<s>
Disk	B-Device
Operating	B-Application
System/360	I-Application
,	O
also	O
DOS/360	O
,	O
or	O
simply	O
DOS	O
,	O
is	O
the	O
discontinued	O
first	O
member	O
of	O
a	O
sequence	O
of	O
operating	B-General_Concept
systems	I-General_Concept
for	O
IBM	B-Application
System/360	I-Application
,	O
System/370	B-Device
and	O
later	O
mainframes	B-Device
.	O
</s>
<s>
In	O
its	O
time	O
,	O
DOS/360	O
was	O
the	O
most	O
widely	O
used	O
operating	B-General_Concept
system	I-General_Concept
in	O
the	O
world	O
.	O
</s>
<s>
The	O
Basic	O
Operating	O
System(BOS )	O
was	O
an	O
early	O
version	O
of	O
DOS	O
and	O
TOS	O
which	O
could	O
provide	O
usable	O
functionality	O
on	O
a	O
system	O
with	O
as	O
little	O
as	O
8KB	O
of	O
main	O
storage	O
and	O
one	O
2311	B-Device
disk	B-Device
drive	I-Device
.	O
</s>
<s>
TOS/360	B-Application
(	O
Tape	O
Operating	B-Application
System/360	I-Application
,	O
not	O
a	O
DOS	O
as	O
such	O
and	O
not	O
so	O
called	O
)	O
was	O
an	O
IBM	O
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
System/360	B-Application
,	O
used	O
in	O
the	O
early	O
days	O
around	O
1965	O
to	O
support	O
the	O
System/360	B-Device
Model	I-Device
30	I-Device
and	O
similar	O
platforms	O
.	O
</s>
<s>
TOS	O
went	O
through	O
14	O
releases	O
,	O
and	O
was	O
discontinued	O
when	O
disks	B-Device
such	O
as	O
the	O
IBM	B-Device
2311	I-Device
and	O
IBM	B-Device
2314	I-Device
became	O
more	O
affordable	O
at	O
the	O
time	O
of	O
System/360	B-Application
,	O
whereas	O
they	O
had	O
been	O
an	O
expensive	O
luxury	O
on	O
the	O
IBM	B-Device
7090	I-Device
.	O
</s>
<s>
DOS/360	O
was	O
the	O
primary	O
operating	B-General_Concept
system	I-General_Concept
for	O
most	O
small	O
to	O
midsize	O
S/360	B-Application
installations	O
.	O
</s>
<s>
It	O
added	O
virtual	B-Architecture
memory	I-Architecture
in	O
support	O
of	O
the	O
new	O
System/370	B-Device
series	O
hardware	O
.	O
</s>
<s>
It	O
used	O
a	O
fixed	O
page	B-General_Concept
table	I-General_Concept
which	O
mapped	O
a	O
single	O
address	B-General_Concept
space	I-General_Concept
of	O
up	O
to	O
16	O
megabytes	O
for	O
all	O
partitions	O
combined	O
.	O
</s>
<s>
DOS/VS	O
was	O
succeeded	O
by	O
DOS/VSE	B-Application
through	O
z/VSE	B-Application
.	O
</s>
<s>
DOS/VSE	B-Application
was	O
introduced	O
in	O
1979	O
as	O
an	O
"	O
extended	O
"	O
version	O
of	O
DOS/VS	O
to	O
support	O
the	O
new	O
4300	B-Device
processors	O
.	O
</s>
<s>
The	O
4300	B-Device
systems	O
included	O
a	O
feature	O
called	O
ECPS:VSE	O
that	O
provided	O
a	O
single-level	O
storage	O
for	O
both	O
the	O
processor	O
and	O
the	O
I/O	O
channels	O
.	O
</s>
<s>
DOS/VSE	B-Application
provided	O
support	O
for	O
ECPS:VSE	O
,	O
but	O
could	O
also	O
run	O
on	O
a	O
System/370	B-Device
without	O
that	O
feature	O
.	O
</s>
<s>
VSE	B-Application
was	O
the	O
last	O
free	O
version	O
