<s>
Software	B-Application
incompatibility	I-Application
is	O
a	O
characteristic	O
of	O
software	O
components	O
or	O
systems	O
which	O
cannot	O
operate	O
satisfactorily	O
together	O
on	O
the	O
same	O
computer	O
,	O
or	O
on	O
different	O
computers	O
linked	O
by	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Software	O
compatibility	O
is	O
a	O
characteristic	O
of	O
software	O
components	O
or	O
systems	O
which	O
can	O
operate	O
satisfactorily	O
together	O
on	O
the	O
same	O
computer	O
,	O
or	O
on	O
different	O
computers	O
linked	O
by	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
A	O
particular	O
program	B-Application
might	O
use	O
a	O
printer	O
(	O
resource	B-General_Concept
A	O
)	O
and	O
a	O
file	B-Operating_System
(	O
resource	B-General_Concept
B	O
)	O
in	O
order	O
to	O
print	O
the	O
file	B-Operating_System
.	O
</s>
<s>
If	O
several	O
such	O
programs	O
P1	O
,	O
P2	O
,	O
P3	O
...	O
operate	O
at	O
the	O
same	O
time	O
,	O
then	O
the	O
first	O
one	O
to	O
execute	B-General_Concept
will	O
block	B-Operating_System
the	O
others	O
until	O
the	O
resources	O
are	O
released	O
,	O
and	O
the	O
programs	O
will	O
execute	B-General_Concept
in	O
turn	O
.	O
</s>
<s>
It	O
makes	O
no	O
difference	O
whether	O
a	O
uni-processor	B-Operating_System
or	O
a	O
multi-processor	B-Operating_System
system	O
is	O
used	O
,	O
as	O
it	O
's	O
the	O
allocation	O
of	O
the	O
resources	O
which	O
determines	O
the	O
order	O
of	O
execution	O
.	O
</s>
<s>
Note	O
,	O
however	O
,	O
that	O
programmers	B-Application
are	O
,	O
in	O
general	O
,	O
not	O
constrained	O
to	O
write	O
programs	O
in	O
a	O
particular	O
way	O
,	O
or	O
even	O
if	O
there	O
are	O
guidelines	O
,	O
then	O
some	O
may	O
differ	O
from	O
the	O
guidelines	O
.	O
</s>
<s>
A	O
variant	O
of	O
the	O
previous	O
program	B-Application
may	O
be	O
:	O
</s>
<s>
However	O
,	O
if	O
several	O
of	O
the	O
Ps	O
are	O
set	O
to	O
run	O
at	O
the	O
same	O
time	O
as	O
several	O
of	O
the	O
Qs	O
,	O
then	O
a	O
deadlock	B-Operating_System
condition	O
can	O
arise	O
.	O
</s>
<s>
Note	O
that	O
the	O
deadlock	B-Operating_System
need	O
not	O
arise	O
,	O
but	O
may	O
.	O
</s>
<s>
This	O
is	O
one	O
kind	O
of	O
example	O
where	O
programs	O
may	O
demonstrate	O
incompatibility	B-Application
.	O
</s>
<s>
The	O
incompatibility	B-Application
could	O
be	O
as	O
simple	O
as	O
a	O
change	O
in	O
the	O
order	O
of	O
parameters	O
between	O
the	O
software	O
component	O
requesting	O
service	O
,	O
and	O
the	O
component	O
providing	O
the	O
service	O
.	O
</s>
<s>
This	O
would	O
be	O
a	O
kind	O
of	O
interface	B-Application
incompatibility	B-Application
.	O
</s>
<s>
This	O
might	O
be	O
considered	O
a	O
bug	B-Error_Name
,	O
but	O
could	O
be	O
very	O
hard	O
to	O
detect	O
in	O
some	O
systems	O
.	O
</s>
<s>
Some	O
