<s>
The	O
Commodore	B-Device
1541	I-Device
(	O
also	O
known	O
as	O
the	O
CBM	O
1541	O
and	O
VIC-1541	B-Device
)	O
is	O
a	O
floppy	B-Device
disk	I-Device
drive	I-Device
which	O
was	O
made	O
by	O
Commodore	O
International	O
for	O
the	O
Commodore	O
64	O
(	O
C64	O
)	O
,	O
Commodore	O
's	O
most	O
popular	O
home	O
computer	O
.	O
</s>
<s>
The	O
best-known	O
floppy	B-Device
disk	I-Device
drive	I-Device
for	O
the	O
C64	O
,	O
the	O
1541	O
is	O
a	O
single-sided	O
170-kilobyte	O
drive	O
for	O
5¼	O
"	O
disks	O
.	O
</s>
<s>
The	O
1541	O
directly	O
followed	O
the	O
Commodore	B-Device
1540	I-Device
(	O
meant	O
for	O
the	O
VIC-20	B-Device
)	O
.	O
</s>
<s>
The	O
disk	O
drive	O
uses	O
group	B-Device
coded	I-Device
recording	I-Device
(	O
GCR	B-Device
)	O
and	O
contains	O
a	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
microprocessor	O
,	O
doubling	O
as	O
a	O
disk	B-General_Concept
controller	I-General_Concept
and	O
on-board	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
processor	O
.	O
</s>
<s>
The	O
number	O
of	O
sectors	O
per	O
track	O
varies	O
from	O
17	O
to	O
21	O
(	O
an	O
early	O
implementation	O
of	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
)	O
.	O
</s>
<s>
The	O
drive	O
's	O
built-in	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
is	O
CBM	B-Device
DOS	I-Device
2.6	I-Device
.	O
</s>
<s>
A	O
C64	O
plus	O
a	O
1541	O
cost	O
about	O
$900	O
,	O
while	O
an	O
Apple	B-Device
II	I-Device
with	O
no	O
disk	O
drive	O
cost	O
$	O
1,295	O
.	O
</s>
<s>
The	O
first	O
1541	O
drives	O
produced	O
in	O
1982	O
have	O
a	O
label	O
on	O
the	O
front	O
reading	O
VIC-1541	B-Device
and	O
have	O
an	O
off-white	O
case	O
to	O
match	O
the	O
VIC-20	B-Device
.	O
</s>
<s>
The	O
company	O
said	O
that	O
the	O
shortage	O
occurred	O
because	O
90%	O
of	O
C64	O
owners	O
bought	O
the	O
1541	O
compared	O
to	O
its	O
30%	O
expectation	O
,	O
but	O
the	O
press	O
discussed	O
what	O
Creative	B-General_Concept
Computing	I-General_Concept
described	O
as	O
"	O
an	O
absolutely	O
alarming	O
return	O
rate	O
"	O
because	O
of	O
defects	O
.	O
</s>
<s>
This	O
style	O
of	O
drive	O
has	O
the	O
popular	O
nickname	O
"	O
Toaster	B-Application
Drive	O
"	O
,	O
because	O
it	O
requires	O
the	O
use	O
of	O
a	O
knife	O
or	O
other	O
hard	O
thin	O
object	O
to	O
pry	O
out	O
the	O
stuck	O
media	O
just	O
like	O
a	O
piece	O
of	O
toast	O
stuck	O
in	O
an	O
actual	O
toaster	B-Application
.	O
</s>
<s>
In	O
addition	O
,	O
Commodore	O
made	O
the	O
drive	O
's	O
controller	O
board	O
smaller	O
and	O
reduced	O
its	O
chip	O
count	O
compared	O
to	O
the	O
early	O
1541s	O
(	O
which	O
had	O
a	O
large	O
PCB	O
running	O
the	O
length	O
of	O
the	O
case	O
,	O
with	O
dozens	O
of	O
TTL	B-General_Concept