of	O
DOS	O
.	O
</s>
<s>
VSE/Advanced	O
Functions	O
(	O
VSE/AF	O
)	O
is	O
a	O
product	O
that	O
adds	O
new	O
device	O
support	O
and	O
functionality	O
to	O
DOS/VSE	B-Application
.	O
</s>
<s>
Many	O
installations	O
installed	O
VSE/AF	O
using	O
products	O
such	O
as	O
VSE	B-Application
System	O
Installation	O
Productivity	O
Option/Extended	O
(	O
VSE	B-Application
System	O
IPO/E	O
)	O
,	O
which	O
combines	O
DOS/VSE	B-Application
,	O
VSE/AF	O
and	O
various	O
other	O
products	O
.	O
</s>
<s>
SSX/VSE	O
(	O
"	O
Small	O
System	O
Executive	O
"	O
)	O
was	O
an	O
attempt	O
by	O
IBM	O
to	O
simplify	O
purchase	O
and	O
installation	O
of	O
VSE	B-Application
by	O
providing	O
a	O
pre-generated	O
system	O
containing	O
the	O
OS	O
and	O
the	O
most	O
popular	O
products	O
.	O
</s>
<s>
SSX	O
was	O
sold	O
by	O
IBM	O
as	O
a	O
bundle	O
of	O
14	O
component	O
products	O
(	O
Advanced	O
Functions/VSE	O
,	O
VSE/POWER	O
,	O
ACF/VTAME	O
,	O
VSE/VSAM	O
,	O
CICS/DOS/VS	O
,	O
DOS/VS	O
,	O
Sort/Merge	O
,	O
VSE/ICCF	O
,	O
VSE/OCCF	O
,	O
VSE/IPCS	O
,	O
DOS/COBOL	O
,	O
Back	O
Up/Restore	O
,	O
Space	O
Management	O
,	O
VSE/DITTO	O
)	O
,	O
and	O
originally	O
would	O
only	O
agree	O
to	O
offer	O
the	O
individual	O
products	O
separately	O
via	O
RPQ	O
,	O
although	O
IBM	O
later	O
agreed	O
to	O
add	O
those	O
products	O
individually	O
to	O
its	O
price	O
list	O
under	O
pressure	O
from	O
ISVs	O
who	O
claimed	O
that	O
the	O
bundling	O
violated	O
antitrust	O
laws	O
.	O
</s>
<s>
In	O
1986	O
IBM	O
released	O
VSE/SP	O
(	O
"	O
System	O
Product	O
"	O
)	O
in	O
conjunction	O
with	O
the	O
announcement	O
of	O
the	O
9370	B-Device
processors	O
.	O
</s>
<s>
VSE/SP	O
replaced	O
SSX/VSE	O
and	O
bundled	O
VSE	B-Application
with	O
the	O
most	O
popular	O
VSE	B-Application
program	O
products	O
such	O
as	O
VSE/AF	O
,	O
ACF/VTAM	O
,	O
CICS	B-Application
,	O
and	O
POWER/VS	O
.	O
</s>
<s>
VSE/ESA	O
was	O
a	O
31-bit	O
DOS/VSE	B-Application
version	O
,	O
which	O
was	O
released	O
in	O
1990	O
with	O
support	O
for	O
up	O
to	O
384MB	O
of	O
real	O
storage	O
.	O
</s>
<s>
It	O
provided	O
up	O
to	O
twelve	O
static	O
partitions	O
and	O
allowed	O
VSE/POWER	O
and	O
ACF/VTAM	O
to	O
be	O
run	O
in	O
private	O
address	B-General_Concept
spaces	I-General_Concept
.	O
</s>
<s>
It	O
introduced	O
a	O
new	O
feature	O
called	O
dynamic	O
partitions	O
which	O
could	O
allow	O
up	O
to	O
150	O
concurrent	O
jobs	O
,	O
each	O
in	O
its	O
own	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
Version	O
2	O
added	O
support	O
for	O
multiprocessing	B-Operating_System
,	O
through	O
the	O
new	O
Turbo	O
Dispatcher	O
,	O
which	O
permits	O
different	O
partitions	O
to	O
execute	O
simultaneously	O
on	O
different	O
processors	O
.	O
</s>
<s>
A	O
partition	O
can	O
only	O
run	O
on	O
one	O
processor	O
at	O
a	O
time	O
,	O
which	O
mostly	O
limits	O
