<s>
86-DOS	B-Operating_System
(	O
known	O
internally	O
as	O
QDOS	B-Operating_System
,	O
for	O
Quick	B-Operating_System
and	I-Operating_System
Dirty	I-Operating_System
Operating	I-Operating_System
System	I-Operating_System
)	O
is	O
a	O
discontinued	O
operating	B-General_Concept
system	I-General_Concept
developed	O
and	O
marketed	O
by	O
Seattle	O
Computer	O
Products	O
(	O
SCP	O
)	O
for	O
its	O
Intel	O
8086-based	O
computer	O
kit	O
.	O
</s>
<s>
86-DOS	B-Operating_System
shared	O
a	O
few	O
of	O
its	O
commands	B-Application
with	O
other	O
operating	B-General_Concept
systems	I-General_Concept
like	O
OS/8	B-Operating_System
and	O
CP/M	B-Application
,	O
which	O
made	O
it	O
easy	O
to	O
port	O
programs	O
from	O
the	O
latter	O
.	O
</s>
<s>
Its	O
application	B-Application
programming	I-Application
interface	I-Application
was	O
very	O
similar	O
to	O
that	O
of	O
CP/M	B-Application
.	O
</s>
<s>
The	O
system	O
was	O
licensed	O
and	O
then	O
purchased	O
by	O
Microsoft	O
and	O
developed	O
further	O
as	O
MS-DOS	B-Application
and	O
PC	O
DOS	B-Device
.	O
</s>
<s>
86-DOS	B-Operating_System
was	O
created	O
because	O
sales	O
of	O
the	O
Seattle	O
Computer	O
Products	O
8086	B-General_Concept
computer	O
kit	O
,	O
demonstrated	O
in	O
June	O
1979	O
and	O
shipped	O
in	O
November	O
,	O
were	O
languishing	O
due	O
to	O
the	O
absence	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
SCP	O
wanted	O
to	O
offer	O
the	O
8086-version	O
of	O
CP/M	B-Application
that	O
Digital	O
Research	O
had	O
initially	O
announced	O
for	O
November	O
1979	O
,	O
but	O
it	O
was	O
delayed	O
and	O
its	O
release	O
date	O
was	O
uncertain	O
.	O
</s>
<s>
This	O
was	O
not	O
the	O
first	O
time	O
Digital	O
Research	O
had	O
lagged	O
behind	O
hardware	O
developments	O
;	O
two	O
years	O
earlier	O
it	O
had	O
been	O
slow	O
to	O
adapt	O
CP/M	B-Application
for	O
new	O
floppy	B-Device
disk	I-Device
formats	O
and	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
In	O
April	O
1980	O
,	O
SCP	O
assigned	O
24-year-old	O
Tim	O
Paterson	O
to	O
develop	O
a	O
substitute	O
for	O
CP/M	B-Operating_System
-86	I-Operating_System
.	O
</s>
<s>
Using	O
a	O
CP/M	B-Application
-80	I-Application
manual	O
as	O
reference	O
Paterson	O
modeled	O
86-DOS	B-Operating_System
after	O
its	O
architecture	O
and	O
interfaces	O
,	O
but	O
adapted	O
to	O
meet	O
the	O
requirements	O
of	O
Intel	O
's	O
8086	B-General_Concept
16-bit	B-Device
processor	I-Device
,	O
for	O
easy	O
(	O
and	O
partially	O
automated	O
)	O
source-level	O
translatability	O
of	O
the	O
many	O
existing	O
8-bit	O
CP/M	B-Application
programs	O
;	O
porting	O
them	O
to	O
either	O
DOS	B-Device
or	O
CP/M	B-Operating_System
-86	I-Operating_System
was	O
about	O
equally	O
difficult	O
,	O
and	O
eased	O
by	O
the	O
fact	O
that	O
Intel	O
had	O
already	O
published	O
a	O
