<s>
Files-11	B-Application
is	O
the	O
file	B-Application
system	I-Application
used	O
in	O
the	O
RSX-11	B-Application
and	O
OpenVMS	B-Operating_System
operating	B-General_Concept
systems	I-General_Concept
from	O
Digital	O
Equipment	O
Corporation	O
.	O
</s>
<s>
It	O
supports	O
record-oriented	O
I/O	B-General_Concept
,	O
remote	O
network	B-Architecture
access	O
,	O
and	O
file	B-Application
versioning	I-Application
.	O
</s>
<s>
The	O
original	O
ODS-1	O
layer	O
is	O
a	O
flat	O
file	B-Application
system	I-Application
;	O
the	O
ODS-2	O
version	O
is	O
a	O
hierarchical	B-Application
file	I-Application
system	I-Application
,	O
with	O
support	O
for	O
access	O
control	O
lists	O
,	O
.	O
</s>
<s>
Files-11	B-Application
is	O
similar	O
to	O
,	O
but	O
significantly	O
more	O
advanced	O
than	O
,	O
the	O
file	B-Application
systems	I-Application
used	O
in	O
previous	O
Digital	O
Equipment	O
Corporation	O
operating	B-General_Concept
systems	I-General_Concept
such	O
as	O
TOPS-20	B-Operating_System
and	O
RSTS/E	B-Operating_System
.	O
</s>
<s>
The	O
native	O
OpenVMS	B-Operating_System
file	B-Application
system	I-Application
is	O
descended	O
from	O
older	O
DEC	O
operating	B-General_Concept
systems	I-General_Concept
and	O
is	O
similar	O
in	O
many	O
ways	O
,	O
both	O
having	O
been	O
designed	O
by	O
Dave	O
Cutler	O
.	O
</s>
<s>
These	O
file	B-Application
systems	I-Application
all	O
provided	O
some	O
form	O
of	O
rudimentary	O
non-hierarchical	O
directory	O
structure	O
,	O
typically	O
based	O
on	O
assigning	O
one	O
directory	O
per	O
user	O
account	O
.	O
</s>
<s>
Under	O
RSTS/E	B-Operating_System
,	O
each	O
user	O
account	O
was	O
represented	O
by	O
two	O
numbers	O
,	O
a	O
 [ project , programmer ] 	O
pair	O
,	O
and	O
had	O
one	O
associated	O
directory	O
.	O
</s>
<s>
While	O
this	O
was	O
suitable	O
for	O
PDP-11	B-Device
systems	O
,	O
which	O
possessed	O
limited	O
permanent	O
storage	O
capacity	O
,	O
VAX	B-Device
systems	O
with	O
much	O
larger	O
hard	B-Device
drives	I-Device
required	O
a	O
more	O
flexible	O
method	O
of	O
file	B-Application
storage	I-Application
:	O
hierarchical	O
directory	O
layout	O
in	O
particular	O
,	O
the	O
most	O
notable	O
improvement	O
in	O
ODS-2	O
.	O
</s>
<s>
"	O
Files-11	B-Application
"	O
is	O
the	O
general	O
term	O
for	O
five	O
separate	O
file	B-Application
systems	I-Application
,	O
known	O
as	O
on-disk	O
structure	O
(	O
ODS	O
)	O
levels	O
1	O
through	O
5	O
.	O
</s>
<s>
ODS-1	O
is	O
the	O
flat	O
file	B-Application
system	I-Application
used	O
by	O
the	O
RSX-11	B-Application
OS	O
,	O
supported	O
by	O
older	O
VMS	B-Operating_System
systems	O
for	O
RSX	O
compatibility	O
,	O
but	O
never	O
used	O
to	O
support	O
VMS	B-Operating_System
itself	O
;	O
it	O
has	O
been	O
largely	O
superseded	O
by	O
ODS-2	O
and	O
ODS-5	B-Application
.	O
</s>
<s>
ODS-2	O
is	O
the	O
standard	O
VMS	B-Operating_System
file	B-Application
system	I-Application
,	O
and	O
remains	O
the	O
most	O
common	O
file	B-Application
system	I-Application
for	O
system	O
disks	O
(	O
the	O
disk	O
on	O
which	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
installed	O
)	O
.	O
</s>
<s>
Although	O
seldom	O
referred	O
to	O
by	O
their	O
ODS	O
level	O
designations	O
,	O
ODS-3	O
and	O
ODS-4	O
are	O
the	O
Files-11	B-Application
support	O
for	O
the	O
CD-ROM	O
ISO	B-Application
9660	I-Application
and	O
High	B-Application
Sierra	I-Application
Format	I-Application
file	B-Application
systems	I-Application
,	O
respectively	O
.	O
</s>
<s>
ODS-5	B-Application
is	O
an	O
extended	O
version	O
of	O
ODS-2	O
available	O
on	O
Alpha	B-Device
and	O
IA-64	B-General_Concept
platforms	O
which	O
adds	O
support	O
for	O
case-preserving	B-Application
filenames	B-Device
with	O
non-ASCII	O
characters	O
and	O
improvements	O
to	O
the	O
hierarchical	O
directory	O
support	O
.	O
</s>
<s>
It	O
was	O
originally	O
intended	O
for	O
file	B-Operating_System
