<s>
A	O
floppy-disk	O
controller	O
(	O
FDC	O
)	O
has	O
evolved	O
from	O
a	O
discrete	O
set	O
of	O
components	O
on	O
one	O
or	O
more	O
circuit	O
boards	O
to	O
a	O
special-purpose	O
integrated	O
circuit	O
(	O
IC	O
or	O
"	O
chip	O
"	O
)	O
or	O
a	O
component	O
thereof	O
.	O
</s>
<s>
An	O
FDC	O
directs	O
and	O
controls	O
reading	O
from	O
and	O
writing	O
to	O
a	O
computer	O
's	O
floppy	B-Device
disk	I-Device
drive	I-Device
(	O
FDD	O
)	O
.	O
</s>
<s>
The	O
FDC	O
is	O
responsible	O
for	O
reading	O
data	O
presented	O
from	O
the	O
host	O
computer	O
and	O
converting	O
it	O
to	O
the	O
drive	O
's	O
on-disk	O
format	O
using	O
one	O
of	O
a	O
number	O
of	O
encoding	B-Protocol
schemes	I-Protocol
,	O
like	O
FM	B-Protocol
encoding	I-Protocol
(	O
single	B-Device
density	I-Device
)	O
or	O
MFM	B-Protocol
encoding	I-Protocol
(	O
double	B-Device
density	I-Device
)	O
,	O
and	O
reading	O
those	O
formats	O
and	O
returning	O
it	O
to	O
its	O
original	O
binary	O
values	O
.	O
</s>
<s>
Depending	O
on	O
the	O
platform	O
,	O
data	O
transfers	O
between	O
the	O
controller	O
and	O
host	O
computer	O
would	O
be	O
controlled	O
by	O
the	O
computer	O
's	O
own	O
microprocessor	B-Architecture
,	O
or	O
an	O
inexpensive	O
dedicated	O
microprocessor	B-Architecture
like	O
the	O
MOS	B-General_Concept
6507	I-General_Concept
or	O
Zilog	B-General_Concept
Z80	I-General_Concept
.	O
</s>
<s>
By	O
the	O
1990s	O
,	O
the	O
floppy	B-Device
disk	I-Device
was	O
increasingly	O
giving	O
way	O
to	O
hard	B-Device
drives	I-Device
,	O
which	O
required	O
similar	O
controllers	O
.	O
</s>
<s>
In	O
these	O
systems	O
,	O
the	O
controller	O
also	O
often	O
combined	O
a	O
microcontroller	B-Architecture
to	O
handle	O
data	O
transfer	O
over	O
standardized	O
connectors	O
like	O
SCSI	B-Architecture
and	O
IDE	B-Protocol
that	O
could	O
be	O
used	O
with	O
any	O
computer	O
.	O
</s>
<s>
In	O
more	O
modern	O
systems	O
,	O
the	O
FDC	O
,	O
if	O
present	O
at	O
all	O
,	O
is	O
typically	O
part	O
of	O
the	O
many	O
functions	O
provided	O
by	O
a	O
single	O
super	B-Device
I/O	I-Device
chip	O
.	O
</s>
<s>
The	O
first	O
floppy	B-Device
disk	I-Device
drive	I-Device
controller	O
(	O
FDC	O
)	O
like	O
the	O
first	O
floppy	B-Device
disk	I-Device
drive	I-Device
(	O
the	O
IBM	O
23FD	O
)	O
shipped	O
in	O
1971	O
as	O
a	O
component	O
in	O
the	O
IBM	O
2385	O
Storage	O
Control	O
Unit	O
for	O
the	O
IBM	O
2305	O
fixed	O
head	O
disk	O
drive	O
,	O
and	O
of	O
the	O
System	O
370	O
Models	O
155	B-Device
and	O
165	B-Device
.	O
</s>
<s>
IBM	O
's	O
1973	O
introduction	O
of	O
the	O
3740	B-Device
Data	I-Device
Entry	I-Device
System	I-Device
created	O
the	O
basic	O
media	O
standard	O
for	O
the	O
8-inch	O
single	B-Architecture
sided	I-Architecture
floppy	B-Device
disk	I-Device
,	O
IBM	O
's	O
"	O
Type	O
1	O
"	O
diskette	B-Device
,	O
which	O
coupled	O
with	O
rapidly	O
increasing	O
requirements	O
for	O
inexpensive	O
,	O
removable	O
direct	O
access	O
storage	O
for	O
many	O
