<s>
The	O
MFS	O
or	O
Media	O
File	B-Application
System	I-Application
is	O
a	O
proprietary	O
file	B-Application
system	I-Application
used	O
on	O
TiVo	B-Application
hard	O
drives	O
for	O
fault	O
tolerant	O
real-time	O
recording	O
of	O
live	O
TV	B-Operating_System
.	O
</s>
<s>
Although	O
MFS	O
is	O
still	O
not	O
particularly	O
well	O
understood	O
by	O
programmers	O
unaffiliated	O
with	O
the	O
TiVo	B-Application
corporation	O
,	O
enough	O
is	O
known	O
about	O
the	O
file	B-Application
system	I-Application
to	O
be	O
able	O
to	O
do	O
reads	O
and	O
limited	O
writes	O
.	O
</s>
<s>
Applications	O
exist	O
to	O
manipulate	O
the	O
file	B-Application
system	I-Application
and	O
objects	O
within	O
it	O
.	O
</s>
<s>
Most	O
of	O
these	O
applications	O
are	O
reverse	O
engineered	O
from	O
software	O
found	O
on	O
the	O
TiVo	B-Application
itself	O
,	O
as	O
many	O
of	O
the	O
early	O
TiVo	B-Application
programs	O
were	O
little	O
more	O
than	O
specialized	O
scripts	O
that	O
manipulated	O
the	O
data	O
.	O
</s>
<s>
The	O
MFS	O
file	B-Application
system	I-Application
is	O
organized	O
more	O
like	O
a	O
database	O
,	O
including	O
transaction	O
logging	O
and	O
rollback	O
capabilities	O
.	O
</s>
<s>
Each	O
object	O
in	O
the	O
TiVo	B-Application
file	B-Application
system	I-Application
is	O
assigned	O
an	O
ID	O
,	O
which	O
is	O
internally	O
called	O
the	O
"	O
FSID	O
"	O
(	O
presumably	O
,	O
file	B-Application
system	I-Application
ID	O
)	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
itself	O
is	O
implemented	O
entirely	O
in	O
the	O
Linux	O
userspace	O
.	O
</s>
<s>
The	O
primary	O
reason	O
TiVo	B-Application
devised	O
such	O
a	O
system	O
is	O
because	O
they	O
needed	O
a	O
way	O
to	O
store	O
large	O
continuous	O
sections	O
of	O
data	O
easily	O
in	O
a	O
manner	O
that	O
lent	O
itself	O
well	O
to	O
streaming	O
that	O
data	O
directly	O
to	O
the	O
media	O
decoders	O
in	O
the	O
TiVo	B-Application
devices	O
,	O
without	O
being	O
CPU	O
dependent	O
.	O
</s>
<s>
Thus	O
,	O
the	O
CPU	O
has	O
very	O
little	O
involvement	O
in	O
playback	O
and	O
recording	O
functionality	O
,	O
simply	O
directing	O
the	O
encoder/decoder	O
chips	O
to	O
stream	O
data	O
directly	O
to	O
the	O
drives	O
via	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
while	O
mapping	O
sections	O
of	O
virtual	O
memory	O
onto	O
the	O
drive	O
.	O
</s>
