<s>
Atari	B-Operating_System
DOS	I-Operating_System
is	O
the	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
used	O
with	O
the	O
Atari	B-Device
8-bit	I-Device
family	I-Device
of	O
computers	O
.	O
</s>
<s>
Operating	B-General_Concept
system	I-General_Concept
extensions	O
loaded	O
into	O
memory	O
were	O
required	O
in	O
order	O
for	O
an	O
Atari	O
computer	O
to	O
manage	O
files	O
stored	O
on	O
a	O
disk	B-Device
drive	I-Device
.	O
</s>
<s>
These	O
extensions	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
added	O
the	O
disk	B-Device
handler	O
and	O
other	O
file	O
management	O
features	O
.	O
</s>
<s>
The	O
most	O
important	O
extension	O
is	O
the	O
disk	B-Device
handler	O
.	O
</s>
<s>
In	O
Atari	B-Operating_System
DOS	I-Operating_System
2.0	O
,	O
this	O
was	O
the	O
File	O
Management	O
System	O
(	O
FMS	O
)	O
,	O
an	O
implementation	O
of	O
a	O
file	B-Application
system	I-Application
loaded	O
from	O
a	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
This	O
meant	O
at	O
least	O
an	O
additional	O
RAM	B-Architecture
was	O
needed	O
to	O
run	O
with	O
DOS	O
loaded	O
.	O
</s>
<s>
There	O
were	O
several	O
versions	O
of	O
Atari	B-Operating_System
DOS	I-Operating_System
available	O
,	O
with	O
the	O
first	O
version	O
released	O
in	O
1979	O
.	O
</s>
<s>
Atari	O
was	O
using	O
a	O
cross	B-Language
assembler	I-Language
with	O
Data	O
General	O
AOS	O
.	O
</s>
<s>
It	O
was	O
bundled	O
with	O
the	O
810	B-Device
disk	B-Device
drives	I-Device
.	O
</s>
<s>
The	O
second	O
,	O
more	O
popular	O
version	O
of	O
DOS	O
from	O
Atari	O
was	O
bundled	O
with	O
the	O
810	B-Device
disk	B-Device
drives	I-Device
and	O
some	O
early	O
1050	B-Device
disk	B-Device
drives	I-Device
.	O
</s>
<s>
It	O
is	O
considered	O
to	O
be	O
the	O
lowest	O
common	O
denominator	O
for	O
Atari	O
DOSes	O
,	O
as	O
any	O
Atari-compatible	O
disk	B-Device
drive	I-Device
can	O
read	O
a	O
disk	B-Device
formatted	O
with	O
DOS	O
2.0S	O
.	O
</s>
<s>
DOS.SYS	O
was	O
loaded	O
into	O
memory	O
,	O
while	O
DUP.SYS	O
contained	O
the	O
disk	B-Device
utilities	O
and	O
was	O
loaded	O
only	O
when	O
the	O
user	O
exited	O
to	O
DOS	O
.	O
</s>
<s>
Version	O
2.0S	O
was	O
for	O
single-density	O
disks	B-Device
,	O
2.0D	O
was	O
for	O
double-density	O
disks	B-Device
.	O
</s>
<s>
2.0D	O
shipped	O
with	O
the	O
815	O
Dual	O
Disk	B-Device
Drive	I-Device
,	O
which	O
was	O
both	O
expensive	O
and	O
incompatible	O
with	O
the	O
standard	O
810	B-Device
,	O
and	O
thus	O
sold	O
only	O
a	O
small	O
number	O
;	O
making	O
DOS	O
version	O
2.0D	O
rare	O
and	O
unusual	O
.	O
</s>
<s>
A	O
new	O
version	O
of	O
DOS	O
that	O
came	O
originally	O
bundled	O
with	O
the	O
5.25-inch	O
Atari	B-Device
1050	I-Device
disk	B-Device
drive	I-Device
.	O
</s>
<s>
This	O
increased	O
storage	O
from	O
88	O
KB	O
to	O
130	O
KB	O
per	O
disk	B-Device
.	O
</s>
<s>
There	O
was	O
a	O
single	O
density	O
(	O
88	O
KB	O
)	O
formatting	B-Application
option	O
to	O
maintain	O
compatibility	O
with	O
older	O
Atari	B-Device
810	I-Device
disk	B-Device
drives	I-Device
.	O
</s>
<s>
By	O
organizing	O
sectors	O
into	O
blocks	O