method	O
that	O
could	O
be	O
used	O
to	O
automatically	O
translate	O
software	O
from	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
processor	O
,	O
for	O
which	O
CP/M	B-Application
had	O
been	O
designed	O
,	O
to	O
the	O
new	O
8086	B-General_Concept
instruction	O
set	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
he	O
made	O
a	O
number	O
of	O
changes	O
and	O
enhancements	O
to	O
address	O
what	O
he	O
saw	O
as	O
CP/M	B-Application
'	O
s	O
shortcomings	O
.	O
</s>
<s>
CP/M	B-Application
cached	B-General_Concept
file	B-Application
system	I-Application
information	O
in	O
memory	O
for	O
speed	O
,	O
but	O
this	O
required	O
a	O
user	O
to	O
force	O
an	O
update	O
to	O
a	O
disk	O
before	O
removing	O
it	O
;	O
if	O
the	O
user	O
forgot	O
,	O
the	O
disk	O
would	O
become	O
corrupt	O
.	O
</s>
<s>
CP/M	B-Application
'	O
s	O
PIP	B-Application
command	O
,	O
which	O
copied	O
files	O
,	O
supported	O
several	O
special	B-Application
file	I-Application
names	O
that	O
referred	O
to	O
hardware	O
devices	O
such	O
as	O
printers	O
and	O
communication	O
ports	O
.	O
</s>
<s>
Paterson	O
built	O
these	O
names	O
into	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
device	B-Application
files	I-Application
so	O
that	O
any	O
program	O
could	O
use	O
them	O
.	O
</s>
<s>
He	O
gave	O
his	O
copying	O
program	O
the	O
more	O
intuitive	O
name	O
COPY	B-Device
.	O
</s>
<s>
Rather	O
than	O
implementing	O
CP/M	B-Application
'	O
s	O
file	B-Application
system	I-Application
,	O
he	O
drew	O
on	O
Microsoft	O
Standalone	O
Disk	O
BASIC-86	O
'	O
s	O
File	B-Application
Allocation	I-Application
Table	I-Application
(	O
FAT	B-Application
)	O
file	B-Application
system	I-Application
.	O
</s>
<s>
By	O
mid-1980	O
SCP	O
advertised	O
86-DOS	B-Operating_System
,	O
priced	O
at	O
for	O
owners	O
of	O
its	O
8086-board	O
and	O
for	O
others	O
.	O
</s>
<s>
It	O
touted	O
the	O
software	O
's	O
ability	O
to	O
read	O
Zilog	B-General_Concept
Z80	I-General_Concept
source	O
code	O
from	O
a	O
CP/M	B-Application
disk	O
and	O
translate	O
it	O
to	O
8086	B-General_Concept
source	O
code	O
,	O
and	O
promised	O
that	O
only	O
"	O
minor	O
hand	O
correction	O
and	O
optimization	O
"	O
was	O
needed	O
to	O
produce	O
8086	B-General_Concept
binaries	O
.	O
</s>
<s>
In	O
October	O
1980	O
,	O
IBM	O
was	O
developing	O
what	O
would	O
become	O
the	O
original	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
.	O
</s>
<s>
CP/M	B-Application
was	O
by	O
far	O
the	O
most	O
popular	O
operating	B-General_Concept
system	I-General_Concept
in	O
use	O
at	O
the	O
time	O
,	O
and	O
IBM	O
felt	O
it	O
needed	O
CP/M	B-Application
in	O
order	O
to	O
compete	O
.	O
</s>
<s>
In	O
later	O
discussions	O
between	O
IBM	O
and	O
Bill	O
Gates	O
,	O
Gates	O
mentioned	O
the	O
existence	O
of	O
86-DOS	B-Operating_System
and	O
IBM	O
representative	O