the	O
multiprocessing	B-Operating_System
to	O
multitasking	B-Operating_System
.	O
</s>
<s>
Those	O
limits	O
remain	O
in	O
the	O
last	O
z/VSE	B-Application
.	O
</s>
<s>
IBM	O
released	O
z/VSE	B-Application
3.1	O
in	O
2005	O
.	O
</s>
<s>
z/VSE	B-Application
4.1	O
released	O
in	O
2007	O
introduced	O
support	O
for	O
64-bit	O
real	O
addressing	O
,	O
with	O
up	O
to	O
8GB	O
of	O
memory	O
.	O
</s>
<s>
However	O
,	O
while	O
parts	O
of	O
the	O
supervisor	O
run	O
in	O
64-bit	O
mode	O
,	O
it	O
only	O
provides	O
31-bit	O
virtual	O
address	B-General_Concept
spaces	I-General_Concept
to	O
problem	O
state	O
applications	O
.	O
</s>
<s>
As	O
of	O
2011	O
one	O
estimate	O
placed	O
the	O
number	O
of	O
sites	O
using	O
z/VSE	B-Application
at	O
around	O
4,000	O
.	O
</s>
<s>
When	O
developing	O
a	O
new	O
hardware	O
generation	O
of	O
unified	O
System/360	B-Application
(	O
or	O
S/360	B-Application
)	O
computers	O
,	O
IBM	O
had	O
originally	O
committed	O
to	O
delivering	O
a	O
single	O
operating	B-General_Concept
system	I-General_Concept
,	O
OS/360	B-Application
,	O
also	O
compatible	O
with	O
low-end	O
machines	O
;	O
but	O
hardware	O
was	O
already	O
available	O
and	O
the	O
OS/360	B-Application
project	O
fell	O
further	O
and	O
further	O
behind	O
schedule	O
,	O
as	O
described	O
at	O
length	O
by	O
Fred	O
Brooks	O
in	O
The	O
Mythical	O
Man-Month	O
.	O
</s>
<s>
BPS/360	B-Application
for	O
machines	O
with	O
at	O
least	O
8KB	O
of	O
core	B-General_Concept
memory	I-General_Concept
and	O
a	O
punched	B-Device
card	I-Device
reader	I-Device
,	O
</s>
<s>
BOS/360	B-Application
for	O
machines	O
with	O
at	O
least	O
8KB	O
memory	O
and	O
a	O
disk	B-Device
drive	I-Device
,	O
</s>
<s>
DOS/360	O
for	O
machines	O
with	O
at	O
least	O
16KB	O
memory	O
and	O
a	O
disk	B-Device
drive	I-Device
,	O
</s>
<s>
TOS/360	B-Application
for	O
machines	O
with	O
at	O
least	O
16KB	O
memory	O
and	O
a	O
tape	O
drive	O
.	O
</s>
<s>
When	O
OS/360	B-Application
was	O
finally	O
released	O
,	O
a	O
year	O
late	O
,	O
it	O
required	O
at	O
least	O
64KB	O
of	O
memory	O
.	O
</s>
<s>
DOS	O
was	O
designed	O
to	O
use	O
little	O
memory	O
,	O
and	O
could	O
run	O
on	O
16KB	O
machines	O
,	O
a	O
configuration	O
available	O
on	O
the	O
low-end	O
S/360	B-Device
model	I-Device
30	I-Device
.	O
</s>
<s>
Unlike	O
OS/360	B-Application
,	O
DOS/360	O
was	O
initially	O
a	O
single-job	O
system	O
which	O
did	O
not	O
support	O
multitasking	B-Operating_System
.	O
</s>
<s>
A	O
version	O
with	O
multitasking	B-Operating_System
,	O
supporting	O
up	O
to	O
three	O
memory	O
partitions	O
,	O
requiring	O
32KB	O
of	O
memory	O
was	O
later	O
released	O
.	O
</s>
<s>
Despite	O
its	O
limitations	O
,	O
DOS/360	O
became	O
the	O
most	O
widely	O
used	O
operating	B-General_Concept
system	I-General_Concept
for	O
processors	O
with	O
less	O
than	O
256KB	O
