<s>
A	O
bit	B-Device
nibbler	I-Device
,	O
or	O
nibbler	O
,	O
is	O
a	O
computer	O
software	O
program	O
designed	O
to	O
copy	O
data	O
from	O
a	O
floppy	B-Device
disk	I-Device
one	O
bit	O
at	O
a	O
time	O
.	O
</s>
<s>
It	O
functions	O
at	O
a	O
very	O
low	O
level	O
directly	O
interacting	O
with	O
the	O
disk	O
drive	O
hardware	O
to	O
override	O
a	O
copy	O
protection	O
scheme	O
that	O
the	O
floppy	B-Device
disk	I-Device
's	O
data	O
may	O
be	O
stored	O
in	O
.	O
</s>
<s>
In	O
most	O
cases	O
the	O
nibbler	O
software	O
still	O
analyses	O
the	O
data	O
on	O
a	O
byte	B-Application
level	O
,	O
only	O
looking	O
to	O
the	O
bit	O
level	O
when	O
dealing	O
with	O
synchronization	O
marks	O
(	O
syncs	O
)	O
,	O
zero-gaps	O
and	O
other	O
sector	O
&	O
track	O
headers	O
.	O
</s>
<s>
When	O
possible	O
,	O
nibblers	O
will	O
work	O
with	O
the	O
low-level	O
data	B-Device
encoding	I-Device
format	I-Device
used	O
by	O
the	O
disk	O
system	O
,	O
being	O
Group	B-Device
Coded	I-Device
Recording	I-Device
(	O
GCR	B-Device
-	O
Apple	B-Device
,	O
Commodore	O
)	O
,	O
Frequency	B-Protocol
Modulation	I-Protocol
(	O
FM	B-Protocol
-	O
Atari	O
)	O
,	O
or	O
Modified	B-Protocol
Frequency	I-Protocol
Modulation	I-Protocol
(	O
MFM	B-Protocol
-	O
Amiga	B-Device
,	O
Atari	O
,	O
IBM	B-Device
PC	I-Device
)	O
.	O
</s>
<s>
Software	O
piracy	O
began	O
to	O
be	O
a	O
concern	O
when	O
floppy	B-Device
disks	I-Device
became	O
the	O
common	O
storage	O
media	O
.	O
</s>
<s>
The	O
ease	O
of	O
copying	O
depended	O
on	O
the	O
system	O
;	O
Jerry	O
Pournelle	O
wrote	O
in	O
BYTE	B-Application
in	O
1983	O
that	O
"	O
CP/M	B-Application
does	O
n't	O
lend	O
itself	O
to	O
copy	O
protection	O
"	O
so	O
its	O
users	O
"	O
have	O
n't	O
been	O
too	O
worried	O
"	O
about	O
it	O
,	O
while	O
"	O
Apple	B-Device
users	O
,	O
though	O
,	O
have	O
always	O
had	O
the	O
problem	O
.	O
</s>
<s>
So	O
have	O
those	O
who	O
used	O
TRS-DOS	B-Operating_System
,	O
and	O
I	O
understand	O
that	O
MS-DOS	B-Application
has	O
copy	O
protection	O
features	O
"	O
.	O
</s>
<s>
Apple	B-Device
and	O
Commodore	O
64	O
copy	O
protection	O
schemes	O
were	O
extremely	O
varied	O
and	O
creative	O
because	O
most	O
of	O
the	O
floppy	B-Device
disk	I-Device
reading	O
and	O
writing	O
was	O
controlled	O
by	O
software	O
(	O
or	O
firmware	B-Application
)	O
,	O
not	O
by	O
hardware	O
.	O
</s>
<s>
By	O
1980	O
,	O
the	O
first	O
'	O
nibble	O
 '	O
copier	O
,	O
Locksmith	O
,	O
was	O
introduced	O
for	O
the	O
Apple	B-Device
II	O
.	O
</s>
<s>
These	O
copiers	O
reproduced	O
copy	O
protected	O
floppy	B-Device
disks	I-Device
an	O
entire	O
track	O
at	O
a	O
time	O
,	O
ignoring	O
how	O
the	O
sectors	O
were	O
marked	O
.	O
</s>
<s>
This	O
was	O
harder	O
to	O
do	O
than	O
it	O
sounds	O
for	O
two	O
reasons	O
:	O
firstly	O
,	O
Apple	B-Device
disks	O
did	O
not	O
use	O
the	O
index	B-Architecture
hole	I-Architecture
to	O
mark	O
the	O
start	O
of	O
a	O
track	O
;	O
their	O
drives	O
could	O
not	O
even	O
detect	O
the	O
index	B-Architecture
hole	I-Architecture
.	O
</s>
<s>
Secondly	O
,	O
Apple	B-Device
used	O
special	O
"	O
self-sync	O
"	O
bytes	B-Application
to	O
achieve	O
agreement	O
between	O
drive	O
controller	O
and	O
computer	O
about	O
where	O
any	O
byte	B-Application
ended	O
and	O
the	O
next	O
one	O
started	O
on	O
the	O
disk	O
.	O
</s>
<s>
These	O
bytes	B-Application