small	O
applications	O
caused	O
a	O
dramatic	O
growth	O
in	O
drive	O
and	O
controller	O
shipments	O
.	O
</s>
<s>
1973	O
:	O
The	O
FDC	O
in	O
IBM	B-Device
's	I-Device
3741	I-Device
is	O
a	O
type	O
of	O
microcontroller	B-Architecture
that	O
accepts	O
commands	O
from	O
the	O
system	O
's	O
microprocessor	B-Architecture
(	O
"	O
MPU	O
"	O
in	O
IBM	O
's	O
terminology	O
)	O
and	O
executes	O
them	O
on	O
the	O
attached	O
33FD	O
as	O
independently	O
as	O
possible	O
.	O
</s>
<s>
This	O
IBM	O
FDC	O
did	O
establish	O
the	O
IBM	O
Type	O
1	O
diskette	B-Device
as	O
the	O
first	O
industry	O
standard	O
floppy	B-Device
disk	I-Device
medium	O
but	O
neither	O
its	O
interface	O
to	O
the	O
host	O
microprocessor	B-Architecture
nor	O
its	O
interface	O
to	O
the	O
33FD	O
were	O
adopted	O
as	O
industry	O
standards	O
.	O
</s>
<s>
1976	O
:	O
Scientific	O
Micro	O
Systems’	O
FD0300	O
FDC	O
built	O
on	O
an	O
8-inch	O
by	O
12-inch	O
contains	O
a	O
microprocessor	B-Architecture
and	O
approximately	O
50	O
integrated	O
circuits	O
and	O
is	O
designed	O
to	O
provide	O
easy	O
attachment	O
to	O
a	O
number	O
of	O
host	O
buses	O
.	O
</s>
<s>
1976	O
:	O
Shugart	O
Associates	O
introduced	O
the	O
first	O
5¼-inch	O
floppy	B-Device
disk	I-Device
drive	I-Device
along	O
with	O
an	O
associated	O
and	O
first	O
FDC	O
for	O
this	O
form	O
factor	O
,	O
the	O
SA4400	O
.	O
</s>
<s>
The	O
SA4400	O
performs	O
control	O
functions	O
to	O
transfer	O
data	O
between	O
a	O
host	O
system	O
and	O
up	O
to	O
3	O
disk	O
drives	O
using	O
an	O
8-bit	O
general	O
purpose	O
host	O
interface	O
which	O
format	O
disks	O
according	O
to	O
a	O
modified	O
IBM	B-Device
3740	I-Device
type	O
media	O
format	O
specifications	O
.	O
</s>
<s>
Its	O
interface	O
to	O
the	O
Apple	O
host	O
as	O
well	O
as	O
its	O
interface	O
to	O
the	O
Apple	O
5¼-inch	O
floppy	B-Device
disk	I-Device
drive	I-Device
is	O
unique	O
and	O
it	O
was	O
not	O
adopted	O
as	O
an	O
industry	O
standard	O
.	O
</s>
<s>
The	O
first	O
FDC	O
implemented	O
as	O
a	O
special	O
purpose	O
integrated	O
circuit	O
is	O
the	O
Western	B-Device
Digital	I-Device
FD1771	I-Device
announced	O
on	O
July	O
19	O
,	O
1976	O
.	O
</s>
<s>
The	O
NEC	B-Device
µPD765	I-Device
,	O
announced	O
in	O
1978	O
became	O
a	O
quasi-industry	O
standard	O
when	O
it	O
was	O
adopted	O
in	O
the	O
original	O
IBM	B-Device
PC	I-Device
(	O
1981	O
)	O
;	O
the	O
FDC	O
was	O
physically	O
located	O
on	O
its	O
own	O
adapter	B-Device
card	I-Device
along	O
with	O
support	O
circuitry	O
.	O
</s>
<s>
In	O
early	O
1987	O
,	O
Intel	O
introduced	O
the	O
82072	O
CHMOS	O
High	O
Integrated	O
Floppy	B-Device
Disk	I-Device
Controller	O
for	O
use	O
in	O
industry	O
standard	O
PC	O
computers	O
.	O
</s>
<s>
Ultimately	O
in	O
most	O
computer	O
systems	O
the	O
FDC	O
became	O
a	O
part	O
of	O
a	O
Super	B-Device
I/O	I-Device
chip	O
or	O
a	O
Southbridge	B-Device
chip	O
.	O
</s>
<s>
A	O
floppy	B-Device
disk	I-Device
stores	O
binary	O
data	O
not	O