serving	O
to	O
Microsoft	B-Application
Windows	I-Application
or	O
other	O
non-VMS	O
systems	O
as	O
part	O
of	O
the	O
"	O
NT	O
Affinity	O
"	O
project	O
,	O
but	O
is	O
also	O
used	O
on	O
user	O
disks	O
and	O
Internet	O
servers	O
.	O
</s>
<s>
All	O
files	O
and	O
directories	O
in	O
a	O
Files-11	B-Application
file	B-Application
system	I-Application
are	O
contained	O
inside	O
one	O
or	O
more	O
parent	O
directories	O
,	O
and	O
eventually	O
under	O
the	O
root	O
directory	O
,	O
the	O
master	O
file	B-Operating_System
directory	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
is	O
therefore	O
organised	O
in	O
a	O
directed	O
acyclic	O
graph	O
(	O
DAG	O
)	O
structure	O
.	O
</s>
<s>
In	O
this	O
example	O
(	O
see	O
right	O
)	O
,	O
File	B-Operating_System
2	O
has	O
a	O
directory	O
entry	O
under	O
both	O
Dir	O
2	O
and	O
Dir	O
3	O
;	O
it	O
is	O
"	O
in	O
"	O
both	O
directories	O
simultaneously	O
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
concept	O
of	O
hard	B-Application
links	I-Application
in	O
UNIX	B-Application
,	O
although	O
care	O
must	O
be	O
taken	O
that	O
the	O
file	B-Operating_System
is	O
not	O
actually	O
deleted	O
on	O
disks	O
that	O
are	O
not	O
set	O
up	O
for	O
hard	B-Application
links	I-Application
(	O
only	O
available	O
on	O
ODS-5	B-Application
disks	O
,	O
and	O
then	O
only	O
if	O
the	O
disk	O
has	O
hard	B-Application
links	I-Application
enabled	O
)	O
.	O
</s>
<s>
An	O
operational	O
VMS	B-Operating_System
system	O
has	O
access	O
to	O
one	O
or	O
more	O
online	O
disks	O
,	O
each	O
of	O
which	O
contains	O
a	O
complete	O
,	O
independent	O
file	B-Application
system	I-Application
.	O
</s>
<s>
In	O
an	O
OpenVMS	B-Operating_System
cluster	O
configuration	O
,	O
non-private	O
disks	O
are	O
shared	O
between	O
all	O
nodes	O
in	O
the	O
cluster	O
(	O
see	O
figure	O
1	O
)	O
.	O
</s>
<s>
In	O
this	O
configuration	O
,	O
the	O
two	O
system	O
disks	O
are	O
accessible	O
to	O
both	O
nodes	O
via	O
the	O
network	B-Architecture
,	O
but	O
the	O
private	O
disk	O
is	O
not	O
shared	O
:	O
it	O
is	O
mounted	O
for	O
use	O
only	O
by	O
a	O
particular	O
user	O
or	O
process	O
on	O
that	O
machine	O
.	O
</s>
<s>
Access	O
to	O
files	O
across	O
a	O
cluster	O
is	O
managed	O
by	O
the	O
OpenVMS	B-Operating_System
Distributed	O
Lock	O
Manager	O
,	O
an	O
integral	O
part	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
File	B-Application
systems	I-Application
on	O
each	O
disk	O
(	O
with	O
the	O
exception	O
of	O
ODS-1	O
)	O
are	O
hierarchical	O
.	O
</s>
<s>
A	O
fully	O
specified	O
filename	B-Device
consists	O
of	O
a	O
nodename	O
,	O
a	O
username	O
and	O
password	O
,	O
a	O
device	O
name	O
,	O
directory	O
,	O
filename	B-Device
,	O
file	B-Operating_System
type	O
,	O
and	O
a	O
version	O
number	O
,	O
in	O
the	O
format	O
:	O
</s>
<s>
For	O
example	O
,	O
[DIR1.DIR2.DIR3]FILE.EXT	O
refers	O
to	O
the	O
latest	O
version	O
of	O
FILE.EXT	O
,	O
on	O
the	O
current	O
default	O
disk	O
,	O
in	O
directory	O
 [ DIR1.DIR2.DIR3 ] 	O
.	O
</s>
<s>
DIR1	O
is	O
a	O
subdirectory	O
of	O
the	O
master	O
file	B-Operating_System
directory	O
(	O
MFD	O
)	O
,	O
or	O
root	O
directory	O
,	O
and	O
DIR2	O
is	O
a	O
subdirectory	O
of	O
DIR1	O
.	O
</s>
<s>
Most	O
parts	O
of	O
the	O
filename	B-Device
can	O
be	O
omitted	O
,	O
in	O
which	O
case	O
they	O
are	O
taken	O
from	O
the	O
current	O
default	O
file	B-Operating_System
specification	O
.	O
</s>
<s>
The	O
default	O
file	B-Operating_System
specification	O
replaces	O
the	O
concept	O
of	O
"	O
current	O
directory	O
"	O
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
by	O
providing	O
a	O
set	O
of	O
defaults	O
for	O
node	O
,	O
device	O
name	O
and	O
directory	O
.	O
</s>
<s>
All	O
processes	O
have	O
a	O
default	O
file	B-Operating_System
specification	O
which	O
includes	O
disk	O
name	O
and	O
directory	O
,	O
and	O
most	O
VMS	B-Operating_System
file	B-Application
system	I-Application
