<s>
The	O
Integrated	B-Device
Woz	I-Device
Machine	I-Device
(	O
or	O
IWM	B-Device
for	O
short	O
)	O
is	O
a	O
single-chip	O
version	O
of	O
the	O
floppy	B-Device
disk	I-Device
controller	I-Device
for	O
the	O
Apple	B-Device
II	I-Device
.	O
</s>
<s>
It	O
was	O
also	O
employed	O
in	O
Macintosh	B-Device
computers	O
.	O
</s>
<s>
When	O
developing	O
a	O
floppy	O
drive	O
for	O
the	O
Apple	B-Device
II	I-Device
,	O
Apple	O
Inc	O
.	O
co-founder	O
Steve	O
Wozniak	O
felt	O
that	O
the	O
existing	O
models	O
available	O
on	O
the	O
market	O
were	O
too	O
complicated	O
,	O
expensive	O
and	O
inefficient	O
.	O
</s>
<s>
Instead	O
of	O
storing	O
810	O
sectors	O
(	O
each	O
holding	O
256	O
bytes	B-Application
of	O
data	O
)	O
per	O
track	B-Device
on	O
a	O
5.25-inch	O
floppy	O
disk	O
something	O
standard	O
at	O
that	O
time	O
,	O
Wozniak	O
utilized	O
group-coded	B-Device
recording	I-Device
(	O
GCR	B-Device
)	O
,	O
and	O
with	O
5-and-3	O
encoding	O
he	O
managed	O
to	O
squeeze	O
as	O
many	O
as	O
13	O
sectors	O
on	O
each	O
track	B-Device
using	O
the	O
same	O
mechanics	O
and	O
the	O
same	O
storage	O
medium	O
.	O
</s>
<s>
In	O
a	O
later	O
revision	O
,	O
this	O
number	O
was	O
bumped	O
up	O
to	O
16	O
sectors	O
per	O
track	B-Device
with	O
6-and-2	O
encoding	O
.	O
</s>
<s>
The	O
floppy	O
drive	O
controller	O
board	O
,	O
the	O
"	O
Disk	O
II	O
interface	O
,	O
"	O
was	O
built	O
with	O
8	O
ICs	O
,	O
one	O
of	O
which	O
is	O
the	O
PROM	B-General_Concept
,	O
containing	O
tables	O
for	O
the	O
encoder	O
and	O
decoder	O
,	O
the	O
state	O
machine	O
,	O
and	O
some	O
code	O
.	O
</s>
<s>
To	O
make	O
it	O
easier	O
to	O
move	O
the	O
controller	O
onto	O
the	O
main	B-Device
board	I-Device
,	O
as	O
in	O
the	O
Apple	O
IIc	O
,	O
Apple	B-Device
IIGS	I-Device
,	O
and	O
Macintosh	B-Device
,	O
Dr.	O
Wendell	O
Sander	O
integrated	O
all	O
these	O
components	O
into	O
one	O
single	O
chipthe	O
IWM	B-Device
.	O
</s>
<s>
The	O
IWM	B-Device
is	O
essentially	O
a	O
disk	O
controller	O
on	O
one	O
IC	O
.	O
</s>
<s>
It	O
was	O
employed	O
in	O
the	O
Apple	O
IIc	O
,	O
and	O
later	O
Apple	B-Device
IIGS	I-Device
,	O
and	O
all	O
Mac	O
models	O
up	O
to	O
the	O
Macintosh	B-Device
II	O
.	O
</s>
<s>
Later	O
,	O
an	O
extended	O
version	O
,	O
known	O
as	O
SWIM	O
(	O
Sander-Wozniak	B-Device
Integrated	I-Device
Machine	I-Device
)	O
,	O
was	O
introduced	O
.	O
</s>
<s>
This	O
new	O
version	O
added	O
the	O
capability	O
of	O
reading	O
and	O
writing	O
FM	B-Protocol
-	O
and	O
MFM-formatted	O
(	O
PC-formatted	O
)	O
floppy	O
disks	O
.	O
</s>
<s>
The	O
floppy	B-Device
controller	I-Device
function	O
still	O
stayed	O
in	O
the	O
chipset	O
for	O
a	O
while	O
,	O
even	O
though	O
the	O
provision	O
of	O
floppy	O
drives	O
for	O
the	O
Macs	O
had	O
already	O
ceased	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
first	O
iMacs	B-Device
still	O
had	O
a	O
floppy	O
drive	O
connector	O
on	O
the	O
motherboard	B-Device
,	O
allowing	O
a	O
floppy	O
drive	O
to	O
be	O
retrofitted	O
by	O
knowledgeable	O
enthusiasts	O
.	O
</s>
