<s>
Direct	B-Algorithm
Graphics	I-Algorithm
Access	I-Algorithm
is	O
a	O
plug-in	B-Application
for	O
the	O
X	B-Operating_System
display	O
servers	O
that	O
allows	O
client	B-Protocol
programs	I-Protocol
direct	O
access	O
to	O
the	O
frame	B-Algorithm
buffer	I-Algorithm
.	O
</s>
<s>
Graphics	B-General_Concept
hardware	I-General_Concept
communicates	O
via	O
a	O
chunk	O
of	O
memory	O
called	O
a	O
frame	B-Algorithm
buffer	I-Algorithm
.	O
</s>
<s>
This	O
is	O
an	O
array	O
of	O
values	O
that	O
represent	O
pixel	B-Algorithm
color	O
values	O
on	O
the	O
screen	O
.	O
</s>
<s>
Writing	O
the	O
appropriate	O
values	O
into	O
the	O
frame	B-Algorithm
buffer	I-Algorithm
therefore	O
allows	O
a	O
program	O
to	O
paint	O
areas	O
of	O
the	O
screen	O
.	O
</s>
<s>
However	O
,	O
as	O
with	O
any	O
shared	B-General_Concept
resource	I-General_Concept
,	O
problems	O
occur	O
when	O
multiple	O
programs	O
attempt	O
to	O
access	O
the	O
same	O
resource	O
,	O
as	O
they	O
tend	O
to	O
write	O
over	O
each	O
other	O
's	O
work	O
.	O
</s>
<s>
In	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
,	O
this	O
is	O
solved	O
by	O
having	O
a	O
central	O
display	O
server	O
that	O
mediates	O
between	O
programs	O
that	O
want	O
to	O
draw	O
on	O
the	O
screen	O
.	O
</s>
<s>
The	O
X	B-Operating_System
server	O
does	O
all	O
this	O
work	O
,	O
freeing	O
programmers	O
from	O
having	O
to	O
write	O
their	O
own	O
drawing	O
code	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
the	O
X	B-Operating_System
architecture	O
is	O
that	O
it	O
works	O
over	O
a	O
network	B-Architecture
,	O
allowing	O
programs	O
on	O
one	O
machine	O
to	O
display	O
output	O
on	O
the	O
screen	O
of	O
another	O
.	O
</s>
<s>
Direct	B-Algorithm
Graphics	I-Algorithm
Access	I-Algorithm
allows	O
direct	O
access	O
to	O
the	O
frame	B-Algorithm
buffer	I-Algorithm
and	O
the	O
X-server	B-Operating_System
hands	O
over	O
control	O
of	O
the	O
frame	B-Algorithm
buffer	I-Algorithm
to	O
the	O
client	B-Protocol
program	I-Protocol
and	O
waits	O
for	O
the	O
client	O
to	O
hand	O
it	O
back	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
client	B-Protocol
program	I-Protocol
has	O
control	O
of	O
the	O
whole	O
screen	O
,	O
and	O
so	O
it	O
is	O
mostly	O
used	O
for	O
full-screen	O
video/games	O
.	O
</s>
