<s>
The	O
floppy	B-Device
disk	I-Device
is	O
a	O
data	O
storage	O
and	O
transfer	O
medium	O
that	O
was	O
ubiquitous	O
from	O
the	O
mid-1970s	O
well	O
into	O
the	O
2000s	O
.	O
</s>
<s>
Besides	O
the	O
3½-inch	O
and	O
5¼-inch	O
formats	O
used	O
in	O
IBM	O
PC	O
compatible	O
systems	O
,	O
or	O
the	O
8-inch	O
format	O
that	O
preceded	O
them	O
,	O
many	O
proprietary	O
floppy	B-Device
disk	I-Device
formats	I-Device
were	O
developed	O
,	O
either	O
using	O
a	O
different	O
disk	B-Device
design	O
or	O
special	O
layout	O
and	O
encoding	O
methods	O
for	O
the	O
data	O
held	O
on	O
the	O
disk	B-Device
.	O
</s>
<s>
In	O
the	O
early	O
1980s	O
,	O
IBM	O
Rochester	O
developed	O
a	O
4-inch	O
floppy	B-Device
disk	I-Device
drive	I-Device
,	O
the	O
Model	O
341	O
and	O
an	O
associated	O
diskette	B-Device
,	O
the	O
DemiDiskette	O
.	O
</s>
<s>
At	O
about	O
half	O
the	O
size	O
of	O
the	O
original	O
8-inch	B-Device
floppy	I-Device
disk	B-Device
the	O
name	O
derived	O
from	O
the	O
prefix	O
demi	O
for	O
"	O
half	O
"	O
.	O
</s>
<s>
Another	O
unsuccessful	O
diskette	B-Device
variant	O
was	O
the	O
Drivette	O
,	O
a	O
3¼-inch	O
diskette	B-Device
drive	O
marketed	O
by	O
Tabor	O
Corporation	O
of	O
Westland	O
,	O
Massachusetts	O
,	O
USA	O
between	O
1983	O
and	O
1985	O
with	O
media	O
supplied	O
by	O
Dysan	O
,	O
Brown	O
and	O
3M	O
.	O
</s>
<s>
The	O
diskettes	B-Device
were	O
named	O
Dysan	O
3¼	O
"	O
Flex	O
Diskette	B-Device
(	O
P/N	O
802950	O
)	O
,	O
Tabor	O
3¼	O
"	O
Flex	O
Diskette	B-Device
(	O
P/N	O
D3251	O
)	O
,	O
sometimes	O
also	O
nicknamed	O
"	O
Tabor	O
"	O
or	O
"	O
Brown	O
"	O
at	O
tradeshows	O
.	O
</s>
<s>
The	O
Microfloppy	O
Disk	B-Device
Drive	I-Device
TC	O
500	O
was	O
a	O
single-sided	O
quad-density	O
drive	O
with	O
a	O
nominal	O
storage	O
capacity	O
of	O
500KB	O
(	O
80tracks	O
,	O
140tpi	O
,	O
16	O
sectors	O
,	O
300rpm	O
,	O
250kbit/s	O
,	O
9,250	O
bpi	O
with	O
MFM	B-Protocol
)	O
.	O
</s>
<s>
It	O
could	O
work	O
with	O
standard	O
controllers	O
for	O
5¼-inch	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
Since	O
August	O
1984	O
,	O
it	O
was	O
used	O
in	O
the	O
Seequa	O
Chameleon	O
325	O
,	O
an	O
early	O
CP/M	B-Application
-80	I-Application
&	O
MS-DOS	B-Application
portable	O
computer	O
with	O
both	O
Z80	B-General_Concept
and	O
8088	B-Device
processors	O
.	O
</s>
<s>
Originally	O
,	O
Educational	O
Microcomputer	O
Systems	O
(	O
EMS	O
)	O
announced	O
a	O
system	O
using	O
this	O
drive	O
as	O
well	O
,	O
but	O
later	O
changed	O
plans	O
to	O
use	O
3½-inch	O
diskette	B-Device
drives	O
instead	O
.	O
</s>
<s>
A	O
magnetic	O
disk	B-Device
in	O
a	O
hard	O
plastic	O
shell	O
was	O
invented	O
by	O
,	O
who	O
was	O
working	O
at	O
the	O
Hungarian	O
Budapest	O
Radio	O
Technology	O
Factory	O
(	O
,	O
BRG	O
)	O
,	O
in	O
1973	O
.	O
</s>
<s>
Versions	O
of	O
the	O
floppy	B-Device
drive	I-Device
was	O
released	O
in	O
minimal	O
quantity	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
and	O
Commodore	O
64	O
,	O
and	O
some	O
computers	O
made	O
in	O
East	O
Germany	O
were	O
also	O
equipped	O
with	O
one	O
.	O
</s>
<s>
The	O
floppies	B-Device
are	O
single	O
sided	O
and	O
can	O
hold	O
up	O
to	O
149	O
KB	O
of	O
data	O
when	O
MFM	B-Protocol
formatted	O
.	O
</s>
<s>
The	O
drives	O
were	O
compatible	O
with	O
contemporary	O
floppy	B-Device
controllers	I-Device
.	O
</s>
<s>
The	O
3-inch	O
"	O
Compact	O
Floppy	B-Device
Disk	I-Device
"	O
or	O
"	O
CF-2	O
"	O
was	O
an	O
intended	O
rival	O
to	O
Sony	O
's	O
3.5	B-Device
"	I-Device
floppy	B-Device
system	O
introduced	O
by	O
a	O
consortium	O
of	O
manufacturers	O
led	O
by	O
Matsushita	O
.	O
</s>
<s>
Hitachi	O
was	O
a	O
manufacturer	O
of	O
3-inch	O
disk	B-Device
drives	I-Device
,	O
and	O
stated	O
in	O
advertisements	O
,	O
"	O
It	O
's	O
clear	O
that	O
the	O
3	O
"	O
floppy	B-Device
will	O
become	O
the	O
new	O
standard.	O
"	O
</s>
<s>
The	O
format	O
was	O
widely	O
used	O
by	O
Amstrad	O
in	O
their	O
CPC	B-Device
and	O
PCW	B-Device
computers	O
,	O
and	O
(	O
after	O
Amstrad	O
took	O
over	O
manufacture	O
of	O
the	O
line	O
)	O
the	O
Sinclair	B-Operating_System
ZX	I-Operating_System
Spectrum	I-Operating_System
+3	O
.	O
</s>
<s>
It	O
was	O
also	O
adopted	O
by	O
some	O
other	O
manufacturers/systems	O
such	O
as	O
Sega	O
,	O
the	O
Tatung	B-Operating_System
Einstein	I-Operating_System
,	O
and	O
Timex	O
of	O
Portugal	O
in	O
the	O
FDD	B-Device
and	I-Device
FDD-3000	I-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
Three-inch	O
diskettes	B-Device
bear	O
much	O
similarity	O
to	O
the	O
-inch	O
size	O
,	O
but	O
with	O
some	O
unique	O
features	O
.	O
</s>
