<s>
The	O
Cambridge	B-Device
CAP	I-Device
computer	I-Device
was	O
the	O
first	O
successful	O
experimental	O
computer	O
that	O
demonstrated	O
the	O
use	O
of	O
security	O
capabilities	O
,	O
both	O
in	O
hardware	O
and	O
software	O
.	O
</s>
<s>
The	O
CAP	O
was	O
designed	O
such	O
that	O
any	O
access	O
to	O
a	O
memory	O
segment	O
or	O
hardware	O
required	O
that	O
the	O
current	O
process	B-Operating_System
held	O
the	O
necessary	O
capabilities	O
.	O
</s>
<s>
The	O
32-bit	O
processor	O
featured	O
microprogramming	O
control	O
,	O
two	O
256-entry	O
caches	B-General_Concept
,	O
a	O
32-entry	O
write	O
buffer	O
and	O
the	O
capability	O
unit	O
itself	O
,	O
which	O
had	O
64	O
registers	O
for	O
holding	O
evaluated	O
capabilities	O
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
operations	O
were	O
available	O
using	O
a	O
single	O
72-bit	O
accumulator	O
.	O
</s>
<s>
The	O
instruction	O
set	O
featured	O
over	O
200	O
instructions	O
,	O
including	O
basic	O
ALU	O
and	O
memory	O
operations	O
,	O
to	O
capability	O
-	O
and	O
process-control	O
instructions	O
.	O
</s>
<s>
Instead	O
of	O
the	O
programmer-visible	O
registers	O
used	O
in	O
Chicago	O
and	O
Plessey	B-Device
System	I-Device
250	I-Device
designs	O
,	O
the	O
CAP	O
would	O
load	O
internal	O
registers	O
silently	O
when	O
a	O
program	O
defined	O
a	O
capability	O
.	O
</s>
<s>
All	O
procedures	O
constituting	O
the	O
operating	B-General_Concept
system	I-General_Concept
were	O
written	O
in	O
ALGOL	B-General_Concept
68C	I-General_Concept
,	O
although	O
a	O
number	O
of	O
other	O
closely	O
associated	O
protected	O
procedures	O
-	O
such	O
as	O
a	O
paginator	O
-	O
are	O
written	O
in	O
BCPL	B-Language
.	O
</s>
<s>
A	O
fully	O
functional	O
computer	O
,	O
it	O
featured	O
a	O
complete	O
operating	B-General_Concept
system	I-General_Concept
,	O
file	B-Application
system	I-Application
,	O
compilers	B-Language
,	O
and	O
so	O
on	O
.	O
</s>
<s>
The	O
OS	O
used	O
a	O
process	B-Operating_System
tree	O
structure	O
,	O
with	O
an	O
initial	O
process	B-Operating_System
called	O
the	O
"	O
Master	O
coordinator	O
"	O
.	O
</s>
<s>
This	O
removed	O
the	O
need	O
for	O
separate	O
modes	O
of	O
operation	O
,	O
as	O
each	O
process	B-Operating_System
could	O
directly	O
access	O
the	O
resources	O
of	O
its	O
children	O
.	O
</s>
<s>
In	O
1981	O
the	O
MACRO	B-Application
SPITBOL	I-Application
version	O
of	O
the	O
SNOBOL4	O
programming	O
language	O
was	O
implemented	O
on	O
the	O
CAP	O
by	O
Nicholas	O
J	O
.	O
L	O
.	O
Brown	O
.	O
</s>