chips	I-General_Concept
)	O
.	O
</s>
<s>
Visually	O
,	O
the	O
first	O
models	O
,	O
of	O
the	O
VIC-1541	B-Device
denomination	O
,	O
have	O
an	O
off-white	O
color	O
like	O
the	O
VIC-20	B-Device
and	O
VIC-1540	B-Device
.	O
</s>
<s>
Then	O
,	O
to	O
match	O
the	O
look	O
of	O
the	O
C64	O
,	O
CBM	O
changed	O
the	O
drive	O
's	O
color	O
to	O
brown-beige	O
and	O
the	O
name	O
to	O
Commodore	B-Device
1541	I-Device
.	O
</s>
<s>
Excelerator+	O
,	O
the	O
MSD	B-Device
Super	I-Device
Disk	I-Device
single	O
and	O
dual	O
drives	O
,	O
the	O
Enhancer	O
2000	O
,	O
the	O
Indus	B-Device
GT	I-Device
,	O
Blue	O
Chip	O
Electronics	O
's	O
BCD/5.25	O
,	O
and	O
CMDs	O
FD-2000	O
and	O
FD-4000	O
.	O
</s>
<s>
The	O
Commodore	B-Device
1570	I-Device
is	O
an	O
upgrade	O
from	O
the	O
1541	O
for	O
use	O
with	O
the	O
Commodore	B-Device
128	I-Device
,	O
available	O
in	O
Europe	O
.	O
</s>
<s>
It	O
offers	O
MFM	B-Protocol
capability	O
for	O
accessing	O
CP/M	B-Application
disks	O
,	O
improved	O
speed	O
,	O
and	O
somewhat	O
quieter	O
operation	O
,	O
but	O
was	O
only	O
manufactured	O
until	O
Commodore	O
got	O
its	O
production	O
lines	O
going	O
with	O
the	O
1571	B-Device
,	O
the	O
double-sided	O
drive	O
.	O
</s>
<s>
Finally	O
,	O
the	O
small	O
,	O
external-power-supply-based	O
,	O
MFM-based	O
Commodore	O
1581	O
3½-inch	O
drive	O
was	O
made	O
,	O
giving	O
800KB	O
access	O
to	O
the	O
C128	O
and	O
C64	O
.	O
</s>
<s>
Unlike	O
the	O
Apple	B-Device
II	I-Device
,	O
where	O
support	O
for	O
two	O
drives	O
is	O
normal	O
,	O
it	O
is	O
relatively	O
uncommon	O
for	O
Commodore	O
software	O
to	O
support	O
this	O
setup	O
,	O
and	O
the	O
CBM	B-Device
DOS	I-Device
copy	O
file	O
command	O
is	O
not	O
able	O
to	O
copy	O
files	O
between	O
drives	O
–	O
a	O
third	O
party	O
copy	O
utility	O
is	O
necessary	O
.	O
</s>
<s>
The	O
MikroBitti	O
review	O
of	O
the	O
1541-II	O
said	O
that	O
its	O
external	O
power	O
source	O
"	O
should	O
end	O
the	O
jokes	O
about	O
toasters	B-Application
"	O
.	O
</s>
<s>
The	O
most	O
common	O
cause	O
of	O
the	O
1541	O
's	O
drive	O
head	O
knocking	O
and	O
subsequent	O
misalignment	O
is	O
copy-protection	B-Application
schemes	O
on	O
commercial	O
software	O
.	O
</s>
<s>
The	O
later	O
1571	B-Device
drive	O
(	O
which	O
is	O
1541-compatible	O
)	O
incorporates	O
track-zero	O
detection	O
by	O
photo-interrupter	O
and	O
is	O
thus	O
immune	O
to	O
the	O
problem	O
.	O
</s>
<s>
Also	O
,	O
a	O
software	O
solution	O
,	O
which	O
resides	O
in	O
the	O
drive	B-General_Concept
controller	I-General_Concept
's	O
ROM	O
,	O
prevents	O
the	O
rereads	O
from	O
occurring	O
,	O
though	O
this	O
can	O
cause	O
problems	O
when	O
genuine	O
errors	O
do	O
occur	O
.	O
</s>
<s>
The	O
1541	O
's	O
PCB	O
consists	O