of	O
memory	O
because	O
:	O
System/360	B-Application
hardware	O
sold	O
very	O
well	O
;	O
DOS/360	O
ran	O
well	O
on	O
System/360	B-Application
processors	O
which	O
medium-sized	O
organizations	O
could	O
afford	O
;	O
and	O
it	O
was	O
better	O
than	O
the	O
"	O
operating	B-General_Concept
systems	I-General_Concept
"	O
these	O
customers	O
had	O
before	O
.	O
</s>
<s>
DOS/360	O
was	O
the	O
operating	B-General_Concept
system	I-General_Concept
which	O
filled	O
the	O
time	O
gap	O
between	O
the	O
announcement	O
of	O
the	O
System/360	B-Application
and	O
the	O
availability	O
of	O
the	O
intended	O
operating	B-General_Concept
system	I-General_Concept
,	O
OS/360	B-Application
.	O
</s>
<s>
IBM	O
expected	O
that	O
DOS/360	O
users	O
would	O
soon	O
upgrade	O
to	O
OS/360	B-Application
,	O
but	O
as	O
a	O
result	O
of	O
those	O
investments	O
,	O
they	O
were	O
reluctant	O
to	O
commit	O
to	O
such	O
conversion	O
.	O
</s>
<s>
IBM	O
then	O
needed	O
to	O
continue	O
to	O
offer	O
DOS/360	O
as	O
an	O
additional	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
Hacker	O
's	O
Jargon	O
File	O
incorrectly	O
states	O
that	O
GECOS	B-Application
(	O
also	O
known	O
as	O
GCOS	B-Application
)	O
was	O
copied	O
from	O
DOS/360	O
,	O
which	O
was	O
not	O
the	O
case	O
,	O
however	O
the	O
Xerox	O
Data	O
Systems	O
Xerox	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
(	O
XOS	O
)	O
was	O
intentionally	O
similar	O
to	O
DOS	O
to	O
simplify	O
program	O
porting	O
.	O
</s>
<s>
DOS/360	O
required	O
a	O
System/360	B-Application
CPU	O
(	O
model	O
25	O
and	O
above	O
)	O
with	O
the	O
standard	O
instruction	O
set	O
(	O
decimal	O
and	O
floating-point	O
instruction	O
sets	O
optional	O
)	O
.	O
</s>
<s>
A	O
1052	B-Device
Model	I-Device
7	I-Device
printer-keyboard	O
,	O
either	O
a	O
selector	O
or	O
multiplexor	O
channel	O
,	O
and	O
at	O
least	O
one	O
disk	B-Device
drive	I-Device
was	O
required	O
—	O
initially	O
a	O
2311	B-Device
holding	O
7.25MB	O
.	O
</s>
<s>
A	O
card	B-Device
reader	I-Device
,	O
card	B-Device
punch	I-Device
and	O
line	O
printer	O
were	O
usually	O
included	O
,	O
but	O
magnetic	B-Architecture
tape	I-Architecture
drives	I-Architecture
could	O
be	O
substituted	O
.	O
</s>
<s>
A	O
typical	O
configuration	O
might	O
consist	O
of	O
a	O
S/360	B-Device
model	I-Device
30	I-Device
with	O
32KB	O
memory	O
and	O
the	O
decimal	O
instruction	O
set	O
,	O
an	O
IBM	B-Device
2540	I-Device
card	O
reader/card	O
punch	O
,	O
an	O
IBM	B-Device
1403	I-Device
printer	O
,	O
two	O
or	O
three	O
IBM	B-Device
2311	I-Device
disks	B-Device
,	O
two	O
IBM	O
2415	O
magnetic	B-Architecture
tape	I-Architecture
drives	I-Architecture
,	O
and	O
the	O
1052-7	O
console	O
.	O
</s>
<s>
Because	O
DOS/360	O
was	O
designed	O
to	O
run	O
on	O
low-end	O
models	O
of	O
System/360	B-Application
memory	O
usage	O
was	O
a	O
