<s>
In	O
computing	O
,	O
a	O
task	O
is	O
a	O
unit	O
of	O
execution	B-General_Concept
or	O
a	O
unit	O
of	O
work	O
.	O
</s>
<s>
The	O
term	O
is	O
ambiguous	O
;	O
precise	O
alternative	O
terms	O
include	O
process	B-Operating_System
,	O
light-weight	B-Operating_System
process	I-Operating_System
,	O
thread	B-Operating_System
(	O
for	O
execution	B-General_Concept
)	O
,	O
step	O
,	O
request	B-Protocol
,	O
or	O
query	B-Library
(	O
for	O
work	O
)	O
.	O
</s>
<s>
In	O
the	O
adjacent	O
diagram	O
,	O
there	O
are	O
queues	O
of	O
incoming	O
work	O
to	O
do	O
and	O
outgoing	O
completed	O
work	O
,	O
and	O
a	O
thread	B-Operating_System
pool	I-Operating_System
of	O
threads	B-Operating_System
to	O
perform	O
this	O
work	O
.	O
</s>
<s>
Either	O
the	O
work	O
units	O
themselves	O
or	O
the	O
threads	B-Operating_System
that	O
perform	O
the	O
work	O
can	O
be	O
referred	O
to	O
as	O
"	O
tasks	O
"	O
,	O
and	O
these	O
can	O
be	O
referred	O
to	O
respectively	O
as	O
requests/responses/threads	O
,	O
incoming	O
tasks/completed	O
tasks/threads	O
(	O
as	O
illustrated	O
)	O
,	O
or	O
requests/responses/tasks	O
.	O
</s>
<s>
In	O
the	O
sense	O
of	O
"	O
unit	O
of	O
execution	B-General_Concept
"	O
,	O
in	O
some	O
operating	B-General_Concept
systems	I-General_Concept
,	O
a	O
task	O
is	O
synonymous	O
with	O
a	O
process	B-Operating_System
,	O
and	O
in	O
others	O
with	O
a	O
thread	B-Operating_System
.	O
</s>
<s>
In	O
non-interactive	O
execution	B-General_Concept
(	O
batch	B-General_Concept
processing	I-General_Concept
)	O
,	O
a	O
task	O
is	O
a	O
unit	O
of	O
execution	B-General_Concept
within	O
a	O
job	B-General_Concept
,	O
with	O
the	O
task	O
itself	O
typically	O
a	O
process	B-Operating_System
.	O
</s>
<s>
The	O
term	O
"	O
multitasking	B-Operating_System
"	O
primarily	O
refers	O
to	O
the	O
processing	O
sense	O
–	O
multiple	O
tasks	O
executing	O
at	O
the	O
same	O
time	O
–	O
but	O
has	O
nuances	O
of	O
the	O
work	O
sense	O
of	O
multiple	O
tasks	O
being	O
performed	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
In	O
the	O
sense	O
of	O
"	O
unit	O
of	O
work	O
"	O
,	O
in	O
a	O
job	B-General_Concept
(	O
meaning	O
"	O
one-off	O
piece	O
of	O
work	O
"	O
)	O
a	O
task	O
can	O
correspond	O
to	O
a	O
single	O
step	O
(	O
the	O
step	O
itself	O
,	O
not	O
the	O
execution	B-General_Concept
thereof	O
)	O
,	O
while	O
in	O
batch	B-General_Concept
processing	I-General_Concept
individual	O
tasks	O
can	O
correspond	O
to	O
a	O
single	O
step	O
of	O
processing	O
a	O
single	O
item	O
in	O
a	O
batch	O
,	O
or	O
to	O
a	O
single	O
step	O
of	O
processing	O
all	O
items	O
in	O
the	O
batch	O
.	O
</s>
<s>
In	O
online	O
systems	O
,	O
tasks	O
most	O
commonly	O
correspond	O
to	O
a	O
single	O
request	B-Protocol
(	O
in	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
architectures	O
)	O
or	O
a	O
query	B-Library
(	O
in	O
information	B-Library
retrieval	I-Library
)	O
,	O
either	O
a	O
single	O
stage	O
of	O
handling	O
,	O
or	O
the	O
whole	O
system-wide	O
handling	O
.	O
</s>
<s>
In	O
the	O
Java	B-Language
programming	I-Language
language	I-Language
,	O
these	O
two	O