,	O
Atari	O
was	O
anticipating	O
larger	O
capacity	O
floppy	B-Device
disks	I-Device
,	O
but	O
this	O
resulted	O
in	O
incompatibility	O
with	O
DOS	O
2.0S	O
.	O
</s>
<s>
Help	O
files	O
needed	O
to	O
be	O
present	O
on	O
the	O
system	O
DOS	O
disk	B-Device
to	O
function	O
properly	O
.	O
</s>
<s>
This	O
allowed	O
the	O
use	O
of	O
Enhanced	O
Density	O
disks	B-Device
,	O
and	O
there	O
was	O
a	O
utility	O
to	O
read	O
DOS	O
3	O
disks	B-Device
.	O
</s>
<s>
An	O
additional	O
option	O
was	O
added	O
to	O
the	O
menu	O
(	O
P	O
.	O
FORMAT	O
SINGLE	O
)	O
to	O
format	O
single-density	O
disks	B-Device
.	O
</s>
<s>
DOS	O
2.5	O
was	O
shipped	O
with	O
1050	B-Device
disk	B-Device
drives	I-Device
and	O
some	O
early	O
XF551	B-Device
disk-drives	O
.	O
</s>
<s>
DOS	O
4.0	O
was	O
not	O
compatible	O
with	O
DOS	O
2	O
or	O
3	O
disks	B-Device
but	O
could	O
read	O
files	O
from	O
them	O
.	O
</s>
<s>
DOS	O
XE	O
supported	O
the	O
double-density	O
and	O
double-sided	O
capabilities	O
of	O
the	O
Atari	B-Device
XF551	I-Device
drive	O
,	O
as	O
well	O
as	O
its	O
burst	O
I/O	O
.	O
</s>
<s>
DOS	O
XE	O
used	O
a	O
new	O
disk	B-Application
format	I-Application
which	O
was	O
incompatible	O
with	O
DOS	O
2.0S	O
and	O
DOS	O
2.5	O
,	O
requiring	O
a	O
separate	O
utility	O
for	O
reading	O
older	O
2.0	O
files	O
.	O
</s>
<s>
It	O
also	O
required	O
bank-switched	O
RAM	B-Architecture
,	O
so	O
it	O
did	O
not	O
run	O
on	O
the	O
400/800	O
machines	O
.	O
</s>
<s>
DOS	O
XE	O
was	O
the	O
last	O
DOS	O
made	O
by	O
Atari	O
for	O
the	O
Atari	B-Device
8-bit	I-Device
family	I-Device
.	O
</s>
<s>
Often	O
,	O
these	O
DOSes	O
could	O
read	O
disks	B-Device
in	O
higher	O
densities	O
,	O
and	O
could	O
set	O
the	O
drive	O
to	O
read	O
disks	B-Device
faster	O
(	O
using	O
Warp	O
Speed	O
or	O
Ultra-Speed	O
techniques	O
)	O
.	O
</s>
<s>
Many	O
enhancements	O
including	O
sector	B-Application
copying	O
and	O
verifying	O
,	O
speed	O
checking	O
,	O
turning	O
on/off	O
file	O
verifying	O
and	O
drive	O
reconfiguration	O
.	O
</s>
<s>
DOS	O
produced	O
by	O
Optimized	B-Operating_System
Systems	I-Operating_System
Software	I-Operating_System
.	O
</s>
<s>
Compatible	O
with	O
DOS	O
2.0	O
-	O
Allowed	O
the	O
use	O
of	O
Double	O
Density	O
floppies	B-Device
.	O
</s>
<s>
DOS	B-Application
XL	I-Application
provided	O
a	O
menu	O
program	O
in	O
addition	O
to	O
the	O
command	O
line	O
.	O
</s>
<s>
This	O
DOS	O
could	O
read	O
SS/SD	O
,	O
SS/ED	O
,	O
SS/DD	O
and	O
DS/DD	O
disks	B-Device
,	O
and	O
made	O
use	O
of	O
all	O
known	O
methods	O
of	O
speeding	O
up	O
disk-reads	O
supported	O
by	O
the	O
various	O
third-party	O
drive	O
manufacturers	O
.	O
</s>
<s>
Sorts	O
disk	B-Device
directory	O
listings	O
and	O
can	O
set	O
display	O
options	O
.	O
</s>
<s>
Some	O
advanced	O
features	O
required	O
a	O
proprietary	B-Application
TOP-DOS	O
format	O
.	O
</s>
<s>
This	O
DOS	O
supports	O
Turbo	O
1050	B-Device
,	O
Happy	O
,	O
Speedy	O
,	O
XF551	B-Device
and	O
US	O
Doubler	O
highspeed	O
drives	O
.	O
</s>
<s>
Was	O
not	O
compatible	O
with	O
DOS	O
2.0	O
,	O
but	O
could	O
read	O
DOS	O
2.0	O
disks	B-Device
.	O
