<s>
Floppy	B-Device
disk	I-Device
format	I-Device
and	O
density	O
refer	O
to	O
the	O
logical	O
and	O
physical	O
layout	O
of	O
data	O
stored	O
on	O
a	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Since	O
their	O
introduction	O
,	O
there	O
have	O
been	O
many	O
popular	O
and	O
rare	O
floppy	B-Device
disk	I-Device
types	O
,	O
densities	O
,	O
and	O
formats	O
used	O
in	O
computing	O
,	O
leading	O
to	O
much	O
confusion	O
over	O
their	O
differences	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
most	O
floppy	B-Device
disk	I-Device
types	O
and	O
formats	O
became	O
obsolete	O
,	O
leaving	O
the	O
-inch	O
disk	O
,	O
using	O
an	O
IBM	B-Device
PC	I-Device
compatible	O
format	O
of	O
1440KB	O
,	O
as	O
the	O
only	O
remaining	O
popular	O
format	O
.	O
</s>
<s>
Different	O
floppy	B-Device
disk	I-Device
types	O
had	O
different	O
recording	O
characteristics	O
,	O
with	O
varying	O
magnetic	O
coercivity	O
(	O
measured	O
in	O
oersteds	O
,	O
or	O
in	O
modern	O
SI	O
units	O
in	O
amperes	B-General_Concept
per	O
meter	O
)	O
,	O
ferrite	O
grain	O
size	O
,	O
and	O
tracks	B-Device
per	I-Device
inch	I-Device
(	O
TPI	O
)	O
.	O
</s>
<s>
The	O
term	O
density	O
has	O
a	O
double	O
meaning	O
for	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
Originally	O
,	O
single	O
density	O
and	O
double	O
density	O
indicated	O
a	O
difference	O
in	O
logical	O
encoding	O
on	O
the	O
same	O
type	O
of	O
physical	O
media	O
:	O
FM	B-Protocol
for	O
single	O
,	O
and	O
MFM	B-Protocol
for	O
double	O
.	O
</s>
<s>
Subsequent	O
use	O
of	O
the	O
term	O
"	O
density	O
"	O
referred	O
to	O
physical	O
characteristics	O
of	O
the	O
media	O
,	O
with	O
MFM	B-Protocol
assumed	O
to	O
be	O
the	O
logical	O
format	O
used	O
.	O
</s>
<s>
GCR	B-Device
was	O
also	O
used	O
on	O
some	O
platforms	O
,	O
but	O
typically	O
in	O
a	O
"	O
double	O
"	O
density	O
form	O
.	O
</s>
<s>
8	O
-	O
and	O
-inch	O
floppy	B-Device
disks	I-Device
were	O
available	O
with	O
both	O
soft	O
sectoring	O
and	O
hard	B-Architecture
sectoring	I-Architecture
.	O
</s>
<s>
Because	O
of	O
the	O
similarity	O
in	O
magnetic	O
characteristics	O
between	O
some	O
disk	O
types	O
,	O
it	O
was	O
possible	O
to	O
use	O
an	O
incorrectly	O
certified	O
disk	O
in	O
a	O
soft	B-Device
sectored	I-Device
drive	O
.	O
</s>
<s>
Quad	O
density	O
-inch	O
disks	O
were	O
rare	O
,	O
so	O
it	O
was	O
not	O
uncommon	O
to	O
use	O
higher	O
quality	O
double	O
density	O
disks	O
,	O
which	O
were	O
usually	O
capable	O
of	O
sustaining	O
the	O
96TPI	O
formatting	O
of	O
quad	O
density	O
,	O
in	O
drives	O
such	O
as	O
the	O
Commodore	B-Device
8050	I-Device
.	O
</s>
<s>
Many	O
(	O
but	O
not	O
all	O
)	O
certified	O
"	O
double	O
sided	O
"	O
8	O
-	O
and	O
-inch	O
floppies	B-Device
had	O
an	O
index	B-Architecture
hole	I-Architecture
on	O
both	O
sides	O
of	O
the	O
disk	O
sleeve	O
to	O
make	O
them	O
usable	O
