<s>
The	O
CMS	B-Application
file	I-Application
system	I-Application
is	O
the	O
native	O
file	B-Application
system	I-Application
of	O
IBM	O
's	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
,	O
a	O
component	O
of	O
VM	B-Application
.	O
</s>
<s>
It	O
was	O
the	O
only	O
file	B-Application
system	I-Application
for	O
CMS	O
until	O
the	O
introduction	O
of	O
the	O
CMS	O
Shared	O
File	B-Application
System	I-Application
with	O
VM/SP	B-Application
.	O
</s>
<s>
CP-67	B-Application
and	O
VM	B-Application
allow	O
an	O
installation	O
to	O
divide	O
a	O
disk	O
volume	O
into	O
virtual	O
disks	O
called	O
minidisks	O
.	O
</s>
<s>
A	O
minidisk	O
may	O
be	O
a	O
CMS	O
minidisk	O
,	O
initialized	O
with	O
the	O
CMS	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
Other	O
minidisks	O
might	O
be	O
formatted	O
for	O
use	O
by	O
,	O
e.g.	O
,	O
OS/360	B-Application
,	O
but	O
these	O
are	O
not	O
CMS	O
minidisks	O
even	O
if	O
they	O
are	O
assigned	O
to	O
a	O
CMS	O
virtual	O
machine	O
.	O
</s>
<s>
A	O
CMS	O
minidisk	O
in	O
early	O
versions	O
of	O
CMS	O
is	O
formatted	O
into	O
800-byte	O
blocks	B-General_Concept
.	O
</s>
<s>
Later	O
versions	O
of	O
CMS	O
allow	O
minidisks	O
formatted	O
as	O
1024-	O
,	O
2048-	O
,	O
or	O
4096-byte	O
blocks	B-General_Concept
,	O
which	O
increased	O
the	O
limits	O
described	O
here	O
to	O
231	O
disk	B-General_Concept
blocks	I-General_Concept
and	O
231	O
records	O
.	O
</s>
<s>
The	O
first	O
two	O
blocks	B-General_Concept
on	O
a	O
minidisk	O
are	O
reserved	O
for	O
IPL	O
.	O
</s>
<s>
The	O
fourth	O
block	O
,	O
called	O
the	O
Master	O
File	B-Application
Directory	I-Application
or	O
MFD	O
,	O
is	O
the	O
directory	B-Application
header	O
for	O
the	O
minidisk	O
.	O
</s>
<s>
CMS	O
uses	O
a	O
flat	O
file	B-Application
system	I-Application
.	O
</s>
<s>
The	O
MFD	O
contains	O
an	O
array	O
of	O
disk	O
addresses	O
of	O
blocks	B-General_Concept
containing	O
File	O
Status	O
Table	O
(	O
FST	O
)	O
(	O
directory	B-Application
)	O
entries	O
.	O
</s>
<s>
The	O
first	O
chain	O
link	O
block	O
contains	O
the	O
disk	O
addresses	O
of	O
up	O
to	O
40	O
additional	O
chain	O
link	O
blocks	B-General_Concept
,	O
followed	O
by	O
the	O
disk	O
addresses	O
of	O
up	O
to	O
60	O
data	O
blocks	B-General_Concept
.	O
</s>
<s>
The	O
remaining	O
chain	O
link	O
blocks	B-General_Concept
each	O
contain	O
the	O
disk	O
addresses	O
of	O
up	O
to	O
400	O
data	O
blocks	B-General_Concept
.	O
</s>
<s>
this	O
results	O
in	O
a	O
maximum	O
size	O
of	O
16,060	O
800-byte	O
blocks	B-General_Concept
,	O
or	O
12,848,000	O
bytes	O
,	O
for	O
any	O
CMS	O
file	O
.	O
</s>
<s>
In	O
1979	O
,	O
Virtual	O
Machine/System	O
Extensions	O
(	O
VM/SE	O
or	O
SEPP	O
)	O
Release	O
2	O
and	O
Virtual	O
Machine/Basic	O
System	O
Extensions	O
(	O
VM/BSE	O
or	O
BSEPP	O
)	O
Release	O
2	O
provided	O
an	O
enhancement	O
to	O
the	O
original	O
CMS	B-Application
file	I-Application
system	I-Application
,	O
called	O
Enhanced	O
Disk	O
Format	O
(	O
EDF	O
)	O
,	O
that	O
allows	O
larger	O
files	O
by	O
expanding	O
the	O
FST	O
and	O
introducing	O
multiple	O
levels	O
of	O
chain	O
link	O
blocks	B-General_Concept
.	O
</s>