<s>
One	O
example	O
is	O
the	O
more	O
elongated	O
plastic	O
casing	O
,	O
taller	O
than	O
a	O
-inch	O
disk	B-Device
,	O
but	O
less	O
wide	O
and	O
thicker	O
(	O
i.e.	O
</s>
<s>
The	O
actual	O
3-inch	O
magnetic-coated	O
disk	B-Device
occupies	O
less	O
than	O
50%	O
of	O
the	O
space	O
inside	O
the	O
casing	O
,	O
the	O
rest	O
being	O
used	O
by	O
the	O
complex	O
protection	O
and	O
sealing	O
mechanisms	O
implemented	O
on	O
the	O
disks	B-Device
,	O
which	O
thus	O
are	O
largely	O
responsible	O
for	O
the	O
thickness	O
,	O
length	O
,	O
and	O
relatively	O
high	O
costs	O
of	O
the	O
disks	B-Device
.	O
</s>
<s>
On	O
the	O
early	O
Amstrad	O
machines	O
(	O
the	O
CPC	B-Device
line	O
and	O
the	O
PCW	B-Device
8256	O
)	O
,	O
the	O
disks	B-Device
are	O
typically	O
flipped	O
over	O
to	O
change	O
the	O
side	O
(	O
acting	O
like	O
2	O
separate	O
single-sided	B-Architecture
disks	I-Architecture
,	O
comparable	O
to	O
the	O
"	O
flippy	O
disks	B-Device
"	O
of	O
-inch	O
media	O
)	O
as	O
opposed	O
to	O
being	O
contiguously	O
double-sided	B-Architecture
.	O
</s>
<s>
Double-sided	B-Architecture
mechanisms	O
were	O
introduced	O
on	O
the	O
later	O
PCW	B-Device
8512	O
and	O
PCW	B-Device
9512	O
,	O
thus	O
removing	O
the	O
need	O
to	O
remove	O
,	O
flip	O
,	O
and	O
then	O
reinsert	O
the	O
disk	B-Device
.	O
</s>
<s>
Mitsumi	O
marketed	O
several	O
3-inch	O
diskette	B-Device
"	O
Quick	O
Disk	B-Device
"	O
formats	O
for	O
OEM	O
use	O
.	O
</s>
<s>
The	O
Japanese	O
Nintendo	B-Device
Famicom	I-Device
Disk	I-Device
System	I-Device
used	O
proprietary	O
3-inch	O
diskettes	B-Device
called	O
"	O
Disk	B-Device
Cards	O
"	O
between	O
1986	O
and	O
1990	O
.	O
</s>
<s>
Many	O
Smith	O
Corona	O
"	O
CoronaPrint	O
"	O
word-processor	O
typewriters	O
used	O
a	O
proprietary	O
double-sided	B-Architecture
3-inch	O
diskette	B-Device
format	I-Device
named	O
"	O
DataDisk	O
"	O
.	O
</s>
<s>
Confusingly	O
,	O
it	O
was	O
labelled	O
2.8-inch	O
reflecting	O
the	O
diameter	O
of	O
the	O
magnetic	O
disk	B-Device
itself	O
rather	O
than	O
the	O
media	O
's	O
case	O
.	O
</s>
<s>
In	O
1986	O
,	O
Sharp	O
introduced	O
a	O
2.5-inch	O
floppy	B-Device
disk	I-Device
format	I-Device
for	O
use	O
with	O
their	O
family	O
of	O
BASIC	O
pocket	B-Device
computers	I-Device
.	O
</s>
<s>
Two	O
drives	O
were	O
produced	O
:	O
the	O
Sharp	B-Device
CE-1600F	I-Device
and	O
the	O
CE-140F	O
(	O
chassis	O
:	O
FDU-250	O
)	O
.	O
</s>
<s>
Both	O
took	O
turnable	O
diskettes	B-Device
named	O
CE-1650F	B-Device
with	O
a	O
total	O
capacity	O
of	O
2×64KB	O
(	O
128KB	O
)	O
at	O
bytes	B-Application
per	O
side	O
(	O
512byte	O
sectors	O
,	O
8sectors/track	O
,	O
16tracks	O
(	O
00	O
..	O
15	O
)	O
,	O
48tpi	O
,	O
250kbit/s	O
,	O
270rpm	O
with	O
GCR	B-Device
(	O
4/5	O
)	O
recording	O
)	O
.	O
</s>
<s>
At	O
least	O
two	O
incompatible	O
floppy	B-Device
disks	I-Device
measuring	O
two	O
inches	O
appeared	O
in	O
the	O
1980s	O
.	O
</s>
<s>
One	O
of	O
these	O
,	O
officially	O
referred	O
to	O
as	O
a	O
Video	O
Floppy	B-Device
(	O
or	O
VF	O
for	O
short	O
)	O
can	O
be	O
used	O
to	O
store	O
video	O
information	O
for	O
still	B-Algorithm
video	I-Algorithm
cameras	I-Algorithm
such	O
as	O
the	O
original	O
Sony	B-Algorithm
Mavica	I-Algorithm
(	O
not	O
to	O
be	O
confused	O
with	O
later	O
Digital	O
Mavica	B-Algorithm
models	O
)	O
and	O
the	O
Ion	O
and	O
Xapshot	O
cameras	O
from	O
Canon	O
.	O
</s>
<s>
VF	O
is	O
not	O
a	O
digital	O
data	O
format	O
;	O
each	O
track	O
on	O
the	O
disk	B-Device
stores	O
one	O
video	O
field	O
in	O
the	O
analog	O
interlaced	O
composite	O
video	O
format	O
in	O
either	O
the	O
North	O
American	O
NTSC	O
or	O
European	O
PAL	B-Language
standard	O
.	O
</s>
<s>
This	O
yields	O
a	O
capacity	O
of	O
25	O
images	O
per	O
disk	B-Device
in	O
frame	O
mode	O
and	O
50	O
in	O
field	O
mode	O
.	O
</s>
<s>
Another	O
2-inch	O
format	O
,	O
the	O
LT-1	O
,	O
is	O
digitally	O
formatted	O
—	O
720kB	O
,	O
245TPI	O
,	O
80tracks/side	O
,	O
double-sided	B-Architecture
,	O
double-density	O
.	O
</s>
<s>
They	O
are	O
used	O
exclusively	O
in	O
the	O
Zenith	B-Device
MinisPORT	I-Device
laptop	O
computer	O
circa	O
1989	O
.	O
</s>
<s>
Although	O
the	O
media	O
exhibited	O
nearly	O
identical	O
performance	O
to	O
the	O
3½-inch	O
disks	B-Device
of	O
the	O
time	O
,	O
they	O
were	O
not	O
very	O
successful	O
.	O
</s>
<s>
This	O
was	O
due	O
in	O
part	O
to	O
the	O
scarcity	O
of	O
other	O
devices	O
using	O
this	O
drive	O
making	O
it	O
impractical	O
for	O
software	O
transfer	O
,	O
and	O
high	O
media	O
cost	O
which	O
was	O
much	O
more	O
than	O
3½-inch	O
and	O
5¼-inch	B-Device
disks	I-Device
of	O