as	O
flippy	O
disks	O
.	O
</s>
<s>
A	O
combination	O
floppy	B-Device
disk	I-Device
and	O
optical	B-Device
disc	I-Device
,	O
known	O
as	O
a	O
Floptical	B-Device
disk	O
exists	O
.	O
</s>
<s>
The	O
formatted	O
disk	O
capacity	O
is	O
always	O
less	O
than	O
the	O
"	O
raw	O
"	O
unformatted	O
capacity	O
specified	O
by	O
the	O
disk	O
's	O
manufacturer	O
,	O
because	O
some	O
portion	O
of	O
each	O
track	B-Device
is	O
used	O
for	O
sector	O
identification	O
and	O
for	O
gaps	O
(	O
empty	O
spaces	O
)	O
between	O
sectors	O
and	O
at	O
the	O
end	O
of	O
the	O
track	B-Device
.	O
</s>
<s>
In	O
hard-sectored	B-Architecture
8-inch	O
and	O
-inch	O
formats	O
,	O
each	O
track	B-Device
is	O
divided	O
into	O
a	O
particular	O
number	O
of	O
sectors	O
determined	O
when	O
the	O
disk	O
is	O
manufactured	O
.	O
</s>
<s>
An	O
additional	O
hole	O
is	O
punched	O
near	O
one	O
of	O
the	O
sector	O
holes	O
to	O
identify	O
the	O
start	O
of	O
the	O
track	B-Device
.	O
</s>
<s>
Data	O
is	O
generally	O
written	O
at	O
a	O
fixed	O
number	O
of	O
bits	O
per	O
second	O
,	O
with	O
only	O
a	O
very	O
small	O
percentage	O
of	O
variation	O
due	O
to	O
component	O
tolerances	O
,	O
so	O
given	O
the	O
nominal	O
speed	O
that	O
the	O
disk	O
rotates	O
it	O
is	O
possible	O
to	O
calculate	O
the	O
number	O
of	O
degrees	O
a	O
given	O
number	O
of	O
bytes	B-Application
will	O
occupy	O
when	O
written	O
.	O
</s>
<s>
In	O
practice	O
the	O
motor	O
speed	O
varies	O
,	O
especially	O
from	O
one	O
drive	O
to	O
another	O
,	O
resulting	O
in	O
those	O
bytes	B-Application
occupying	O
more	O
degrees	O
of	O
the	O
track	B-Device
at	O
high	O
motor	O
speeds	O
or	O
fewer	O
degrees	O
at	O
low	O
motor	O
speeds	O
.	O
</s>
<s>
When	O
a	O
soft-sectored	O
disk	O
is	O
low-level	O
"	O
formatted	O
"	O
,	O
each	O
track	B-Device
is	O
written	O
with	O
a	O
number	O
of	O
bytes	B-Application
calculated	O
to	O
fit	O
within	O
360	O
degrees	O
at	O
the	O
highest	O
expected	O
motor	O
speed	O
.	O
</s>
<s>
Special	O
bit	O
patterns	O
are	O
written	O
right	O
before	O
the	O
location	O
where	O
a	O
sector	O
should	O
start	O
,	O
and	O
serve	O
as	O
identifiers	O
,	O
similar	O
to	O
the	O
punched	O
holes	O
used	O
by	O
hard-sectored	B-Architecture
disks	O
.	O
</s>
<s>
Thus	O
,	O
the	O
full	O
constellation	O
of	O
punched	O
holes	O
is	O
not	O
needed	O
,	O
and	O
only	O
a	O
single	O
hole	O
is	O
retained	O
,	O
to	O
indicate	O
the	O
start	O
of	O
the	O
track	B-Device
(	O
-inch	O
disks	O
use	O
an	O
alignment	O
pin	O
rather	O
than	O
a	O
hole	O
)	O
.	O
</s>
<s>
If	O
the	O
motor	O
is	O
spinning	O
any	O
slower	O
than	O
the	O
highest	O
acceptable	O
speed	O
,	O
which	O
is	O
usually	O
the	O
case	O
,	O
the	O
data	O
will	O
fit	O
in	O
fewer	O
than	O
360degrees	O
,	O
resulting	O
in	O
a	O
gap	O
at	O
the	O
end	O
of	O
the	O
track	B-Device
.	O
</s>
<s>
Additionally	O
,	O
if	O
a	O
sector	O
were	O
