<s>
A	O
Deferred	B-Device
Procedure	I-Device
Call	I-Device
(	O
DPC	O
)	O
is	O
a	O
Microsoft	B-Application
Windows	I-Application
operating	I-Application
system	I-Application
mechanism	O
which	O
allows	O
high-priority	O
tasks	O
(	O
e.g.	O
</s>
<s>
an	O
interrupt	B-General_Concept
handler	I-General_Concept
)	O
to	O
defer	O
required	O
but	O
lower-priority	O
tasks	O
for	O
later	O
execution	O
.	O
</s>
<s>
This	O
permits	O
device	B-Application
drivers	I-Application
and	O
other	O
low-level	O
event	O
consumers	O
to	O
perform	O
the	O
high-priority	O
part	O
of	O
their	O
processing	O
quickly	O
,	O
and	O
schedule	O
non-critical	O
additional	O
processing	O
for	O
execution	O
at	O
a	O
lower	O
priority	O
.	O
</s>
<s>
DPCs	O
are	O
implemented	O
by	O
DPC	O
objects	O
which	O
are	O
created	O
and	O
initialized	O
by	O
the	O
kernel	B-Operating_System
when	O
a	O
device	B-Application
driver	I-Application
or	O
some	O
other	O
kernel	B-Operating_System
mode	O
program	O
issues	O
DPC	O
requests	O
.	O
</s>
<s>
DPC	O
requests	O
are	O
added	O
to	O
the	O
end	O
of	O
a	O
DPC	O
queue	B-Application
.	O
</s>
<s>
Each	O
processor	O
has	O
a	O
separate	O
DPC	O
queue	B-Application
.	O
</s>
<s>
When	O
Windows	O
drops	O
to	O
an	O
IRQL	O
of	O
Dispatch/DPC	O
level	O
,	O
it	O
checks	O
the	O
DPC	O
queue	B-Application
for	O
any	O
pending	O
DPCs	O
and	O
executes	O
them	O
until	O
the	O
queue	B-Application
is	O
empty	O
or	O
some	O
other	O
interrupt	O
with	O
a	O
higher	O
IRQL	O
occurs	O
.	O
</s>
<s>
For	O
example	O
,	O
when	O
the	O
clock	O
interrupt	O
is	O
generated	O
,	O
the	O
clock	O
interrupt	B-General_Concept
handler	I-General_Concept
generally	O
increments	O
the	O
counter	O
of	O
the	O
current	O
thread	O
to	O
calculate	O
the	O
total	O
execution	O
time	O
of	O
that	O
thread	O
,	O
and	O
decrements	O
its	O
quantum	O
time	O
remaining	O
by	O
1	O
.	O
</s>
<s>
So	O
the	O
clock	O
interrupt	B-General_Concept
handler	I-General_Concept
requests	O
a	O
DPC	O
object	O
and	O
adds	O
it	O
to	O
the	O
end	O
of	O
the	O
DPC	O
queue	B-Application
which	O
will	O
process	O
the	O
dispatching	O
when	O
the	O
processor	O
's	O
IRQL	O
drops	O
to	O
DPC/Dispatch	O
level	O
.	O
</s>