as	O
a	O
series	O
of	O
values	O
,	O
but	O
a	O
series	O
of	O
changes	O
in	O
value	O
.	O
</s>
<s>
Each	O
of	O
these	O
changes	O
,	O
recorded	O
in	O
the	O
polarity	O
of	O
the	O
magnetic	O
recording	O
media	O
,	O
causes	O
a	O
voltage	O
to	O
be	O
induced	O
in	O
the	O
drive	B-Device
head	I-Device
as	O
the	O
disk	O
surface	O
rotates	O
past	O
it	O
.	O
</s>
<s>
Some	O
controllers	O
require	O
this	O
encoding	O
to	O
be	O
performed	O
externally	O
,	O
but	O
most	O
designs	O
provide	O
standard	O
encodings	O
like	O
FM	B-Protocol
and	O
MFM	B-Protocol
.	O
</s>
<s>
These	O
typically	O
include	O
the	O
movement	O
of	O
the	O
drive	B-Device
head	I-Device
to	O
center	O
over	O
the	O
separate	O
tracks	O
on	O
the	O
disk	O
,	O
tracking	O
the	O
location	O
of	O
the	O
head	O
and	O
returning	O
it	O
to	O
zero	O
,	O
and	O
sometimes	O
functionally	O
to	O
format	O
a	O
disk	O
based	O
on	O
simple	O
inputs	O
like	O
the	O
number	O
of	O
tracks	O
,	O
sectors	O
per	O
track	O
and	O
number	O
of	O
bytes	O
per	O
sector	O
.	O
</s>
<s>
In	O
some	O
systems	O
,	O
like	O
the	O
Apple	B-Device
II	I-Device
and	O
IBM	B-Device
PC	I-Device
,	O
this	O
is	O
controlled	O
by	O
software	O
running	O
on	O
the	O
computer	O
's	O
host	O
microprocessor	B-Architecture
and	O
the	O
drive	O
interface	O
is	O
connected	O
directly	O
to	O
the	O
processor	O
using	O
an	O
expansion	B-Device
card	I-Device
.	O
</s>
<s>
On	O
other	O
systems	O
,	O
like	O
the	O
Commodore	O
64	O
and	O
Atari	B-Device
8-bit	I-Device
family	I-Device
,	O
there	O
is	O
no	O
direct	O
path	O
from	O
the	O
controller	O
to	O
the	O
host	O
CPU	O
and	O
a	O
second	O
processor	O
like	O
the	O
MOS	B-General_Concept
6507	I-General_Concept
or	O
Zilog	B-General_Concept
Z80	I-General_Concept
is	O
used	O
inside	O
the	O
drive	O
for	O
this	O
purpose	O
.	O
</s>
<s>
The	O
original	O
Apple	B-Device
II	I-Device
controller	O
was	O
in	O
the	O
form	O
of	O
a	O
plug-in	O
card	O
on	O
the	O
host	O
computer	O
.	O
</s>
<s>
The	O
IBM	B-Device
PC	I-Device
took	O
a	O
more	O
conventional	O
approach	O
,	O
their	O
adaptor	O
card	O
could	O
support	O
up	O
to	O
four	O
drives	O
;	O
on	O
the	O
PC	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
DMA	O
)	O
to	O
the	O
drives	O
was	O
performed	O
using	O
DMA	O
channel	O
2	O
and	O
IRQ	B-General_Concept
6	O
.	O
</s>
<s>
The	O
diagram	O
below	O
shows	O
a	O
conventional	O
floppy	B-Device
disk	I-Device
controller	O
which	O
communicates	O
with	O
the	O
CPU	O
via	O
an	O
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
(	O
ISA	O
)	O
bus	O
or	O
similar	O
bus	O
and	O
communicates	O
with	O
the	O
floppy	B-Device
disk	I-Device
drive	I-Device
with	O
a	O
34	O
pin	O
ribbon	O
cable	O
.	O
</s>
<s>
An	O
alternative	O
arrangement	O
that	O
is	O
more	O
usual	O
in	O
recent	O
designs	O
has	O
the	O
FDC	O
included	O
in	O
a	O
super	B-Device
I/O	I-Device
chip	O
which	O
communicates	O
via	O
a	O
Low	O
Pin	O
Count	O
(	O
LPC	O
)	O
bus	O
.	O
</s>
<s>
Most	O
of	O
the	O
