<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
a	O
rich	O
client	B-Protocol
(	O
also	O
called	O
heavy	O
,	O
fat	O
or	O
thick	O
client	B-Protocol
)	O
is	O
a	O
computer	O
(	O
a	O
"	O
client	B-Protocol
"	O
in	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
network	O
architecture	O
)	O
that	O
typically	O
provides	O
rich	O
functionality	O
independent	O
of	O
the	O
central	O
server	B-Application
.	O
</s>
<s>
This	O
kind	O
of	O
computer	O
was	O
originally	O
known	O
as	O
just	O
a	O
"	O
client	B-Protocol
"	O
or	O
"	O
thick	O
client	B-Protocol
,	O
"	O
in	O
contrast	O
with	O
"	O
thin	B-Device
client	I-Device
"	O
,	O
which	O
describes	O
a	O
computer	O
heavily	O
dependent	O
on	O
a	O
server	B-Application
's	O
applications	O
.	O
</s>
<s>
A	O
rich	O
client	B-Protocol
may	O
be	O
described	O
as	O
having	O
a	O
rich	B-Application
user	I-Application
interaction	I-Application
.	O
</s>
<s>
While	O
a	O
rich	O
client	B-Protocol
still	O
requires	O
at	O
least	O
periodic	O
connection	O
to	O
a	O
network	O
or	O
central	O
server	B-Application
,	O
it	O
is	O
often	O
characterised	O
by	O
the	O
ability	O
to	O
perform	O
many	O
functions	O
without	O
a	O
connection	O
.	O
</s>
<s>
In	O
contrast	O
,	O
a	O
thin	B-Device
client	I-Device
generally	O
does	O
as	O
little	O
processing	O
as	O
possible	O
on	O
the	O
client	B-Protocol
,	O
relying	O
on	O
access	O
to	O
the	O
server	B-Application
each	O
time	O
input	O
data	O
needs	O
to	O
be	O
processed	O
or	O
validated	O
.	O
</s>
<s>
The	O
designer	O
of	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
application	O
decides	O
which	O
parts	O
of	O
the	O
task	O
should	O
be	O
executed	O
on	O
the	O
client	B-Protocol
,	O
and	O
which	O
on	O
the	O
server	B-Application
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
drawing	O
package	O
could	O
require	O
download	O
of	O
an	O
initial	O
image	O
from	O
a	O
server	B-Application
,	O
and	O
allow	O
all	O
edits	O
to	O
be	O
made	O
locally	O
,	O
returning	O
the	O
revised	O
drawing	O
to	O
the	O
server	B-Application
upon	O
completion	O
.	O
</s>
<s>
This	O
would	O
require	O
a	O
rich	O
client	B-Protocol
and	O
might	O
be	O
characterised	O
by	O
a	O
long	O
delay	O
to	O
start	O
and	O
stop	O
(	O
while	O
a	O
whole	O
complex	O
drawing	O
was	O
transferred	O
)	O
,	O
but	O
quick	O
to	O
edit	O
.	O
</s>
<s>
Conversely	O
,	O
a	O
thin	B-Device
client	I-Device
could	O
download	O
just	O
the	O
visible	O
parts	O
of	O
the	O
drawing	O
at	O
the	O
beginning	O
and	O
send	O
each	O
change	O
back	O
to	O
the	O
server	B-Application
to	O
update	O
the	O
drawing	O
.	O
</s>
<s>
The	O
original	O
server	B-Application
clients	O
were	O
simple	O
text	O
display	O
terminals	O
including	O
Wyse	O
VDUs	O
,	O
and	O
rich	O
clients	O
were	O
generally	O
not	O
used	O
until	O
the	O
increase	O
in	O
PC	O
usage	O
.	O
</s>
<s>
The	O
original	O
driving	O
force	O
for	O
thin	B-Device
client	I-Device
computing	O
was	O