routines	O
accept	O
a	O
default	O
file	B-Operating_System
specification	O
which	O
can	O
also	O
include	O
the	O
file	B-Operating_System
type	O
;	O
the	O
TYPE	O
command	O
,	O
for	O
example	O
,	O
defaults	O
to	O
"	O
.LIS	O
"	O
as	O
the	O
file	B-Operating_System
type	O
,	O
so	O
the	O
command	O
TYPE	O
F	O
,	O
with	O
no	O
extension	O
,	O
attempts	O
to	O
open	O
the	O
file	B-Operating_System
F.LIS	O
.	O
</s>
<s>
Every	O
file	B-Operating_System
has	O
a	O
version	O
number	O
,	O
which	O
defaults	O
to	O
1	O
if	O
no	O
other	O
versions	O
of	O
the	O
same	O
filename	B-Device
are	O
present	O
(	O
otherwise	O
one	O
higher	O
than	O
the	O
greatest	O
version	O
)	O
.	O
</s>
<s>
Every	O
time	O
a	O
file	B-Operating_System
is	O
saved	O
,	O
rather	O
than	O
overwriting	O
the	O
existing	O
version	O
,	O
a	O
new	O
file	B-Operating_System
with	O
the	O
same	O
name	O
but	O
an	O
incremented	O
version	O
number	O
is	O
created	O
.	O
</s>
<s>
Old	O
versions	O
can	O
be	O
deleted	O
explicitly	O
,	O
with	O
the	O
DELETE	O
or	O
the	O
PURGE	O
command	O
,	O
or	O
optionally	O
,	O
older	O
versions	O
of	O
a	O
file	B-Operating_System
can	O
be	O
deleted	O
automatically	O
when	O
the	O
file	B-Operating_System
's	O
version	O
limit	O
is	O
reached	O
(	O
set	O
by	O
SET	O
FILE/VERSION_LIMIT	O
)	O
.	O
</s>
<s>
ODS-2	O
is	O
limited	O
to	O
eight	O
levels	O
of	O
subdirectories	O
,	O
and	O
only	O
uppercase	O
,	O
alphanumeric	O
names	O
(	O
plus	O
the	O
underscore	O
,	O
dash	O
,	O
and	O
dollar	O
sign	O
)	O
up	O
to	O
39.39	O
characters	O
(	O
39	O
for	O
the	O
filename	B-Device
and	O
another	O
39	O
for	O
the	O
extension	O
)	O
.	O
</s>
<s>
ODS-5	B-Application
expands	O
the	O
character	O
set	O
to	O
lowercase	O
letters	O
and	O
most	O
other	O
printable	O
ASCII	B-Protocol
characters	I-Protocol
,	O
as	O
well	O
as	O
ISO	O
Latin-1	O
and	O
Unicode	O
characters	O
,	O
increases	O
the	O
maximum	O
filename	B-Device
length	O
and	O
allows	O
unlimited	O
levels	O
of	O
subdirectories	O
.	O
</s>
<s>
When	O
constructing	O
a	O
pathname	O
for	O
an	O
ODS-5	B-Application
file	B-Operating_System
which	O
uses	O
characters	O
not	O
allowed	O
under	O
ODS-2	O
,	O
a	O
special	O
"	O
^	O
"	O
syntax	O
is	O
used	O
to	O
preserve	O
backwards	O
compatibility	O
;	O
the	O
file	B-Operating_System
"	O
file.tar.gz	O
;	O
1	O
"	O
on	O
an	O
ODS-5	B-Application
disk	O
,	O
for	O
example	O
,	O
would	O
be	O
referred	O
to	O
as	O
"	O
file^	O
.tar.gz	O
"	O
—	O
the	O
file	B-Operating_System
's	O
name	O
is	O
"	O
file.tar	O
"	O
,	O
and	O
the	O
extension	O
is	O
"	O
.gz	O
"	O
.	O
</s>
<s>
VMS	B-Operating_System
file	B-Operating_System
security	O
is	O
defined	O
by	O
two	O
mechanisms	O
,	O
UIC-based	O
access	O
control	O
and	O
ACL-based	O
access	O
control	O
.	O
</s>
<s>
UIC	O
access	O
control	O
is	O
based	O
on	O
the	O
owner	O
of	O
the	O
file	B-Operating_System
and	O
the	O
UIC	O
,	O
or	O
user	O
,	O
accessing	O
the	O
file	B-Operating_System
.	O
</s>
<s>
The	O
"	O
system	O
"	O
access	O
applies	O
to	O
any	O
user	O
whose	O
UIC	O
group	O
code	O
is	O
less	O
than	O
or	O
equal	O
to	O
the	O
SYSGEN	O
parameter	O
MAXSYSGROUP	O
(	O
typically	O
8	O
,	O
or	O
10	O
octal	O
)	O
(	O
for	O
example	O
the	O
SYSTEM	O
user	O
)	O
;	O
"	O
owner	O
"	O
and	O
"	O
group	O
"	O
apply	O
to	O
the	O
owner	O
of	O
the	O
file	B-Operating_System
and	O
that	O
user	O
's	O
user	O
group	O
,	O
and	O
"	O
world	O
"	O
applies	O
to	O
any	O
other	O
user	O
.	O
</s>
<s>
There	O
is	O
also	O
a	O
fifth	O
permission	O
bit	O
,	O
"	O
Control	O
"	O
,	O
which	O
is	O
used	O
to	O
determine	O
access	O
to	O
change	O
file	B-Operating_System
metadata	O
such	O
as	O
protection	O
.	O
</s>
<s>
BYPASS	O
:	O
user	O
implicitly	O
has	O
RWED	O
access	O
to	O
all	O
files	O
,	O
regardless	O
of	O
file	B-Operating_System
protection	O
;	O
</s>
<s>
GRPPRV	O
:	O
user	O
may	O
access	O
files	O
based	O
on	O
System	O
protection	O
if	O
their	O
UIC	O
group	O
matches	O
the	O