Jack	O
Sams	O
told	O
him	O
to	O
get	O
a	O
license	O
for	O
it	O
.	O
</s>
<s>
Microsoft	O
purchased	O
a	O
non-exclusive	O
license	O
for	O
86-DOS	B-Operating_System
from	O
Seattle	O
Computer	O
Products	O
in	O
December	O
1980	O
for	O
.	O
</s>
<s>
In	O
May	O
1981	O
,	O
it	O
hired	O
Tim	O
Paterson	O
to	O
port	O
the	O
system	O
to	O
the	O
IBMPC	B-Device
,	O
which	O
used	O
the	O
slower	O
and	O
less	O
expensive	O
Intel	B-Device
8088	I-Device
processor	O
and	O
had	O
its	O
own	O
specific	O
family	O
of	O
peripherals	O
.	O
</s>
<s>
In	O
July	O
1981	O
,	O
a	O
month	O
before	O
the	O
PC	O
's	O
release	O
,	O
Microsoft	O
purchased	O
all	O
rights	O
to	O
86-DOS	B-Operating_System
from	O
SCP	O
for	O
.	O
</s>
<s>
It	O
met	O
IBM	O
's	O
main	O
criteria	O
:	O
it	O
looked	O
like	O
CP/M	B-Application
,	O
and	O
it	O
was	O
easy	O
to	O
adapt	O
existing	O
8-bit	O
CP/M	B-Application
programs	O
to	O
run	O
under	O
it	O
,	O
notably	O
thanks	O
to	O
the	O
TRANS	O
command	O
which	O
would	O
translate	O
source	O
files	O
from	O
8080	B-General_Concept
to	O
8086	B-General_Concept
machine	O
instructions	O
.	O
</s>
<s>
Microsoft	O
licensed	O
86-DOS	B-Operating_System
to	O
IBM	O
,	O
and	O
it	O
became	O
PCDOS1.0	O
.	O
</s>
<s>
This	O
license	O
also	O
permitted	O
Microsoft	O
to	O
sell	O
DOS	B-Device
to	O
other	O
companies	O
,	O
which	O
it	O
did	O
.	O
</s>
<s>
The	O
deal	O
was	O
spectacularly	O
successful	O
,	O
and	O
SCP	O
later	O
claimed	O
in	O
court	O
that	O
Microsoft	O
had	O
concealed	O
its	O
relationship	O
with	O
IBM	O
in	O
order	O
to	O
purchase	O
the	O
operating	B-General_Concept
system	I-General_Concept
cheaply	O
.	O
</s>
<s>
When	O
Digital	O
Research	O
founder	O
Gary	O
Kildall	O
examined	O
PCDOS	O
and	O
found	O
that	O
it	O
duplicated	O
CP/M	B-Application
'	O
s	O
programming	B-Application
interface	I-Application
,	O
he	O
wanted	O
to	O
sue	O
IBM	O
,	O
which	O
at	O
the	O
time	O
claimed	O
that	O
PCDOS	O
was	O
its	O
own	O
product	O
.	O
</s>
<s>
Nonetheless	O
,	O
Kildall	O
confronted	O
IBM	O
and	O
persuaded	O
them	O
to	O
offer	O
CP/M	B-Operating_System
-86	I-Operating_System
with	O
the	O
PC	O
in	O
exchange	O
for	O
a	O
release	O
of	O
liability	O
.	O
</s>
<s>
Perhaps	O
the	O
most	O
sensational	O
claim	O
came	O
from	O
Jerry	O
Pournelle	O
,	O
who	O
said	O
that	O
Kildall	O
personally	O
demonstrated	O
to	O
him	O
that	O
DOS	B-Device
contained	O
CP/M	B-Application
code	O
by	O
entering	O
a	O
command	O
in	O
DOS	B-Device
that	O
displayed	O
Kildall	O
's	O
name	O
,	O
but	O
Pournelle	O
never	O
revealed	O
the	O
command	O
and	O
nobody	O
has	O
come	O
forward	O
to	O
corroborate	O
his	O
story	O
.	O
</s>
<s>
A	O
2004	O
book	O
about	O
Kildall	O
says	O
that	O
he	O
used	O
such	O
an	O
encrypted	O
message	O
to	O
demonstrate	O
that	O
other	O
manufacturers	O
had	O
copied	O
CP/M	B-Application
