<s>
Cooperative	B-Operating_System
Linux	I-Operating_System
,	O
abbreviated	O
as	O
coLinux	B-Operating_System
,	O
is	O
software	O
which	O
allows	O
Microsoft	B-Application
Windows	I-Application
and	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
to	O
run	O
simultaneously	O
in	O
parallel	O
on	O
the	O
same	O
machine	O
.	O
</s>
<s>
Cooperative	B-Operating_System
Linux	I-Operating_System
utilizes	O
the	O
concept	O
of	O
a	O
Cooperative	B-Operating_System
Virtual	I-Operating_System
Machine	I-Operating_System
(	O
CVM	O
)	O
.	O
</s>
<s>
In	O
contrast	O
to	O
traditional	O
virtual	B-Architecture
machines	I-Architecture
,	O
the	O
CVM	O
shares	O
resources	O
that	O
already	O
exist	O
in	O
the	O
host	O
OS	B-General_Concept
.	O
</s>
<s>
In	O
traditional	O
VM	O
hosts	O
,	O
resources	O
are	O
virtualized	O
for	O
every	O
(	O
guest	O
)	O
OS	B-General_Concept
.	O
</s>
<s>
The	O
CVM	O
gives	O
both	O
OSs	O
complete	O
control	O
of	O
the	O
host	O
machine	O
while	O
the	O
traditional	O
VM	O
sets	O
every	O
guest	O
OS	B-General_Concept
in	O
an	O
unprivileged	O
state	O
to	O
access	O
the	O
real	O
machine	O
.	O
</s>
<s>
In	O
effect	O
Cooperative	B-Operating_System
Linux	I-Operating_System
turns	O
the	O
two	O
different	O
operating	B-General_Concept
system	I-General_Concept
kernels	B-Operating_System
into	O
two	O
big	O
coroutines	B-Architecture
.	O
</s>
<s>
Each	O
kernel	B-Operating_System
has	O
its	O
own	O
complete	O
CPU	O
context	O
and	O
address	O
space	O
,	O
and	O
each	O
kernel	B-Operating_System
decides	O
when	O
to	O
give	O
control	O
back	O
to	O
its	O
partner	O
.	O
</s>
<s>
However	O
,	O
while	O
both	O
kernels	B-Operating_System
theoretically	O
have	O
full	O
access	O
to	O
the	O
real	O
hardware	O
,	O
modern	O
PC	O
hardware	O
is	O
not	O
designed	O
to	O
be	O
controlled	O
by	O
two	O
different	O
operating	B-General_Concept
systems	I-General_Concept
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
host	O
kernel	B-Operating_System
is	O
left	O
in	O
control	O
of	O
the	O
real	O
hardware	O
and	O
the	O
guest	O
kernel	B-Operating_System
contains	O
special	O
drivers	O
that	O
communicate	O
with	O
the	O
host	O
and	O
provide	O
various	O
important	O
devices	O
to	O
the	O
guest	O
OS	B-General_Concept
.	O
</s>
<s>
The	O
host	O
can	O
be	O
any	O
OS	B-General_Concept
kernel	B-Operating_System
that	O
exports	O
basic	O
primitives	O
that	O
allow	O
the	O
Cooperative	B-Operating_System
Linux	I-Operating_System
portable	O
driver	O
to	O
run	O
in	O
CPL0	B-Operating_System
mode	O
(	O
ring	B-Operating_System
0	I-Operating_System
)	O
and	O
allocate	O
memory	O
.	O
</s>
<s>
Dan	O
Aloni	O
originally	O
started	O
the	O
development	O
of	O
Cooperative	B-Operating_System
Linux	I-Operating_System
as	O
a	O
research	O
project	O
based	O
on	O
similar	O
work	O
with	O
User-mode	B-Application
Linux	I-Application
.	O
</s>
<s>
In	O
July	O
2004	O
he	O
presented	O
a	O
paper	O
at	O
the	O
Linux	B-Operating_System
Symposium	O
.	O
</s>
<s>
The	O
source	B-Application
was	O
released	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
Cooperative	B-Operating_System
Linux	I-Operating_System
is	O
significantly	O
different	O
from	O
full	O
x86	B-General_Concept
virtualization	I-General_Concept
,	O
which	O
generally	O
works	O
by	O
running	O
the	O
guest	O
OS	B-General_Concept
in	O
a	O
less	O
privileged	B-Operating_System
mode	I-Operating_System
than	O
that	O
of	O
the	O
host	O
kernel	B-Operating_System
,	O
and	O
having	O
all	O
resources	O
delegated	O
by	O
the	O
host	O
kernel	B-Operating_System
.	O
</s>
<s>
In	O
contrast	O
,	O
Cooperative	B-Operating_System
Linux	I-Operating_System
runs	O
a	O
specially	O
modified	O
Linux	B-Operating_System
kernel	I-Operating_System
that	O
is	O
Cooperative	O
in	O
that	O
it	O
takes	O
responsibility	O
for	O
sharing	O
resources	O
with	O
the	O
NT	O
kernel	B-Operating_System
and	O
not	O
instigating	O
race	B-Operating_System
conditions	I-Operating_System
.	O
</s>
<s>
Most	O
of	O
the	O
changes	O
in	O
the	O
Cooperative	B-Operating_System