the	O
time	O
.	O
</s>
<s>
Much	O
later	O
,	O
another	O
2-inch	O
(	O
case	O
size	O
:	O
54.5mm	O
×	O
50.2mm	O
×	O
2.0mm	O
)	O
miniature	O
disk	B-Device
format	O
was	O
Iomega	O
's	O
PocketZip	B-Device
(	O
originally	O
named	O
Clik	B-Device
!	I-Device
</s>
<s>
The	O
disks	B-Device
could	O
store	O
40MB	O
.	O
</s>
<s>
The	O
external	O
drives	O
were	O
available	O
as	O
PC	B-Architecture
Card	I-Architecture
TypeII	O
and	O
with	O
USB	B-Protocol
interface	O
.	O
</s>
<s>
A	O
flippy	O
disk	B-Device
(	O
sometimes	O
known	O
as	O
a	O
"	O
flippy	O
"	O
)	O
is	O
a	O
double-sided	B-Architecture
-inch	O
floppy	B-Device
disk	I-Device
,	O
specially	O
modified	O
so	O
that	O
the	O
two	O
sides	O
can	O
be	O
used	O
independently	O
(	O
but	O
not	O
simultaneously	O
)	O
in	O
single-sided	O
drives	O
.	O
</s>
<s>
Many	O
commercial	O
publishers	O
of	O
computer	O
software	O
(	O
mainly	O
,	O
relatively	O
small	O
programs	O
like	O
arcade	O
games	O
that	O
could	O
fit	O
on	O
a	O
single-sided	O
floppy	B-Device
disk	I-Device
)	O
distributed	O
their	O
products	O
on	O
flippy	O
disks	B-Device
formatted	O
for	O
two	O
different	O
brands	O
of	O
computer	O
,	O
e.g.	O
</s>
<s>
TRS-80	B-Device
on	O
one	O
side	O
and	O
Apple	O
on	O
the	O
other	O
.	O
</s>
<s>
For	O
Disk	B-Operating_System
Operating	I-Operating_System
Systems	I-Operating_System
that	O
do	O
not	O
use	O
the	O
index	O
hole	O
in	O
the	O
disk	B-Device
to	O
mark	O
the	O
beginnings	O
of	O
tracks	O
,	O
the	O
"	O
flippy	O
"	O
modification	O
required	O
only	O
a	O
new	O
write-enable	O
notch	O
to	O
be	O
cut	O
if	O
the	O
disk	B-Device
was	O
designed	O
to	O
be	O
written	O
to	O
.	O
</s>
<s>
For	O
this	O
purpose	O
,	O
specially	O
designed	O
single-rectangular-hole	O
punchers	O
,	O
commonly	O
known	O
as	O
disk	B-Device
doublers	O
,	O
were	O
produced	O
and	O
sold	O
by	O
third-party	O
computer	O
accessory	O
manufacturers	O
.	O
</s>
<s>
For	O
disk	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
that	O
do	O
use	O
index	O
sync	O
,	O
a	O
second	O
index	O
hole	O
window	O
has	O
to	O
be	O
punched	O
in	O
both	O
sides	O
of	O
the	O
jacket	O
,	O
and	O
for	O
hard-sectored	O
formats	O
,	O
an	O
additional	O
window	O
must	O
be	O
punched	O
for	O
the	O
sector	O
holes	O
.	O
</s>
<s>
While	O
cutting	O
a	O
second	O
notch	O
is	O
relatively	O
safe	O
,	O
cutting	O
an	O
additional	O
window	O
into	O
the	O
jacket	O
is	O
a	O
great	O
peril	O
to	O
the	O
disk	B-Device
itself	O
.	O
</s>
<s>
A	O
number	O
of	O
floppy-disk	O
manufacturers	O
produced	O
ready-made	O
"	O
flippy	O
"	O
media	O
.	O
</s>
<s>
As	O
the	O
cost	O
of	O
media	O
went	O
down	O
and	O
double-sided	B-Architecture
drives	O
became	O
the	O
standard	O
,	O
"	O
flippies	O
"	O
became	O
obsolete	O
.	O
</s>
<s>
IBM	O
developed	O
,	O
and	O
several	O
companies	O
copied	O
,	O
an	O
autoloader	O
mechanism	O
that	O
can	O
load	O
a	O
stack	O
of	O
floppies	B-Device
one	O
at	O
a	O
time	O
into	O
a	O
drive	O
.	O
</s>
<s>
The	O
smaller	O
5¼	O
-	O
and	O
3½-inch	O
floppies	B-Device
made	O
this	O
a	O
much	O
easier	O
technology	O
to	O
perfect	O
.	O
</s>
<s>
A	O
number	O
of	O
companies	O
,	O
including	O
IBM	O
and	O
Burroughs	O
,	O
experimented	O
with	O
using	O
large	O
numbers	O
of	O
unenclosed	O
disks	B-Device
to	O
create	O
massive	O
amounts	O
of	O
storage	O
.	O
</s>
<s>
The	O
Burroughs	O
system	O
uses	O
a	O
stack	O
of	O
256	O
12-inch	O
disks	B-Device
,	O
spinning	O
at	O
a	O
high	O
speed	O
.	O
</s>
<s>
The	O
disk	B-Device
to	O
be	O
accessed	O
is	O
selected	O
by	O
using	O
air	O
jets	O
to	O
part	O
the	O
stack	O
,	O
and	O
then	O
a	O
pair	O
of	O
heads	O
flies	O
over	O
the	O
surface	O
as	O
in	O
some	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
This	O
approach	O
in	O
some	O
ways	O
anticipated	O
the	O
Bernoulli	O
disk	B-Device
technology	O
implemented	O
in	O
the	O
Iomega	B-Device
Bernoulli	I-Device
Box	I-Device
,	O
but	O
head	O
crashes	O
or	O
air	O
failures	O
were	O
spectacularly	O
messy	O
.	O
</s>
<s>
A	O
number	O
of	O
attempts	O
were	O
made	O
by	O
various	O
companies	O
to	O
introduce	O
newer	O
floppy-disk	O
formats	O
based	O
on	O
the	O
standard	O
3½-inch	O
physical	O
format	O
.	O
</s>
<s>
Most	O
of	O
these	O
systems	O
provide	O
the	O
ability	O
to	O
read	O
and	O
write	O
standard	O
DD	B-Application
and	O
HD	O
disks	B-Device
,	O
while	O
at	O
the	O
same	O
time	O
introducing	O
a	O
much	O
higher-capacity	O
format	O
as	O
well	O
.	O
</s>
<s>
None	O
of	O
these	O
ever	O
reached	O
the	O
point	O
where	O
it	O
could	O
be	O
assumed	O
that	O
every	O
current	O
PC	O
would	O
have	O
one	O
,	O
and	O
they	O
have	O
now	O
largely	O
been	O