were	O
written	O
as	O
normal	O
data	O
bytes	B-Application
followed	O
by	O
a	O
slightly	O
longer	O
than	O
normal	O
pause	O
,	O
which	O
was	O
notoriously	O
unreliable	O
to	O
detect	O
on	O
read-back	O
;	O
still	O
,	O
you	O
had	O
to	O
get	O
the	O
self-sync	O
bytes	B-Application
roughly	O
right	O
as	O
without	O
them	O
being	O
present	O
in	O
the	O
right	O
places	O
,	O
the	O
copy	O
would	O
not	O
work	O
,	O
and	O
with	O
them	O
present	O
in	O
too	O
many	O
places	O
,	O
the	O
track	O
would	O
not	O
fit	O
on	O
the	O
destination	O
disk	O
.	O
</s>
<s>
Locksmith	O
copied	O
Apple	B-Device
II	O
disks	O
by	O
taking	O
advantage	O
of	O
the	O
fact	O
that	O
these	O
sync	O
fields	O
between	O
sectors	O
almost	O
always	O
consisted	O
of	O
a	O
long	O
string	O
of	O
FF	O
(	O
hex	O
-	O
all	O
'	O
1	O
 '	O
bits	O
)	O
bytes	B-Application
.	O
</s>
<s>
It	O
found	O
the	O
longest	O
string	O
of	O
FFs	O
,	O
which	O
usually	O
occurred	O
between	O
the	O
last	O
and	O
first	O
sectors	O
on	O
each	O
track	O
,	O
and	O
began	O
writing	O
the	O
track	O
in	O
the	O
middle	O
of	O
that	O
;	O
also	O
it	O
assumed	O
that	O
any	O
long	O
string	O
of	O
FF	O
bytes	B-Application
was	O
a	O
sync	O
sequence	O
and	O
introduced	O
the	O
necessary	O
short	O
pauses	O
after	O
writing	O
each	O
of	O
them	O
to	O
the	O
copy	O
.	O
</s>
<s>
The	O
next	O
advance	O
came	O
from	O
Henry	O
Roberts	O
 '	O
thesis	O
on	O
software	O
copy	O
protection	O
,	O
which	O
devised	O
a	O
way	O
of	O
replacing	O
Apple	B-Device
’s	O
sync	O
field	O
of	O
FFs	O
with	O
random	O
appearing	O
patterns	O
of	O
bytes	B-Application
.	O
</s>
<s>
Because	O
the	O
graduate	O
student	O
had	O
frequent	O
copy	O
protection	O
discussions	O
with	O
Apple	B-Device
’s	O
copy	O
protection	O
engineer	O
,	O
Apple	B-Device
developed	O
a	O
copy	O
protection	O
system	O
which	O
made	O
use	O
of	O
this	O
technique	O
.	O
</s>
<s>
The	O
back	O
and	O
forth	O
struggle	O
between	O
copy	O
protection	O
engineers	O
and	O
nibble	O
copiers	O
continued	O
until	O
the	O
Apple	B-Device
II	O
became	O
obsolete	O
and	O
was	O
replaced	O
by	O
the	O
IBM	B-Device
PC	I-Device
and	O
its	O
clones	O
.	O
</s>
<s>
Part	O
of	O
the	O
Fast	B-Application
Hack'em	I-Application
disk	O
copy	O
software	O
was	O
a	O
nibbler	O
used	O
to	O
produce	O
copies	O
of	O
copy	O
protected	O
Commodore	O
64	O
commercial	O
software	O
.	O
</s>
<s>
When	O
using	O
the	O
nibbler	O
,	O
disk	O
copying	O
was	O
done	O
on	O
a	O
very	O
low	O
level	O
,	O
bit-by-bit	O
rather	O
than	O
using	O
standard	O
Commodore	B-Device
DOS	I-Device
commands	O
.	O
</s>
<s>
NIBtools	O
is	O
a	O
modern	O
(	O
circa	O
2006	O
)	O
open	O
source	O
software	O
that	O
performs	O
the	O
same	O
function	O
,	O
intended	O
mainly	O
for	O
archiving	O
data	O
from	O
old	O
floppies	B-Device
that	O
may	O
be	O
copyright-protected	O
or	O
damaged	O
.	O
</s>
<s>
Instead	O
of	O
reading	O
bit-by-bit	O
,	O
one	O
can	O
also	O
read	O
many	O
1.25	O
KB	O
stretches	O
and	O
then	O
assemble	O
them	O
together	O
in	O
a	O
way	O
akin	O
to	O
shotgun	O
sequencing	O
,	O
an	O
approach	O
necessary	O
for	O
using	O
slow	O
connections	O
on	O
the	O
Commodore	B-Device
1541	I-Device
.	O
</s>
<s>
They	O
used	O
a	O
$00	O
value	O
in	O
between	O
sectors	O
which	O
caused	O
copiers	O
to	O
become	O
"	O
flaky	O
"	O
as	O
it	O
was	O
an	O
illegal	O
GCR	B-Device
value	O
.	O
</s>
