<s>
Input/Output	B-Application
Control	I-Application
System	I-Application
(	O
IOCS	B-Application
)	O
is	O
any	O
of	O
several	O
packages	O
on	O
early	O
IBM	O
entry-level	O
and	O
mainframe	B-Architecture
computers	I-Architecture
that	O
provided	O
low	B-Language
level	I-Language
access	O
to	O
records	B-Application
on	O
peripheral	O
equipment	O
.	O
</s>
<s>
IOCS	B-Application
provides	O
functionality	O
similar	O
to	O
1960s	O
packages	O
from	O
other	O
vendors	O
,	O
e.g.	O
,	O
File	O
Control	O
Processor	O
(	O
FCP	O
)	O
in	O
RCA	O
3301	O
Realcom	O
Operating	B-General_Concept
System	I-General_Concept
,	O
GEFRC	O
in	O
GECOS	B-Application
,	O
and	O
to	O
the	O
later	O
Record	B-Application
Management	I-Application
Services	I-Application
(	O
RMS	B-Application
)	O
in	O
DEC	O
VAX/VMS	B-Operating_System
(	O
later	O
OpenVMS	B-Operating_System
.	O
)	O
</s>
<s>
Computers	O
in	O
the	O
1950s	O
and	O
1960s	O
typically	O
dealt	O
with	O
data	O
that	O
were	O
organized	O
into	O
records	B-Application
either	O
by	O
the	O
nature	O
of	O
the	O
media	O
,	O
e.g.	O
,	O
lines	O
of	O
print	O
,	O
or	O
by	O
application	O
requirements	O
.	O
</s>
<s>
IOCS	B-Application
was	O
intended	O
to	O
allow	O
Assembler	B-Language
language	I-Language
programmers	O
to	O
read	O
and	O
write	O
records	B-Application
without	O
having	O
to	O
worry	O
about	O
the	O
details	O
of	O
the	O
various	O
devices	O
or	O
the	O
blocking	O
of	O
logical	O
records	B-Application
into	O
physical	O
records	B-Application
.	O
</s>
<s>
IOCS	B-Application
provided	O
the	O
run	O
time	O
I/O	O
support	O
for	O
several	O
compilers	O
.	O
</s>
<s>
Computers	O
of	O
this	O
era	O
often	O
did	O
not	O
have	O
operating	B-General_Concept
systems	I-General_Concept
in	O
the	O
modern	O
sense	O
.	O
</s>
<s>
Application	O
programs	O
called	O
IOCS	B-Application
routines	O
in	O
a	O
resident	B-Application
monitor	I-Application
,	O
or	O
included	O
macro	O
instructions	O
that	O
expanded	O
to	O
IOCS	B-Application
routines	O
.	O
</s>
<s>
In	O
some	O
cases	O
IOCS	B-Application
was	O
designed	O
to	O
coexist	O
with	O
Simultaneous	B-Device
Peripheral	I-Device
Operations	I-Device
On-line	I-Device
(	O
SPOOL	B-Device
)	O
software	O
.	O
</s>
<s>
The	O
level	O
of	O
access	O
is	O
at	O
a	O
higher	O
level	O
than	O
that	O
provided	O
by	O
BIOS	B-Operating_System
and	O
BDOS	B-Operating_System
in	O
the	O
PC	O
world	O
;	O
in	O
fact	O
,	O
IOCS	B-Application
has	O
no	O
support	O
for	O
character-oriented	O
I/O	O
,	O
primarily	O
because	O
the	O
systems	O
for	O
which	O
it	O
was	O
designed	O
did	O
n't	O
support	O
it	O
.	O
</s>
<s>
Versions	O
of	O
IOCS	B-Application
existed	O
for	O
the	O
IBM	B-Device
705	I-Device
III	I-Device
,	O
1401/1440/1460	B-Device
,	O
1410/7010	B-Device
,	O
7070/7072/7074	B-Device
,	O
7080	B-Device
and	O
7040/7044/7090/7094	B-Device
.	O
</s>
<s>
These	O
systems	O
heavily	O
influenced	O
the	O
data	O
management	O
components	O
of	O