replaced	O
by	O
optical	B-Device
disc	I-Device
burners	O
and	O
flash	B-Device
storage	I-Device
.	O
</s>
<s>
Nevertheless	O
,	O
the	O
5¼	O
-	O
and	O
3½-inch	O
sizes	O
remain	O
to	O
this	O
day	O
as	O
the	O
standards	O
for	O
drive	B-Device
bays	I-Device
in	O
computer	B-General_Concept
cases	I-General_Concept
,	O
the	O
former	O
used	O
for	O
optical	O
drives	O
(	O
including	O
Blu-ray	O
)	O
,	O
and	O
the	O
latter	O
for	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
The	O
main	O
technological	O
change	O
for	O
the	O
higher-capacity	O
formats	O
was	O
the	O
addition	O
of	O
tracking	O
information	O
on	O
the	O
disk	B-Device
surface	O
to	O
allow	O
the	O
read/write	O
heads	O
to	O
be	O
positioned	O
more	O
accurately	O
.	O
</s>
<s>
Normal	O
disks	B-Device
have	O
no	O
such	O
information	O
,	O
so	O
the	O
drives	O
use	O
feedforward	O
(	O
blind	O
)	O
positioning	O
by	O
a	O
stepper	O
motor	O
in	O
order	O
to	O
position	O
their	O
heads	O
over	O
the	O
desired	O
track	O
.	O
</s>
<s>
For	O
good	O
interoperability	O
of	O
disks	B-Device
among	O
drives	O
,	O
this	O
requires	O
precise	O
alignment	O
of	O
the	O
drive	O
heads	O
to	O
a	O
reference	O
standard	O
,	O
somewhat	O
similar	O
to	O
the	O
alignment	O
required	O
to	O
get	O
the	O
best	O
performance	O
out	O
of	O
an	O
audio	O
tape	O
deck	O
.	O
</s>
<s>
The	O
newer	O
systems	O
generally	O
use	O
position	O
information	O
on	O
the	O
surfaces	O
of	O
the	O
disk	B-Device
to	O
find	O
the	O
tracks	O
,	O
allowing	O
the	O
track	O
width	O
to	O
be	O
greatly	O
reduced	O
.	O
</s>
<s>
In	O
1990	O
,	O
an	O
attempt	O
was	O
made	O
to	O
standardize	O
details	O
for	O
a	O
20	O
megabyte	O
3½-inch	O
format	O
floppy	B-Device
.	O
</s>
<s>
One	O
major	O
goal	O
was	O
that	O
the	O
to-be-developed	O
standard	O
drive	O
be	O
backward	B-General_Concept
compatible	I-General_Concept
:	O
that	O
it	O
be	O
able	O
to	O
read	O
720	O
KB	O
and	O
1.44	O
MB	O
floppies	B-Device
.	O
</s>
<s>
As	O
early	O
as	O
1987	O
,	O
Brier	O
Technology	O
announced	O
the	O
Flextra	O
BR3020	O
,	O
which	O
boasts	O
21.4MB	O
(	O
a	O
value	O
used	O
for	O
marketing	O
:	O
its	O
true	O
size	O
is	O
21,040	O
kB	O
,	O
2	O
sides	O
×	O
526	O
cylinders	O
×	O
40	O
sectors	O
×	O
512	O
bytes	B-Application
or	O
25	O
MB	O
unformatted	O
)	O
.	O
</s>
<s>
Around	O
1990	O
,	O
it	O
announced	O
the	O
BR3225	O
drive	O
,	O
which	O
was	O
supposed	O
to	O
double	O
the	O
capacity	O
and	O
also	O
read	O
standard	O
DD	B-Application
,	O
HD	O
and	O
ED	O
3½-inch	O
disks	B-Device
.	O
</s>
<s>
In	O
1991	O
,	O
Insite	O
Peripherals	O
introduced	O
the	O
"	O
Floptical	B-Device
"	O
,	O
which	O
uses	O
an	O
infra-red	O
LED	O
to	O
position	O
the	O
heads	O
over	O
marks	O
in	O
the	O
disk	B-Device
surface	O
.	O
</s>
<s>
The	O
original	O
drive	O
stores	O
21MB	O
,	O
while	O
also	O
reading	O
and	O
writing	O
standard	O
DD	B-Application
and	O
HD	O
floppies	B-Device
.	O
</s>
<s>
In	O
order	O
to	O
improve	O
data	O
transfer	O
speeds	O
and	O
make	O
the	O
high-capacity	O
drive	O
usefully	O
quick	O
as	O
well	O
,	O
the	O
drives	O
are	O
attached	O
to	O
the	O
system	O
using	O
a	O
SCSI	B-Architecture
connector	O
instead	O
of	O
the	O
normal	O
floppy	B-Device
controller	I-Device
.	O
</s>
<s>
The	O
most	O
popular	O
of	O
these	O
,	O
by	O
far	O
,	O
was	O
the	O
LS-120	B-Device
,	O
mentioned	O
below	O
.	O
</s>
<s>
In	O
1994	O
,	O
Iomega	O
introduced	O
the	O
Zip	B-Operating_System
drive	I-Operating_System
.	O
</s>
<s>
Although	O
neither	O
size	O
(	O
the	O
original	O
or	O
the	O
later	O
Pocket	B-Device
Zip	I-Device
drive	I-Device
)	O
conforms	O
to	O
the	O
3½-inch	O
form	O
factor	O
and	O
hence	O
is	O
not	O
compatible	O
with	O
standard	O
1.44MB	O
drives	O
,	O
the	O
original	O
physical	O
size	O
still	O
became	O
the	O
most	O
popular	O
of	O
the	O
"	O
super	O
floppies	B-Device
"	O
.	O
</s>
<s>
The	O
first	O
version	O
boasted	O
100	O
MB	O
;	O
later	O
versions	O
boasted	O
250	O
MB	O
and	O
then	O
750	O
MB	O
of	O
storage	O
,	O
until	O
the	O
PocketZip	B-Device
(	O
formerly	O
known	O
as	O
Clik	B-Device
!	I-Device
)	O
</s>
<s>
Though	O
Zip	B-Operating_System
drives	I-Operating_System
gained	O
in	O
popularity	O
for	O
several	O
years	O
they	O
never	O
reached	O
the	O
same	O
market	O
penetration	O
as	O
standard	O
floppy	B-Device
drives	I-Device
,	O
since	O
only	O
some	O
new	O
computers	O
were	O
sold	O
with	O
the	O
drives	O
.	O
</s>
<s>
Zip	B-Operating_System
disks	I-Operating_System
greatly	O
eased	O
the	O
exchange	O
of	O
files	O
that	O
were	O
too	O
big	O
to	O
fit	O
on	O
a	O
standard	O
3.5-inch	O
floppy	B-Device
or	O
an	O
email	O
attachment	O
,	O