,	O
but	O
does	O
not	O
say	O
that	O
he	O
found	O
the	O
message	O
in	O
DOS	B-Device
;	O
instead	O
Kildall	O
's	O
memoir	O
(	O
a	O
source	O
for	O
the	O
book	O
)	O
pointed	O
to	O
the	O
well-known	O
interface	O
similarity	O
.	O
</s>
<s>
Paterson	O
insists	O
that	O
the	O
86-DOS	B-Operating_System
software	O
was	O
his	O
original	O
work	O
,	O
and	O
has	O
denied	O
referring	O
to	O
or	O
otherwise	O
using	O
CP/M	B-Application
code	O
while	O
writing	O
it	O
.	O
</s>
<s>
QDOS	B-Operating_System
0.10	O
1980-07	O
Roughly	O
half	O
completed	O
version	O
of	O
the	O
OS	O
.	O
</s>
<s>
It	O
implemented	O
the	O
original	O
form	O
of	O
Paterson	O
's	O
derivation	O
of	O
Microsoft	O
's	O
FAT	B-Application
filesystem	I-Application
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
earlier	O
8-bit	O
FAT	B-Application
filesystem	I-Application
found	O
in	O
Standalone	O
Disk	O
BASIC-86	O
,	O
this	O
variant	O
already	O
supported	O
12-bit	O
table	O
elements	O
,	O
reduced	O
the	O
number	O
of	O
FATs	O
from	O
3	O
to	O
2	O
,	O
redefined	O
the	O
semantics	O
of	O
some	O
of	O
the	O
reserved	O
cluster	O
values	O
,	O
and	O
modified	O
the	O
disk	O
layout	O
,	O
so	O
that	O
the	O
root	O
directory	O
was	O
now	O
located	O
between	O
the	O
FAT	B-Application
and	O
the	O
data	O
area	O
.	O
</s>
<s>
Paterson	O
also	O
increased	O
the	O
previous	O
9-character	O
length	O
limit	O
to	O
11	O
characters	O
in	O
order	O
to	O
support	O
CP/M	B-Application
-style	O
8.3	O
filenames	O
and	O
File	B-Operating_System
Control	I-Operating_System
Blocks	I-Operating_System
.	O
</s>
<s>
This	O
variant	O
,	O
however	O
,	O
still	O
used	O
16-byte	O
directory	O
entries	O
and	O
therefore	O
is	O
not	O
compatible	O
with	O
what	O
became	O
later	O
known	O
as	O
FAT12	B-Application
in	O
MS-DOS/PC	O
DOS	B-Device
.	O
</s>
<s>
QDOS	B-Operating_System
0.11	O
1980-08	O
Bug	O
fix	O
shipment	O
.	O
</s>
<s>
QDOS/86	O
-DOS	O
0.2	O
1980-08	O
EDLIN	B-Application
added	O
.	O
</s>
<s>
Renamed	O
to	O
86-DOS	B-Operating_System
by	O
August	O
1980	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.3	O
15	O
November	O
1980	O
First	O
version	O
licensed	O
by	O
SCP	O
to	O
Microsoft	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.33	O
1980-12	O
First	O
version	O
distributed	O
by	O
SCP	O
to	O
OEMs	O
and	O
Microsoft	O
as	O
86-DOS	B-Operating_System
.	O
</s>
<s>
86-DOS	B-Operating_System
0.34	O
29	O
December	O
1980	O
Cleaned	O
up	O
release	O
for	O
SCP	O
OEMs	O
including	O
Microsoft	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.42	O
25	O
February	O
1981	O
At	O
the	O
indirect	O
request	O
of	O
IBM	O
(	O
through	O
Microsoft	O
)	O
size	O
of	O
directory	O
entries	O
changed	O
from	O
16	O
to	O
32	O
bytes	O
(	O
similar	O
to	O
MDOS/MIDAS	O
)	O
in	O
order	O
to	O
add	O
support	O
for	O
a	O
last-modified	O
date	O
stamp	O
(	O
