<s>
VSEn	O
(	O
Virtual	O
Storage	O
Extended	O
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
for	O
IBM	B-Device
mainframe	I-Device
computers	O
,	O
the	O
latest	O
one	O
in	O
the	B-Application
DOS/360	I-Application
lineage	I-Application
,	O
which	O
originated	O
in	O
1965	O
.	O
</s>
<s>
DOS/VSE	B-Application
was	O
introduced	O
in	O
1979	O
as	O
a	O
successor	O
to	O
DOS/VS	O
;	O
in	O
turn	O
,	O
DOS/VSE	B-Application
was	O
succeeded	O
by	O
VSE/SP	O
version	O
1	O
in	O
1983	O
,	O
and	O
VSE/SP	O
version	O
2	O
in	O
1985	O
.	O
</s>
<s>
In	O
February	O
2005	O
,	O
IBM	O
announced	O
z/VSE	B-Application
as	O
successor	O
to	O
VSE/ESA	O
2.7	O
,	O
which	O
was	O
named	O
to	O
reflect	O
the	O
new	O
System	B-Device
z	I-Device
branding	O
for	O
IBM	O
's	O
mainframe	O
product	O
line	O
.	O
</s>
<s>
In	O
June	O
2021	O
,	O
21st	O
Century	O
Software	O
Inc	O
announced	O
that	O
it	O
had	O
licensed	O
the	O
z/VSE	B-Application
source	O
code	O
from	O
IBM	O
with	O
the	O
intention	O
of	O
developing	O
new	O
versions	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
As	O
part	O
of	O
this	O
transfer	O
,	O
z/VSE	B-Application
was	O
renamed	O
to	O
VSEn	O
.	O
</s>
<s>
It	O
is	O
less	O
common	O
than	O
z/OS	B-Application
and	O
is	O
mostly	O
used	O
on	O
smaller	O
machines	O
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
there	O
was	O
a	O
widespread	O
perception	O
among	O
VSE	B-Application
customers	O
that	O
IBM	O
was	O
planning	O
to	O
discontinue	O
VSE	B-Application
and	O
migrate	O
its	O
customers	O
to	O
MVS	O
instead	O
,	O
although	O
IBM	O
relented	O
and	O
agreed	O
to	O
continue	O
to	O
produce	O
new	O
versions	O
of	O
VSE	B-Application
.	O
</s>
<s>
IBM	O
released	O
z/VSE	B-Application
Version	O
4	O
,	O
which	O
requires	O
64-bit	B-Device
z/Architecture	B-Device
hardware	O
and	O
can	O
use	O
64-bit	B-Device
real	O
mode	O
addressing	O
,	O
in	O
2007	O
.	O
</s>
<s>
With	O
z/VSE	B-Application
5.1	O
(	O
available	O
since	O
2011	O
)	O
z/VSE	B-Application
introduced	O
64-bit	B-Device
virtual	O
addressing	O
and	O
memory	O
objects	O
(	O
chunks	O
of	O
virtual	O
storage	O
)	O
,	O
that	O
are	O
allocated	O
above	O
2GB	O
.	O
</s>
<s>
A	O
Job	B-Application
Control	I-Application
Language	I-Application
(	O
JCL	O
)	O
that	O
continues	O
in	O
the	O
positional-parameter	O
orientation	O
of	O
earlier	O
DOS	O
systems	O
is	O
VSEn	O
's	O
batch	B-General_Concept
processing	I-General_Concept
primary	O
user	O
interface	O
.	O
</s>
<s>
There	O
is	O
also	O
another	O
,	O
special	O
interface	O
for	O
system	B-Device
console	I-Device
operators	O
.	O
</s>
<s>
VSEn	O
,	O
like	O
z/OS	B-Application
systems	O
,	O
had	O
traditionally	O
provided	O
3270	B-Operating_System
terminal	I-Operating_System
user	O
interfaces	O
.	O
</s>
<s>
However	O
,	O
most	O
VSEn	O
installations	O
have	O
at	O
least	O
begun	O
to	O
add	O
Web	B-Application
browser	I-Application
access	O
to	O
VSEn	O
applications	O
.	O
</s>
<s>
VSEn	O
's	O
TCP/IP	B-Protocol
is	O
a	O
separately	O
priced	O
option	O
for	O
historic	O
reasons	O
,	O
and	O
is	O
available	O
in	O
two	O
different	O
versions	O
from	O
two	O
vendors	O
.	O
</s>
<s>
Both	O
vendors	O
provide	O
a	O
full	O
function	O
TCP/IP	B-Protocol
stack	I-Protocol
with	O
applications	O
,	O
such	O
as	O
telnet	O
and	O
FTP	B-Protocol
.	O
</s>
<s>
One	O
TCP/IP	B-Protocol
stack	I-Protocol
provides	O
IPv4	O
communication	O
only	O
,	O
the	O
other	O
IPv4	O
and	O
IPv6	O
communication	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
commercially	O
available	O
TCP/IP	B-Protocol
stacks	I-Protocol
for	O
VSEn	O
,	O
IBM	O
also	O
provides	O
the	O
Linux	O
Fastpath	O
method	O
which	O
uses	O
IUCV	B-Application
socket	O
or	O
Hipersockets	B-Device
connections	O
to	O
communicate	O
with	O
a	O
Linux	O
guest	O
,	O
also	O
running	O
on	O
the	O
mainframe	O
.	O
</s>
<s>
Using	O
this	O
method	O
the	O
VSEn	O
system	O
is	O
able	O
to	O
fully	O
exploit	O
the	O
native	O
Linux	O
TCP/IP	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
IBM	O
recommends	O
that	O
z/VSE	B-Application
customers	O
run	O
Linux	B-Application
on	I-Application
IBM	I-Application
Z	I-Application
alongside	O
,	O
on	O
the	O
same	O
physical	O
system	O
,	O
to	O
provide	O
another	O
64-bit	B-Device
application	O
environment	O
that	O
can	O
access	O
and	O
extend	O
z/VSE	B-Application
applications	O
and	O
data	O
via	O
Hipersockets	B-Device
using	O
a	O
wide	O
variety	O
of	O
middleware	B-General_Concept
.	O
</s>
<s>
CICS	B-Application
,	O
one	O
of	O
the	O
most	O
popular	O
enterprise	O
transaction	B-Application
processing	I-Application
systems	I-Application
,	O
is	O
extremely	O
popular	O
among	O
VSEn	O
users	O
and	O
now	O
implements	O
recent	O
innovations	O
such	O
as	O
Web	O
services	O
.	O
</s>
<s>
Db2	B-Application
is	O
also	O
available	O
and	O
popular	O
.	O
</s>
<s>
Fibre	B-Architecture
Channel	I-Architecture
access	O
to	O
SCSI	O
storage	O
devices	O
was	O
initially	O
available	O
on	O
z/VSE	B-Application
3.1	O
on	O
a	O
limited	O
basis	O
(	O
including	O
on	O
IBM	O
's	O
Enterprise	B-Device
Storage	I-Device
Server	I-Device
(	O
ESS	O
)	O
,	O
IBM	B-Device
System	I-Device
Storage	I-Device
DS8000	I-Device
,	O
DS6000	O
series	O
)	O
,	O
but	O
the	O
limitations	O
disappeared	O
with	O
4.2	O
(	O
thus	O
including	O
IBM	B-Device
Storwize	I-Device
V7000	I-Device
,	O
V5000	O
,	O
V3700	O
and	O
V9000	O
)	O
.	O
</s>
