<s>
A	O
stacking	B-Device
window	I-Device
manager	I-Device
(	O
also	O
called	O
floating	O
window	B-Application
manager	I-Application
)	O
is	O
a	O
window	B-Application
manager	I-Application
that	O
draws	O
and	O
allows	O
windows	O
to	O
overlap	O
,	O
without	O
using	O
a	O
compositing	O
algorithm	O
.	O
</s>
<s>
All	O
window	B-Application
managers	I-Application
that	O
allow	O
the	O
overlapping	O
of	O
windows	O
but	O
are	O
not	O
compositing	B-Operating_System
window	I-Operating_System
managers	I-Operating_System
are	O
considered	O
stacking	B-Device
window	I-Device
managers	I-Device
,	O
although	O
it	O
is	O
possible	O
that	O
not	O
all	O
use	O
exactly	O
the	O
same	O
methods	O
.	O
</s>
<s>
Other	O
window	B-Application
managers	I-Application
that	O
are	O
not	O
considered	O
stacking	B-Device
window	I-Device
managers	I-Device
are	O
those	O
that	O
do	O
not	O
allow	O
the	O
overlapping	O
of	O
windows	O
,	O
which	O
are	O
called	O
tiling	O
window	B-Application
managers	I-Application
.	O
</s>
<s>
Stacking	B-Device
window	I-Device
managers	I-Device
allow	O
windows	O
to	O
overlap	O
using	O
clipping	O
to	O
allow	O
applications	O
to	O
write	O
only	O
to	O
the	O
visible	O
parts	O
of	O
the	O
windows	O
they	O
present	O
.	O
</s>
<s>
The	O
order	O
in	O
which	O
windows	O
are	O
to	O
be	O
stacked	O
is	O
called	O
their	O
z-order	B-Algorithm
.	O
</s>
<s>
Some	O
window	B-Application
managers	I-Application
may	O
be	O
able	O
to	O
treat	O
the	O
foreground	O
window	O
in	O
an	O
entirely	O
different	O
way	O
,	O
by	O
rendering	O
it	O
indirectly	O
,	O
and	O
sending	O
its	O
output	O
to	O
the	O
video	O
card	O
to	O
be	O
added	O
to	O
the	O
outgoing	O
raster	B-Algorithm
.	O
</s>
<s>
While	O
this	O
technique	O
may	O
be	O
possible	O
to	O
accomplish	O
within	O
some	O
stacking	B-Device
window	I-Device
managers	I-Device
,	O
it	O
is	O
technically	O
compositing	O
,	O
with	O
the	O
foreground	O
window	O
and	O
the	O
screen	O
raster	B-Algorithm
being	O
treated	O
the	O
same	O
way	O
two	O
windows	O
would	O
be	O
in	O
a	O
compositing	B-Operating_System
window	I-Operating_System
manager	I-Operating_System
.	O
</s>
<s>
Unfortunately	O
interacting	O
with	O
objects	O
outside	O
the	O
original	O
area	O
of	O
the	O
foreground	O
window	O
might	O
also	O
be	O
impossible	O
,	O
since	O
the	O
window	B-Application
manager	I-Application
would	O
not	O
be	O
able	O
to	O
determine	O
what	O
the	O
user	O
is	O
seeing	O
,	O
and	O
would	O
pass	O
such	O
mouse	O
clicks	O
to	O
whatever	O
programs	O
occupied	O
those	O
areas	O
of	O
the	O
screen	O
during	O
the	O
last	O
stacking	O
event	O
.	O
</s>
<s>
Many	O
windows	B-Application
managers	I-Application
under	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
provide	O
stacking	O
window	O
functionality	O
:	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
1.0	I-Application
displayed	O
windows	O
using	O
a	O
tiling	O
window	B-Application
manager	I-Application
.	O
</s>
<s>
In	O
Windows	B-Application
2.0	I-Application
,	O
it	O
was	O
replaced	O
with	O
a	O
stacking	B-Device
window	I-Device
manager	I-Device
,	O
which	O
allowed	O
windows	O
to	O
overlap	O
.	O
</s>
<s>
Microsoft	O
kept	O
the	O
stacking	B-Device
window	I-Device
manager	I-Device
up	O
through	O
Windows	B-Application
XP	I-Application
,	O
which	O
presented	O
severe	O
limitations	O
to	O
its	O
ability	O
to	O
display	O
3D-accelerated	O
content	O
inside	O
normal	O
windows	O
.	O
</s>
<s>
From	O
Windows	B-Application
Vista	I-Application
onward	O
,	O
a	O
new	O
compositing	B-Operating_System
window	I-Operating_System
manager	I-Operating_System
is	O
the	O
default	O
on	O
compatible	O
systems	O
.	O
</s>
<s>
1970s	O
:	O
The	O
Xerox	B-Device
Alto	I-Device
which	O
contained	O
the	O
first	O
working	O
commercial	O
GUI	B-Application
used	O
a	O
stacking	B-Device
window	I-Device
manager	I-Device
.	O
</s>
<s>
Early	O
1980s	O
:	O
The	O
Xerox	B-Operating_System
Star	I-Operating_System
,	O
successor	O
to	O
the	O
Alto	B-Device
,	O
used	O
tiling	O
for	O
most	O
main	O
application	O
windows	O
,	O
and	O
used	O
overlapping	O
only	O
for	O
dialogue	O
windows	O
removing	O
the	O
need	O
for	O
full	O
stacking	O
.	O
</s>
<s>
The	O
Classic	B-Application
Mac	I-Application
OS	I-Application
was	O
one	O
of	O
the	O
earliest	O
commercially	O
successful	O
examples	O
of	O
a	O
GUI	B-Application
which	O
used	O
stacking	O
windows	O
.	O
</s>
<s>
GEM	B-Application
predated	O
Microsoft	O
Windows	O
and	O
used	O
stacking	O
,	O
allowing	O
all	O
windows	O
to	O
overlap	O
.	O
</s>
<s>
Amiga	B-Application
OS	I-Application
contains	O
an	O
early	O
example	O
of	O
a	O
highly	O
advanced	O
stacking	B-Device
window	I-Device
manager	I-Device
.	O
</s>