2	O
bytes	O
)	O
and	O
theoretical	O
file	O
sizes	O
larger	O
than	O
16	O
MB	O
(	O
4	O
bytes	O
)	O
,	O
thereby	O
implementing	O
the	O
earliest	O
form	O
of	O
the	O
12-bit	O
FAT	B-Application
file	I-Application
system	I-Application
logically	O
fully	O
compatible	O
with	O
what	O
became	O
known	O
as	O
FAT12	B-Application
in	O
MS-DOS/PC	O
DOS	B-Device
later	O
on	O
.	O
</s>
<s>
86-DOS	B-Operating_System
retained	O
the	O
capability	O
to	O
read	O
volumes	O
written	O
under	O
older	O
versions	O
of	O
86-DOS	B-Operating_System
up	O
to	O
MS-DOS	B-Application
1.14	O
at	O
the	O
least	O
,	O
whereas	O
generic	O
MS-DOS	B-Application
1.20	O
/	O
PC	O
DOS	B-Device
1.1	O
and	O
higher	O
no	O
longer	O
supported	O
it	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.56	O
23	O
March	O
1981	O
Support	O
for	O
disk	O
blocking/deblocking	O
as	O
requested	O
since	O
1981-01-15	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.60	O
27	O
March	O
1981	O
The	O
file	O
DOSIO.ASM	O
found	O
in	O
86-DOS	B-Operating_System
1.00	O
mentions	O
that	O
it	O
is	O
the	O
"	O
I/O	O
System	O
for	O
86-DOS	B-Operating_System
version	O
0.60	O
and	O
later	O
"	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.74	O
15	O
April	O
1981	O
Added	O
device	B-Application
files	I-Application
.	O
</s>
<s>
86-DOS	B-Operating_System
0.75	O
17	O
April	O
1981	O
Bug	O
fix	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.76	O
23	O
April	O
1981	O
Bug	O
fix	O
.	O
</s>
<s>
86-DOS	B-Operating_System
0.80	O
27	O
April	O
1981	O
Added	O
system	O
calls	O
.	O
</s>
<s>
86-DOS	B-Operating_System
1.00	O
28	O
April	O
1981	O
Modified	O
system	O
calls	O
.	O
</s>
<s>
86-DOS	B-Operating_System
1.01	O
12	O
May	O
1981	O
Bug	O
fix	O
.	O
</s>
<s>
86-DOS	B-Operating_System
1.10	O
21	O
July	O
1981	O
Purchased	O
by	O
Microsoft	O
and	O
renamed	O
to	O
MS-DOS	B-Application
on	O
27	O
July	O
1981	O
,	O
therefore	O
the	O
last	O
version	O
with	O
genuinely	O
matching	O
86-DOS	B-Operating_System
and	O
MS-DOS	B-Application
version	O
numbers	O
.	O
</s>
<s>
86-DOS	B-Operating_System
1.14	O
1981-10/11	O
According	O
to	O
Tim	O
Paterson	O
PC	O
DOS	B-Device
1.0	O
basically	O
reflects	O
86-DOS	B-Operating_System
1.14	O
,	O
other	O
sources	O
find	O
a	O
match	O
of	O
PC	O
DOS	B-Device
1.0	O
with	O
MS-DOS/86	O
-DOS	O
1.10	O
as	O
of	O
21	O
July	O
1981	O
more	O
likely	O
.	O
</s>
<s>
The	O
following	O
list	O
of	O
commands	B-Application
is	O
supported	O
by	O
86-DOS	B-Operating_System
.	O
</s>
<s>
By	O
1982	O
,	O
when	O
IBM	O
asked	O
Microsoft	O
to	O
release	O
a	O
version	O
of	O
DOS	B-Device
that	O
was	O
compatible	O
with	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
,	O
PC	O
DOS	B-Device
2.0	O
was	O
an	O
almost	O
complete	O
rewrite	O
of	O
DOS	B-Device
,	O
so	O
by	O
March	O
1983	O
,	O
very	O
little	O
of	O
86-DOS	B-Operating_System
