<s>
OS/390	B-Application
is	O
an	O
IBM	O
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
System/390	B-Device
IBM	B-Device
mainframe	I-Device
computers	I-Device
.	O
</s>
<s>
OS/390	B-Application
was	O
introduced	O
in	O
late	O
1995	O
in	O
an	O
effort	O
to	O
simplify	O
the	O
packaging	O
and	O
ordering	O
for	O
the	O
key	O
,	O
entitled	O
elements	O
needed	O
to	O
complete	O
a	O
fully	O
functional	O
MVS	B-Application
operating	I-Application
system	I-Application
package	O
.	O
</s>
<s>
An	O
additional	O
benefit	O
of	O
the	O
OS/390	B-Application
packaging	O
concept	O
was	O
to	O
improve	O
reliability	B-General_Concept
,	I-General_Concept
availability	I-General_Concept
and	I-General_Concept
serviceability	I-General_Concept
(	O
RAS	O
)	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
the	O
number	O
of	O
different	O
combinations	O
of	O
elements	O
that	O
a	O
customer	O
could	O
order	O
and	O
run	O
was	O
drastically	O
reduced	O
.	O
</s>
<s>
This	O
reduced	O
the	O
overall	O
time	O
required	O
for	O
customers	O
to	O
test	O
and	O
deploy	O
the	O
operating	B-General_Concept
system	I-General_Concept
in	O
their	O
environments	O
,	O
as	O
well	O
as	O
reducing	O
the	O
number	O
of	O
customer-reported	O
problems	O
(	O
PMRs	O
)	O
,	O
errors	O
(	O
APARs	B-Application
)	O
and	O
fixes	O
(	O
PTFs	B-Application
)	O
arising	O
from	O
the	O
variances	O
in	O
element	O
levels	O
.	O
</s>
<s>
In	O
December	O
2001	O
IBM	O
extended	O
OS/390	B-Application
to	O
include	O
support	O
for	O
64-bit	O
zSeries	O
processors	O
and	O
added	O
various	O
other	O
improvements	O
,	O
and	O
the	O
result	O
is	O
now	O
named	O
z/OS	B-Application
.	O
</s>
<s>
IBM	O
ended	O
support	O
for	O
the	O
older	O
OS/390	B-Application
-branded	O
versions	O
in	O
late	O
2004	O
.	O
</s>