mainly	O
of	O
a	O
6502	B-General_Concept
CPU	O
,	O
two	O
6522	B-Device
VIA	I-Device
chips	O
,	O
and	O
2k	O
of	O
work	O
RAM	O
.	O
</s>
<s>
Up	O
to	O
48k	O
of	O
RAM	O
can	O
be	O
added	O
;	O
this	O
is	O
mainly	O
useful	O
for	O
defeating	O
copy	B-Application
protection	I-Application
schemes	O
since	O
an	O
entire	O
disk	O
track	O
could	O
be	O
loaded	O
into	O
drive	O
RAM	O
,	O
while	O
the	O
standard	O
2k	O
only	O
accommodates	O
a	O
few	O
sectors	O
(	O
theoretically	O
eight	O
,	O
but	O
some	O
of	O
the	O
RAM	O
was	O
used	O
by	O
CBM	B-Device
DOS	I-Device
as	O
work	O
space	O
)	O
.	O
</s>
<s>
The	O
1541	O
uses	O
a	O
proprietary	B-Protocol
serialized	I-Protocol
derivative	I-Protocol
of	O
the	O
IEEE-488	O
parallel	O
interface	O
,	O
found	O
in	O
previous	O
disk	O
drives	O
for	O
the	O
PET/CBM	B-Device
range	O
of	O
personal	O
and	O
business	O
computers	O
,	O
but	O
when	O
the	O
VIC-20	B-Device
was	O
in	O
development	O
,	O
a	O
cheaper	O
alternative	O
to	O
the	O
expensive	O
IEEE-488	O
cables	O
was	O
sought	O
.	O
</s>
<s>
To	O
ensure	O
a	O
ready	O
supply	O
of	O
inexpensive	O
cabling	O
for	O
its	O
home	O
computer	O
peripherals	O
,	O
Commodore	O
chose	O
standard	O
DIN	B-Architecture
connectors	I-Architecture
for	O
the	O
serial	O
interface	O
.	O
</s>
<s>
Disk	O
drives	O
and	O
other	O
peripherals	O
such	O
as	O
printers	O
connect	O
to	O
the	O
computer	O
via	O
a	O
daisy	B-Application
chain	I-Application
setup	O
,	O
necessitating	O
only	O
a	O
single	O
connector	O
on	O
the	O
computer	O
itself	O
.	O
</s>
<s>
The	O
C-64	O
'	O
s	O
designers	O
blamed	O
the	O
1541	O
's	O
slow	O
speed	O
on	O
the	O
marketing	O
department	O
's	O
insistence	O
that	O
the	O
computer	O
be	O
compatible	O
with	O
the	O
1540	O
,	O
which	O
is	O
slow	O
because	O
of	O
a	O
flaw	O
in	O
the	O
6522	B-Device
VIA	I-Device
interface	O
controller	O
.	O
</s>
<s>
Initially	O
,	O
Commodore	O
intended	O
to	O
use	O
a	O
hardware	O
shift	B-General_Concept
register	I-General_Concept
(	O
one	O
component	O
of	O
the	O
6522	B-Device
)	O
to	O
maintain	O
fast	O
drive	O
speeds	O
with	O
the	O
new	O
serial	O
interface	O
.	O
</s>
<s>
As	O
implemented	O
on	O
the	O
VIC-20	B-Device
and	O
C64	O
,	O
Commodore	B-Device
DOS	I-Device
transfers	O
300	O
bytes	O
per	O
second	O
,	O
compared	O
to	O
the	O
Atari	B-Device
810	I-Device
's	O
2,400	O
bytes	O
per	O
second	O
,	O
the	O
Apple	B-Device
Disk	I-Device
II	I-Device
's	O
15,000	O
bytes	O
per	O
second	O
,	O
and	O
the	O
300-baud	O
data	O
rate	O
of	O
the	O
Commodore	B-Device
Datasette	I-Device
storage	O
system	O
.	O
</s>
<s>
Without	O
hardware	O
modifications	O
,	O
some	O
"	O
fast	B-Device
loader	I-Device
"	O
utilities	O
(	O
which	O
bypassed	O
routines	O
in	O
the	O
1541	O
's	O