remained	O
.	O
</s>
<s>
The	O
most	O
enduring	O
element	O
of	O
86-DOS	B-Operating_System
was	O
its	O
primitive	O
line	O
editor	O
,	O
EDLIN	B-Application
,	O
which	O
remained	O
the	O
only	O
editor	O
supplied	O
with	O
Microsoft	O
versions	O
of	O
DOS	B-Device
until	O
the	O
June	O
1991	O
release	O
of	O
MS-DOS	B-Application
5.0	O
,	O
which	O
included	O
a	O
text-based	B-Application
user	I-Application
interface	I-Application
editor	O
called	O
MS-DOS	B-Application
Editor	I-Application
,	O
based	O
on	O
QBasic	B-Language
.	O
</s>
<s>
EDLIN	B-Application
can	O
still	O
be	O
used	O
on	O
contemporary	O
machines	O
,	O
since	O
there	O
is	O
an	O
emulated	O
DOS	B-Device
environment	O
up	O
to	O
Windows	O
10	O
(	O
32	O
bit	O
)	O
.	O
</s>
<s>
Seattle	O
Computer	O
Products	O
 '	O
86-DOS	B-Operating_System
supported	O
the	O
FAT12	B-Application
filesystem	B-Application
on	O
a	O
range	O
of	O
8-inch	O
and	O
5.25-inch	O
floppy	B-Device
disk	I-Device
drives	I-Device
on	O
S-100	B-Architecture
floppy	B-Device
disk	I-Device
controller	O
hardware	O
manufactured	O
by	O
Cromemco	O
,	O
Tarbell	B-Device
Electronics	I-Device
and	O
North	O
Star	O
Computers	O
.	O
</s>
<s>
The	O
Western	O
Digital	O
FD1771-based	O
Cromemco	O
and	O
Tarbell	B-Device
boards	O
supported	O
one-sided	O
,	O
single-density	O
soft-sectored	O
drives	O
.	O
</s>
<s>
A	O
Tarbell	B-Device
double-density	O
board	O
utilizing	O
the	O
FD1791	B-Device
was	O
supported	O
as	O
well	O
.	O
</s>
<s>
Later	O
,	O
SCP	O
offered	O
advanced	O
floppy	B-Device
disk	I-Device
controllers	O
,	O
like	O
the	O
Disk	O
Master	O
series	O
.	O
</s>
<s>
86-DOS	B-Operating_System
did	O
not	O
take	O
advantage	O
of	O
a	O
FAT	B-Application
ID	O
byte	O
or	O
BIOS	B-Device
parameter	I-Device
block	I-Device
(	O
BPB	B-Device
)	O
,	O
as	O
later	O
DOS	B-Device
versions	O
do	O
,	O
to	O
distinguish	O
between	O
different	O
media	O
formats	O
;	O
instead	O
different	O
drive	O
letters	O
were	O
hard-coded	O
at	O
time	O
of	O
compilation	O
to	O
be	O
associated	O
with	O
different	O
physical	O
floppy	B-Device
drives	I-Device
,	O
sides	O
and	O
densities	O
.	O
</s>
<s>
That	O
meant	O
,	O
depending	O
on	O
its	O
type	B-Device
,	O
a	O
disk	O
had	O
to	O
be	O
addressed	O
under	O
a	O
certain	O
drive	O
letter	O
to	O
be	O
recognized	O
correctly	O
.	O
</s>
<s>
This	O
concept	O
was	O
later	O
emulated	O
with	O
more	O
flexibility	O
by	O
DRIVER.SYS	O
under	O
DOS	B-Device
3.x	O
and	O
later	O
versions	O
.	O
</s>
<s>
Two	O
logical	O
format	O
variants	O
of	O
the	O
86-DOS	B-Operating_System
12-bit	O
FAT	B-Application
format	O
existed	O
—	O
the	O
original	O
format	O
with	O
16-byte	O
directory	O
entries	O
and	O
the	O
later	O
format	O
(	O
since	O
86-DOS	B-Operating_System
0.42	O
)	O
with	O
32-byte	O
directory	O
entries	O
.	O
</s>
<s>
Only	O
the	O
second	O
one	O