</s>
<s>
Supports	O
subdirectories	O
and	O
hard	O
drives	O
being	O
capable	O
of	O
handling	O
filesystems	B-Application
sized	O
up	O
to	O
16	O
MB	O
.	O
</s>
<s>
It	O
was	O
shipped	O
on	O
a	O
64	O
KB	O
ROM	B-Protocol
cartridge	I-Protocol
.	O
</s>
<s>
It	O
has	O
a	O
much	O
lower	O
memory	O
footprint	O
compared	O
to	O
the	O
original	O
SpartaDOS	O
and	O
does	O
not	O
use	O
the	O
RAM	B-Architecture
under	O
the	O
ROM	O
of	O
XL/XE	O
machines	O
,	O
allowing	O
it	O
to	O
be	O
used	O
on	O
the	O
older	O
Atari	O
400/800	O
models	O
.	O
</s>
<s>
A	O
number	O
of	O
different	O
formats	O
existed	O
for	O
Atari	O
disks	B-Device
.	O
</s>
<s>
Atari	B-Operating_System
DOS	I-Operating_System
2.0S	O
,	O
single-sided	O
,	O
single-density	O
disk	B-Device
had	O
720	O
sectors	O
divided	O
into	O
40	O
tracks	O
.	O
</s>
<s>
After	O
formatting	B-Application
,	O
707	O
sectors	O
were	O
free	O
.	O
</s>
<s>
Each	O
128-byte	O
sector	B-Application
used	O
the	O
last	O
3	O
bytes	O
for	O
housekeeping	O
data	O
(	O
bytes	O
used	O
,	O
file	O
number	O
,	O
next	O
sector	B-Application
)	O
,	O
leaving	O
125	O
bytes	O
for	O
data	O
.	O
</s>
<s>
This	O
meant	O
each	O
disk	B-Device
held	O
707	O
×	O
125	O
=	O
88,375	O
bytes	O
of	O
user	O
data	O
.	O
</s>
<s>
The	O
single-density	O
disk	B-Device
holding	O
a	O
mere	O
88	O
KB	O
per	B-Device
side	I-Device
remained	O
the	O
most	O
popular	O
Atari	B-Device
8-bit	I-Device
disk	B-Application
format	I-Application
throughout	O
the	O
series	O
 '	O
lifetime	O
,	O
and	O
almost	O
all	O
commercial	O
software	O
continued	O
to	O
be	O
sold	O
in	O
that	O
format	O
(	O
or	O
variants	O
of	O
it	O
modified	O
for	O
copy	B-Application
protection	I-Application
)	O
,	O
since	O
it	O
was	O
compatible	O
with	O
all	O
Atari-made	O
disk	B-Device
drives	I-Device
.	O
</s>
<s>
Single-Sided	O
,	O
Single-Density	O
:	O
40	O
tracks	O
with	O
18	O
sectors	O
per	O
track	O
,	O
128	O
bytes	O
per	O
sector	B-Application
.	O
</s>
<s>
Single-Sided	O
,	O
Enhanced-Density	O
:	O
40	O
tracks	O
with	O
26	O
sectors	O
per	O
track	O
,	O
128	O
bytes	O
per	O
sector	B-Application
.	O
</s>
<s>
Readable	O
by	O
the	O
1050	B-Device
and	O
the	O
XF551	B-Device
.	O
</s>
<s>
Single-Sided	O
,	O
Double-Density	O
:	O
40	O
tracks	O
with	O
18	O
sectors	O
per	O
track	O
,	O
256	O
bytes	O
per	O
sector	B-Application
.	O
</s>
<s>
Readable	O
by	O
the	O
XF551	B-Device
,	O
the	O
815	O
,	O
or	O
modified/upgraded	O
1050	B-Device
.	O
</s>
<s>
Double-Sided	O
,	O
Double-Density	O
:	O
80	O
tracks	O
(	O
40	O
tracks	O
per	B-Device
side	I-Device
)	O
with	O
18	O
sectors	O
per	O
track	O
,	O
256	O
bytes	O
per	O
sector	B-Application
.	O
</s>
<s>
Readable	O
by	O
the	O
XF551	B-Device
only	O
.	O
</s>
<s>
In	O
1978	O
,	O
Percom	B-Device
established	O
a	O
double-density	O
layout	O
standard	O
which	O
all	O
other	O
manufacturers	O
of	O
Atari-compatible	O
disk	B-Device
drives	I-Device
such	O
as	O
Indus	B-Device
,	O
Amdek	O
,	O
and	O
Rana	O
—	O
except	O
Atari	O
itself	O
—	O
followed	O
.	O
</s>
<s>
A	O
configuration	O
block	O
of	O
12	O
bytes	O
defines	O
the	O
disk	B-Device
layout	O
.	O
</s>
