<s>
Tagged	B-Device
queuing	I-Device
is	O
a	O
method	O
for	O
allowing	O
a	O
hardware	B-Architecture
device	O
or	O
controller	O
to	O
process	O
commands	O
received	O
from	O
a	O
device	B-Application
driver	I-Application
out	O
of	O
order	O
.	O
</s>
<s>
It	O
requires	O
that	O
the	O
device	B-Application
driver	I-Application
attaches	O
a	O
tag	O
to	O
each	O
command	O
which	O
the	O
controller	O
or	O
device	O
can	O
later	O
use	O
to	O
identify	O
the	O
response	O
to	O
the	O
command	O
.	O
</s>
<s>
Tagged	O
queueing	O
can	O
speed	O
up	O
processing	O
considerably	O
if	O
a	O
controller	O
serves	O
devices	O
of	O
very	O
different	O
speeds	O
,	O
such	O
as	O
an	O
SCSI	B-Architecture
controller	O
serving	O
a	O
mix	O
of	O
CD-ROM	B-Device
drives	O
and	O
high-speed	O
disks	B-Device
.	O
</s>
<s>
In	O
such	O
cases	O
if	O
a	O
request	O
to	O
fetch	O
data	O
from	O
the	O
CD-ROM	B-Device
is	O
shortly	O
followed	O
by	O
a	O
request	O
to	O
read	O
from	O
the	O
disk	B-Device
,	O
the	O
controller	O
does	O
n't	O
have	O
to	O
wait	O
for	O
the	O
CD-ROM	B-Device
to	O
fetch	O
the	O
data	O
,	O
it	O
can	O
instead	O
instruct	O
the	O
disk	B-Device
to	O
fetch	O
the	O
data	O
and	O
return	O
the	O
value	O
to	O
the	O
device	B-Application
driver	I-Application
,	O
while	O
the	O
CD-ROM	B-Device
is	O
probably	O
still	O
seeking	O
.	O
</s>
