<s>
The	O
FD1771	B-Device
,	O
sometimes	O
WD1771	B-Device
,	O
is	O
the	O
first	O
in	O
a	O
line	O
of	O
floppy	B-Device
disk	I-Device
controllers	I-Device
produced	O
by	O
Western	O
Digital	O
.	O
</s>
<s>
It	O
uses	O
single	B-Device
density	I-Device
FM	B-Protocol
encoding	I-Protocol
introduced	O
in	O
the	O
IBM	B-Device
3740	I-Device
.	O
</s>
<s>
It	O
is	O
packaged	O
in	O
a	O
40-pin	O
DIP	B-Algorithm
.	O
</s>
<s>
Later	O
models	O
in	O
the	O
series	O
added	O
support	O
for	O
MFM	B-Protocol
encoding	I-Protocol
and	O
increasingly	O
added	O
onboard	O
circuitry	O
that	O
formerly	O
had	O
to	O
be	O
implemented	O
in	O
external	O
components	O
.	O
</s>
<s>
Originally	O
packaged	O
as	O
40-pin	O
dual	B-Algorithm
in-line	I-Algorithm
package	I-Algorithm
(	O
DIP	B-Algorithm
)	O
format	O
,	O
later	O
models	O
moved	O
to	O
a	O
28-pin	O
format	O
that	O
further	O
lowered	O
implementation	O
costs	O
.	O
</s>
<s>
The	O
FD1771	B-Device
was	O
succeeded	O
by	O
many	O
derivatives	O
that	O
were	O
mostly	O
software-compatible	O
:	O
</s>
<s>
The	O
FD1781	O
was	O
designed	O
for	O
double	B-Device
density	I-Device
,	O
but	O
required	O
external	O
modulation	O
and	O
demodulation	O
circuitry	O
,	O
so	O
it	O
could	O
support	O
MFM	B-Protocol
,	O
M2FM	O
,	O
GCR	B-Device
or	O
other	O
double-density	O
encodings	O
.	O
</s>
<s>
The	O
FD1791-FD1797	O
series	O
added	O
internal	O
support	O
for	O
double	B-Device
density	I-Device
(	O
MFM	B-Protocol
)	O
modulation	O
,	O
compatible	O
with	O
the	O
IBM	B-Device
System/34	I-Device
disk	O
format	O
.	O
</s>
<s>
The	O
WD1761-WD1767	O
series	O
were	O
versions	O
of	O
the	O
FD179x	O
series	O
rated	O
for	O
a	O
maximum	O
clock	O
frequency	O
of	O
1	O
MHz	O
,	O
resulting	O
in	O
a	O
data	O
rate	O
limit	O
of	O
125	O
kbit/s	O
for	O
single	B-Device
density	I-Device
and	O
250	O
kbit/s	O
for	O
double	B-Device
density	I-Device
,	O
thus	O
preventing	O
them	O
from	O
being	O
used	O
for	O
8-in	O
(	O
200mm	O
)	O
floppy	O
drives	O
or	O
the	O
later	O
"	O
high-density	O
"	O
or	O
90mm	O
floppy	O
drives	O
.	O
</s>
<s>
The	O
WD1770	B-Device
,	O
WD1772	O
,	O
and	O
WD1773	O
added	O
an	O
internal	O
digital	O
data	O
separator	O
and	O
write	O
precompensator	O
,	O
eliminating	O
the	O
need	O
for	O
external	O
passive	O
components	O
but	O
raising	O
the	O
clock	O
rate	O
requirement	O
to	O
8MHz	O
.	O
</s>
<s>
They	O
supported	O
double	B-Device
density	I-Device
,	O
despite	O
the	O
apparent	O
regression	O
of	O
the	O
part	O
number	O
,	O
and	O
were	O
packaged	O
in	O
28-pin	O
DIP	B-Algorithm
packages	O
.	O
</s>
<s>
The	O
chip	O
was	O
codenamed	O
"	O
Ajax	B-Device
"	O
,	O
had	O
the	O
number	O
C302096	O
and	O
was	O
produced	O
by	O
Toshiba	O
.	O
</s>
<s>
These	O
were	O
used	O
in	O
many	O
microcomputers	B-Architecture
including	O
the	O
TRS-80	B-Device
,	O
Acorn	B-Device
Electron	I-Device
,	O
BBC	B-Device
Master	I-Device
,	O
Atari	B-Device
ST	I-Device
,	O
Acorn	B-Device
Archimedes	I-Device
,	O
and	O
the	O
SAM	B-Device
Coupé	I-Device
,	O
as	O
well	O
as	O
the	O
+D	B-Device
and	O
DISCiPLE	B-Device
disk	O
interfaces	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
the	O
Commodore	O
157x/1581	O
for	O
the	O
Commodore	O
64	O
and	O
the	O
Atari	B-Device
XF551	I-Device
for	O
the	O
Atari_8-bit_family	O
.	O
</s>