when	O
there	O
was	O
no	O
high-speed	O
connection	O
to	O
transfer	O
the	O
file	O
to	O
the	O
recipient	O
.	O
</s>
<s>
Eventually	O
the	O
falling	O
prices	O
of	O
compact	O
disc	O
optical	B-Device
media	I-Device
and	O
,	O
later	O
,	O
flash	B-Device
storage	I-Device
,	O
along	O
with	O
notorious	O
hardware	O
failures	O
(	O
the	O
so-called	O
"	O
click	B-Error_Name
of	I-Error_Name
death	I-Error_Name
"	O
)	O
,	O
reduced	O
the	O
popularity	O
of	O
the	O
Zip	B-Operating_System
drive	I-Operating_System
.	O
</s>
<s>
Announced	O
in	O
1995	O
,	O
the	O
"	O
SuperDisk	B-Device
"	O
marketed	O
as	O
the	O
LS-120	B-Device
drive	I-Device
,	O
often	O
seen	O
with	O
the	O
brand	O
names	O
Matsushita	O
(	O
Panasonic	O
)	O
and	O
Imation	O
,	O
had	O
an	O
initial	O
capacity	O
of	O
120	O
MB	O
(	O
120.375	O
MB	O
)	O
.	O
</s>
<s>
This	O
worked	O
very	O
well	O
at	O
the	O
time	O
and	O
as	O
a	O
result	O
failures	O
associated	O
with	O
magnetic	O
fields	O
wiping	O
the	O
Zip	B-Operating_System
drive	I-Operating_System
alignment	O
Z	O
tracks	O
were	O
less	O
of	O
a	O
problem	O
.	O
</s>
<s>
It	O
was	O
also	O
able	O
to	O
read	O
and	O
write	O
to	O
standard	O
floppy	B-Device
disks	I-Device
about	O
5	O
times	O
as	O
fast	O
as	O
standard	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
It	O
was	O
upgraded	O
(	O
as	O
the	O
"	O
LS-240	B-Device
"	O
)	O
to	O
240	O
MB	O
(	O
240.75	O
MB	O
)	O
.	O
</s>
<s>
Not	O
only	O
can	O
the	O
drive	O
read	O
and	O
write	O
1,440	O
kB	O
disks	B-Device
,	O
but	O
the	O
last	O
versions	O
of	O
the	O
drives	O
can	O
write	O
32	O
MB	O
onto	O
a	O
normal	O
1,440	O
kB	O
disk	B-Device
.	O
</s>
<s>
Unfortunately	O
,	O
popular	O
opinion	O
held	O
the	O
Super	B-Device
Disks	I-Device
to	O
be	O
quite	O
unreliable	O
,	O
though	O
no	O
more	O
so	O
than	O
the	O
Zip	B-Operating_System
drives	I-Operating_System
and	O
SyQuest	O
Technology	O
offerings	O
of	O
the	O
same	O
period	O
and	O
there	O
were	O
also	O
many	O
reported	O
problems	O
moving	O
standard	O
floppies	B-Device
between	O
LS-120	B-Device
drives	I-Device
and	O
normal	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
of	O
many	O
motherboards	O
even	O
to	O
this	O
day	O
supports	O
LS-120	B-Device
drives	I-Device
as	O
a	O
boot	O
option	O
.	O
</s>
<s>
LS-120	B-Device
drives	I-Device
were	O
available	O
as	O
options	O
on	O
many	O
computers	O
,	O
including	O
desktop	O
and	O
notebook	O
computers	O
from	O
Compaq	O
Computer	O
Corporation	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
Compaq	O
notebooks	O
,	O
the	O
LS-120	B-Device
drive	I-Device
replaced	O
the	O
standard	O
floppy	B-Device
drive	I-Device
in	O
a	O
multibay	O
configuration	O
.	O
</s>
<s>
Sony	O
introduced	O
its	O
own	O
floptical-like	O
system	O
in	O
1997	O
as	O
the	O
"	O
150MB	O
Sony	O
HiFD	O
"	O
which	O
was	O
originally	O
supposed	O
to	O
hold	O
150MB	O
(	O
157.3decimal	O
megabytes	O
)	O
of	O
data	O
.	O
</s>
<s>
Although	O
by	O
this	O
time	O
the	O
LS-120	B-Device
had	O
already	O
garnered	O
some	O
market	O
penetration	O
,	O
industry	O
observers	O
nevertheless	O
confidently	O
predicted	O
the	O
HiFD	O
would	O
be	O
the	O
real	O
standard-floppy-killer	O
and	O
finally	O
replace	O
standard	O
floppies	B-Device
in	O
all	O
machines	O
.	O
</s>
<s>
By	O
this	O
point	O
the	O
market	O
was	O
already	O
saturated	O
by	O
the	O
Zip	B-Operating_System
disk	I-Operating_System
,	O
so	O
it	O
never	O
gained	O
much	O
market	O
share	O
.	O
</s>
<s>
The	O
UHD144	B-Device
drive	O
surfaced	O
early	O
in	O
1998	O
as	O
the	O
it	B-Device
drive	I-Device
,	O
and	O
provides	O
144	O
MB	O
of	O
storage	O
while	O
also	O
being	O
compatible	O
with	O
the	O
standard	O
1.44	O
MB	O
floppies	B-Device
.	O
</s>
<s>
Commodore	O
started	O
its	O
tradition	O
of	O
special	O
disk	B-Device
formats	O
with	O
the	O
5¼-inch	B-Device
disk	I-Device
drives	O
accompanying	O
its	O
PET/CBM	B-Device
,	O
VIC-20	B-Device
,	O
and	O
Commodore	O
64	O
home	O
computers	O
,	O
the	O
same	O
as	O
the	O
1540	B-Device
and	O
1541	B-Device
drives	O
used	O
with	O
the	O
later	O
two	O
machines	O
.	O
</s>
<s>
The	O
standard	O
Commodore	O
Group	B-Device
Coded	I-Device
Recording	I-Device
(	O
GCR	B-Device
)	O
scheme	O
used	O
in	O
1541	B-Device
and	O
compatibles	O
employed	O
four	O
different	O
data	O
rates	O
depending	O
upon	O
track	O
position	O
(	O
see	O
zone	B-Architecture
bit	I-Architecture
recording	I-Architecture
)	O
.	O
</s>
<s>
Tracks	O
1	O
to	O
17	O
had	O
21	O
sectors	O
,	O
18	O
to	O
24	O
had	O
19	O
,	O
25	O
to	O
30	O
had	O
18	O
,	O
and	O
31	O
to	O
35	O
had	O
17	O
,	O
for	O
a	O
disk	B-Device
capacity	O
of	O
170.75KB	O
(	O