onboard	O
ROM	O
)	O
managed	O
to	O
achieve	O
speeds	O
of	O
up	O
to	O
4KB/s	O
.	O
</s>
<s>
The	O
most	O
common	O
of	O
these	O
products	O
are	O
the	O
Epyx	B-Application
Fast	I-Application
Load	I-Application
,	O
the	O
Final	B-Device
Cartridge	I-Device
,	O
and	O
the	O
Action	B-Device
Replay	I-Device
plug-in	O
ROM	B-Protocol
cartridges	I-Protocol
,	O
which	O
all	O
have	O
machine	B-General_Concept
code	I-General_Concept
monitor	I-General_Concept
and	O
disk	B-Application
editor	I-Application
software	O
on	O
board	O
as	O
well	O
.	O
</s>
<s>
Even	O
though	O
each	O
1541	O
has	O
its	O
own	O
on-board	O
disk	B-General_Concept
controller	I-General_Concept
and	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
it	O
is	O
not	O
possible	O
for	O
a	O
user	O
to	O
command	O
two	O
1541	O
drives	O
to	O
copy	O
a	O
disk	O
(	O
one	O
drive	O
reading	O
and	O
the	O
other	O
writing	O
)	O
as	O
with	O
older	O
dual	O
drives	O
like	O
the	O
4040	B-Device
that	O
was	O
often	O
found	O
with	O
the	O
PET	B-Device
computer	I-Device
,	O
and	O
which	O
the	O
1541	O
is	O
backward-compatible	O
with	O
(	O
it	O
can	O
read	O
4040	B-Device
disks	O
but	O
not	O
write	O
to	O
them	O
as	O
a	O
minor	O
difference	O
in	O
the	O
number	O
of	O
header	O
bytes	O
makes	O
the	O
4040	B-Device
and	O
1541	O
only	O
read-compatible	O
)	O
.	O
</s>
<s>
Only	O
when	O
Fast	B-Application
Hack'em	I-Application
and	O
,	O
later	O
,	O
other	O
disk	O
backup	O
programs	O
were	O
released	O
,	O
was	O
true	O
drive-to-drive	O
copying	O
possible	O
for	O
a	O
pair	O
of	O
1541s	O
.	O
</s>
<s>
The	O
user	O
could	O
,	O
if	O
they	O
wished	O
,	O
unplug	O
the	O
C64	O
from	O
the	O
drives	O
(	O
i.e.	O
,	O
from	O
the	O
first	O
drive	O
in	O
the	O
daisy	B-Application
chain	I-Application
)	O
and	O
do	O
something	O
else	O
with	O
the	O
computer	O
as	O
the	O
drives	O
proceeded	O
to	O
copy	O
the	O
entire	O
disk	O
.	O
</s>
<s>
The	O
1541	O
drive	O
uses	O
standard	O
5¼-inch	O
double-density	O
floppy	B-Device
media	O
;	O
high-density	O
media	O
will	O
not	O
work	O
due	O
to	O
its	O
different	O
magnetic	O
coating	O
requiring	O
a	O
higher	O
magnetic	O
coercivity	O
.	O
</s>
<s>
As	O
the	O
GCR	B-Device
encoding	I-Device
scheme	O
does	O
not	O
use	O
the	O
index	O
hole	O
,	O
the	O
drive	O
was	O
also	O
compatible	O
with	O
hard-sectored	O
disks	O
.	O
</s>
<s>
The	O
standard	O
CBM	B-Device
DOS	I-Device
format	O
is	O
170	O
KB	O
with	O
35	O
tracks	O
and	O
256-byte	O
sectors	O
.	O
</s>
<s>
It	O
is	O
similar	O
to	O
the	O
format	O
used	O
on	O
the	O
PET	O
2031	O
,	O
2040	O
&	O
4040	B-Device
drives	O
,	O
but	O
a	O
minor	O
difference	O
in	O
the	O
number	O
of	O
header	O
bytes	O
makes	O
these	O
drives	O
and	O
the	O
1541	O
only	O
read-compatible	O
