<s>
A	O
page	B-General_Concept
address	I-General_Concept
register	I-General_Concept
(	O
PAR	O
)	O
contains	O
the	O
physical	O
addresses	O
of	O
pages	O
currently	O
held	O
in	O
the	O
main	O
memory	O
of	O
a	O
computer	O
system	O
.	O
</s>
<s>
PARs	O
are	O
used	O
in	O
order	O
to	O
avoid	O
excessive	O
use	O
of	O
an	O
address	O
table	O
in	O
some	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
A	O
PAR	O
may	O
check	O
a	O
page	O
's	O
number	O
against	O
all	O
entries	O
in	O
the	O
PAR	O
simultaneously	O
,	O
allowing	O
it	O
to	O
retrieve	O
the	O
pages	O
physical	B-General_Concept
address	I-General_Concept
quickly	O
.	O
</s>
<s>
A	O
PAR	O
is	O
used	O
by	O
a	O
single	O
process	B-Operating_System
and	O
is	O
only	O
used	O
for	O
pages	O
which	O
are	O
frequently	O
referenced	O
(	O
though	O
these	O
pages	O
may	O
change	O
as	O
the	O
process	B-Operating_System
's	O
behaviour	O
changes	O
in	O
accordance	O
with	O
the	B-General_Concept
principle	I-General_Concept
of	I-General_Concept
locality	I-General_Concept
)	O
.	O
</s>
<s>
An	O
example	O
computer	O
which	O
made	O
use	O
of	O
PARs	O
is	O
the	O
Atlas	B-Device
.	O
</s>