175decimal	O
kB	O
)	O
.	O
</s>
<s>
Unique	O
among	O
personal	O
computer	O
architectures	O
,	O
the	O
operating	O
system	O
on	O
the	O
computer	O
itself	O
is	O
unaware	O
of	O
the	O
details	O
of	O
the	O
disk	B-Device
and	O
filesystem	O
;	O
disk	B-Device
operations	O
are	O
handled	O
by	O
Commodore	B-Device
DOS	I-Device
instead	O
,	O
which	O
was	O
implemented	O
with	O
an	O
extra	O
MOS-6502	B-General_Concept
processor	O
on	O
the	O
disk	B-Device
drive	I-Device
.	O
</s>
<s>
Many	O
programs	O
such	O
as	O
GEOS	B-Device
bypass	O
Commodore	O
's	O
DOS	O
completely	O
,	O
and	O
replace	O
it	O
with	O
fast-loading	O
(	O
for	O
the	O
time	O
)	O
programs	O
in	O
the	O
1541	B-Device
drive	O
.	O
</s>
<s>
Eventually	O
Commodore	O
gave	O
in	O
to	O
disk	B-Device
format	O
standardization	O
,	O
and	O
made	O
its	O
last	O
5¼-inch	O
drives	O
,	O
the	O
1570	B-Device
and	O
1571	B-Device
,	O
compatible	O
with	O
Modified	B-Protocol
Frequency	I-Protocol
Modulation	I-Protocol
(	O
MFM	B-Protocol
)	O
,	O
to	O
enable	O
the	O
Commodore	B-Device
128	I-Device
to	O
work	O
with	O
CP/M	B-Application
disks	B-Device
from	O
several	O
vendors	O
.	O
</s>
<s>
Equipped	O
with	O
one	O
of	O
these	O
drives	O
,	O
the	O
C128	O
is	O
able	O
to	O
access	O
both	O
C64	O
and	O
CP/M	B-Application
disks	B-Device
,	O
as	O
it	O
needs	O
to	O
,	O
as	O
well	O
as	O
MS-DOS	B-Application
disks	B-Device
(	O
using	O
third-party	O
software	O
)	O
,	O
which	O
was	O
a	O
crucial	O
feature	O
for	O
some	O
office	O
work	O
.	O
</s>
<s>
Commodore	O
also	O
developed	O
a	O
3½-inch	O
800KB	O
disk	B-Device
format	O
for	O
its	O
8-bit	O
machines	O
with	O
the	O
1581	O
disk	B-Device
drive	I-Device
,	O
which	O
uses	O
only	O
MFM	B-Protocol
.	O
</s>
<s>
The	O
GEOS	B-Device
operating	I-Device
system	I-Device
uses	O
a	O
disk	B-Device
format	O
that	O
is	O
largely	O
identical	O
to	O
the	O
Commodore	B-Device
DOS	I-Device
format	O
with	O
a	O
few	O
minor	O
extensions	O
;	O
while	O
generally	O
compatible	O
with	O
standard	O
Commodore	O
disks	B-Device
,	O
certain	O
disk	B-Device
maintenance	O
operations	O
can	O
corrupt	O
the	O
filesystem	O
without	O
proper	O
supervision	O
from	O
the	O
GEOS	B-Device
kernel	O
.	O
</s>
<s>
The	O
combination	O
of	O
DOS	O
and	O
hardware	O
(	O
810	O
,	O
1050	O
and	O
XF551	O
disk	B-Device
drives	I-Device
)	O
for	O
Atari	O
8-bit	O
floppy	B-Device
usage	O
allows	O
sectors	O
numbered	O
from	O
1	O
to	O
720	O
(	O
1040	O
in	O
the	O
1050	O
disk	B-Device
drive	I-Device
,	O
1440	O
in	O
XF551	O
)	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
DOS	O
's	O
2.0	O
disk	B-Device
bitmap	O
provides	O
information	O
on	O
sector	O
allocation	O
,	O
counts	O
from	O
0	O
to	O
719	O
.	O
</s>
<s>
OSS	O
)	O
accept	O
(	O
and	O
format	O
)	O
disks	B-Device
with	O
up	O
to	O
1040	O
sectors	O
,	O
resulting	O
in	O
130KB	O
of	O
storage	O
capacity	O
per	O
disk	B-Device
side	O
on	O
drives	O
equipped	O
with	O
double-density	O
controllers	O
(	O
i.e.	O
</s>
<s>
A	O
true	O
double-density	O
Atari	O
floppy	B-Device
format	O
(	O
from	O
180	O
KB	O
upwards	O
)	O
uses	O
128-byte	O
sectors	O
for	O
sectors	O
1-3	O
,	O
then	O
256-byte	O
sectors	O
for	O
the	O
rest	O
.	O
</s>
<s>
The	O
first	O
three	O
sectors	O
typically	O
contain	O
boot	O
code	O
as	O
used	O
by	O
the	O
onboard	O
ROM	O
OS	O
;	O
it	O
is	O
up	O
to	O
the	O
resulting	O
boot	O
program	O
(	O
such	O
as	O
SpartaDOS	O
)	O
to	O
recognize	O
the	O
density	O
of	O
the	O
formatted	O
disk	B-Device
structure	I-Device
.	O
</s>
<s>
While	O
this	O
format	O
was	O
developed	O
by	O
Atari	O
for	O
their	O
DOS	O
2.0D	O
and	O
their	O
(	O
canceled	O
)	O
180	O
KB	O
Atari	O
815	O
floppy	B-Device
drive	I-Device
,	O
that	O
double-density	O
DOS	O
was	O
never	O
widely	O
released	O
and	O
the	O
format	O
was	O
generally	O
used	O
by	O
third-party	O
DOS	O
products	O
.	O
</s>
<s>
The	O
Atari-brand	O
DOS	O
II	O
versions	O
and	O
compatible	O
use	O
three	O
bytes	B-Application
per	O
sector	O
for	O
housekeeping	O
and	O
to	O
link-list	O
to	O
the	O
next	O
sector	O
.	O
</s>
<s>
Later	O
,	O
mostly	O
third-party	O
DOS	O
systems	O
added	O
features	O
such	O
as	O
double-sided	B-Architecture
drives	O
,	O
subdirectories	O
,	O
and	O
drive	O
types	O
such	O
as	O
720	O
KB	O
,	O
1.2	O
MB	O
,	O
1.44	O
MB	O
.	O
</s>
<s>
Well-known	O
3rd	O
party	O
Atari	O
DOS	O
products	O
include	O
SmartDOS	O
(	O
distributed	O
with	O
the	O
Rana	O
disk	B-Device
drive	I-Device
)	O
,	O
TopDos	O
,	O
MyDos	O
and	O
SpartaDOS	O
.	O
</s>
<s>
The	O
Amiga	B-Device
computers	I-Device
use	O
an	O
880KB	O
format	O
(	O
11×	O
512-byte	O
sectors	O
per	O
track	O
,	O
times	O
80	O