concern	O
.	O
</s>
<s>
It	O
was	O
possible	O
to	O
generate	O
a	O
DOS	O
supervisor	O
,	O
the	O
resident	O
portion	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
small	O
as	O
5902	O
bytes	O
.	O
</s>
<s>
Detailed	O
charts	O
listed	O
memory	O
requirements	O
for	O
each	O
sysgen	B-Application
option	O
,	O
often	O
as	O
little	O
as	O
100	O
bytes	O
.	O
</s>
<s>
A	O
minimum	O
system	O
would	O
leave	O
just	O
over	O
10KB	O
of	O
storage	O
available	O
for	O
a	O
single	O
batch	B-General_Concept
partition	O
which	O
was	O
enough	O
to	O
run	O
utilities	O
and	O
all	O
compilers	B-Language
except	O
COBOL	B-Application
,	O
PL/I	B-Language
,	O
and	O
full	O
FORTRAN	B-Application
IV	O
.	O
</s>
<s>
To	O
keep	O
memory	O
usage	O
as	O
small	O
as	O
possible	O
,	O
DOS	O
was	O
coded	O
entirely	O
in	O
assembly	B-Language
language	I-Language
.	O
</s>
<s>
This	O
was	O
done	O
as	O
part	O
of	O
the	O
reliability	O
,	O
availability	O
,	O
and	O
serviceability	O
(	O
RAS	O
)	O
enhancements	O
for	O
the	O
System/370	B-Device
.	O
</s>
<s>
Like	O
OS/360	B-Application
,	O
initial	O
releases	O
of	O
DOS	O
could	O
run	O
only	O
one	O
program	O
at	O
a	O
time	O
.	O
</s>
<s>
Later	O
versions	O
of	O
"	O
real	O
"	O
DOS	O
were	O
able	O
to	O
run	O
up	O
to	O
three	O
programs	O
concurrently	O
,	O
in	O
separate	O
memory	O
partitions	O
,	O
supported	O
by	O
the	O
same	O
hardware	O
memory	O
protection	O
features	O
of	O
the	O
more	O
scalable	O
OS/360	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Multiprogramming	O
was	O
an	O
optional	O
feature	O
of	O
DOS/360	O
,	O
selectable	O
at	O
system	B-Application
generation	I-Application
.	O
</s>
<s>
A	O
later	O
SYSGEN	B-Application
option	O
allowed	O
batch	B-General_Concept
operation	O
run	O
in	O
either	O
FG	O
partition	O
.	O
</s>
<s>
When	O
the	O
Core	O
Image	O
Library	O
became	O
full	O
,	O
it	O
had	O
to	O
be	O
compressed	O
by	O
a	O
utility	B-Application
program	I-Application
,	O
and	O
this	O
could	O
halt	O
development	O
work	O
until	O
it	O
was	O
complete	O
.	O
</s>
<s>
A	O
relocatable	O
library	O
for	O
linkable	O
object	O
programs	O
and	O
a	O
source	O
statement	O
library	O
for	O
assembler	B-Language
macros	O
and	O
include	O
text	O
were	O
also	O
supported	O
.	O
</s>
<s>
Installations	O
could	O
define	O
additional	O
private	O
relocatable	O
and	O
source	O
statement	O
libraries	O
on	O
other	O
disk	B-Device
volumes	O
.	O
</s>
<s>
DOS/360	O
had	O
a	O
set	O
of	O
utility	B-Application
programs	I-Application
,	O
an	O
Assembler	B-Language
,	O
and	O
compilers	B-Language
for	O
FORTRAN	B-Application
,	O
COBOL	B-Application
and	O
eventually	O
PL/I	B-Language
,	O
and	O
it	O
supported	O
a	O
range	O
of	O
file	O
organizations	O
with	O
access	B-Application
methods	I-Application
to	O
help	O
in	O
using	O
them	O
:	O
</s>
<s>
In	O
indexed	O
(	O
ISAM	B-Application
