<s>
The	O
Extended	B-Device
System	I-Device
Configuration	I-Device
Data	I-Device
(	O
ESCD	B-Device
)	O
is	O
a	O
specification	O
for	O
configuring	O
x86	B-Operating_System
computers	O
of	O
the	O
ISA	B-Device
PNP	I-Device
era	O
.	O
</s>
<s>
It	O
consists	O
of	O
a	O
method	O
for	O
storing	O
configuration	O
information	O
in	O
nonvolatile	B-Device
BIOS	I-Device
memory	I-Device
and	O
three	O
BIOS	B-Operating_System
functions	O
for	O
working	O
with	O
that	O
data	O
.	O
</s>
<s>
The	O
ESCD	B-Device
data	O
may	O
at	O
one	O
time	O
have	O
been	O
stored	O
in	O
the	O
latter	O
portion	O
of	O
the	O
128	O
byte	O
extended	O
bank	O
of	O
battery-backed	O
CMOS	B-Device
RAM	I-Device
but	O
eventually	O
it	O
became	O
too	O
large	O
and	O
so	O
was	O
moved	O
to	O
BIOS	B-Operating_System
flash	O
.	O
</s>
<s>
It	O
contains	O
information	O
about	O
ISA	B-Device
PnP	I-Device
devices	O
is	O
stored	O
.	O
</s>
<s>
It	O
is	O
used	O
by	O
the	O
BIOS	B-Operating_System
to	O
allocate	O
resources	O
for	O
devices	O
like	O
expansion	B-Device
cards	I-Device
.	O
</s>
<s>
The	O
ESCD	B-Device
data	O
is	O
stored	O
using	O
the	O
data	O
serialization	O
format	O
used	O
for	O
EISA	B-Device
.	O
</s>
<s>
PCI	O
configuration	O
can	O
also	O
be	O
stored	O
in	O
ESCD	B-Device
,	O
using	O
virtual	O
slots	O
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
also	O
updates	O
the	O
ESCD	B-Device
each	O
time	O
the	O
hardware	B-Architecture
configuration	O
changes	O
,	O
after	O
deciding	O
how	O
to	O
re-allocate	O
resources	O
like	O
IRQ	B-General_Concept
and	O
memory	O
mapping	O
ranges	O
.	O
</s>
<s>
After	O
the	O
ESCD	B-Device
has	O
been	O
updated	O
,	O
the	O
decision	O
need	O
not	O
be	O
made	O
again	O
,	O
which	O
thereafter	O
results	O
in	O
faster	O
startup	O
without	O
conflicts	O
until	O
the	O
next	O
hardware	B-Architecture
configuration	O
change	O
.	O
</s>
