<s>
The	O
Motorola	B-General_Concept
68851	I-General_Concept
is	O
an	O
external	O
Memory	B-General_Concept
Management	I-General_Concept
Unit	I-General_Concept
(	O
MMU	O
)	O
which	O
is	O
designed	O
to	O
provide	O
paged	O
memory	O
support	O
for	O
the	O
68020	B-Device
using	O
that	O
processor	O
's	O
coprocessor	O
interface	O
.	O
</s>
<s>
In	O
theory	O
it	O
can	O
be	O
used	O
with	O
other	O
processors	O
such	O
as	O
the	O
68010	B-Device
by	O
simulating	O
the	O
coprocessor	O
interface	O
in	O
software	O
.	O
</s>
<s>
Later	O
68K	O
family	O
processors	O
such	O
as	O
the	O
68030	B-Device
,	O
68040	B-Device
,	O
and	O
68060	B-General_Concept
have	O
an	O
internal	O
MMU	O
,	O
and	O
will	O
not	O
operate	O
with	O
the	O
68851	B-General_Concept
,	O
except	O
possibly	O
by	O
simulation	O
of	O
the	O
coprocessor	O
interface	O
.	O
</s>
<s>
The	O
68851	B-General_Concept
was	O
available	O
as	O
an	O
option	O
for	O
the	O
Apple	B-Device
Macintosh	I-Device
II	I-Device
,	O
and	O
was	O
necessary	O
to	O
run	O
Apple	O
's	O
A/UX	B-Operating_System
operating	O
system	O
.	O
</s>
<s>
On	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
Connectix	O
Virtual	O
was	O
released	O
in	O
early	O
1989	O
and	O
used	O
the	O
68851	B-General_Concept
to	O
provide	O
virtual	O
memory	O
,	O
which	O
was	O
later	O
integrated	O
into	O
System	B-Operating_System
7	I-Operating_System
.	O
</s>
<s>
Very	O
few	O
cards	O
for	O
the	O
Amiga	B-Device
make	O
use	O
of	O
the	O
68851	B-General_Concept
primarily	O
because	O
it	O
can	O
only	O
be	O
used	O
with	O
a	O
small	O
range	O
of	O
processors	O
and	O
most	O
Amigas	B-Device
and	O
accelerator	O
cards	O
use	O
a	O
processor	O
which	O
either	O
has	O
its	O
own	O
MMU	O
or	O
cannot	O
support	O
an	O
MMU	O
.	O
</s>