floppy	B-Device
disk	I-Device
controller	O
(	O
FDC	O
)	O
functions	O
are	O
performed	O
by	O
the	O
integrated	O
circuit	O
but	O
some	O
are	O
performed	O
by	O
external	O
hardware	O
circuits	O
.	O
</s>
<s>
The	O
FDC	O
has	O
three	O
I/O	B-General_Concept
ports	O
.	O
</s>
<s>
Before	O
initiating	O
a	O
floppy	B-Device
disk	I-Device
operation	O
the	O
software	O
reads	O
this	O
port	O
to	O
confirm	O
the	O
readiness	O
condition	O
of	O
the	O
FDC	O
and	O
the	O
disk	O
drives	O
to	O
verify	O
the	O
status	O
of	O
the	O
previously	O
initiated	O
command	O
.	O
</s>
<s>
A	O
controller	O
connects	O
to	O
one	O
or	O
more	O
drives	O
using	O
a	O
flat	O
ribbon	O
cable	O
,	O
50	O
wires	O
for	O
8	B-Device
"	I-Device
drives	O
and	O
34	O
wires	O
for	O
3.5	B-Device
"	I-Device
&	O
5.25	B-Device
"	I-Device
drives	O
.	O
</s>
<s>
A	O
"	O
universal	O
cable	O
"	O
has	O
four	O
drive	O
connectors	O
,	O
two	O
each	O
for	O
3.5	B-Device
"	I-Device
&	O
5.25	B-Device
"	I-Device
drives	O
.	O
</s>
<s>
In	O
the	O
IBM	B-Device
PC	I-Device
family	O
and	O
compatibles	O
,	O
a	O
twist	O
in	O
the	O
cable	O
is	O
used	O
to	O
distinguish	O
disk	O
drives	O
by	O
the	O
socket	O
to	O
which	O
they	O
are	O
connected	O
.	O
</s>
<s>
When	O
the	O
controller	O
and	O
disk	O
drive	O
are	O
assembled	O
as	O
one	O
device	O
,	O
as	O
it	O
is	O
the	O
case	O
with	O
some	O
external	O
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
e.g.	O
,	O
Commodore	B-Device
1540	I-Device
and	O
USB	B-Protocol
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
the	O
internal	O
floppy	B-Device
disk	I-Device
drive	I-Device
and	O
its	O
interface	O
are	O
unchanged	O
,	O
while	O
the	O
assembled	O
device	O
presents	O
a	O
different	O
interface	O
such	O
as	O
IEEE	O
488	O
,	O
parallel	B-Device
port	I-Device
or	O
USB	B-Protocol
.	O
</s>
<s>
Many	O
mutually	O
incompatible	O
floppy	B-Device
disk	I-Device
formats	I-Device
are	O
possible	O
;	O
aside	O
from	O
the	O
physical	O
format	O
on	O
the	O
disk	O
,	O
incompatible	O
file	O
systems	O
are	O
also	O
possible	O
.	O
</s>
<s>
Drive	O
Format	O
Capacity	O
Transfer	O
speed	O
 [ kbit/s ] 	O
RPM	O
Tracks	O
TPI	B-Device
Comment	O
8-inch	O
SD	O
8-inch	O
SD	O
80	O
KB	O
33.333	O
360	O
32	O
48	O
Only	O
on	O
old	O
controllers	O
.	O
</s>
<s>
5.25-inch	O
SSDD	O
5.25-inch	O
SSDD	O
171	O
KB	O
300	O
35	O
48	O
Only	O
on	O
C1541	B-Device
compatibles	O
.	O
</s>
<s>
5.25-inch	O
DD	O
5.25-inch	O
QD	O
(	O
2DD	O
)	O
800	O
KB	O
250	O
300	O
80	O
96	O
5.25-inch	O
HD	O
5.25-inch	O
DD	O
360	O
KB	O
300	O
360	O
40	O
48	O
5.25	B-Device
"	I-Device
HD	O
5.25	B-Device
"	I-Device
HD	O
1200	O
KB	O
500	O
360	O
80	O
96	O
Up	O
to	O
83	O
tracks	O
.	O
</s>
<s>
Different	O
biasing	O
current.iesleonardo.info	O
–	O
This	O
diskette	B-Device
tutorial	O
provides	O
technical	O
information	O
concerning	O
diskettesoldskool.org	O
–	O
Let	O
HD	O
5	O
,	O
25	O
"	O
FDDs	O
operate	O
at	O
300	O
rpm	O
instead	O
of	O
360	O
rpm	O
5.25	B-Device
"	I-Device
