<s>
IBM	B-Device
mainframes	I-Device
are	O
large	O
computer	O
systems	O
produced	O
by	O
IBM	O
since	O
1952	O
.	O
</s>
<s>
Current	O
mainframe	B-Architecture
computers	I-Architecture
in	O
IBM	O
's	O
line	O
of	O
business	O
computers	O
are	O
developments	O
of	O
the	O
basic	O
design	O
of	O
the	O
IBM	B-Application
System/360	I-Application
.	O
</s>
<s>
From	O
1952	O
into	O
the	O
late	O
1960s	O
,	O
IBM	O
manufactured	O
and	O
marketed	O
several	O
large	O
computer	O
models	O
,	O
known	O
as	O
the	O
IBM	B-Device
700/7000	I-Device
series	I-Device
.	O
</s>
<s>
The	O
first-generation	O
700s	O
were	O
based	O
on	O
vacuum	O
tubes	O
,	O
while	O
the	O
later	O
,	O
second-generation	O
7000s	O
used	O
transistors	B-Application
.	O
</s>
<s>
These	O
machines	O
established	O
IBM	O
's	O
dominance	O
in	O
electronic	B-Application
data	I-Application
processing	I-Application
(	O
"	O
EDP	O
"	O
)	O
.	O
</s>
<s>
The	O
two	O
categories	O
,	O
scientific	O
and	O
commercial	O
,	O
generally	O
used	O
common	O
peripherals	O
but	O
had	O
completely	O
different	O
instruction	B-General_Concept
sets	I-General_Concept
,	O
and	O
there	O
were	O
incompatibilities	O
even	O
within	O
each	O
category	O
.	O
</s>
<s>
Later	O
,	O
IBM	O
provided	O
compilers	B-Language
for	O
the	O
newly	O
developed	O
higher-level	O
programming	O
languages	O
Fortran	B-Application
,	O
COMTRAN	B-Language
and	O
later	O
COBOL	B-Application
.	O
</s>
<s>
The	O
first	O
operating	B-General_Concept
systems	I-General_Concept
for	O
IBM	O
computers	O
were	O
written	O
by	O
IBM	O
customers	O
who	O
did	O
not	O
wish	O
to	O
have	O
their	O
very	O
expensive	O
machines	O
( $2M	O
USD	O
in	O
the	O
mid-1950s	O
)	O
sitting	O
idle	O
while	O
operators	O
set	O
up	O
jobs	O
manually	O
.	O
</s>
<s>
These	O
first	O
operating	B-General_Concept
systems	I-General_Concept
were	O
essentially	O
scheduled	O
work	O
queues	O
.	O
</s>
<s>
It	O
is	O
generally	O
thought	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
used	O
for	O
real	O
work	O
was	O
GM-NAA	B-Application
I/O	I-Application
,	O
produced	O
by	O
General	O
Motors	O
 '	O
Research	O
division	O
in	O
1956	O
.	O
</s>
<s>
IBM	O
enhanced	O
one	O
of	O
GM-NAA	B-Application
I/O	I-Application
'	O
s	O
successors	O
,	O
the	O
SHARE	B-Application
Operating	I-Application
System	I-Application
,	O
and	O
provided	O
it	O
to	O
customers	O
under	O
the	O
name	O
IBSYS	B-Operating_System
.	O
</s>
<s>
As	O
software	O
became	O
more	O
complex	O
and	O
important	O
,	O
the	O
cost	O
of	O
supporting	O
it	O
on	O
so	O
many	O
different	O
designs	O
became	O
burdensome	O
,	O
and	O
this	O
was	O
one	O
of	O
the	O
factors	O
which	O
led	O
IBM	O
to	O
develop	O
System/360	B-Application
and	O
its	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	O
second	O
generation	O
(	O
transistor-based	O
)	O
products	O
were	O
a	O
mainstay	O
of	O
IBM	O
's	O
business	O
and	O
IBM	O
continued	O
to	O
make	O
them	O
for	O
several	O
years	O
after	O
the	O
introduction	O
of	O
the	O
System/360	B-Application
.	O
</s>
<s>
(	O
Some	O
IBM	B-Device
7094s	I-Device
remained	O
in	O
service	O
into	O
the	O
1980s	O
.	O
)	O
</s>
<s>
Prior	O
to	O
System/360	B-Application
,	O
IBM	O
also	O
sold	O
computers	O
smaller	O
in	O
scale	O
that	O
were	O