tracks	O
,	O
times	O
two	O
sides	O
)	O
on	O
a	O
3½-inch	O
floppy	B-Device
.	O
</s>
<s>
The	O
Amiga	B-Device
floppy	B-Device
controller	I-Device
is	O
basic	O
but	O
much	O
more	O
flexible	O
than	O
the	O
one	O
on	O
the	O
PC	O
:	O
it	O
is	O
free	O
of	O
arbitrary	O
format	O
restrictions	O
,	O
encoding	O
such	O
as	O
MFM	B-Protocol
and	O
GCR	B-Device
can	O
be	O
done	O
in	O
software	O
,	O
and	O
developers	O
were	O
able	O
to	O
create	O
their	O
own	O
proprietary	O
disk	B-Device
formats	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
foreign	O
formats	O
such	O
as	O
the	O
IBM	O
PC	O
compatible	O
's	O
can	O
be	O
handled	O
with	O
ease	O
(	O
by	O
use	O
of	O
CrossDOS	B-Application
,	O
which	O
was	O
included	O
with	O
later	O
versions	O
of	O
AmigaOS	B-Application
)	O
.	O
</s>
<s>
With	O
the	O
correct	O
filesystem	O
driver	B-Application
,	O
an	O
Amiga	B-Device
can	O
theoretically	O
read	O
any	O
arbitrary	O
format	O
on	O
the	O
3½-inch	O
floppy	B-Device
,	O
including	O
those	O
recorded	O
at	O
a	O
slightly	O
different	O
rotation	O
rate	O
.	O
</s>
<s>
On	O
the	O
PC	O
,	O
however	O
,	O
there	O
is	O
no	O
way	O
to	O
read	O
an	O
Amiga	B-Device
disk	B-Device
without	O
special	O
hardware	O
,	O
such	O
as	O
a	O
Individual	B-Device
Computers	I-Device
Catweasel	I-Device
,	O
and	O
a	O
second	O
floppy	B-Device
drive	I-Device
.	O
</s>
<s>
Another	O
alternative	O
to	O
read	O
Amiga	B-Device
disk	B-Device
is	O
open	O
source	O
and	O
open	O
hardware	O
project	O
Greaseweazle	O
.	O
</s>
<s>
It	O
is	O
simple	O
STM32	O
based	O
USB	B-Protocol
to	O
FD	O
interface	O
adapter	O
capable	O
of	O
reading	O
magnetic	O
flux	O
image	O
.	O
</s>
<s>
With	O
proper	O
software	O
,	O
it	O
is	O
possible	O
to	O
read	O
and	O
write	O
Amiga	B-Device
and	O
almost	O
any	O
other	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Commodore	O
never	O
upgraded	O
the	O
Original	B-Device
Chip	I-Device
Set	I-Device
to	O
support	O
high-density	O
floppies	B-Device
,	O
but	O
sold	O
a	O
custom	O
drive	O
(	O
made	O
by	O
Chinon	O
)	O
that	O
spins	O
at	O
half	O
speed	O
(	O
150	O
RPM	O
)	O
when	O
a	O
high-density	O
floppy	B-Device
was	O
inserted	O
,	O
enabling	O
the	O
existing	O
floppy	B-Device
controller	I-Device
to	O
be	O
used	O
.	O
</s>
<s>
This	O
drive	O
was	O
built	O
into	O
the	O
Amiga	B-Device
3000	I-Device
,	O
although	O
the	O
later	O
Amiga	B-Application
1200	I-Application
was	O
only	O
fitted	O
with	O
the	O
standard	O
DD	B-Application
drive	O
.	O
</s>
<s>
The	O
Amiga	B-Device
HD	O
disks	B-Device
can	O
handle	O
1760KB	O
,	O
but	O
using	O
special	O
software	O
programs	O
they	O
can	O
hold	O
even	O
more	O
data	O
.	O
</s>
<s>
A	O
company	O
named	O
Kolff	O
Computer	O
Supplies	O
also	O
made	O
an	O
external	O
HD	O
floppy	B-Device
drive	I-Device
(	O
KCS	O
Dual	O
HD	O
Drive	O
)	O
available	O
which	O
can	O
handle	O
HD	O
format	O
diskettes	B-Device
on	O
all	O
Amiga	B-Device
computer	I-Device
systems	O
.	O
</s>
<s>
Because	O
of	O
storage	O
reasons	O
,	O
the	O
use	O
of	O
emulators	O
and	O
preserving	O
data	O
,	O
many	O
disks	B-Device
were	O
packed	O
into	O
disk	B-Application
images	I-Application
.	O
</s>
<s>
Currently	O
popular	O
formats	O
are	O
.ADF	O
(	O
Amiga	B-Device
Disk	B-Device
File	O
)	O
,	O
.DMS	B-Application
(	O
DiskMasher	B-Application
)	O
and	O
.IPF	O
(	O
Interchangeable	O
Preservation	O
Format	O
)	O
files	O
.	O
</s>
<s>
The	O
DiskMasher	B-Application
format	O
is	O
copy-protected	O
and	O
has	O
problems	O
storing	O
particular	O
sequences	O
of	O
bits	O
due	O
to	O
bugs	O
in	O
the	O
compression	O
algorithm	O
,	O
but	O
was	O
widely	O
used	O
in	O
the	O
pirate	O
and	O
demo	O
scenes	O
.	O
</s>
<s>
ADF	O
has	O
been	O
around	O
for	O
almost	O
as	O
long	O
as	O
the	O
Amiga	B-Device
itself	O
though	O
it	O
was	O
not	O
initially	O
called	O
by	O
that	O
name	O
.	O
</s>
<s>
Only	O
with	O
the	O
advent	O
of	O
the	O
internet	O
and	O
Amiga	B-Device
emulators	O
has	O
it	O
become	O
a	O
popular	O
way	O
of	O
distributing	O
disk	B-Application
images	I-Application
.	O
</s>
<s>
The	O
British	O
company	O
Acorn	O
Computers	O
used	O
non-standard	O
disk	B-Device
formats	O
in	O
their	O
8-bit	O
BBC	B-Device
Micro	I-Device
and	O
Acorn	B-Device
Electron	I-Device
,	O
and	O
their	O
successor	O
the	O
32-bit	O
Acorn	B-Device
Archimedes	I-Device
.	O
</s>
<s>
Acorn	O
however	O
,	O
used	O
standard	O
disk	B-Device
controllers	O
:	O
initially	O
FM	B-Protocol
,	O
though	O
they	O
quickly	O
transitioned	O
to	O
MFM	B-Protocol
.	O
</s>
<s>
The	O
original	O
disk	B-Device
implementation	O
for	O
the	O
BBC	B-Device
Micro	I-Device
stores	O
100	O
KB	O
(	O