file	B-Operating_System
's	O
group	O
.	O
</s>
<s>
ACLs	O
can	O
be	O
marked	O
as	O
inherited	O
,	O
where	O
a	O
directory	O
file	B-Operating_System
's	O
ACL	O
applies	O
to	O
all	O
files	O
underneath	O
it	O
.	O
</s>
<s>
would	O
allow	O
the	O
user	O
HTTP$SERVER	O
to	O
read	O
and	O
execute	O
the	O
file	B-Operating_System
.	O
</s>
<s>
A	O
logical	O
name	O
is	O
a	O
system	O
variable	O
which	O
may	O
reference	O
a	O
disk	O
,	O
directory	O
or	O
file	B-Operating_System
,	O
or	O
contain	O
other	O
program-specific	O
information	O
.	O
</s>
<s>
SYS$LOGIN	O
:	O
which	O
is	O
the	O
user	O
's	O
login	O
(	O
home	O
)	O
directory	O
(	O
or	O
directories	O
)	O
;	O
these	O
logicals	O
cannot	O
be	O
used	O
as	O
true	O
disk	O
names—SYS$LOGIN:[DIR]FILE	O
is	O
not	O
a	O
valid	O
file	B-Operating_System
specification	O
.	O
</s>
<s>
would	O
allow	O
HOME:[DIR]FILE	O
to	O
be	O
used	O
.	O
</s>
<s>
In	O
a	O
manner	O
similar	O
to	O
Unix	B-Application
,	O
VMS	B-Operating_System
defines	O
several	O
standard	B-Operating_System
input	I-Operating_System
and	I-Operating_System
output	I-Operating_System
channels	I-Operating_System
which	O
are	O
accessed	O
through	O
the	O
logical	O
names	O
SYS$INPUT	O
,	O
SYS$OUTPUT	O
,	O
SYS$ERROR	O
and	O
SYS$COMMAND	O
.	O
</s>
<s>
Logical	O
names	O
do	O
not	O
have	O
a	O
close	O
equivalent	O
in	O
POSIX	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
They	O
resemble	O
Unix	B-Application
environment	O
variables	O
,	O
except	O
they	O
are	O
expanded	O
by	O
the	O
file	B-Application
system	I-Application
,	O
instead	O
of	O
the	O
command	O
shell	O
or	O
application	O
program	O
.	O
</s>
<s>
They	O
must	O
be	O
defined	O
before	O
use	O
,	O
so	O
it	O
is	O
common	O
for	O
many	O
logical	O
names	O
to	O
be	O
defined	O
in	O
the	O
system	O
startup	O
command	O
file	B-Operating_System
,	O
as	O
well	O
as	O
user	O
login	O
command	O
files	O
.	O
</s>
<s>
In	O
VMS	B-Operating_System
,	O
logical	O
names	O
may	O
reference	O
other	O
logical	O
names	O
(	O
up	O
to	O
a	O
predefined	O
nesting	O
limit	O
of	O
10	O
)	O
,	O
and	O
may	O
contain	O
lists	O
of	O
names	O
to	O
search	O
for	O
an	O
existing	O
filename	B-Device
.	O
</s>
<s>
Used	O
in	O
a	O
batch	O
file	B-Operating_System
,	O
it	O
reads	O
batch	O
file	B-Operating_System
lines	O
not	O
preceded	O
with	O
a	O
$	O
symbol	O
,	O
or	O
specified	O
as	O
an	O
input	O
deck	O
using	O
the	O
DECK	O
command.SYS	O
$OUTPUT	O
standard	O
output	O
-	O
it	O
will	O
output	O
to	O
the	O
terminal	O
display	O
or	O
the	O
batch	O
log	O
file	B-Operating_System
depending	O
on	O
whether	O
the	O
process	O
is	O
interactive	O
or	O
not.SYS	O
$ERROR	O
standard	O
error	O
-	O
it	O
will	O
output	O
to	O
the	O
terminal	O
display	O
or	O
the	O
batch	O
error	O
log	O
file	B-Operating_System
depending	O
on	O
whether	O
the	O
process	O
is	O
interactive	O
or	O
not.SYS	O
$COMMAND	O
source	O
of	O
batch	O
file	B-Operating_System
commands	O
.	O
</s>
<s>
The	O
closest	O
non-DEC	O
operating	B-General_Concept
system	I-General_Concept
to	O
support	O
the	O
concept	O
of	O
logical	O
names	O
is	O
AmigaOS	B-Application
,	O
through	O
the	O
ASSIGN	O
command	O
.	O
</s>
<s>
AmigaOS	B-Application
's	O
disk	O
operating	B-General_Concept
system	I-General_Concept
,	O
AmigaDOS	B-Operating_System
,	O
which	O
is	O
a	O
port	O
of	O
TRIPOS	B-Operating_System
,	O
bears	O
some	O
resemblance	O
to	O
DEC	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
However	O
,	O
since	O
the	O
system	O
can	O
boot	O
from	O
any	O
attached	O
drive	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
creates	O
the	O
SYS	O
:	O
assignment	O
to	O
automatically	O
reference	O
the	O
boot	O
device	O
used	O
.	O
</s>
<s>
Record	B-Application
Management	I-Application
Services	I-Application
is	O
the	O
structured	O
I/O	B-General_Concept
layer	O
of	O
the	O
VMS	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
RMS	B-Application
provides	O