not	O
considered	O
mainframes	B-Architecture
,	O
though	O
they	O
were	O
still	O
bulky	O
and	O
expensive	O
by	O
modern	O
standards	O
.	O
</s>
<s>
IBM	O
had	O
difficulty	O
getting	O
customers	O
to	O
upgrade	O
from	O
the	O
smaller	O
machines	O
to	O
the	O
mainframes	B-Architecture
because	O
so	O
much	O
software	O
had	O
to	O
be	O
rewritten	O
.	O
</s>
<s>
The	O
7010	O
was	O
introduced	O
in	O
1962	O
as	O
a	O
mainframe-sized	O
1410	O
.	O
</s>
<s>
A	O
desk-size	O
machine	O
with	O
a	O
different	O
instruction	B-General_Concept
set	I-General_Concept
,	O
the	O
IBM	B-Device
1130	I-Device
,	O
was	O
released	O
concurrently	O
with	O
the	O
System/360	B-Application
to	O
address	O
the	O
niche	O
occupied	O
by	O
the	O
1620	O
.	O
</s>
<s>
It	O
used	O
the	O
same	O
EBCDIC	B-Language
character	O
encoding	O
as	O
the	O
360	O
and	O
was	O
mostly	O
programmed	O
in	O
Fortran	B-Application
,	O
which	O
was	O
relatively	O
easy	O
to	O
adapt	O
to	O
larger	O
machines	O
when	O
necessary	O
.	O
</s>
<s>
IBM	O
also	O
introduced	O
smaller	O
machines	O
after	O
S/360	B-Application
.	O
</s>
<s>
Midrange	B-Device
computer	I-Device
is	O
a	O
designation	O
used	O
by	O
IBM	O
for	O
a	O
class	O
of	O
computer	O
systems	O
which	O
fall	O
in	O
between	O
mainframes	B-Architecture
and	O
microcomputers	O
.	O
</s>
<s>
IBM	O
announced	O
the	O
System/360	B-Application
(	O
S/360	B-Application
)	O
line	O
of	O
mainframes	B-Architecture
in	O
April	O
1964	O
.	O
</s>
<s>
The	O
System/360	B-Application
was	O
a	O
single	O
series	O
of	O
compatible	O
models	O
for	O
both	O
commercial	O
and	O
scientific	O
use	O
.	O
</s>
<s>
System/360	B-Application
incorporated	O
features	O
which	O
had	O
previously	O
been	O
present	O
on	O
only	O
either	O
the	O
commercial	O
line	O
(	O
such	O
as	O
decimal	O
arithmetic	O
and	O
byte	O
addressing	O
)	O
or	O
the	O
engineering	O
and	O
scientific	O
line	O
(	O
such	O
as	O
floating-point	B-Algorithm
arithmetic	I-Algorithm
)	O
.	O
</s>
<s>
Some	O
of	O
the	O
arithmetic	O
units	O
and	O
addressing	O
features	O
were	O
optional	O
on	O
some	O
models	O
of	O
the	O
System/360	B-Application
.	O
</s>
<s>
The	O
System/360	B-Application
was	O
also	O
the	O
first	O
computer	O
in	O
wide	O
use	O
to	O
include	O
dedicated	O
hardware	O
provisions	O
for	O
the	O
use	O
of	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Hardware	O
memory	O
protection	O
was	O
provided	O
to	O
protect	O
the	O
operating	B-General_Concept
system	I-General_Concept
from	O
the	O
user	O
programs	O
(	O
tasks	O
)	O
and	O
user	O
tasks	O
from	O
each	O
other	O
.	O
</s>
<s>
The	O
new	O
machine	O
also	O
had	O
a	O
larger	O
address	B-General_Concept
space	I-General_Concept
than	O
the	O
older	O
mainframes	B-Architecture
,	O
24	O
bits	O
addressing	O
8-bit	O
bytes	O
vs.	O
a	O
typical	O
18	O
bits	O
addressing	O
36-bit	O
words	O
.	O
</s>
<s>
The	O
smaller	O
models	O
in	O
the	O
System/360	B-Application
line	O
(	O
e.g.	O
</s>
<s>
To	O
smooth	O
the	O
transition	O
from	O
the	O
second	O
generation	O
to	O
the	O
new	O
line	O
,	O
IBM	O
used	O
the	O
360	O
's	O
microprogramming	B-Device
capability	O
to	O
emulate	O
the	O
more	O
popular	O
older	O
models	O
.	O
</s>
<s>
Many	O
customers	O
kept	O
using	O
their	O
old	O
software	O
and	O
one	O
