Page 15 - slides.dvi

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1.
–
3.
–
2.
–
⇒
Operating
Need
Need
Same
set
i.e.
use
the
use
Hence
(viz.
Usually
every
a
when
to
to
Systems
(Modern
—
OS
Protecting
need
use
CPU
timer
same
tick
a
scheme
value
to
timer
to
gets
ensure
ensure
the
timers
the
Structures
privileged
can
to
(e.g.
&
hits
scheme
only
that
initial
be
have
whole
prevent
run
device.
as
CPU
zero,
OS
the
1µs),
Protection
countdown
for
any
used
value
time.
OS
a
can
to
instructions,
timer
Mechanisms
timer,
(e.g.
other
load
stays
interrupt.
periodically
programmable
in
e.g.
malicious
and
memory
timer,
implement
tick
devices.
or
do
0xFFFF).
decrements
and
control.
its
rate.)
value.
that
protection)
stuff.
time-sharing
badly-written
interrupt
(more
on
cannot
application
this
be
from
later).
masked.
‘hogging’
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