interface	B-Application
incompatibilities	B-Application
can	O
easily	O
be	O
detected	O
during	O
the	O
build	O
stage	O
,	O
particularly	O
for	O
strongly	O
typed	O
systems	O
,	O
others	O
may	O
be	O
hard	O
to	O
find	O
and	O
may	O
only	O
be	O
detected	O
at	O
run	B-Library
time	I-Library
,	O
while	O
others	O
may	O
be	O
almost	O
impossible	O
to	O
detect	O
without	O
a	O
detailed	O
program	B-Application
analysis	O
.	O
</s>
<s>
If	O
P	O
now	O
calls	O
Q''	O
with	O
=	O
101	O
,	O
then	O
the	O
results	O
of	O
the	O
computation	O
will	O
be	O
incorrect	O
,	O
but	O
may	O
not	O
cause	O
a	O
program	B-Application
failure	B-General_Concept
.	O
</s>
<s>
If	O
P	O
calls	O
Q''	O
with	O
y	O
=	O
102	O
then	O
the	O
results	O
are	O
unpredictable	O
,	O
and	O
failure	B-General_Concept
may	O
arise	O
,	O
possibly	O
due	O
to	O
divide	B-Algorithm
by	I-Algorithm
zero	I-Algorithm
or	O
other	O
errors	O
such	O
as	O
arithmetic	B-Algorithm
overflow	I-Algorithm
.	O
</s>
<s>
If	O
P	O
calls	O
Q''	O
with	O
y	O
=	O
103	O
then	O
in	O
the	O
event	O
that	O
P	O
uses	O
the	O
result	O
in	O
a	O
division	O
operation	O
,	O
then	O
a	O
divide	B-Algorithm
by	I-Algorithm
zero	I-Algorithm
failure	B-General_Concept
may	O
occur	O
.	O
</s>
<s>
This	O
example	O
shows	O
how	O
one	O
program	B-Application
P1	O
may	O
be	O
always	O
compatible	O
with	O
another	O
Q1	O
,	O
but	O
that	O
there	O
can	O
be	O
constructed	O
other	O
programs	O
Q1	O
 '	O
and	O
Q1''	O
such	O
that	O
P1	O
and	O
Q1	O
 '	O
are	O
sometimes	O
incompatible	O
,	O
and	O
P1	O
and	O
Q1''	O
are	O
always	O
incompatible	O
.	O
</s>
<s>
This	O
can	O
particularly	O
happen	O
where	O
the	O
computer	O
uses	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
The	O
result	O
may	O
be	O
that	O
disk	B-General_Concept
thrashing	I-General_Concept
occurs	O
,	O
and	O
one	O
or	O
both	O
programs	O
will	O
have	O
significantly	O
reduced	O
performance	O
.	O
</s>
<s>
This	O
form	O
of	O
incompatibility	B-Application
can	O
occur	O
if	O
P	O
and	O
Q	O
are	O
intended	O
to	O
cooperate	O
,	O
but	O
can	O
also	O
occur	O
if	O
P	O
and	O
Q	O
are	O
completely	O
unrelated	O
but	O
just	O
happen	O
to	O
run	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
An	O
example	O
might	O
be	O
if	O
P	O
is	O
a	O
program	B-Application
which	O
produces	O
large	O
output	O
files	O
,	O
which	O
happen	O
to	O
be	O
stored	O
in	O
main	O
memory	O
,	O
and	O
Q	O
is	O
an	O
anti-virus	O
program	B-Application
which	O
scans	O
many	O
files	O
on	O
the	O
hard	O
disk	O
.	O
</s>
<s>
If	O
a	O
memory	B-General_Concept
cache	I-General_Concept
is	O
used	O
for	O
virtual	B-Architecture
memory	I-Architecture
,	O
then	O
it	O
is	O
possible	O
for	O
the	O
two	O
programs	O
to	O
interact	O
adversely	O
and	O
the	O
performance	O
of	O
each	O
will	O
be	O
drastically	O
reduced	O
.	O
</s>