)	O
files	O
a	O
specified	O
section	O
of	O
each	O
record	O
was	O
defined	O
as	O
a	O
key	O
which	O
could	O
be	O
used	O
to	O
look	O
up	O
specific	O
records	O
.	O
</s>
<s>
In	O
direct	O
access	O
(	O
BDAM	B-Application
)	O
files	O
,	O
the	O
application	O
program	O
had	O
to	O
specify	O
the	O
physical	O
location	O
on	O
the	O
disk	B-Device
of	O
the	O
data	O
it	O
wanted	O
to	O
access	O
.	O
</s>
<s>
BDAM	B-Application
programming	O
was	O
not	O
easy	O
and	O
most	O
customers	O
never	O
used	O
it	O
themselves	O
;	O
but	O
it	O
was	O
the	O
fastest	O
way	O
to	O
access	O
data	O
on	O
disks	B-Device
and	O
many	O
software	O
companies	O
used	O
it	O
in	O
their	O
products	O
,	O
especially	O
database	B-Application
management	I-Application
systems	I-Application
such	O
as	O
ADABAS	B-Application
,	O
IDMS	B-Application
and	O
IBM	O
's	O
DBOMP	B-Application
and	O
DL/I	B-Language
.	O
</s>
<s>
Sequential	O
and	O
ISAM	B-Application
files	O
could	O
store	O
either	O
fixed-length	O
or	O
variable-length	O
records	O
,	O
and	O
all	O
types	O
could	O
occupy	O
more	O
than	O
one	O
disk	B-Device
volume	O
.	O
</s>
<s>
DOS/360	O
offered	O
Basic	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
(	O
BTAM	B-Application
)	O
and	O
Queued	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
(	O
QTAM	B-Application
)	O
.	O
</s>
<s>
BTAM	B-Application
was	O
primitive	O
and	O
hard	O
to	O
use	O
by	O
later	O
standards	O
,	O
but	O
it	O
allowed	O
communication	O
with	O
almost	O
any	O
type	O
of	O
terminal	O
,	O
which	O
was	O
a	O
big	O
advantage	O
at	O
a	O
time	O
when	O
there	O
was	O
little	O
standardization	O
of	O
communications	O
protocols	O
.	O
</s>
<s>
The	O
simplicity	O
of	O
its	O
API	B-Application
also	O
allowed	O
the	O
relatively	O
easy	O
interface	O
of	O
external	O
communications	O
processors	O
,	O
which	O
facilitated	O
DOS/360	O
machines	O
becoming	O
nodes	O
in	O
the	O
multi-tier	O
networks	O
of	O
large	O
organizations	O
.	O
</s>
<s>
Conversely	O
,	O
QTAM	B-Application
users	O
did	O
n't	O
need	O
as	O
much	O
knowledge	O
about	O
individual	O
devices	O
because	O
QTAM	B-Application
operated	O
at	O
the	O
logical	O
level	O
using	O
the	O
OPEN/CLOSE/GET/PUT	O
macros	O
.	O
</s>
<s>
All	O
DOS	O
job	B-Application
control	I-Application
statements	I-Application
began	O
with	O
""	O
in	O
card	O
columns	O
one	O
and	O
two	O
except	O
end-of-job	O
which	O
was	O
""	O
,	O
end-of-data	O
,	O
""	O
,	O
and	O
comments	O
,	O
""	O
.	O
</s>
<s>
The	O
end	O
of	O
job	B-Application
statement	I-Application
marks	O
the	O
end	O
of	O
a	O
job	O
,	O
and	O
may	O
indicate	O
the	O
end	O
of	O
data	O
to	O
be	O
flushed	O
if	O
the	O
job	O
terminates	O
abnormally	O
.	O
</s>
<s>
The	O
statement	O
provides	O
disk	B-Device
or	O
tape	O
volume	O
label	O
information	O
for	O
standard	O
label	O
checking	O
.	O
</s>
<s>
