<s>
The	O
Commodore	B-Device
4040	I-Device
is	O
the	O
replacement	O
for	O
the	O
previous	O
models	O
2040	O
(	O
U.S.	O
)	O
and	O
3040	O
(	O
Europe	O
)	O
.	O
</s>
<s>
It	O
's	O
a	O
dual-drive	O
5¼	O
"	O
floppy	B-Device
disk	I-Device
subsystem	O
for	O
Commodore	O
Business	O
Machines	O
.	O
</s>
<s>
It	O
uses	O
a	O
wide-case	O
form	O
,	O
and	O
uses	O
the	O
parallel	O
IEEE-488	O
interface	O
common	O
to	O
Commodore	B-Device
PET/CBM	I-Device
computers	O
.	O
</s>
<s>
These	O
drive	O
models	O
use	O
a	O
single-density	O
,	O
single-side	O
floppy	B-Device
data	O
storage	O
format	O
similar	O
to	O
that	O
used	O
by	O
the	O
Commodore	B-Device
1540	I-Device
&	O
1541	B-Device
drives	O
,	O
but	O
with	O
a	O
slightly	O
different	O
data	O
marker	O
indicating	O
which	O
model	O
originally	O
formatted	O
the	O
disk	O
.	O
</s>
<s>
The	O
drive	O
also	O
uses	O
variable	O
bit-clock	O
to	O
enable	O
increased	O
data	B-Device
density	I-Device
on	O
a	O
standard	O
single-density	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
It	O
is	O
a	O
form	O
of	O
constant	B-Device
bit-density	I-Device
recording	O
done	O
by	O
gradually	O
increasing	O
the	O
clock	O
rate	O
(	O
zone	B-Architecture
constant	I-Architecture
angular	I-Architecture
velocity	I-Architecture
,	O
ZCAV	B-Architecture
)	O
and	O
storing	O
more	O
physical	O
sectors	O
on	O
the	O
outer	O
tracks	O
than	O
on	O
the	O
inner	O
ones	O
(	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
,	O
ZBR	O
)	O
.	O
</s>
<s>
Starting	O
with	O
the	O
Commodore	B-Device
2040	I-Device
drive	O
,	O
this	O
enabled	O
Commodore	O
to	O
fit	O
170	O
KB	O
on	O
a	O
standard	O
single-sided	O
single-density	O
5.25	B-Device
"	I-Device
floppy	B-Device
.	O
</s>