comprehensive	O
program	O
support	O
for	O
managing	O
structured	O
files	O
,	O
such	O
as	O
record-based	O
and	O
indexed	O
database	O
files	O
.	O
</s>
<s>
The	O
VMS	B-Operating_System
file	B-Application
system	I-Application
,	O
in	O
conjunction	O
with	O
RMS	B-Application
,	O
extends	O
files	O
access	O
past	O
simple	O
byte-streams	O
and	O
allows	O
OS-level	O
support	O
for	O
a	O
variety	O
of	O
rich	O
files	O
types	O
.	O
</s>
<s>
Each	O
file	B-Operating_System
in	O
the	O
VMS	B-Operating_System
file	B-Application
system	I-Application
may	O
be	O
thought	O
of	O
as	O
a	O
database	O
,	O
containing	O
a	O
series	O
of	O
records	O
,	O
each	O
of	O
which	O
has	O
one	O
of	O
more	O
individual	O
fields	B-Application
.	O
</s>
<s>
A	O
text	O
file	B-Operating_System
,	O
for	O
example	O
,	O
is	O
a	O
list	O
of	O
records	O
(	O
lines	O
)	O
separated	O
by	O
a	O
newline	O
character	O
.	O
</s>
<s>
RMS	B-Application
is	O
an	O
example	O
of	O
a	O
record-oriented	B-Application
filesystem	I-Application
.	O
</s>
<s>
There	O
are	O
four	O
record	O
formats	O
defined	O
by	O
RMS	B-Application
:	O
</s>
<s>
Fixed	O
length	O
-	O
all	O
records	O
in	O
the	O
file	B-Operating_System
have	O
the	O
same	O
length	O
.	O
</s>
<s>
Variable	O
length	O
-	O
records	O
vary	O
in	O
length	O
,	O
and	O
every	O
record	O
is	O
prefixed	O
by	O
a	O
count	O
byte	B-Application
giving	O
its	O
length	O
.	O
</s>
<s>
A	O
text	O
file	B-Operating_System
is	O
an	O
example	O
of	O
a	O
stream-format	O
file	B-Operating_System
using	O
line	O
feed	O
or	O
carriage	O
return	O
to	O
separate	O
records	O
.	O
</s>
<s>
Sequential	O
Access	O
-	O
starting	O
with	O
a	O
particular	O
records	O
,	O
subsequent	O
records	O
are	O
retrieved	O
in	O
order	O
until	O
the	O
end	O
of	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Relative	O
Record	O
Number	O
Access	O
-	O
records	O
are	O
retrieved	O
via	O
a	O
record	O
number	O
relative	O
to	O
the	O
beginning	O
of	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Record	O
File	B-Operating_System
Address	O
Access	O
-	O
records	O
are	O
retrieved	O
directly	O
by	O
their	O
location	O
in	O
the	O
file	B-Operating_System
(	O
RFA	O
,	O
or	O
Record	O
File	B-Operating_System
Address	O
)	O
.	O
</s>
<s>
Indexed	O
Access	O
-	O
records	O
are	O
retrieved	O
via	O
a	O
key	O
,	O
in	O
a	O
form	O
of	O
key-value	B-Application
mapping	I-Application
.	O
</s>
<s>
At	O
the	O
disk	O
level	O
,	O
ODS	O
represents	O
the	O
file	B-Application
system	I-Application
as	O
an	O
array	O
of	O
blocks	O
,	O
a	O
block	O
being	O
512	O
contiguous	O
bytes	B-Application
on	O
one	O
physical	O
disk	O
(	O
volume	O
)	O
.	O
</s>
<s>
A	O
file	B-Operating_System
on	O
the	O
disk	O
will	O
ideally	O
be	O
entirely	O
contiguous	O
,	O
i.e.	O
</s>
<s>
the	O
blocks	O
which	O
contain	O
the	O
file	B-Operating_System
will	O
be	O
sequential	O
,	O
but	O
disk	O
fragmentation	O
will	O
sometimes	O
require	O
the	O
file	B-Operating_System
to	O
be	O
located	O
in	O
discontiguous	O
clusters	O
in	O
which	O
case	O
the	O
fragments	O
are	O
called	O
extents	B-Application
.	O
</s>
<s>
Every	O
file	B-Operating_System
on	O
a	O
Files-11	B-Application
disk	O
(	O
or	O
volume	O
set	O
)	O
has	O
a	O
unique	O
file	B-Operating_System
identification	O
(	O
FID	O
)	O
,	O
composed	O
of	O
three	O
numbers	O
:	O
the	O
file	B-Operating_System
number	O
(	O
NUM	O
)	O
,	O
the	O
file	B-Operating_System
sequence	O
number	O
(	O
SEQ	O
)	O
,	O
and	O
the	O
relative	O
volume	O
number	O
(	O
RVN	O
)	O
.	O
</s>
<s>
The	O
NUM	O
indicates	O
where	O
in	O
the	O
INDEXF.SYS	O
file	B-Operating_System
(	O
see	O
below	O
)	O
the	O
metadata	O
for	O
the	O
file	B-Operating_System
is	O
located	O
;	O
the	O
SEQ	O
is	O
a	O
generation	O
number	O
which	O
incremented	O
when	O
the	O
file	B-Operating_System
is	O
deleted	O
and	O
another	O
file	B-Operating_System
is	O
created	O
reusing	O
the	O
same	O
INDEXF.SYS	O
entry	O
(	O
so	O
any	O
dangling	O
