<s>
The	O
Commodore	B-Device
1571	I-Device
is	O
Commodore	O
's	O
high-end	O
5¼	O
"	O
floppy	B-Device
disk	I-Device
drive	I-Device
,	O
announced	O
in	O
the	O
summer	O
of	O
1985	O
.	O
</s>
<s>
With	O
its	O
double-sided	B-Architecture
drive	O
mechanism	O
,	O
it	O
has	O
the	O
ability	O
to	O
use	O
double-sided	B-Architecture
,	O
double-density	O
(	O
DS/DD	O
)	O
floppy	B-Device
disks	I-Device
,	O
storing	O
a	O
total	O
of	O
360kB	O
per	O
floppy	B-Device
.	O
</s>
<s>
Earlier	O
Commodore	O
drives	O
used	O
a	O
custom	O
group	B-Device
coded	I-Device
recording	I-Device
format	O
that	O
stored	O
170kB	O
per	O
side	O
of	O
a	O
disk	O
.	O
</s>
<s>
The	O
1571	O
was	O
designed	O
to	O
partner	O
with	O
the	O
new	O
Commodore	B-Device
128	I-Device
(	O
C128	O
)	O
,	O
which	O
introduced	O
support	O
for	O
CP/M	B-Application
.	O
</s>
<s>
Adding	O
double-density	O
MFM	B-Protocol
encoding	I-Protocol
allowed	O
the	O
drive	O
to	O
read	O
and	O
write	O
contemporary	O
CP/M	B-Application
disks	O
(	O
and	O
many	O
others	O
)	O
.	O
</s>
<s>
In	O
contrast	O
to	O
its	O
single-sided	O
predecessors	O
,	O
the	O
1541	B-Device
and	O
the	O
briefly-available	O
1570	B-Device
,	O
the	O
1571	O
can	O
use	O
both	O
sides	O
of	O
the	O
disk	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Because	O
flipping	O
the	O
disk	O
also	O
reverses	O
the	O
direction	O
of	O
rotation	O
,	O
the	O
two	O
methods	O
are	O
not	O
interchangeable	O
;	O
disks	O
which	O
had	O
their	O
back	O
side	O
created	O
in	O
a	O
1541	B-Device
by	O
flipping	O
them	O
over	O
would	O
have	O
to	O
be	O
flipped	O
in	O
the	O
1571	O
too	O
,	O
and	O
the	O
back	O
side	O
of	O
disks	O
written	O
in	O
a	O
1571	O
using	O
the	O
native	O
support	O
for	O
two-sided	O
operation	O
could	O
not	O
be	O
read	O
in	O
a	O
1541	B-Device
.	O
</s>
<s>
The	O
1571	O
was	O
released	O
to	O
match	O
the	O
Commodore	B-Device
128	I-Device
,	O
both	O
design-wise	O
and	O
feature-wise	O
.	O
</s>
<s>
A	O
double-sided	B-Architecture
disk	I-Architecture
on	O
the	O
1571	O
would	O
have	O
a	O
capacity	O
of	O
340	O
kB	O
(	O
70	O
tracks	O
,	O
1,360	O
disk	O
blocks	O
of	O
256	O
bytes	B-Application
each	O
)	O
;	O
as	O
8	O
kB	O
are	O
reserved	O
for	O
system	O
use	O
(	O
directory	O
and	O
block	O
availability	O
information	O
)	O
and	O
,	O
under	O
of	O
each	O
block	O
serve	O
as	O
pointers	O
to	O
the	O
next	O
logical	O
block	O
,	O
=	O
337,312	O
B	B-Application
or	O
about	O
were	O
available	O
for	O
user	O
data	O
.	O
</s>
<s>
This	O
mode	O
replaced	O
the	O
slow	O
bit-banging	B-Algorithm
serial	O
routines	O
of	O
the	O
1541	B-Device
with	O
a	O
true	O
serial	O
shift	B-General_Concept
register	I-General_Concept
implemented	O
in	O
hardware	O
,	O
thus	O
dramatically	O
increasing	O
the	O
drive	O
speed	O
.	O
</s>
<s>
Although	O
this	O
originally	O
had	O
been	O
planned	O
when	O
Commodore	O
first	O
switched	O
from	O
the	O
parallel	O
IEEE-488	O
interface	O
to	O
the	O
CBM-488	B-Protocol
custom	O
serial	O
interface	O
,	O
hardware	O
bugs	O
in	O
the	O
VIC-20	O
'	O
s	O
6522	B-Device
VIA	I-Device
shift	B-General_Concept
register	I-General_Concept
prevented	O
it	O
from	O
working	O
properly	O
.	O
</s>
<s>
When	O
connected	O
to	O
a	O
C128	O
,	O
the	O
1571	O
would	O
default	O
to	O
double-sided	B-Architecture
mode	O
,	O
which	O
allowed	O
the	O
drive	O
to	O
read	O
its	O
own	O
340k	O
disks	O
as	O
well	O
as	O
single-sided	O