concepts	O
(	O
unit	O
of	O
work	O
and	O
unit	O
of	O
execution	B-General_Concept
)	O
are	O
conflated	O
when	O
working	O
directly	O
with	O
threads	B-Operating_System
,	O
but	O
clearly	O
distinguished	O
in	O
the	O
framework	O
:	O
</s>
<s>
A	O
unit	O
of	O
work	O
representing	O
one	O
of	O
the	O
steps	O
in	O
a	O
process	B-Operating_System
.	O
</s>
<s>
A	O
unit	O
of	O
work	O
to	O
be	O
accomplished	O
by	O
a	O
device	O
or	O
process	B-Operating_System
.	O
</s>
<s>
A	O
process	B-Operating_System
and	O
the	O
procedures	O
that	O
run	O
the	O
process	B-Operating_System
.	O
</s>
<s>
In	O
a	O
parallel	O
job	B-General_Concept
,	O
two	O
or	O
more	O
concurrent	O
tasks	O
work	O
together	O
through	O
message	O
passing	O
and	O
shared	O
memory	O
.	O
</s>
<s>
In	O
z/OS	B-Application
specifically	O
,	O
it	O
is	O
defined	O
precisely	O
as	O
:	O
</s>
<s>
The	O
term	O
task	O
in	O
OS/360	B-Application
through	O
z/OS	B-Application
is	O
roughly	O
equivalent	O
to	O
light-weight	B-Operating_System
process	I-Operating_System
;	O
the	O
tasks	O
in	O
a	O
job	B-General_Concept
step	O
share	O
an	O
address	O
space	O
.	O
</s>
<s>
However	O
,	O
in	O
MVS/ESA	O
through	O
z/OS	B-Application
,	O
a	O
task	O
or	O
Service	B-Application
Request	I-Application
Block	I-Application
(	O
SRB	O
)	O
may	O
have	O
access	O
to	O
other	O
address	O
spaces	O
via	O
its	O
access	O
list	O
.	O
</s>
<s>
The	O
term	O
task	O
is	O
used	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
(	O
at	O
least	O
since	O
v2.6.13	O
,	O
up	O
to	O
and	O
including	O
v4.8	O
)	O
to	O
refer	O
to	O
a	O
unit	O
of	O
execution	B-General_Concept
,	O
which	O
may	O
share	O
various	O
system	O
resources	O
with	O
other	O
tasks	O
on	O
the	O
system	O
.	O
</s>
<s>
Depending	O
on	O
the	O
level	O
of	O
sharing	O
,	O
the	O
task	O
may	O
be	O
regarded	O
as	O
a	O
conventional	O
thread	B-Operating_System
or	O
process	B-Operating_System
.	O
</s>
<s>
The	O
term	O
task	O
for	O
a	O
part	O
of	O
a	O
job	B-General_Concept
dates	O
to	O
multiprogramming	O
in	O
the	O
early	O
1960s	O
,	O
as	O
in	O
this	O
example	O
from	O
1961	O
:	O
</s>
<s>
The	O
term	O
was	O
popularized	O
with	O
the	O
introduction	O
of	O
OS/360	B-Application
(	O
announced	O
1964	O
)	O
,	O
which	O
featured	O
Multiprogramming	O
with	O
a	O
Fixed	O
number	O
of	O
Tasks	O
(	O
MFT	O
)	O
and	O
Multiprogramming	O
with	O
a	O
Variable	O
number	O
of	O
Tasks	O
(	O
MVT	O
)	O
.	O
</s>
<s>
In	O
this	O
case	O
tasks	O
were	O
identified	O
with	O
light-weight	B-Operating_System
processes	I-Operating_System
,	O
a	O
job	B-General_Concept
consisted	O
of	O
a	O
number	O
of	O
tasks	O
,	O
and	O
,	O
later	O
,	O
tasks	O
could	O
have	O
sub-tasks	O
(	O
in	O
modern	O
terminology	O
,	O
child	O
processes	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Windows	O
Task	O
Manager	O
manages	O
(	O
running	O
)	O
processes	O
,	O
while	O
Windows	O
Task	O
Scheduler	O
schedules	O
programs	O
to	O
execute	O
in	O
future	O
,	O
what	O
is	O
traditionally	O
known	O
as	O
a	O
job	B-General_Concept
scheduler	I-General_Concept
,	O
and	O
uses	O
the	O
.job	O
extension	O
.	O
</s>