references	O
to	O
the	O
old	O
file	B-Operating_System
do	O
not	O
accidentally	O
point	O
to	O
the	O
new	O
one	O
)	O
;	O
and	O
the	O
RVN	O
indicates	O
the	O
volume	O
number	O
on	O
which	O
the	O
file	B-Operating_System
is	O
stored	O
when	O
using	O
a	O
volume	O
set	O
.	O
</s>
<s>
The	O
structural	O
support	O
of	O
an	O
ODS	O
volume	O
is	O
provided	O
by	O
a	O
directory	O
file	B-Operating_System
—	O
a	O
special	O
file	B-Operating_System
containing	O
a	O
list	O
of	O
file	B-Operating_System
names	O
,	O
file	B-Operating_System
version	O
numbers	O
and	O
their	O
associated	O
FIDs	O
,	O
similar	O
to	O
VSAM	O
catalogs	O
on	O
MVS	B-Application
.	O
</s>
<s>
At	O
the	O
root	O
of	O
the	O
directory	O
structure	O
is	O
the	O
master	O
file	B-Operating_System
directory	O
(	O
MFD	O
)	O
,	O
the	O
root	O
directory	O
which	O
contains	O
(	O
directly	O
or	O
indirectly	O
)	O
every	O
file	B-Operating_System
on	O
the	O
volume	O
.	O
</s>
<s>
This	O
diagram	O
shows	O
an	O
example	O
directory	O
containing	O
3	O
files	O
,	O
and	O
the	O
way	O
each	O
filename	B-Device
is	O
mapped	O
to	O
the	O
INDEXF.SYS	O
entry	O
(	O
each	O
INDEXF	O
entry	O
contains	O
more	O
information	O
;	O
only	O
the	O
first	O
few	O
items	O
are	O
shown	O
here	O
)	O
.	O
</s>
<s>
At	O
the	O
top	O
level	O
of	O
an	O
ODS	O
file	B-Application
system	I-Application
is	O
the	O
master	O
file	B-Operating_System
directory	O
(	O
MFD	O
)	O
,	O
which	O
contains	O
all	O
top-level	O
directory	O
files	O
(	O
including	O
itself	O
)	O
,	O
and	O
several	O
system	O
files	O
used	O
to	O
store	O
file	B-Application
system	I-Application
information	O
.	O
</s>
<s>
On	O
ODS-1	O
volumes	O
,	O
a	O
two-level	O
directory	O
structure	O
is	O
used	O
:	O
each	O
user	O
identification	O
code	O
(	O
UIC	O
)	O
has	O
an	O
associated	O
user	O
file	B-Operating_System
directory	O
(	O
UFD	O
)	O
,	O
of	O
the	O
form	O
 [ GROUP.USER ] 	O
.	O
</s>
<s>
On	O
ODS-2	O
and	O
later	O
volumes	O
,	O
the	O
layout	O
of	O
directories	O
under	O
the	O
MFD	O
is	O
free-form	O
,	O
subject	O
to	O
a	O
limit	O
on	O
the	O
nesting	O
of	O
directories	O
(	O
8	O
levels	O
on	O
ODS-2	O
and	O
unlimited	O
on	O
ODS-5	B-Application
)	O
.	O
</s>
<s>
Note	O
that	O
the	O
file	B-Application
system	I-Application
implementation	O
itself	O
does	O
not	O
refer	O
to	O
these	O
files	O
by	O
name	O
,	O
but	O
by	O
their	O
file	B-Operating_System
IDs	O
,	O
which	O
always	O
have	O
the	O
same	O
values	O
.	O
</s>
<s>
Thus	O
,	O
INDEXF.SYS	O
is	O
always	O
the	O
file	B-Operating_System
with	O
NUM	O
=	O
1	O
and	O
SEQ	O
=	O
1	O
.	O
</s>
<s>
The	O
index	O
file	B-Operating_System
contains	O
the	O
most	O
basic	O
information	O
about	O
a	O
Files-11	B-Application
volume	O
set	O
.	O
</s>
<s>
With	O
the	O
traditional	O
organization	O
,	O
block	O
1	O
is	O
the	O
boot	O
block	O
,	O
which	O
contains	O
the	O
location	O
of	O
the	O
primary	O
bootstrap	O
image	O
,	O
used	O
to	O
load	O
the	O
VMS	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
This	O
contains	O
the	O
volume	O
name	O
,	O
the	O
location	O
of	O
the	O
extents	B-Application
comprising	O
the	O
remainder	O
of	O
the	O
index	O
file	B-Operating_System
,	O
the	O
volume	O
owner	O
's	O
UIC	O
,	O
and	O
the	O
volume	O
protection	O
information	O
.	O
</s>
<s>
These	O
structures	O
are	O
not	O
included	O
in	O
INDEXF.SYS	O
,	O
and	O
the	O
blocks	O
of	O
the	O
INDEXF.SYS	O
file	B-Operating_System
are	O
unused	O
.	O
</s>
<s>
The	O
rest	O
of	O
the	O
index	O
file	B-Operating_System
is	O
composed	O
of	O
file	B-Operating_System
headers	O
,	O
which	O
describe	O
the	O
extents	B-Application
allocated	O
to	O
the	O
files	O
residing	O
on	O
the	O
volume	O
,	O
and	O
file	B-Operating_System
metadata	O
such	O
as	O
the	O
owner	O
UIC	O
,	O
ACLs	O
and	O
protection	O
information	O
.	O
</s>
<s>
Each	O
file	B-Operating_System
is	O
described	O
by	O
one	O
or	O
more	O
file	B-Operating_System
headers	O
—	O
more	O
