<s>
z/OS	B-Application
UNIX	B-Operating_System
System	I-Operating_System
Services	I-Operating_System
(	O
z/OS	B-Application
UNIX	B-Application
,	O
or	O
informally	O
USS	O
)	O
is	O
a	O
base	O
element	O
of	O
z/OS	B-Application
.	O
</s>
<s>
z/OS	B-Application
UNIX	B-Application
is	O
a	O
certified	O
UNIX	B-Application
operating	I-Application
system	I-Application
implementation	O
(	O
XPG4	O
UNIX	B-Application
95	O
)	O
optimized	O
for	O
mainframe	O
architecture	O
.	O
</s>
<s>
It	O
is	O
the	O
first	O
UNIX	B-Application
95	O
to	O
not	O
be	O
derived	O
from	O
the	O
AT&T	O
source	O
code	O
.	O
</s>
<s>
Through	O
integration	O
with	O
the	O
rest	O
of	O
z/OS	B-Application
,	O
additional	O
Time	B-Application
Sharing	I-Application
Option	I-Application
(	O
TSO	O
)	O
commands	O
are	O
available	O
alongside	O
the	O
usual	O
UNIX	B-Application
services	O
,	O
making	O
it	O
possible	O
to	O
process	O
UNIX	B-Application
files	O
using	O
ISPF	B-Operating_System
.	O
</s>
<s>
Extensions	O
in	O
JCL	B-Application
make	O
it	O
possible	O
to	O
use	O
these	O
files	O
in	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
UNIX	B-Operating_System
System	I-Operating_System
Services	I-Operating_System
allows	O
UNIX	B-Application
applications	O
from	O
other	O
platforms	O
to	O
run	O
on	O
IBM	B-Device
System	I-Device
z	I-Device
mainframes	O
running	O
z/OS	B-Application
.	O
</s>
<s>
In	O
many	O
cases	O
only	O
a	O
recompile	O
is	O
necessary	O
,	O
although	O
additional	O
effort	O
may	O
be	O
advisable	O
for	O
z/OS	B-Application
integration	O
(	O
such	O
as	O
SMP/E	B-Application
installation	O
support	O
)	O
.	O
</s>
<s>
While	O
z/OS	B-Application
UNIX	B-Application
supports	O
ASCII	O
and	O
Unicode	O
,	O
and	O
there	O
's	O
no	O
technical	O
requirement	O
to	O
modify	O
ASCII	O
and	O
Unicode	O
UNIX	B-Application
applications	O
,	O
many	O
z/OS	B-Application
users	O
often	O
prefer	O
EBCDIC	B-Language
support	O
in	O
their	O
applications	O
including	O
those	O
running	O
in	O
z/OS	B-Application
UNIX	B-Application
.	O
</s>
<s>
Consequently	O
,	O
z/OS	B-Application
UNIX	B-Application
provides	O
application	O
and	O
administrator	O
services	O
for	O
converting	O
to/from	O
EBCDIC	B-Language
.	O
</s>
<s>
Programs	O
running	O
under	O
z/OS	B-Application
UNIX	B-Application
have	O
full	O
,	O
secure	O
access	O
to	O
the	O
other	O
internal	O
functions	O
of	O
z/OS	B-Application
.	O
</s>
<s>
Database	O
access	O
(	O
Db2	B-Application
via	O
Call	O
Attach	O
)	O
is	O
one	O
example	O
of	O
how	O
z/OS	B-Application
UNIX	B-Application
can	O
access	O
services	O
found	O
elsewhere	O
in	O
z/OS	B-Application
.	O
</s>
<s>
Naturally	O
such	O
programs	O
cannot	O
be	O
ported	O
to	O
non-mainframe	O
platforms	O
without	O
rewriting	O
if	O
they	O
use	O
these	O
z/OS	B-Application
-specific	O
services	O
.	O
</s>
<s>
Conversely	O
,	O
if	O
a	O
program	O
adheres	O
to	O
UNIX	B-Application
standards	O
such	O
as	O
POSIX	O
and	O
ANSI	O
C	O
,	O
it	O
will	O
be	O
easier	O
to	O
move	O
it	O
between	O
different	O
UNIX	B-Application
operating	I-Application
systems	I-Application
including	O
z/OS	B-Application
UNIX	B-Application
.	O
</s>
<s>
The	O
file	O
systems	O
for	O
z/OS	B-Application
UNIX	B-Application
(	O
the	O
older	O
HFS	B-Application
and	O
the	O
now	O
preferred	O
zFS	B-Application
)	O
,	O
which	O
support	O
UNIX-style	O
long	O
filenames	O
,	O
appear	O
as	O
special	O
VSAM	O
datasets	O
to	O
the	O
rest	O
of	O
z/OS	B-Application
.	O
</s>
<s>
Numerous	O
core	O
z/OS	B-Application
subsystems	O
and	O
applications	O
rely	O
on	O
UNIX	B-Operating_System
System	I-Operating_System
Services	I-Operating_System
,	O
including	O
the	O
z/OS	B-Application
Management	O
Facility	O
,	O
XML	O
parsing	O
and	O
generation	O
services	O
,	O
OpenSSH	B-Language
,	O
the	O
IBM	O
HTTP	O
Server	O
for	O
z/OS	B-Application
,	O
the	O
z/OS	B-Application
SDK	O
for	O
Java	B-Language
,	O
and	O
some	O
z/OS	B-Application
PKI	O
services	O
as	O
examples	O
.	O
</s>
<s>
z/OS	B-Application
UNIX	B-Application
also	O
provides	O
a	O
shell	B-Operating_System
environment	O
,	O
OMVS	O
.	O
</s>
<s>
z/OS	B-Application
UNIX	B-Application
's	O
predecessor	O
was	O
an	O
operating	B-General_Concept
system	I-General_Concept
component	O
called	O
OpenEdition	B-Operating_System
MVS	I-Operating_System
,	O
first	O
implemented	O
in	O
MVS/ESA	O
4.3	O
and	O
enhanced	O
in	O
MVS/ESA	O
5.1	O
.	O
</s>
<s>
OpenEdition	B-Operating_System
MVS	I-Operating_System
only	O
supported	O
the	O
POSIX	O
standards	O
.	O
</s>
<s>
IBM	O
continues	O
to	O
enhance	O
UNIX	B-Operating_System
System	I-Operating_System
Services	I-Operating_System
.	O
</s>
<s>
Typically	O
every	O
release	O
of	O
z/OS	B-Application
includes	O
enhancements	O
to	O
z/OS	B-Application
UNIX	B-Application
.	O
</s>
