.	O
</s>
<s>
Even	O
Yggdrasil	B-Application
Linux	I-Application
advertised	O
itself	O
as	O
"	O
Plug	B-Device
and	I-Device
Play	I-Device
Linux	O
"	O
at	O
least	O
two	O
years	O
before	O
Windows	B-Application
95	I-Application
.	O
</s>
<s>
But	O
the	O
term	O
plug	B-Device
and	I-Device
play	I-Device
gradually	O
became	O
universal	O
due	O
to	O
worldwide	O
acceptance	O
of	O
Windows	O
.	O
</s>
<s>
Typically	O
,	O
non-PnP	O
devices	O
need	O
to	O
be	O
identified	O
in	O
the	O
computer	O
's	O
BIOS	B-Operating_System
setup	O
so	O
that	O
the	O
PnP	O
system	O
will	O
not	O
reassign	O
those	O
devices	O
.	O
</s>
<s>
Problems	O
in	O
the	O
interactions	O
between	O
legacy	O
non-PnP	O
devices	O
and	O
the	O
PnP	O
system	O
can	O
cause	O
it	O
to	O
fail	O
,	O
leading	O
to	O
this	O
technology	O
having	O
historically	O
been	O
referred	O
to	O
as	O
"	O
plug	B-Device
and	I-Device
pray	I-Device
"	O
.	O
</s>
<s>
Legacy	B-Device
Plug	I-Device
and	I-Device
Play	I-Device
Specification	O
was	O
defined	O
by	O
Microsoft	O
and	O
Intel	O
,	O
which	O
proposed	O
changes	O
to	O
legacy	O
hardware	O
,	O
as	O
well	O
as	O
the	O
BIOS	B-Operating_System
to	O
support	O
operating	O
system-bound	O
discovery	O
of	O
devices	O
.	O
</s>
<s>
These	O
roles	O
were	O
later	O
assumed	O
by	O
the	O
ACPI	B-Device
standard	O
,	O
which	O
also	O
moves	O
support	O
for	O
power	O
management	O
and	O
configuration	O
into	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
opposed	O
to	O
the	O
firmware	O
as	O
previously	O
required	O
by	O
the	O
"	O
Plug	B-Device
and	I-Device
Play	I-Device
BIOS	I-Device
"	O
and	O
APM	B-Device
specifications	O
.	O
</s>
<s>
The	O
following	O
standards	O
compose	O
what	O
Microsoft	O
describe	O
as	O
Legacy	B-Device
Plug	I-Device
and	I-Device
Play	I-Device
,	O
as	O
opposed	O
to	O
native	O
Plug-and-Play	B-Device
specifications	O
such	O
as	O
PCI	B-Protocol
and	O
USB	B-Protocol
.	O
</s>
<s>
Windows	B-Application
Vista	I-Application
requires	O
an	O
ACPI-compliant	O
BIOS	B-Operating_System
,	O
and	O
the	O
ISAPnP	B-Device
is	O
disabled	O
by	O
default	O
.	O
</s>
<s>
To	O
use	O
Plug	B-Device
and	I-Device
Play	I-Device
,	O
three	O
requirements	O
have	O
to	O
be	O
met	O
:	O
</s>
<s>
The	O
OS	B-General_Concept
must	O
be	O
compatible	O
with	O
Plug	B-Device
and	I-Device
Play	I-Device
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
must	O
support	O
Plug	B-Device
and	I-Device
Play	I-Device
.	O
</s>
<s>
The	O
device	O
to	O
be	O
installed	O
must	O
be	O
a	O
Plug	B-Device
and	I-Device
Play	I-Device
compliant	O
device	O
.	O
</s>
<s>
Plug-and-play	B-Device
hardware	O
typically	O
also	O
requires	O
some	O
sort	O
of	O
ID	O
code	O
that	O
it	O
can	O
supply	O
,	O
in	O
order	O
for	O
the	O
computer	O
software	O
to	O
correctly	O
identify	O
it	O
.	O
</s>
<s>
This	O
ID	O
code	O
system	O
was	O
not	O
integrated	O
into	O
the	O
early	O
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
(	O
ISA	O
)	O
hardware	O
common	O
in	O
PCs	O
when	O
Plug	B-Device
and	I-Device
Play	I-Device
was	O
first	O
introduced	O
.	O
</s>
<s>
ISA	B-Device
Plug	I-Device
and	I-Device
Play	I-Device
caused	O
some	O
of	O
the	O
greatest	O
difficulties	O
that	O
made	O
PnP	O
initially	O
very	O
unreliable	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
derisive	O
term	O
"	O
Plug	B-Device
and	I-Device
Pray	I-Device
"	O
,	O
since	O
I/O	O
addresses	O
and	O
IRQ	B-General_Concept
lines	O
were	O
often	O
set	O
incorrectly	O
in	O
the	O
early	O
days	O
.	O
</s>
<s>
Later	O
computer	B-General_Concept
buses	I-General_Concept
like	O
MCA	B-Device
,	O
EISA	B-Device
and	O
PCI	B-Protocol
(	O
which	O
was	O
becoming	O
the	O
industry	O
standard	O
at	O
that	O
time	O
)	O
integrated	O
this	O
functionality	O
.	O
</s>
<s>
Finally	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
of	O
the	O
computer	O
needs	O
to	O
be	O
able	O
to	O
handle	O
these	O
changes	O
.	O
</s>
<s>
Typically	O
,	O
this	O
means	O
looking	O
for	O
interrupts	B-Application
from	O
the	O
bus	O
saying	O
that	O
the	O
configuration	O
has	O
changed	O
,	O
and	O
then	O
reading	O
the	O
information	O
from	O
the	O
bus	O
to	O
locate	O
what	O
happened	O
.	O
</s>
<s>
More	O
modern	O
designs	O
use	O
some	O
sort	O
of	O
system	O
to	O
either	O
reduce	O
or	O
eliminate	O
this	O
"	O
hunt	O
"	O
;	O
for	O
example	O
,	O
USB	B-Protocol
uses	O
a	O
hub	O
system	O
for	O
this	O
purpose	O
.	O
</s>
<s>
When	O
the	O
change	O
is	O
located	O
,	O
the	O
OS	B-General_Concept
then	O
examines	O
the	O
information	O
in	O
the	O
device	O
to	O
figure	O
out	O
what	O
it	O
is	O
.	O
</s>
<s>
It	O
then	O
has	O
to	O
load	O
up	O
the	O
appropriate	O
device	B-Application
drivers	I-Application
in	O
order	O
to	O
make	O
it	O
work	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
this	O
was	O
an	O
all-or-nothing	O
affair	O
,	O
but	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
often	O
include	O
the	O
ability	O
to	O
find	O
the	O
proper	O
driver	O
on	O
the	O
Internet	O
and	O
install	O
it	O
automatically	O
.	O
</s>