170	O
kB	O
1541	B-Device
disks	O
.	O
</s>
<s>
If	O
the	O
C128	O
was	O
switched	O
into	O
C64	O
mode	O
by	O
typing	O
GO	O
64	O
from	O
BASIC	O
,	O
the	O
1571	O
will	O
stay	O
in	O
double-sided	B-Architecture
mode	O
.	O
</s>
<s>
There	O
is	O
also	O
an	O
undocumented	O
command	O
which	O
allows	O
the	O
user	O
to	O
independently	O
control	O
either	O
of	O
the	O
read/write	O
heads	O
of	O
the	O
1571	O
,	O
making	O
it	O
possible	O
to	O
format	O
both	O
sides	O
of	O
a	O
diskette	B-Device
separate	O
from	O
each	O
other	O
,	O
however	O
the	O
resultant	O
disk	O
cannot	O
be	O
read	O
in	O
a	O
1541	B-Device
as	O
it	O
would	O
be	O
spinning	O
in	O
reverse	O
direction	O
when	O
flipped	O
upside	O
down	O
.	O
</s>
<s>
In	O
the	O
same	O
vein	O
,	O
"	O
flippy	O
"	O
disks	O
created	O
with	O
a	O
1541	B-Device
cannot	O
be	O
read	O
on	O
a	O
1571	O
with	O
this	O
feature	O
;	O
they	O
must	O
be	O
inserted	O
upside	O
down	O
.	O
</s>
<s>
The	O
1571	O
is	O
not	O
100%	O
low-level	O
compatible	O
with	O
the	O
1541	B-Device
,	O
however	O
this	O
is	O
n't	O
a	O
problem	O
except	O
in	O
some	O
software	O
that	O
uses	O
advanced	O
copy	B-Application
protections	I-Application
such	O
as	O
the	O
RapidLok	O
system	O
found	O
on	O
Microprose	O
and	O
Accolade	O
games	O
.	O
</s>
<s>
The	O
1571	O
was	O
noticeably	O
quieter	O
than	O
its	O
predecessor	O
and	O
tended	O
to	O
run	O
cooler	O
as	O
well	O
,	O
even	O
though	O
,	O
like	O
the	O
1541	B-Device
,	O
it	O
had	O
an	O
internal	O
power	O
supply	O
(	O
later	O
Commodore	O
drives	O
,	O
like	O
the	O
1541-II	O
and	O
the	O
3½	O
"	O
1581	O
,	O
came	O
with	O
external	O
power	O
supplies	O
)	O
.	O
</s>
<s>
The	O
1541-II/1581	O
power	O
supply	O
makes	O
mention	O
of	O
a	O
1571-II	O
,	O
hinting	O
that	O
Commodore	O
may	O
have	O
intended	O
to	O
release	O
a	O
version	O
of	O
the	O
1571	O
with	O
an	O
external	O
power	O
supply	O
.	O
</s>
<s>
A	O
version	O
2	O
ROM	O
was	O
released	O
,	O
but	O
though	O
it	O
cured	O
the	O
initial	O
bug	O
,	O
it	O
introduced	O
some	O
minor	O
quirks	O
of	O
its	O
own	O
-	O
particularly	O
with	O
the	O
1541	B-Device
emulation	O
.	O
</s>
<s>
As	O
with	O
the	O
1541	B-Device
,	O
Commodore	O
initially	O
could	O
not	O
meet	O
demand	O
for	O
the	O
1571	O
,	O
and	O
that	O
lack	O
of	O
availability	O
and	O
the	O
drive	O
's	O
relatively	O
high	O
price	O
(	O
about	O
US$300	O
)	O
presented	O
an	O
opportunity	O
for	O
cloners	O
.	O
</s>
<s>
Commodore	O
announced	O
at	O
the	O
1985	O
Consumer	O
Electronics	O
Show	O
a	O
dual-drive	O
version	O
of	O
the	O
1571	O
,	O
to	O
be	O
called	O
the	O
Commodore	B-Device
1572	I-Device
,	O
but	O
quickly	O
canceled	O
it	O
,	O
reportedly	O
due	O
to	O
technical	O
difficulties	O
with	O
the	O
1572	O
DOS	O
.	O
</s>
<s>
The	O
1572	O
would	O
have	O
allowed	O
for	O
fast	O
disk	O
backups	O
of	O
non-copy-protected	B-Application
media	O
,	O
much	O
like	O
the	O
old	O
4040	B-Device
,	O
8050	B-Device
,	O
and	O
8250	O
dual	O
drives	O
.	O
</s>
<s>
It	O
includes	O
a	O
newer	O
DOS	O
,	O
version	O
3.1	O
,	O
replaces	O
the	O
MOS	B-Device
Technology	I-Device
CIA	I-Device
interface	O
chip	O
,	O
of	O
which	O
only	O
a	O
few	O
features	O
were	O
used	O
by	O
the	O
1571	O
DOS	O
,	O
with	O
a	O
very	O
much	O
simplified	O
chip	O
called	O
5710	O
,	O
and	O
has	O
some	O
compatibility	O
issues	O
with	O
the	O
stand-alone	O
drive	O
.	O
</s>
<s>
Because	O
this	O
internal	O
