<s>
xv6	B-Operating_System
is	O
a	O
modern	O
reimplementation	O
of	O
Sixth	B-Operating_System
Edition	I-Operating_System
Unix	I-Operating_System
in	O
ANSI	O
C	B-Language
for	O
multiprocessor	B-Operating_System
x86	B-Operating_System
and	O
RISC-V	B-Device
systems	O
.	O
</s>
<s>
MIT	O
's	O
Operating	O
System	O
Engineering	O
course	O
formerly	O
used	O
the	O
original	O
V6	B-Operating_System
source	O
code	O
.	O
</s>
<s>
xv6	B-Operating_System
was	O
created	O
as	O
a	O
modern	O
replacement	O
,	O
because	O
PDP-11	B-Device
machines	O
are	O
not	O
widely	O
available	O
and	O
the	O
original	O
operating	O
system	O
was	O
written	O
in	O
archaic	O
pre-ANSI	O
C	B-Language
.	O
Unlike	O
Linux	B-Application
or	O
BSD	B-Operating_System
,	O
xv6	B-Operating_System
is	O
simple	O
enough	O
to	O
cover	O
in	O
a	O
semester	O
,	O
yet	O
still	O
contains	O
the	O
important	O
concepts	O
and	O
organization	O
of	O
Unix	B-Application
.	O
</s>
<s>
One	O
feature	O
of	O
the	O
Makefile	O
for	O
xv6	B-Operating_System
is	O
the	O
option	O
to	O
produce	O
a	O
PDF	B-Application
of	O
the	O
entire	O
source	O
code	O
listing	O
in	O
a	O
readable	O
format	O
.	O
</s>
<s>
This	O
is	O
reminiscent	O
of	O
the	O
original	O
V6	B-Operating_System
source	O
code	O
,	O
which	O
was	O
published	O
in	O
a	O
similar	O
form	O
in	O
Lions	O
 '	O
Commentary	O
on	O
UNIX	B-Application
6th	O
Edition	O
,	O
with	O
Source	O
Code	O
.	O
</s>
<s>
xv6	B-Operating_System
has	O
been	O
used	O
in	O
operating	O
systems	O
courses	O
at	O
many	O
universities	O
,	O
including	O
:	O
</s>