;	O
disks	O
formatted	O
with	O
one	O
drive	O
cannot	O
be	O
written	O
to	O
by	O
the	O
other	O
.	O
</s>
<s>
The	O
4040	B-Device
drives	O
use	O
Shugart	O
SA-400s	O
,	O
which	O
were	O
35-track	O
units	O
,	O
thus	O
the	O
format	O
there	O
is	O
due	O
to	O
physical	O
limitations	O
of	O
the	O
drive	O
mechanism	O
.	O
</s>
<s>
The	O
1541	O
uses	O
40	O
track	O
mechanisms	O
,	O
but	O
Commodore	O
intentionally	O
limited	O
the	O
CBM	B-Device
DOS	I-Device
format	O
to	O
35	O
tracks	O
because	O
of	O
reliability	O
issues	O
with	O
the	O
early	O
units	O
.	O
</s>
<s>
It	O
is	O
possible	O
via	O
low-level	O
programming	O
to	O
move	O
the	O
drive	O
head	O
to	O
tracks	O
36	O
–	O
40	O
and	O
write	O
on	O
them	O
,	O
this	O
is	O
sometimes	O
done	O
by	O
commercial	O
software	O
for	O
copy	B-Application
protection	I-Application
purposes	O
and/or	O
to	O
get	O
additional	O
data	O
on	O
the	O
disk	O
.	O
</s>
<s>
However	O
,	O
one	O
track	O
is	O
reserved	O
by	O
DOS	O
for	O
directory	O
and	O
file	O
allocation	O
information	O
(	O
the	O
BAM	O
,	O
block	B-Application
availability	I-Application
map	I-Application
)	O
.	O
</s>
<s>
Owing	O
to	O
the	O
drive	O
's	O
non-use	O
of	O
the	O
index	O
hole	O
,	O
it	O
is	O
also	O
possible	O
to	O
make	O
"	O
flippy	O
floppies	B-Device
"	O
by	O
inserting	O
the	O
diskette	B-Device
upside-down	O
and	O
formatting	O
the	O
other	O
side	O
,	O
and	O
it	O
is	O
commonplace	O
and	O
normal	O
for	O
commercial	O
software	O
to	O
be	O
distributed	O
on	O
such	O
disks	O
.	O
</s>
<s>
The	O
bitrate	O
is	O
the	O
raw	O
one	O
between	O
the	O
read/write	O
head	O
and	O
signal	O
circuitry	O
so	O
actual	O
useful	O
data	O
rate	O
is	O
a	O
factor	O
5/4	O
less	O
due	O
to	O
GCR	B-Device
encoding	I-Device
.	O
</s>
<s>
Early	O
copy	B-Application
protection	I-Application
schemes	O
deliberately	O
introduce	O
read	O
errors	O
on	O
the	O
disk	O
,	O
the	O
software	O
refusing	O
to	O
load	O
unless	O
the	O
correct	O
error	O
message	O
is	O
returned	O
.	O
</s>
<s>
When	O
one	O
of	O
these	O
errors	O
is	O
encountered	O
,	O
the	O
disk	O
drive	O
(	O
as	O
do	O
many	O
floppy	B-Device
disk	I-Device
drives	I-Device
)	O
will	O
attempt	O
one	O
or	O
more	O
reread	O
attempts	O
after	O
first	O
resetting	O
the	O
head	O
to	O
track	O
zero	O
.	O
</s>
<s>
Commodore	O
copy	B-Application
protection	I-Application
sometimes	O
fails	O
on	O
specific	O
hardware	O
configurations	O
.	O
</s>
<s>
Gunship	B-Application
,	O
for	O
example	O
,	O
does	O
not	O
load	O
if	O
a	O
second	O
disk	O
drive	O
or	O
printer	O
is	O
connected	O
to	O
the	O
computer	O
.	O
</s>
<s>
The	O
tape	O
version	O
will	O
even	O
crash	O
if	O
a	O
floppy	B-Device
drive	I-Device
is	O
switched	O
on	O
while	O
the	O
game	O
is	O
running	O
.	O
</s>