often	O
cost	O
;	O
at	O
a	O
time	O
when	O
CRT	O
terminals	O
and	O
PCs	O
were	O
relatively	O
expensive	O
,	O
the	O
thin-client	B-Device
–	O
server	B-Application
architecture	O
enabled	O
the	O
ability	O
to	O
deploy	O
the	O
desktop	O
computing	O
experience	O
to	O
many	O
users	O
.	O
</s>
<s>
As	O
PC	O
prices	O
decreased	O
,	O
combined	O
with	O
a	O
drop	O
in	O
software	O
licensing	O
costs	O
,	O
rich	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
architectures	I-Operating_System
became	O
more	O
attractive	O
.	O
</s>
<s>
For	O
users	O
,	O
the	O
rich	O
client	B-Protocol
device	O
provided	O
a	O
more-responsive	O
platform	O
and	O
often	O
an	O
improved	O
Graphical	B-Application
User	I-Application
Interface	I-Application
(	O
GUI	B-Application
)	O
than	O
what	O
could	O
be	O
achieved	O
in	O
a	O
thin	B-Device
client	I-Device
environment	O
.	O
</s>
<s>
In	O
more	O
recent	O
years	O
,	O
the	O
Internet	O
has	O
tended	O
to	O
drive	O
the	O
thin	B-Device
client	I-Device
model	O
despite	O
the	O
prodigious	O
processing	O
power	O
that	O
a	O
modern	O
PC	O
has	O
available	O
.	O
</s>
<s>
Probably	O
the	O
thinnest	O
clients	O
,	O
sometimes	O
called	O
"	O
ultra	O
thin	O
,	O
"	O
are	O
remote	B-Protocol
desktop	I-Protocol
applications	O
,	O
e.g.	O
</s>
<s>
the	O
Citrix	B-Application
products	O
,	O
and	O
Microsoft	O
's	O
Remote	B-Protocol
Desktop	I-Protocol
Services	I-Protocol
,	O
which	O
effectively	O
allow	O
applications	O
to	O
run	O
on	O
a	O
centrally-hosted	O
virtual	O
PC	O
and	O
copy	O
keystrokes	O
and	O
screen	O
images	O
between	O
the	O
local	O
PC	O
and	O
the	O
virtual	O
PC	O
.	O
</s>
<s>
These	O
ultra-thin	B-Device
clients	I-Device
are	O
often	O
used	O
to	O
make	O
available	O
complex	O
or	O
data-hungry	O
applications	O
that	O
have	O
been	O
implemented	O
as	O
rich	O
clients	O
but	O
the	O
true	O
client	B-Protocol
is	O
hosted	O
very	O
near	O
to	O
the	O
network	B-Application
server	I-Application
.	O
</s>
<s>
Lower	O
server	B-Application
requirements	O
.	O
</s>
<s>
A	O
rich	O
client	B-Operating_System
server	I-Operating_System
does	O
not	O
require	O
as	O
high	O
a	O
level	O
of	O
performance	O
as	O
a	O
thin	B-Device
client	B-Operating_System
server	I-Operating_System
(	O
since	O
the	O
rich	O
clients	O
themselves	O
do	O
much	O
of	O
the	O
application	O
processing	O
)	O
.	O
</s>
<s>
Rich	O
clients	O
have	O
advantages	O
in	O
that	O
a	O
constant	O
connection	O
to	O
the	O
central	O
server	B-Application
is	O
often	O
not	O
required	O
.	O
</s>
<s>
Running	O
this	O
software	O
in	O
a	O
thin	B-Device
client	I-Device
environment	O
can	O
be	O
difficult	O
.	O
</s>
<s>
Higher	O
server	B-Application
capacity	O
.	O
</s>
<s>
The	O
more	O
work	O
that	O
is	O
carried	O
out	O
by	O
the	O
client	B-Protocol
,	O
the	O
less	O
the	O
server	B-Application
needs	O
to	O
do	O
,	O
increasing	O
the	O
number	O
of	O
users	O
each	O
server	B-Application
can	O
support	O
.	O
</s>
