<s>
Singularity	B-Operating_System
is	O
an	O
experimental	O
operating	B-General_Concept
system	I-General_Concept
developed	O
by	O
Microsoft	O
Research	O
between	O
July	O
9	O
,	O
2003	O
,	O
and	O
February	O
7	O
,	O
2015	O
.	O
</s>
<s>
It	O
was	O
designed	O
as	O
a	O
high	O
dependability	B-Application
OS	O
in	O
which	O
the	O
kernel	B-Operating_System
,	O
device	B-Application
drivers	I-Application
,	O
and	O
application	B-Application
software	I-Application
were	O
all	O
written	O
in	O
managed	O
code	O
.	O
</s>
<s>
Internal	O
security	O
uses	O
type	B-Language
safety	I-Language
instead	O
of	O
hardware	B-Architecture
memory	B-General_Concept
protection	I-General_Concept
.	O
</s>
<s>
The	O
lowest-level	O
x86	B-Operating_System
interrupt	B-Application
dispatch	O
code	O
is	O
written	O
in	O
assembly	B-Language
language	I-Language
and	O
C	B-Language
.	O
Once	O
this	O
code	O
has	O
done	O
its	O
job	O
,	O
it	O
invokes	O
the	O
kernel	B-Operating_System
,	O
which	O
runtime	B-Device
system	I-Device
and	O
garbage	B-General_Concept
collector	I-General_Concept
are	O
written	O
in	O
Sing#	O
(	O
an	O
extended	O
version	O
of	O
Spec#	O
,	O
itself	O
an	O
extension	O
of	O
C#	B-Application
)	O
and	O
runs	O
in	O
unprotected	O
mode	O
.	O
</s>
<s>
The	O
hardware	B-Operating_System
abstraction	I-Operating_System
layer	I-Operating_System
is	O
written	O
in	O
C++	B-Language
and	O
runs	O
in	O
protected	O
mode	O
.	O
</s>
<s>
There	O
is	O
also	O
some	O
C	B-Language
code	O
to	O
handle	O
debugging	O
.	O
</s>
<s>
The	O
computer	O
's	O
basic	B-Operating_System
input/output	I-Operating_System
system	I-Operating_System
(	O
BIOS	B-Operating_System
)	O
is	O
invoked	O
during	O
the	O
16-bit	O
real	B-Application
mode	I-Application
bootstrap	O
stage	O
;	O
once	O
in	O
32-bit	O
mode	O
,	O
Singularity	B-Operating_System
never	O
invokes	O
the	O
BIOS	B-Operating_System
again	O
,	O
but	O
invokes	O
device	B-Application
drivers	I-Application
written	O
in	O
Sing#	O
.	O
</s>
<s>
During	O
installation	O
,	O
Common	O
Intermediate	O
Language	O
(	O
CIL	O
)	O
opcodes	B-Language
are	O
compiled	O
into	O
x86	B-Operating_System
opcodes	B-Language
using	O
the	O
Bartok	B-Application
compiler	I-Application
.	O
</s>
<s>
Singularity	B-Operating_System
is	O
a	O
microkernel	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Unlike	O
most	O
historic	O
microkernels	B-Operating_System
,	O
its	O
components	O
execute	O
in	O
the	O
same	O
address	B-General_Concept
space	I-General_Concept
(	O
process	B-Operating_System
)	O
,	O
which	O
contains	O
software-isolated	O
processes	O
(	O
SIPs	O
)	O
.	O
</s>
<s>
Protection	O
in	O
this	O
system	O
is	O
provided	O
by	O
a	O
set	O
of	O
rules	O
called	O
invariants	B-Application
that	O
are	O
verified	O
by	O
static	O
program	O
analysis	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
memory-invariant	O
states	O
there	O
must	O
be	O
no	O
cross-references	O
(	O
or	O
memory	O
pointers	O
)	O
between	O
two	O
SIPs	O
;	O
communication	O
between	O
SIPs	O
occurs	O
via	O
higher-order	O
communication	O
channels	O
managed	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Invariants	B-Application
are	O
checked	O
during	O
installation	O
of	O
the	O
application	O
.	O
</s>
<s>
(	O
In	O
Singularity	B-Operating_System
,	O
installation	O
is	O
managed	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
)	O
</s>
<s>
Most	O
of	O
the	O
invariants	B-Application
rely	O
on	O
the	O
use	O
of	O
safer	O
memory-managed	B-General_Concept
languages	O
,	O
such	O
as	O
Sing#	O
,	O
which	O
have	O
a	O
garbage	B-General_Concept
collector	I-General_Concept
,	O
allow	O
no	O
arbitrary	O
pointers	O
,	O
and	O
allow	O
code	O
to	O
be	O
verified	O
to	O
meet	O
a	O
given	O
computer	O
security	O
policy	O
.	O
</s>
<s>
The	O
first	O
Singularity	B-Operating_System
Research	O
Development	O
Kit	O
(	O
RDK	O
)	O
,	O
RDK	O
1.1	O
,	O
was	O
initially	O
released	O
on	O
March	O
4	O
,	O
2008	O
,	O
being	O
released	O
under	O
a	O
shared	B-License
source	I-License
license	I-License
allowing	O
academic	O
non-commercial	O
use	O
and	O
available	O
from	O
CodePlex	B-Protocol
.	O
</s>