of	O
the	O
features	O
of	O
the	O
later	O
System/370	B-Device
was	O
the	O
ability	O
to	O
switch	O
to	O
emulation	O
mode	O
and	O
back	O
under	O
operating	B-General_Concept
system	I-General_Concept
control	O
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
for	O
the	O
System/360	B-Application
family	O
included	O
OS/360	B-Application
(	O
with	O
PCP	O
,	O
MFT	O
,	O
and	O
MVT	O
)	O
,	O
BOS/360	B-Application
,	O
TOS/360	B-Application
,	O
and	O
DOS/360	O
.	O
</s>
<s>
The	O
System/360	B-Application
later	O
evolved	O
into	O
the	O
System/370	B-Device
,	O
the	O
System/390	B-Device
,	O
and	O
the	O
64-bit	B-Device
zSeries	B-Device
,	I-Device
System	I-Device
z	I-Device
,	I-Device
and	I-Device
zEnterprise	I-Device
machines	O
.	O
</s>
<s>
System/370	B-Device
introduced	O
virtual	B-Architecture
memory	I-Architecture
capabilities	O
in	O
all	O
models	O
other	O
than	O
the	O
very	O
first	O
System/370	B-Device
models	O
;	O
the	O
OS/VS1	B-Application
variant	O
of	O
OS/360	B-Application
MFT	O
,	O
the	O
OS/VS2	B-Application
(	O
SVS	O
)	O
variant	O
of	O
OS/360	B-Application
MVT	O
,	O
and	O
the	O
DOS/VS	O
variant	O
of	O
DOS/360	O
were	O
introduced	O
to	O
use	O
the	O
virtual	B-Architecture
memory	I-Architecture
capabilities	O
,	O
followed	O
by	O
MVS	B-Application
,	O
which	O
,	O
unlike	O
the	O
earlier	O
virtual-memory	O
operating	B-General_Concept
systems	I-General_Concept
,	O
ran	O
separate	O
programs	O
in	O
separate	O
address	B-General_Concept
spaces	I-General_Concept
,	O
rather	O
than	O
running	O
all	O
programs	O
in	O
a	O
single	O
virtual	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
virtual	B-Architecture
memory	I-Architecture
capabilities	O
also	O
allowed	O
the	O
system	O
to	O
support	O
virtual	B-Architecture
machines	I-Architecture
;	O
the	O
VM/370	B-Application
hypervisor	B-Operating_System
would	O
run	O
one	O
or	O
more	O
virtual	B-Architecture
machines	I-Architecture
running	O
either	O
standard	O
System/360	B-Application
or	O
System/370	B-Device
operating	B-General_Concept
systems	I-General_Concept
or	O
the	O
single-user	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
.	O
</s>
<s>
A	O
time-sharing	B-General_Concept
VM	B-Application
system	O
could	O
run	O
multiple	O
virtual	B-Architecture
machines	I-Architecture
,	O
one	O
per	O
user	O
,	O
with	O
each	O
virtual	B-Architecture
machine	I-Architecture
running	O
an	O
instance	O
of	O
CMS	O
.	O
</s>
<s>
The	O
IBM	B-Device
Z	I-Device
family	O
,	O
introduced	O
in	O
2000	O
with	O
the	O
z900	O
,	O
supports	O
z/Architecture	B-Device
,	O
which	O
extends	O
the	O
architecture	O
used	O
by	O
the	O
System/390	B-Device
mainframes	B-Architecture
to	O
64	B-Device
bits	I-Device
.	O
</s>
<s>
The	O
different	O
processors	O
on	O
current	O
IBM	B-Device
mainframes	I-Device
are	O
:	O
</s>
<s>
These	O
are	O
essentially	O
identical	O
,	O
but	O
distinguished	O
for	O
software	O
cost	O
control	O
:	O
all	O
but	O
CP	O
are	O
slightly	O
restricted	O
such	O
they	O
cannot	O
be	O
used	O
to	O
run	O
arbitrary	O
operating	B-General_Concept
systems	I-General_Concept
,	O
and	O
thus	O
do	O
not	O
count	O
in	O
software	O
licensing	O
costs	O
(	O
which	O
are	O
typically	O
based	O
on	O
the	O
number	O
of	O
CPs	O
)	O
.	O