than	O
one	O
can	O
be	O
required	O
when	O
a	O
file	B-Operating_System
has	O
a	O
large	O
number	O
of	O
extents	B-Application
.	O
</s>
<s>
The	O
file	B-Operating_System
header	O
is	O
a	O
fixed-length	O
block	O
,	O
but	O
contains	O
both	O
fixed	O
–	O
and	O
variable	O
–	O
length	O
sections	O
:	O
</s>
<s>
The	O
header	O
contains	O
the	O
NUM	O
and	O
SEQ	O
,	O
the	O
protection	O
(	O
security	O
)	O
information	O
,	O
and	O
the	O
location	O
of	O
the	O
rest	O
of	O
the	O
file	B-Operating_System
header	O
.	O
</s>
<s>
The	O
ident	O
section	O
contains	O
the	O
accounting	O
metadata	O
:	O
the	O
filename	B-Device
,	O
creation	O
and	O
modification	O
times	O
,	O
and	O
the	O
time	O
of	O
the	O
last	O
backup	B-Protocol
.	O
</s>
<s>
The	O
map	O
describes	O
which	O
physical	O
disk	O
blocks	O
(	O
extents	B-Application
)	O
map	O
to	O
each	O
virtual	O
block	O
of	O
the	O
file	B-Operating_System
.	O
</s>
<s>
The	O
access	O
control	O
list	O
contains	O
the	O
ACL	O
information	O
for	O
the	O
file	B-Operating_System
.	O
</s>
<s>
The	O
reserved	O
area	O
is	O
space	O
at	O
the	O
end	O
of	O
the	O
file	B-Operating_System
header	O
which	O
is	O
not	O
used	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
last	O
two	O
bytes	B-Application
of	O
the	O
header	O
are	O
a	O
checksum	B-Algorithm
of	O
the	O
previous	O
255	O
words	O
,	O
to	O
verify	O
the	O
validity	O
of	O
the	O
header	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
ACL	O
is	O
too	O
long	O
,	O
or	O
the	O
file	B-Operating_System
contains	O
too	O
many	O
extents	B-Application
,	O
there	O
will	O
not	O
be	O
enough	O
space	O
in	O
the	O
primary	O
header	O
to	O
store	O
them	O
.	O
</s>
<s>
The	O
file	B-Operating_System
header	O
begins	O
with	O
4	O
offsets	O
(	O
IDOFFSET	O
,	O
MPOFFSET	O
,	O
ACOFFSET	O
and	O
ROFFSET	O
)	O
.	O
</s>
<s>
Each	O
offset	O
is	O
the	O
number	O
of	O
16-bit	O
words	O
from	O
the	O
beginning	O
of	O
the	O
file	B-Operating_System
header	O
to	O
the	O
beginning	O
of	O
that	O
area	O
.	O
</s>
<s>
If	O
the	O
file	B-Operating_System
requires	O
multiple	O
headers	O
,	O
the	O
extension	O
segment	O
number	O
(	O
SEGNUM	O
)	O
contains	O
the	O
sequence	O
number	O
of	O
this	O
header	O
,	O
beginning	O
at	O
0	O
in	O
the	O
first	O
entry	O
in	O
INDEXF.SYS	O
.	O
</s>
<s>
STRUCLEV	O
contains	O
the	O
current	O
structure	O
level	O
(	O
in	O
the	O
high	O
byte	B-Application
)	O
and	O
version	O
(	O
in	O
the	O
low	O
byte	B-Application
)	O
of	O
the	O
file	B-Application
system	I-Application
;	O
ODS-2	O
being	O
structure	O
level	O
2	O
.	O
</s>
<s>
W_FID	O
(	O
containing	O
three	O
values	O
:	O
FID_NUM	O
,	O
FID_SEQ	O
and	O
FID_RVN	O
,	O
corresponding	O
to	O
the	O
file	B-Operating_System
,	O
sequence	O
,	O
and	O
relative	O
volume	O
number	O
)	O
contains	O
the	O
ID	O
of	O
this	O
file	B-Operating_System
;	O
EXT_FID	O
(	O
again	O
composed	O
of	O
three	O
values	O
)	O
holds	O
the	O
location	O
of	O
the	O
next	O
extension	O
header	O
,	O
if	O
any	O
.	O
</s>
<s>
FILECHAR	O
contains	O
several	O
flags	O
which	O
affect	O
how	O
the	O
file	B-Operating_System
is	O
handled	O
or	O
organised	O
:	O
</s>
<s>
NOBACKUP	O
causes	O
this	O
file	B-Operating_System
to	O
be	O
ignored	O
when	O
a	O
backup	B-Protocol
is	O
run	O
.	O
</s>
<s>
WRITEBACK	O
enables	O
cached	O
(	O
delayed	O
)	O
writes	O
to	O
the	O
file	B-Operating_System
.	O
</s>
<s>
READCHECK	O
causes	O
all	O
reads	O
of	O
the	O
file	B-Operating_System
to	O
be	O
done	O
twice	O
,	O
and	O
compared	O
to	O
ensure	O
data	O
integrity	O
.	O
</s>
<s>
CONTIGB	O
causes	O
the	O
OS	O
to	O
attempt	O
to	O
allocate	O
storage	O
for	O
the	O
file	B-Operating_System
in	O
as	O
contiguous	O
a	O
manner	O
as	O
possible	O
.	O
</s>
<s>
LOCKED	O
is	O
set	O
if	O
the	O
file	B-Operating_System
is	O
deaccess-locked	O
.	O
</s>
<s>
If	O
set	O
,	O
this	O
indicates	O
that	O
the	O
file	B-Operating_System
was	O
not	O
properly	O
closed	O
after	O
its	O
last	O