40	O
track	O
)	O
or	O
200	O
KB	O
(	O
80	O
track	O
)	O
per	O
side	O
on	O
5¼-inch	B-Device
disks	I-Device
in	O
a	O
custom	O
format	O
using	O
the	O
Disc	B-Application
Filing	I-Application
System	I-Application
(	O
DFS	O
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
incompatibility	O
between	O
40	O
-	O
and	O
80-track	O
drives	O
,	O
much	O
software	O
was	O
distributed	O
on	O
combined	O
40/80	O
-track	O
disks	B-Device
.	O
</s>
<s>
The	O
loader	O
program	O
detects	O
which	O
type	O
of	O
drive	O
is	O
in	O
use	O
,	O
and	O
loads	O
the	O
main	O
software	O
program	O
straight	O
from	O
disk	B-Device
bypassing	O
the	O
DFS	O
,	O
double-stepping	O
for	O
80-track	O
drives	O
and	O
single-stepping	O
for	O
40-track	O
.	O
</s>
<s>
This	O
effectively	O
achieves	O
downgraded	O
capacity	O
to	O
100KB	O
from	O
either	O
disk	B-Device
format	O
,	O
but	O
enabled	O
distributed	O
software	O
to	O
be	O
effectively	O
compatible	O
with	O
either	O
drive	O
.	O
</s>
<s>
For	O
their	O
Electron	O
floppy-disk	O
add-on	O
,	O
Acorn	O
chose	O
3½-inch	O
disks	B-Device
and	O
developed	O
the	O
Advanced	B-Device
Disk	I-Device
Filing	I-Device
System	I-Device
(	O
ADFS	O
)	O
.	O
</s>
<s>
It	O
uses	O
double-density	O
recording	O
and	O
adds	O
the	O
ability	O
to	O
treat	O
both	O
sides	O
of	O
the	O
disk	B-Device
as	O
a	O
single	O
disk	B-Device
.	O
</s>
<s>
L	O
(	O
large	O
)	O
:	O
640KB	O
,	O
80-track	O
double-sided	B-Architecture
.	O
</s>
<s>
Even	O
on	O
the	O
eight-bit	O
machines	O
,	O
load	O
addresses	O
are	O
stored	O
in	O
32-bit	O
format	O
,	O
since	O
those	O
machines	O
support	O
16	B-Device
-	I-Device
and	O
32-bit	O
coprocessors	B-General_Concept
.	O
</s>
<s>
The	O
ADFS	O
format	O
was	O
later	O
adopted	O
into	O
the	O
BBC	O
line	O
upon	O
release	O
of	O
the	O
BBC	B-Device
Master	I-Device
.	O
</s>
<s>
The	O
BBC	B-Device
Master	I-Device
Compact	O
marked	O
the	O
move	O
to	O
3½-inch	O
disks	B-Device
,	O
using	O
the	O
same	O
ADFS	O
formats	O
.	O
</s>
<s>
The	O
Acorn	B-Device
Archimedes	I-Device
adds	O
D	O
format	O
,	O
which	O
increases	O
the	O
number	O
of	O
objects	O
per	O
directory	O
from	O
44	O
to	O
77	O
and	O
increases	O
the	O
storage	O
space	O
to	O
800KB	O
.	O
</s>
<s>
The	O
Archimedes	B-Device
uses	O
special	O
values	O
in	O
the	O
ADFS	O
load/execute	O
address	O
metadata	O
to	O
store	O
a	O
12-bit	O
filetype	O
field	O
and	O
a	O
40-bit	O
timestamp	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
2	O
introduces	O
E	O
format	O
,	O
which	O
retains	O
the	O
same	O
physical	O
layout	O
as	O
D	O
format	O
,	O
but	O
supports	O
file	O
fragmentation	O
and	O
auto-compaction	O
.	O
</s>
<s>
Post-1991	O
machines	O
including	O
the	O
A5000	O
and	O
Risc	B-Device
PC	I-Device
add	O
support	O
for	O
high-density	B-Device
disks	I-Device
with	O
F	O
format	O
,	O
storing	O
1,600	O
KB	O
.	O
</s>
<s>
However	O
,	O
the	O
PC	O
combo	B-Device
IO	I-Device
chips	O
used	O
are	O
unable	O
to	O
format	O
disks	B-Device
with	O
sector	O
skew	O
,	O
losing	O
some	O
performance	O
.	O
</s>
<s>
ADFS	O
and	O
the	O
PC	O
controllers	O
also	O
support	O
extra-high	B-Device
density	I-Device
(	O
ED	O
)	O
disks	B-Device
as	O
G	O
format	O
,	O
storing	O
3,200	O
KB	O
,	O
but	O
ED	O
drives	O
were	O
never	O
fitted	O
to	O
production	O
machines	O
.	O
</s>
<s>
With	O
RISC	B-Operating_System
OS	I-Operating_System
3	O
,	O
the	O
Archimedes	B-Device
can	O
also	O
read	O
and	O
write	O
disk	B-Device
formats	O
from	O
other	O
machines	O
(	O
for	O
example	O
the	O
Atari	B-Device
ST	I-Device
and	O
the	O
IBM	O
PC	O
,	O
which	O
are	O
largely	O
compatible	O
depending	O
on	O
the	O
ST	O
's	O
OS	O
version	O
)	O
.	O
</s>
<s>
With	O
third-party	O
software	O
it	O
can	O
even	O
read	O
the	O
BBC	B-Device
Micro	I-Device
's	O
original	O
single-density	O
5¼-inch	O
DFS	O
disks	B-Device
.	O
</s>
<s>
The	O
Amiga	B-Device
's	O
disks	B-Device
cannot	O
be	O
read	O
by	O
this	O
system	O
as	O
they	O
omitted	O
the	O
usual	O
sector	O
gap	O
markers	O
.	O
</s>
<s>
Because	O
of	O
this	O
modular	O
design	O
,	O
it	O
is	O
easy	O
in	O
RISC	B-Operating_System
OS	I-Operating_System
3	O
to	O
add	O
support	O
for	O
so-called	O
image	O
filing	O
systems	O
.	O
</s>
<s>
These	O
are	O
used	O
to	O
implement	O
completely	O
transparent	O
support	O
for	O
IBM	O
PC	O
format	O
floppy	B-Device
disks	I-Device
,	O
including	O
the	O
slightly	O
different	O
Atari	B-Device
ST	I-Device
format	O
.	O
</s>
<s>
Computer	O
Concepts	O
released	O
a	O
package	O
that	O
implements	O
an	O
image	O
filing	O
system	O
to	O
allow	O
access	O
to	O
high	O
density	O
Macintosh	B-Device
format	O
disks	B-Device
.	O
</s>