the	O
operating	B-General_Concept
systems	I-General_Concept
for	O
the	O
System/360	B-Application
;	O
the	O
name	O
IOCS	B-Application
was	O
carried	O
through	O
in	O
DOS/360	O
through	O
z/VSE	B-Application
,	O
with	O
a	O
distinction	O
between	O
Logical	O
IOCS	B-Application
(	O
LIOCS	O
)	O
and	O
Physical	O
IOCS	B-Application
(	O
PIOCS	O
)	O
.	O
</s>
<s>
Although	O
some	O
technical	O
details	O
and	O
nomenclature	O
are	O
different	O
among	O
the	O
various	O
IOCS	B-Application
packages	O
,	O
the	O
fundamental	O
concepts	O
are	O
the	O
same	O
.	O
</s>
<s>
For	O
concreteness	O
,	O
the	O
discussion	O
and	O
examples	O
in	O
this	O
article	O
will	O
mostly	O
be	O
in	O
terms	O
of	O
7070	O
IOCS	B-Application
.	O
</s>
<s>
An	O
IOCS	B-Application
program	O
must	O
do	O
three	O
things	O
,	O
each	O
discussed	O
in	O
a	O
subsection	O
below	O
.	O
</s>
<s>
For	O
the	O
7070	O
these	O
are	O
done	O
using	O
7070	O
Autocoder	B-Device
declarative	O
statements	O
and	O
macro	O
instructions	O
.	O
</s>
<s>
Some	O
services	O
offered	O
by	O
IOCS	B-Application
were	O
not	O
needed	O
by	O
all	O
applications	O
,	O
e.g.	O
,	O
checkpoints	O
,	O
label	O
processing	O
.	O
</s>
<s>
An	O
IOCS	B-Application
program	O
must	O
identify	O
the	O
particular	O
devices	O
types	O
and	O
services	O
it	O
uses	O
.	O
</s>
<s>
A	O
7070	O
IOCS	B-Application
program	O
must	O
specify	O
one	O
or	O
more	O
DIOCS	O
statements	O
:	O
</s>
<s>
These	O
declarative	O
statements	O
identify	O
index	O
registers	O
reserved	O
for	O
the	O
use	O
of	O
IOCS	B-Application
,	O
indicate	O
channels	O
used	O
,	O
indicate	O
whether	O
the	O
program	O
is	O
to	O
coexist	O
with	O
SPOOL	B-Device
and	O
provide	O
processing	O
options	O
.	O
</s>
<s>
The	O
END	O
DIOCS	O
statement	O
causes	O
the	O
assembly	O
of	O
IOCS	B-Application
unless	O
a	O
preassembled	O
version	O
is	O
requested	O
.	O
</s>
<s>
In	O
some	O
other	O
IOCS	B-Application
packages	O
similar	O
functions	O
are	O
provided	O
by	O
control	O
cards	O
.	O
</s>
<s>
An	O
IOCS	B-Application
program	O
must	O
create	O
a	O
control	O
block	O
for	O
each	O
file	O
,	O
specifying	O
information	O
unique	O
to	O
the	O
file	O
.	O
</s>
<s>
For	O
7070	O
IOCS	B-Application
these	O
are	O
entries	O
in	O
the	O
File	O
Specification	O
Table	O
for	O
tape	O
files	O
,	O
each	O
of	O
which	O
is	O
generated	O
by	O
a	O
DTF	O
statement	O
,	O
or	O
separate	O
control	O
blocks	O
generated	O
by	O
DDF	O
or	O
DUF	O
statements	O
.	O
</s>
<s>
In	O
some	O
other	O
IOCS	B-Application
packages	O
similar	O
functions	O
are	O
provided	O
by	O
control	O
cards	O
.	O
</s>
<s>
Any	O
IOCS	B-Application
program	O
must	O
specify	O
the	O
actions	O
that	O
it	O
wishes	O
to	O
perform	O
.	O
</s>
<s>
In	O
7070	O
IOCS	B-Application
this	O
is	O
done	O
with	O
processing	O
macros	O
.	O
</s>
<s>
In	O
some	O
other	O
IOCS	B-Application
packages	O
similar	O
functions	O
are	O
provided	O
by	O
explicit	O
subroutine	O
calls	O
.	O
</s>