1571	O
does	O
not	O
have	O
an	O
unused	O
8-bit	O
input/output	O
port	O
on	O
any	O
chip	O
,	O
unlike	O
most	O
other	O
Commodore	O
drives	O
,	O
it	O
is	O
not	O
possible	O
to	O
install	O
a	O
parallel	O
cable	O
in	O
this	O
drive	O
,	O
such	O
as	O
that	O
used	O
by	O
SpeedDOS	O
,	O
DolphinDOS	B-Device
and	O
some	O
other	O
fast	O
third-party	O
Commodore	B-Device
DOS	I-Device
replacements	O
.	O
</s>
<s>
With	O
the	O
GCR	B-Device
recording	O
format	O
a	O
problem	O
occurs	O
in	O
the	O
read	O
signal	O
waveform	O
.	O
</s>
<s>
The	O
original	O
1541	B-Device
drives	O
uses	O
a	O
one-shot	O
to	O
correct	O
the	O
condition	O
.	O
</s>
<s>
The	O
drive	O
uses	O
the	O
MOS	B-General_Concept
6502	I-General_Concept
CPU	O
,	O
WD1770	B-Device
or	O
WD1772	O
floppy	B-Device
controller	O
,	O
2x	O
MOS	B-Device
Technology	I-Device
6522	I-Device
I/O	O
controllers	O
and	O
1x	O
MOS	B-Device
Technology	I-Device
6526	I-Device
.	O
</s>
<s>
Unlike	O
the	O
1541	B-Device
,	O
which	O
was	O
limited	O
to	O
GCR	B-Device
formatting	O
,	O
the	O
1571	O
could	O
read	O
both	O
GCR	B-Device
and	O
MFM	B-Protocol
disk	O
formats	O
.	O
</s>
<s>
The	O
version	O
of	O
CP/M	B-Application
included	O
with	O
the	O
C128	O
supported	O
the	O
following	O
formats	O
:	O
</s>
<s>
The	O
1571	O
can	O
read	O
any	O
of	O
the	O
many	O
CP/M	B-Application
-disk	O
formats	O
.	O
</s>
<s>
If	O
the	O
CP/M	B-Application
BIOS	O
is	O
modified	O
,	O
it	O
is	O
possible	O
to	O
read	O
any	O
soft	O
sector	O
40-track	O
MFM	B-Protocol
format	O
.	O
</s>
<s>
Single	O
density	O
(	O
FM	B-Protocol
)	O
formats	O
are	O
not	O
supported	O
because	O
the	O
density	O
selector	O
pin	O
on	O
the	O
MFM	B-Protocol
controller	O
chip	O
in	O
the	O
drive	O
is	O
disabled	O
(	O
wired	O
to	O
ground	O
)	O
.	O
</s>
<s>
A	O
1571	O
cannot	O
boot	O
from	O
MFM	B-Protocol
disks	O
;	O
the	O
user	O
must	O
boot	O
CP/M	B-Application
from	O
a	O
GCR	B-Device
disk	O
and	O
then	O
switch	O
to	O
MFM	B-Protocol
disks	O
.	O
</s>
<s>
With	O
additional	O
software	O
,	O
it	O
was	O
possible	O
to	O
read	O
and	O
write	O
to	O
MS-DOS-formatted	O
floppies	B-Device
as	O
well	O
.	O
</s>
<s>
Reading	O
or	O
disks	O
was	O
possible	O
as	O
well	O
with	O
special	O
software	O
,	O
but	O
the	O
standard	O
format	O
,	O
which	O
used	O
FM	B-Protocol
rather	O
than	O
MFM	B-Protocol
encoding	I-Protocol
,	O
could	O
not	O
be	O
handled	O
by	O
the	O
1571	O
hardware	O
without	O
modifying	O
the	O
drive	O
circuitry	O
as	O
the	O
control	O
line	O
that	O
determines	O
if	O
FM	B-Protocol
or	O
MFM	B-Protocol
encoding	I-Protocol
is	O
used	O
by	O
the	O
disc	O
controller	O
chip	O
was	O
permanently	O
wired	O
to	O
ground	O
(	O
MFM	B-Protocol
mode	O
)	O
rather	O
than	O
being	O
under	O
software	O
control	O
.	O
</s>
<s>
In	O
the	O
1541	B-Device
format	O
,	O
while	O
40	O
tracks	O
are	O
possible	O
for	O
a	O
drive	O
like	O
the	O
154x/157x	O
,	O
only	O
are	O
used	O
.	O
</s>
<s>
For	O
compatibility	O
and	O
ease	O
of	O
implementation	O
,	O
the	O
1571	O
's	O
double-sided	B-Architecture
format	O
of	O
one	O
logical	O
disk	O
side	O
with	O
was	O
created	O
by	O
putting	O
together	O
the	O
lower	O
35	O
physical	O
tracks	O
on	O
each	O
of	O
the	O
physical	O
sides	O
of	O
the	O
disk	O
rather	O
than	O
using	O
two	O
times	O
even	O
though	O
there	O
were	O
no	O
more	O
quality	O
problems	O
with	O
the	O
mechanisms	O
of	O
the	O
1571	O
drives	O
.	O
</s>