use	O
,	O
and	O
the	O
contents	O
may	O
be	O
inconsistent	O
.	O
</s>
<s>
CONTIG	O
indicates	O
that	O
the	O
file	B-Operating_System
is	O
stored	O
contiguously	O
on	O
disk	O
;	O
that	O
is	O
,	O
each	O
virtual	O
block	O
is	O
mapped	O
to	O
the	O
logical	O
(	O
physical	O
)	O
block	O
,	O
for	O
some	O
constant	O
.	O
</s>
<s>
BADACL	O
is	O
set	O
if	O
the	O
file	B-Operating_System
has	O
an	O
invalid	O
access	O
control	O
list	O
.	O
</s>
<s>
SPOOL	O
is	O
set	O
if	O
the	O
file	B-Operating_System
is	O
a	O
spool	O
file	B-Operating_System
,	O
such	O
as	O
an	O
intermediate	O
file	B-Operating_System
used	O
during	O
printing	O
.	O
</s>
<s>
DIRECTORY	O
is	O
set	O
if	O
the	O
file	B-Operating_System
is	O
a	O
directory	O
.	O
</s>
<s>
BADBLOCK	O
is	O
set	O
if	O
the	O
file	B-Operating_System
contains	O
bad	O
blocks	O
.	O
</s>
<s>
MARKDEL	O
is	O
set	O
if	O
the	O
file	B-Operating_System
has	O
been	O
marked	O
for	O
deletion	O
,	O
but	O
is	O
still	O
in	O
use	O
;	O
it	O
will	O
be	O
deleted	O
once	O
closed	O
by	O
the	O
last	O
user	O
.	O
</s>
<s>
NOCHARGE	O
,	O
if	O
set	O
,	O
causes	O
space	O
used	O
by	O
the	O
file	B-Operating_System
to	O
not	O
be	O
taken	O
from	O
the	O
owner	O
's	O
storage	O
quota	O
.	O
</s>
<s>
ERASE	O
causes	O
the	O
file	B-Operating_System
's	O
contents	O
to	O
be	O
overwritten	O
when	O
it	O
is	O
deleted	O
.	O
</s>
<s>
ACCMODE	O
describes	O
the	O
privilege	O
level	O
at	O
which	O
a	O
process	O
must	O
be	O
running	O
in	O
order	O
to	O
access	O
the	O
file	B-Operating_System
.	O
</s>
<s>
VMS	B-Operating_System
defines	O
four	O
privilege	O
levels	O
:	O
user	O
,	O
supervisor	O
,	O
exec	O
,	O
and	O
kernel	O
.	O
</s>
<s>
FILEPROT	O
contains	O
the	O
discretionary	O
access	O
control	O
information	O
for	O
the	O
file	B-Operating_System
.	O
</s>
<s>
If	O
the	O
file	B-Operating_System
header	O
is	O
an	O
extension	O
header	O
,	O
BACKLINK	O
contains	O
the	O
file	B-Operating_System
ID	O
of	O
the	O
primary	O
header	O
;	O
otherwise	O
,	O
it	O
contains	O
the	O
file	B-Operating_System
ID	O
of	O
the	O
directory	O
file	B-Operating_System
containing	O
the	O
primary	O
entry	O
for	O
the	O
file	B-Operating_System
.	O
</s>
<s>
The	O
bitmap	O
file	B-Operating_System
is	O
responsible	O
for	O
storing	O
information	O
regarding	O
used	O
and	O
available	O
space	O
on	O
a	O
volume	O
.	O
</s>
<s>
In	O
early	O
versions	O
of	O
VMS	B-Operating_System
the	O
cluster	O
comprised	O
3	O
blocks	O
but	O
as	O
disk	O
sizes	O
have	O
increased	O
,	O
so	O
has	O
the	O
cluster	O
size	O
.	O
</s>
<s>
The	O
bad	O
block	O
file	B-Operating_System
contains	O
all	O
of	O
the	O
known	O
bad	O
blocks	O
on	O
the	O
physical	O
volume	O
.	O
</s>
<s>
This	O
file	B-Operating_System
was	O
used	O
more	O
in	O
the	O
early	O
days	O
when	O
disks	O
were	O
typically	O
manufactured	O
with	O
more	O
bad	O
patches	O
on	O
the	O
surface	O
.	O
</s>
<s>
When	O
a	O
file	B-Operating_System
on	O
a	O
multi-volume	O
set	O
crosses	O
the	O
boundary	O
of	O
two	O
constituent	O
volumes	O
,	O
the	O
continuation	O
file	B-Operating_System
is	O
used	O
as	O
its	O
extension	O
header	O
and	O
describes	O
the	O
volume	O
where	O
the	O
rest	O
of	O
the	O
file	B-Operating_System
can	O
be	O
found	O
.	O
</s>
<s>
The	O
quota	O
file	B-Operating_System
contains	O
information	O
of	O
each	O
UIC	O
's	O
disk	O
space	O
usage	O
on	O
a	O
volume	O
.	O
</s>
<s>
This	O
file	B-Operating_System
overlays	O
and	O
protects	O
the	O
MBR	O
(	O
Master	O
Boot	O
Record	O
)	O
and	O
GPT	O
(	O
GUID	O
Partitioning	O
Table	O
)	O
disk	B-Device
structures	I-Device
utilized	O
for	O
and	O
by	O
the	O
Extensible	O
Firmware	O
Interface-compliant	O
firmware	O
.	O
</s>
<s>
This	O
file	B-Operating_System
is	O
created	O
by	O
default	O
during	O
OpenVMS	B-Operating_System
I64	O
disk	O
initialization	O
,	O
and	O
is	O
optionally	O
created	O
(	O
with	O
INITIALIZE/GPT	O
)	O
on	O
OpenVMS	B-Operating_System
Alpha	B-Device
.	O
</s>
