<s>
and	O
are	O
basic	O
memory	B-General_Concept
management	I-General_Concept
system	B-Operating_System
calls	I-Operating_System
used	O
in	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
to	O
control	O
the	O
amount	O
of	O
memory	O
allocated	O
to	O
the	O
data	B-General_Concept
segment	I-General_Concept
of	O
the	O
process	B-Operating_System
.	O
</s>
<s>
These	O
functions	O
are	O
typically	O
called	O
from	O
a	O
higher-level	O
memory	B-General_Concept
management	I-General_Concept
library	O
function	O
such	O
as	O
.	O
</s>
<s>
In	O
the	O
original	O
Unix	B-Application
system	I-Application
,	O
and	O
were	O
the	O
only	O
ways	O
in	O
which	O
applications	O
could	O
acquire	O
additional	O
data	O
space	O
;	O
later	O
versions	O
allowed	O
this	O
to	O
also	O
be	O
done	O
using	O
the	O
call	O
.	O
</s>
<s>
The	O
brk	O
and	O
sbrk	B-General_Concept
calls	O
dynamically	B-General_Concept
change	I-General_Concept
the	O
amount	O
of	O
space	O
allocated	O
for	O
the	O
data	B-General_Concept
segment	I-General_Concept
of	O
the	O
calling	O
process	B-Operating_System
.	O
</s>
<s>
The	O
change	O
is	O
made	O
by	O
resetting	O
the	O
program	O
break	O
of	O
the	O
process	B-Operating_System
,	O
which	O
determines	O
the	O
maximum	O
space	O
that	O
can	O
be	O
allocated	O
.	O
</s>
<s>
The	O
break	O
value	O
can	O
be	O
automatically	O
rounded	O
up	O
to	O
a	O
size	O
appropriate	O
for	O
the	O
memory	B-General_Concept
management	I-General_Concept
architecture	O
.	O
</s>
<s>
and	O
were	O
considered	O
legacy	O
even	O
by	O
1997	O
standards	O
(	O
Single	O
UNIX	B-Application
Specification	O
v2	O
or	O
POSIX.1-1998	O
)	O
.	O
</s>
<s>
Not	O
every	O
Unix-like	B-Operating_System
system	I-Operating_System
entertains	O
the	O
concept	O
of	O
having	O
the	O
user	O
control	O
the	O
data	B-General_Concept
segment	I-General_Concept
.	O
</s>
<s>
The	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
implementation	O
of	O
is	O
an	O
emulation	O
and	O
has	O
a	O
maximum	O
allocation	O
of	O
4	O
megabytes	O
.	O
</s>
<s>
The	O
requested	O
change	O
sets	O
the	O
break	O
value	O
to	O
a	O
value	O
greater	O
than	O
or	O
equal	O
to	O
the	O
start	O
address	O
of	O
any	O
attached	O
shared	B-Operating_System
memory	I-Operating_System
segment	O
.	O
</s>