HD	O
5.25	B-Device
"	I-Device
HD	O
720	O
KB	O
300	O
360	O
80	O
Up	O
to	O
83	O
tracks	O
.	O
</s>
<s>
3.5	B-Device
"	I-Device
DD	O
3.5	B-Device
"	I-Device
DD	O
720	O
KB	O
250	O
300	O
80	O
135	O
Up	O
to	O
83	O
tracks.intel.com	O
–	O
Intel	O
82077SL	O
for	O
Super	O
Dense	O
Floppies	B-Device
3.5	B-Device
"	I-Device
DD	O
3.5	B-Device
"	I-Device
DD	O
800	O
KB	O
394	O
–	O
590	O
80	O
Used	O
by	O
Apple	O
Macintosh	B-Device
.	O
</s>
<s>
3.5	B-Device
"	I-Device
DD	O
3.5	B-Device
"	I-Device
DD	O
800	O
KB	O
250	O
300	O
80	O
Used	O
by	O
Commodore	O
1581	O
.	O
</s>
<s>
3.5	B-Device
"	I-Device
DD	O
3.5	B-Device
"	I-Device
DD	O
880	O
KB	O
250	O
300	O
80	O
Up	O
to	O
83	O
tracks	O
.	O
</s>
<s>
Used	O
by	O
Amiga	B-Device
computers	I-Device
.	O
</s>
<s>
3.5	B-Device
"	I-Device
DD	O
3.5	B-Device
"	I-Device
DD	O
360	O
KB	O
250	O
300	O
40	O
3.5	B-Device
"	I-Device
HD	O
3.5	B-Device
"	I-Device
DD	O
720	O
KB	O
250	O
300	O
80	O
Up	O
to	O
83	O
tracks	O
.	O
</s>
<s>
3.5	B-Device
"	I-Device
HD	O
3.5	B-Device
"	I-Device
HD	O
1280	O
KB	O
500	O
360	O
80	O
135	O
Up	O
to	O
83	O
tracks	O
.	O
</s>
<s>
"	O
3mode	O
"	O
3.5	B-Device
"	I-Device
HD	O
3.5	B-Device
"	I-Device
HD	O
1440	O
KB	O
500	O
300	O
80	O
135	O
Up	O
to	O
83	O
tracks.yi.org	O
–	O
High	O
Density	O
Floppy	B-Device
Disks	I-Device
Mf2hd	O
Disk	O
3	O
5	O
1	O
Pk	O
3.5	B-Device
"	I-Device
HD	O
3.5	B-Device
"	I-Device
HD	O
1760	O
KB	O
250	O
150	O
80	O
Used	O
by	O
Amiga	B-Device
computers	I-Device
.	O
</s>
<s>
Primarily	O
in	O
Japan	O
there	O
are	O
3.5	B-Device
"	I-Device
high-density	O
floppy	B-Device
drives	I-Device
that	O
support	O
three	O
modes	O
of	O
disk	O
formats	O
instead	O
of	O
the	O
normal	O
two	O
–	O
1440KB	O
(	O
2MB	O
unformatted	O
)	O
,	O
1.2MB	O
(	O
1.6MB	O
unformatted	O
)	O
and	O
720KB	O
(	O
1MB	O
unformatted	O
)	O
.	O
</s>
<s>
Originally	O
,	O
the	O
high-density	O
mode	O
for	O
3.5	B-Device
"	I-Device
floppy	B-Device
drives	I-Device
in	O
Japan	O
only	O
supported	O
a	O
capacity	O
of	O
1.2MB	O
instead	O
of	O
the	O
1440KB	O
capacity	O
that	O
was	O
used	O
elsewhere	O
.	O
</s>
<s>
While	O
the	O
more	O
common	O
1440KB	O
format	O
spun	O
at	O
300rpm	O
,	O
the	O
1.2MB	O
format	O
instead	O
spun	O
at	O
360rpm	O
,	O
thereby	O
closely	O
resembling	O
the	O
1.2MB	O
format	O
with	O
15	O
sectors	O
per	O
track	O
previously	O
found	O
on	O
5.25	B-Device
"	I-Device
high-density	O
floppy	B-Device
drives	I-Device
or	O
1.2MB	O
format	O
with	O
8	O
sectors	O
per	O
track	O
previously	O
found	O
on	O
8	B-Device
"	I-Device
Double-density	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
Later	O
Japanese	O
floppy	B-Device
drives	I-Device
incorporated	O
support	O
for	O
both	O
high-density	O
formats	O
(	O
as	O
well	O
as	O
the	O
double-density	O
format	O
)	O
,	O
hence	O
the	O
name	O
3mode	O
.	O
</s>
<s>
Some	O
BIOSes	O
have	O
a	O
configuration	O
setting	O
to	O
enable	O
this	O
mode	O
for	O
floppy	B-Device
drives	I-Device
supporting	O
it	O
.	O
</s>