DOS	O
originally	O
provided	O
the	O
statement	O
for	O
tape	O
label	O
information	O
and	O
the	O
and	O
statements	O
for	O
disk	B-Device
label	O
and	O
extent	O
information	O
.	O
</s>
<s>
DOS	O
JCL	B-Application
was	O
designed	O
for	O
parsing	O
speed	O
and	O
simplicity	O
;	O
the	O
resulting	O
positional	O
syntax	O
was	O
significantly	O
more	O
cryptic	O
than	O
OS/360	B-Application
keyword-driven	O
job	O
control	O
.	O
</s>
<s>
Early	O
DOS	O
included	O
no	O
spooling	B-Device
sub-system	O
to	O
improve	O
the	O
efficiency	O
of	O
punched	B-Architecture
card	I-Architecture
and	O
line	O
printer	O
I/O	O
.	O
</s>
<s>
IBM	O
's	O
spooler	B-Device
was	O
an	O
option	O
called	O
POWER	O
,	O
and	O
Software	O
Design	O
,	O
Inc.	O
,	O
an	O
independent	O
software	O
company	O
,	O
sold	O
a	O
spooler	B-Device
called	O
GRASP	B-Application
.	O
</s>
<s>
DOS/360	O
had	O
no	O
relocating	O
loader	B-Operating_System
,	O
so	O
programmers	O
had	O
to	O
link	B-Application
edit	I-Application
a	O
separate	O
executable	O
version	O
of	O
each	O
program	O
for	O
each	O
partition	O
,	O
or	O
address	B-General_Concept
space	I-General_Concept
,	O
in	O
which	O
the	O
program	O
was	O
likely	O
to	O
be	O
run	O
.	O
</s>
<s>
Alternatively	O
assembler-language	O
programs	O
could	O
be	O
written	O
as	O
self-relocating	O
,	O
but	O
that	O
imposed	O
additional	O
complexity	O
and	O
a	O
size	O
penalty	O
,	O
albeit	O
a	O
small	O
one	O
.	O
</s>
<s>
Large	O
DOS	O
shops	O
with	O
multiple	O
machines	O
and	O
multiple	O
partition	O
layouts	O
often	O
wrote	O
their	O
own	O
relocating	O
loader	B-Operating_System
to	O
circumvent	O
this	O
issue	O
.	O
</s>
<s>
The	O
DOS/360	O
application	B-Application
programming	I-Application
interface	I-Application
was	O
incompatible	O
with	O
OS/360	B-Application
.	O
</s>
<s>
High	B-Language
level	I-Language
language	I-Language
programs	O
written	O
for	O
DOS	O
needed	O
to	O
be	O
compiled	B-Language
and	O
linked	O
before	O
they	O
could	O
be	O
used	O
with	O
OS/360	B-Application
.	O
</s>
<s>
Minor	O
differences	O
between	O
compilers	B-Language
of	O
DOS	O
as	O
opposed	O
to	O
OS	O
sometimes	O
required	O
modifications	O
to	O
programs	O
.	O
</s>
<s>
Since	O
OS/360	B-Application
had	O
significantly	O
more	O
features	O
supported	O
in	O
its	O
API	B-Application
,	O
any	O
use	O
of	O
those	O
features	O
would	O
have	O
to	O
be	O
removed	O
from	O
programs	O
being	O
ported	O
to	O
DOS	O
.	O
</s>
<s>
This	O
was	O
less	O
of	O
a	O
problem	O
for	O
programmers	O
working	O
in	O
high	B-Language
level	I-Language
languages	I-Language
such	O
as	O
COBOL	B-Application
.	O
</s>
<s>
Assembler	B-Language
programs	I-Language
,	O
on	O
the	O
other	O
hand	O
,	O
tended	O
to	O
utilize	O
those	O
very	O
features	O
more	O
often	O
and	O
usually	O
needed	O
greater	O
modification	O
to	O
run	O
on	O
DOS	O
.	O
</s>
