<s>
The	O
SPIN	O
operating	B-General_Concept
system	I-General_Concept
is	O
a	O
research	O
project	O
implemented	O
in	O
the	O
computer	O
programming	O
language	O
Modula-3	B-Language
,	O
and	O
is	O
an	O
open	B-License
source	I-License
project	O
.	O
</s>
<s>
It	O
is	O
designed	O
with	O
three	O
goals	O
:	O
flexibility	B-Application
,	O
safety	B-Application
,	O
and	O
performance	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
can	O
be	O
extended	O
by	O
dynamic	B-Operating_System
loading	I-Operating_System
of	O
modules	O
which	O
implement	O
interfaces	B-Application
that	O
represent	O
domains	B-Algorithm
.	O
</s>
<s>
These	O
domains	B-Algorithm
are	O
defined	O
by	O
Modula-3	B-Language
INTERFACE	O
.	O
</s>
<s>
All	O
kernel	B-Operating_System
extensions	O
are	O
written	O
in	O
Modula-3	B-Language
safe	O
subset	O
with	O
metalanguage	O
constructs	O
and	O
type	B-Language
safe	I-Language
casting	O
system	O
.	O
</s>
<s>
The	O
system	O
also	O
issued	O
a	O
special	O
run-time	O
extension	O
compiler	B-Language
.	O
</s>
<s>
One	O
set	O
of	O
kernel	B-Operating_System
extensions	O
provides	O
an	O
application	B-General_Concept
programming	I-General_Concept
interface	I-General_Concept
(	O
API	B-General_Concept
)	O
that	O
emulates	O
the	O
Digital	B-Operating_System
UNIX	I-Operating_System
system	O
call	O
interface	O
.	O
</s>