Linux	I-Operating_System
patch	O
are	O
on	O
the	O
i386	B-General_Concept
tree	O
—	O
the	O
only	O
supported	O
architecture	O
for	O
Cooperative	O
at	O
the	O
time	O
of	O
this	O
writing	O
.	O
</s>
<s>
Most	O
of	O
the	O
changes	O
in	O
the	O
i386	B-General_Concept
tree	O
involve	O
the	O
initialization	O
and	O
setup	O
code	O
.	O
</s>
<s>
It	O
is	O
a	O
goal	O
of	O
the	O
Cooperative	B-Operating_System
Linux	I-Operating_System
kernel	B-Operating_System
design	O
to	O
remain	O
as	O
close	O
as	O
possible	O
to	O
the	O
standalone	O
i386	B-General_Concept
kernel	B-Operating_System
,	O
so	O
all	O
changes	O
are	O
localized	O
and	O
minimized	O
as	O
much	O
as	O
possible	O
.	O
</s>
<s>
The	O
coLinux	B-Operating_System
package	O
installs	O
a	O
port	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
a	O
virtual	B-Protocol
network	I-Protocol
device	I-Protocol
and	O
can	O
run	O
simultaneously	O
under	O
a	O
version	O
of	O
the	O
Windows	B-Application
operating	I-Application
system	I-Application
such	O
as	O
Windows	B-Application
2000	I-Application
or	O
Windows	B-Application
XP	I-Application
.	O
</s>
<s>
It	O
does	O
not	O
use	O
a	O
virtual	B-Architecture
machine	I-Architecture
such	O
as	O
VMware	O
.	O
</s>
<s>
Debian	O
,	O
Ubuntu	B-Operating_System
,	O
Fedora	O
and	O
Gentoo	B-Application
are	O
especially	O
popular	O
with	O
the	O
coLinux	B-Operating_System
users	O
.	O
</s>
<s>
Due	O
to	O
the	O
rather	O
unusual	O
structure	O
of	O
the	O
virtual	B-General_Concept
hardware	I-General_Concept
,	O
installing	O
Linux	B-Operating_System
distributions	O
under	O
coLinux	B-Operating_System
is	O
generally	O
difficult	O
.	O
</s>
<s>
Therefore	O
,	O
users	O
in	O
most	O
cases	O
use	O
either	O
an	O
existing	O
Linux	B-Operating_System
installation	O
on	O
a	O
real	O
partition	O
or	O
a	O
ready	O
made	O
filesystem	O
image	O
distributed	O
by	O
the	O
project	O
.	O
</s>
<s>
The	O
filesystem	O
images	O
are	O
made	O
by	O
a	O
variety	O
of	O
methods	O
,	O
including	O
taking	O
images	O
of	O
a	O
normal	O
Linux	B-Operating_System
system	O
,	O
finding	O
ways	O
to	O
make	O
installers	O
run	O
with	O
the	O
strange	O
hardware	O
,	O
building	O
up	O
installs	O
by	O
hand	O
using	O
the	O
package	O
manager	O
or	O
simply	O
upgrading	O
existing	O
images	O
using	O
tools	O
like	O
yum	B-Application
and	O
apt	B-Application
.	O
</s>
<s>
An	O
easier	O
way	O
to	O
get	O
an	O
up-to-date	O
filesystem	O
image	O
is	O
to	O
use	O
QEMU	B-Application
to	O
install	O
Linux	B-Operating_System
and	O
"	O
convert	O
"	O
the	O
image	O
by	O
stripping	O
off	O
the	O
first	O
63	O
512-byte	O
blocks	O
as	O
described	O
in	O
the	O
coLinux	B-Operating_System
wiki	O
.	O
</s>
<s>
Since	O
coLinux	B-Operating_System
does	O
not	O
have	O
access	O
to	O
native	O
graphics	O
hardware	O
,	O
X	B-Operating_System
Window	I-Operating_System
or	O
X	B-Operating_System
Servers	I-Operating_System
will	O
not	O
run	O
under	O
coLinux	B-Operating_System
directly	O
,	O
but	O
one	O
can	O
install	O
an	O
X	B-Operating_System
Server	O
under	O
Windows	O
,	O
such	O
as	O
Cygwin/X	B-Application
or	O
Xming	B-Application
and	O
use	O
KDE	B-Application
or	O
GNOME	B-Application
and	O
almost	O
any	O
other	O
Linux	B-Operating_System
application	O
and	O
distribution	O
.	O
</s>
<s>
All	O
of	O
these	O
issues	O
are	O
fixed	O
by	O
using	O
coLinux	B-Operating_System
based	O
distributions	O
such	O
as	O
andLinux	O
,	O
based	O
on	O
Ubuntu	B-Operating_System
,	O
or	O
TopologiLinux	O
,	O
based	O
on	O
Slackware	B-Application
.	O
</s>
<s>
Ethernet	O
network	O
via	O
TAP	B-Protocol
,	O
PCAP	B-Language
,	O
NDIS	B-Application
and	O
SLiRP	B-Protocol
.	O
</s>
<s>
Does	O
not	O
yet	O
support	O
64-bit	O
Windows	O
or	O
Linux	B-Operating_System
(	O
nor	O
utilize	O
more	O
than	O
4GB	O
memory	O
)	O
,	O
but	O
a	O
port	O
is	O
under	O
development	O
by	O
the	O
community	O
.	O
</s>
<s>
Linux	B-Operating_System
applications	O
and	O
the	O
underlying	O
kernel	B-Operating_System
are	O
able	O
to	O
use	O
only	O
one	O
CPU	O
.	O
</s>
