<s>
Fixed-priority	O
preemptive	B-Operating_System
scheduling	I-Operating_System
is	O
a	O
scheduling	O
system	O
commonly	O
used	O
in	O
real-time	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
With	O
fixed	O
priority	O
preemptive	B-Operating_System
scheduling	I-Operating_System
,	O
the	O
scheduler	O
ensures	O
that	O
at	O
any	O
given	O
time	O
,	O
the	O
processor	B-General_Concept
executes	O
the	O
highest	O
priority	O
task	B-General_Concept
of	O
all	O
those	O
tasks	O
that	O
are	O
currently	O
ready	O
to	O
execute	O
.	O
</s>
<s>
The	O
preemptive	B-Operating_System
scheduler	I-Operating_System
has	O
a	O
clock	O
interrupt	O
task	B-General_Concept
that	O
can	O
provide	O
the	O
scheduler	O
with	O
options	O
to	O
switch	B-Operating_System
after	O
the	O
task	B-General_Concept
has	O
had	O
a	O
given	O
period	O
to	O
execute	O
—	O
the	O
time	O
slice	O
.	O
</s>
<s>
This	O
scheduling	O
system	O
has	O
the	O
advantage	O
of	O
making	O
sure	O
no	O
task	B-General_Concept
hogs	O
the	O
processor	B-General_Concept
for	O
any	O
time	O
longer	O
than	O
the	O
time	O
slice	O
.	O
</s>
<s>
Most	O
real-time	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
(	O
RTOSs	O
)	O
have	O
preemptive	B-Operating_System
schedulers	I-Operating_System
.	O
</s>
<s>
Also	O
turning	O
off	O
time	O
slicing	O
effectively	O
gives	O
you	O
the	O
non-preemptive	O
RTOS	B-Operating_System
.	O
</s>
<s>
Preemptive	B-Operating_System
scheduling	I-Operating_System
is	O
often	O
differentiated	O
with	O
cooperative	O
scheduling	O
,	O
in	O
which	O
a	O
task	B-General_Concept
can	O
run	O
continuously	O
from	O
start	O
to	O
end	O
without	O
being	O
preempted	O
by	O
other	O
tasks	O
.	O
</s>
<s>
To	O
have	O
a	O
task	B-General_Concept
switch	B-Operating_System
,	O
the	O
task	B-General_Concept
must	O
explicitly	O
call	O
the	O
scheduler	O
.	O
</s>
<s>
Cooperative	O
scheduling	O
is	O
used	O
in	O
a	O
few	O
RTOS	B-Operating_System
such	O
as	O
Salvo	O
or	O
TinyOS	B-Device
.	O
</s>
