<s>
On	O
the	O
Amiga	B-Device
,	O
the	O
Old	O
File	O
System	O
was	O
the	O
filesystem	O
for	O
AmigaOS	B-Application
before	O
the	O
Amiga	B-Device
Fast	I-Device
File	I-Device
System	I-Device
.	O
</s>
<s>
Even	O
though	O
it	O
used	O
512-byte	O
blocks	O
,	O
it	O
reserved	O
the	O
first	O
small	O
portion	O
of	O
each	O
block	B-General_Concept
for	O
metadata	O
,	O
leaving	O
an	O
actual	O
data	O
block	B-General_Concept
capacity	O
of	O
488	O
bytes	O
per	O
block	B-General_Concept
.	O
</s>
<s>
It	O
was	O
n't	O
very	O
suitable	O
for	O
anything	O
except	O
floppy	B-Device
disks	I-Device
,	O
and	O
it	O
was	O
soon	O
replaced	O
.	O
</s>
<s>
Originally	O
known	O
as	O
the	O
Amiga	B-Device
File	O
System	O
,	O
it	O
came	O
from	O
the	O
filesystem	O
of	O
TRIPOS	B-Operating_System
,	O
which	O
formed	O
the	O
basis	O
of	O
the	O
first	O
versions	O
of	O
AmigaDOS	B-Operating_System
.	O
</s>
<s>
It	O
received	O
the	O
nickname	O
of	O
"	O
Old	O
"	O
or	O
"	O
Original	O
"	O
File	O
System	O
when	O
Fast	B-Device
File	I-Device
System	I-Device
was	O
released	O
with	O
AmigaOS	B-Application
1.3	O
.	O
</s>
<s>
The	O
idea	O
to	O
create	O
non-standard	O
autobootable	O
disks	O
was	O
born	O
in	O
a	O
primitive	O
attempt	O
to	O
prevent	O
copy	O
of	O
such	O
disks	O
and	O
to	O
avoid	O
the	O
loading	O
and	O
launch	O
of	O
Amiga	B-Device
DOS	O
,	O
in	O
order	O
to	O
directly	O
access	O
the	O
Amiga	B-Device
graphic	O
,	O
audio	O
and	O
memory	O
chipsets	O
.	O
</s>
<s>
DiskDoctor	O
in	O
fact	O
changed	O
autostart	O
disks	O
bootblocks	O
into	O
standard	O
AmigaDOS-based	O
ones	O
,	O
renaming	O
a	O
disk	O
with	O
"	O
Lazarus	O
"	O
namedisk	O
,	O
and	O
made	O
the	O
autostart	O
disk	O
unusable	O
.	O
</s>
<s>
Amiga	B-Device
uses	O
MFM	O
encoding/decoding	O
by	O
default	O
when	O
handling	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
There	O
are	O
80	O
cylinders	O
on	O
an	O
Amiga	B-Device
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Each	O
cylinder	O
has	O
2	O
MFM	B-Protocol
tracks	O
,	O
one	O
on	O
each	O
side	O
of	O
the	O
disk	O
.	O
</s>
<s>
Double	O
density	O
(	O
DD	O
)	O
disks	O
have	O
11	O
sectors	O
per	O
MFM	B-Protocol
track	O
,	O
high	O
density	O
(	O
HD	O
)	O
disks	O
have	O
22	O
sectors	O
.	O
</s>
<s>
The	O
geometry	O
of	O
an	O
Amiga	B-Device
floppy	B-Device
disk	I-Device
is	O
as	O
follows	O
:	O
</s>
<s>
Amiga	B-Device
stores	O
880	O
KiB	O
on	O
a	O
DD	O
disk	O
and	O
1760	O
KiB	O
on	O
an	O
HD	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Prior	O
to	O
AmigaOS	B-Application
3.5	O
,	O
AmigaDOS	B-Operating_System
file	O
handles	O
maintained	O
a	O
32-bit	O
wide	O
offset	O
parameter	O
(	O
unsigned	O
)	O
,	O
telling	O
where	O
to	O
start	O
the	O
next	O