</s>
<s>
There	O
are	O
other	O
supporting	O
processors	O
typically	O
installed	O
inside	O
mainframes	B-Architecture
such	O
as	O
cryptographic	O
accelerators	O
(	O
CryptoExpress	O
)	O
,	O
the	O
OSA-Express	O
networking	O
processor	O
,	O
and	O
FICON	B-Architecture
Express	O
disk	B-Device
I/O	B-Device
processors	I-Device
.	O
</s>
<s>
Software	O
to	O
allow	O
users	O
to	O
run	O
"	O
traditional	O
"	O
workloads	O
on	O
zIIPs	B-Device
and	O
zAAPs	B-Language
was	O
briefly	O
marketed	O
by	O
Neon	O
Enterprise	O
Software	O
as	O
"	O
zPrime	O
"	O
but	O
was	O
withdrawn	O
from	O
the	O
market	O
in	O
2011	O
after	O
a	O
lawsuit	O
by	O
IBM	O
.	O
</s>
<s>
The	O
primary	O
operating	B-General_Concept
systems	I-General_Concept
in	O
use	O
on	O
current	O
IBM	B-Device
mainframes	I-Device
include	O
z/OS	B-Application
(	O
which	O
followed	O
MVS/ESA	O
and	O
OS/390	B-Application
in	O
the	O
OS/360	B-Application
lineage	O
)	O
,	O
z/VM	B-Application
(	O
which	O
followed	O
VM/ESA	B-Application
and	O
VM/XA	O
SP	O
in	O
the	O
CP-40	B-Application
lineage	O
)	O
,	O
z/VSE	B-Application
(	O
which	O
is	O
in	O
the	O
DOS/360	B-Application
lineage	I-Application
)	O
,	O
z/TPF	B-Operating_System
(	O
a	O
successor	O
of	O
Transaction	B-Operating_System
Processing	I-Operating_System
Facility	I-Operating_System
in	O
the	O
Airlines	B-Application
Control	I-Application
Program	I-Application
lineage	O
)	O
,	O
and	O
Linux	B-Application
on	I-Application
IBM	I-Application
Z	I-Application
(	O
e.g.	O
,	O
Debian	O
,	O
Red	O
Hat	O
Enterprise	O
Linux	B-Application
,	O
SUSE	O
Linux	B-Application
Enterprise	O
Server	O
)	O
.	O
</s>
<s>
Some	O
systems	O
run	O
MUSIC/SP	B-Application
,	O
as	O
well	O
as	O
UTS	B-Operating_System
(	O
Mainframe	B-Architecture
UNIX	O
)	O
.	O
</s>
<s>
In	O
October	O
2008	O
,	O
Sine	O
Nomine	O
Associates	O
introduced	O
OpenSolaris	B-Application
on	I-Application
System	I-Application
z	I-Application
;	O
it	O
has	O
since	O
been	O
discontinued	O
.	O
</s>
<s>
Current	O
IBM	B-Device
mainframes	I-Device
run	O
all	O
the	O
major	O
enterprise	O
transaction	B-General_Concept
processing	I-General_Concept
environments	O
and	O
databases	O
,	O
including	O
CICS	B-Application
,	O
IMS	B-Application
,	O
WebSphere	B-Language
Application	O
Server	O
,	O
IBM	B-Application
Db2	I-Application
,	O
and	O
Oracle	B-General_Concept
.	O
</s>
<s>
In	O
many	O
cases	O
these	O
software	O
subsystems	O
can	O
run	O
on	O
more	O
than	O
one	O
mainframe	B-Architecture
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
There	O
are	O
software-based	O
emulators	O
for	O
the	O
System/370	B-Device
,	O
System/390	B-Device
,	O
and	O
System	B-Device
z	I-Device
hardware	O
,	O
including	O
FLEX-ES	O
,	O
which	O
runs	O
under	O
UnixWare	B-Operating_System
or	O
Linux	B-Application
,	O
and	O
the	O
freely	O
available	O
Hercules	B-Application
,	O
which	O
runs	O
under	O
Linux	B-Application
,	O
FreeBSD	B-Operating_System
,	O
Solaris	B-Application
,	O
macOS	B-Application
and	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
IBM	O
offers	O
an	O
emulator	O
called	O
zPDT	O
(	O
System	B-Device
z	I-Device
Personal	O
Development	O
Tool	O
)	O
which	O
runs	O
on	O
Linux	B-Application
on	O
x86-64	B-Device
machines	O
.	O
</s>