to	O
be	O
rewritten	O
on	O
a	O
drive	O
running	O
faster	O
than	O
the	O
drive	O
was	O
running	O
when	O
the	O
track	B-Device
was	O
formatted	O
,	O
the	O
new	O
data	O
would	O
be	O
larger	O
(	O
occupy	O
more	O
degrees	O
of	O
rotation	O
)	O
than	O
the	O
original	O
sector	O
.	O
</s>
<s>
Commodore	O
's	O
Amiga	B-Device
used	O
an	O
unusual	O
format	O
which	O
got	O
closer	O
to	O
the	O
disk	O
's	O
raw	O
(	O
unformatted	O
)	O
capacity	O
by	O
eliminating	O
the	O
gaps	O
between	O
sectors	O
and	O
simplifying	O
the	O
identification	O
data	O
.	O
</s>
<s>
This	O
meant	O
that	O
individual	O
sectors	O
could	O
not	O
be	O
rewritten	O
;	O
the	O
Amiga	B-Device
would	O
simply	O
rewrite	O
the	O
entire	O
track	B-Device
.	O
</s>
<s>
Formatted	O
capacity	O
numbers	O
are	O
based	O
on	O
the	O
resulting	O
number	O
of	O
logical	O
sectors	O
and	O
the	O
byte	B-Application
payload	O
they	O
can	O
carry	O
,	O
that	O
is	O
,	O
they	O
depend	O
on	O
the	O
physical	O
parameters	O
and	O
modulation	O
,	O
but	O
are	O
independent	O
of	O
a	O
particular	O
file	O
system	O
.	O
</s>
<s>
Sometimes	O
floppies	B-Device
are	O
superformatted	O
to	O
use	O
more	O
tracks	O
or	O
sectors	O
per	O
track	B-Device
to	O
accommodate	O
slightly	O
more	O
data	O
.	O
</s>
<s>
Some	O
floppy-based	O
Linux	O
distributions	O
utilize	O
such	O
techniques	O
.	O
</s>
<s>
Most	O
floppy	B-Device
disks	I-Device
used	O
by	O
PCs	O
use	O
the	O
FAT12	B-Application
file	O
system	O
format	O
,	O
which	O
imposes	O
certain	O
practical	O
defaults	O
on	O
the	O
logical	O
geometry	O
in	O
order	O
to	O
be	O
recognizable	O
by	O
all	O
operating	O
systems	O
.	O
</s>
<s>
SSDD	O
originally	O
referred	O
to	O
Single	O
Sided	O
,	O
Double	O
Density	O
,	O
a	O
format	O
of	O
(	O
usually	O
-inch	O
)	O
floppy	B-Device
disks	I-Device
which	O
could	O
typically	O
hold	O
35-40	O
tracks	O
of	O
nine	O
512-byte	O
(	O
or	O
18	O
256-byte	O
)	O
sectors	O
each	O
.	O
</s>
<s>
Single-sided	B-Architecture
disks	I-Architecture
began	O
to	O
become	O
obsolete	O
after	O
the	O
introduction	O
of	O
IBM	O
PCDOS1.1	O
in	O
1982	O
,	O
which	O
added	O
support	O
for	O
double-side	O
diskette	B-Device
drives	O
with	O
capacity	O
of	O
320KB	O
to	O
the	O
IBM5150	O
PC	B-Device
.	O
</s>
<s>
In	O
1983	O
PCDOS2.0	O
pushed	O
the	O
formatting	O
capacity	O
to	O
180KB	O
single-sided	O
or	O
360KB	O
double-sided	O
by	O
utilizing	O
9	O
instead	O
of	O
only	O
8	O
sectors	O
per	O
track	B-Device
.	O
</s>
<s>
Variables	O
included	O
the	O
size	O
of	O
media	O
(	O
nominal	O
8-inch	O
,	O
-inch	O
,	O
-inch	O
and	O
others	O
)	O
,	O
encoding	O
of	O
data	O
on	O
the	O
media	O
(	O
FM	B-Protocol
,	O
MFM	B-Protocol
,	O
M²FM	O
,	O
GCR	B-Device
)	O
,	O
the	O
number	O
of	O
disk	O
tracks	O
,	O
one	O
or	O
two	O
sides	O
,	O
the	O
number	O
of	O
sectors	O
in	O
each	O
track	B-Device
,	O
and	O
hard	O
-	O
or	O
soft-sectoring	O
.	O
</s>