read	O
or	O
write	O
operation	O
.	O
</s>
<s>
The	O
biggest	O
size	O
for	O
any	O
single	O
Amiga	B-Device
file	O
under	O
these	O
operating	O
systems	O
therefore	O
comes	O
to	O
232	O
=	O
4	O
GiB	O
.	O
</s>
<s>
After	O
Amiga	B-Application
OS	I-Application
3.5	O
,	O
file	O
handles	O
may	O
reference	O
264	O
=	O
16	O
EiB	O
files	O
.	O
</s>
<s>
An	O
OFS	O
datablock	O
stores	O
block	B-General_Concept
size	I-General_Concept
BSIZE-24	O
bytes	O
(	O
i.e.	O
</s>
<s>
The	O
rootblock	O
is	O
located	O
at	O
the	O
physical	O
middle	O
of	O
the	O
media	O
:	O
block	B-General_Concept
number	O
880	O
for	O
DD	O
disks	O
,	O
block	B-General_Concept
1760	O
for	O
HDs	O
.	O
</s>
<s>
The	O
date	O
fields	O
in	O
the	O
root	O
block	B-General_Concept
(	O
and	O
other	O
blocks	O
)	O
are	O
structured	O
in	O
the	O
form	O
of	O
DAYS	O
,	O
MINS	O
and	O
TICKS	O
.	O
</s>
<s>
Since	O
the	O
DAYS	O
value	O
is	O
stored	O
as	O
a	O
32-bit	O
number	O
,	O
the	O
Amiga	B-Device
filesystem	O
does	O
not	O
have	O
an	O
inherent	O
Year	B-Error_Name
2000	I-Error_Name
problem	I-Error_Name
or	O
Year	B-Application
2038	I-Application
problem	I-Application
.	I-Application
</s>
<s>
To	O
reach	O
a	O
file	O
,	O
directory	O
or	O
link	O
,	O
AmigaDOS	B-Operating_System
uses	O
a	O
hash	B-Error_Name
function	I-Error_Name
to	O
calculate	O
which	O
32-bit	O
word	O
in	O
the	O
disk	B-General_Concept
block	I-General_Concept
to	O
use	O
as	O
a	O
pointer	O
to	O
a	O
hash	B-Error_Name
bucket	O
list	O
,	O
which	O
in	O
turn	O
contains	O
the	O
file	O
,	O
directory	O
,	O
or	O
link	O
record	O
.	O
</s>
<s>
A	O
bucket	O
list	O
is	O
used	O
to	O
support	O
filesystem	O
objects	O
with	O
names	O
that	O
hash	B-Error_Name
to	O
the	O
same	O
offset	O
.	O
</s>
<s>
For	O
example	O
:	O
file_1a	O
,	O
file_24	O
and	O
file_5u	O
have	O
the	O
same	O
hash	B-Error_Name
value	I-Error_Name
.	O
</s>
<s>
Files	O
are	O
composed	O
of	O
a	O
file	O
header	O
block	B-General_Concept
,	O
which	O
contains	O
information	O
about	O
the	O
file	O
(	O
size	O
,	O
last	O
access	O
time	O
,	O
data	O
block	B-General_Concept
pointers	O
,	O
etc	O
.	O
</s>
<s>
The	O
file	O
header	O
block	B-General_Concept
contains	O
up	O
to	O
BSIZE/4	O
-56	O
data	O
block	B-General_Concept
pointers	O
(	O
which	O
amounts	O
to	O
72	O
entries	O
with	O
the	O
usual	O
512	O
byte	O
blocks	O
)	O
.	O
</s>
<s>
If	O
a	O
file	O
is	O
larger	O
than	O
that	O
,	O
file	O
extension	O
blocks	O
will	O
be	O
allocated	O
to	O
hold	O
the	O
data	O
block	B-General_Concept
pointers	O
.	O
</s>
<s>
File	O
extension	O
blocks	O
are	O
organised	O
in	O
a	O
linked	O
list	O
,	O
which	O
starts	O
in	O
the	O
file	O
header	O
block	B-General_Concept
( 	O
 '	O
extension	O
 '	O
field	O
)	O
.	O
</s>