is	O
logically	O
compatible	O
with	O
the	O
FAT12	B-Application
format	O
known	O
since	O
the	O
release	O
of	O
MS-DOS	B-Application
and	O
PCDOS	O
.	O
</s>
<s>
MS-DOS	B-Application
still	O
cannot	O
mount	O
such	O
volumes	O
,	O
as	O
in	O
absence	O
of	O
a	O
BPB	B-Device
it	O
falls	O
back	O
to	O
retrieve	O
the	O
FAT	B-Application
ID	O
in	O
the	O
FAT	B-Application
entry	O
for	O
cluster	O
0	O
to	O
choose	O
among	O
hard-coded	O
disk	O
geometry	O
profiles	O
.	O
</s>
<s>
In	O
all	O
formats	O
of	O
a	O
volume	O
formatted	O
under	O
MS-DOS	B-Application
that	O
would	O
otherwise	O
be	O
supported	O
by	O
both	O
systems	O
and	O
typically	O
also	O
in	O
all	O
other	O
formats	O
,	O
this	O
ID	O
is	O
located	O
in	O
the	O
first	O
byte	O
of	O
logical	O
sector	O
1	O
—	O
that	O
is	O
,	O
the	O
volume	O
's	O
second	O
sector	O
with	O
physical	O
cylinder-head-sector	B-Device
(	O
CHS	O
)	O
address	O
0/0/2	O
or	O
logical	B-Device
block	I-Device
addressing	I-Device
(	O
LBA	O
)	O
address	O
1	O
—	O
since	O
MS-DOS	B-Application
assumes	O
a	O
single	O
reserved	O
sector	O
,	O
the	O
boot	O
sector	O
.	O
</s>
<s>
Under	O
86-DOS	B-Operating_System
,	O
the	O
reserved	O
sectors	O
area	O
is	O
significantly	O
larger	O
(	O
whole	O
tracks	O
)	O
,	O
and	O
therefore	O
the	O
prototypical	O
FAT	B-Application
ID	O
(	O
and	O
)	O
is	O
located	O
elsewhere	O
on	O
disk	O
,	O
making	O
it	O
impossible	O
for	O
MS-DOS	B-Application
to	O
retrieve	O
it	O
,	O
and	O
even	O
if	O
it	O
would	O
,	O
the	O
hard-coded	O
disk	O
profile	O
associated	O
with	O
it	O
would	O
not	O
take	O
this	O
larger	O
reserved	O
sectors	O
region	O
under	O
86-DOS	B-Operating_System
into	O
account	O
.	O
</s>
<s>
CP/M	B-Application
2	O
floppy	B-Device
media	O
were	O
readable	O
through	O
RDCPM	O
.	O
</s>
<s>
86-DOS	B-Operating_System
did	O
not	O
offer	O
any	O
specific	O
support	O
for	O
fixed	B-Device
disks	I-Device
,	O
but	O
third-party	O
solutions	O
in	O
form	O
of	O
hard	B-Device
disk	I-Device
controllers	O
and	O
corresponding	O
I/O	O
system	O
extensions	O
for	O
86-DOS	B-Operating_System
were	O
available	O
from	O
companies	O
like	O
Tallgrass	O
Technologies	O
,	O
making	O
hard	B-Device
disks	I-Device
accessible	O
similar	O
to	O
superfloppies	O
within	O
the	O
size	O
limits	O
of	O
the	O
FAT12	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
Various	O
OEM	O
versions	O
of	O
MS-DOS	B-Application
1.2x	O
and	O
2.x	O
supported	O
a	O
number	O
of	O
similar	O
8-inch	O
FAT12	B-Application
floppy	B-Device
disk	I-Device
formats	O
as	O
well	O
,	O
although	O
not	O
identical	O
to	O
those	O
supported	O
by	O
86-DOS	B-Operating_System
.	O
</s>
<s>
Disk	O
formats	O
supported	O
by	O
one	O
of	O
the	O
last	O
versions	O
developed	O
by	O
Tim	O
Paterson	O
at	O
Microsoft	O
,	O
MS-DOS	B-Operating_System
1.25	I-Operating_System
(	O
March	O
1982	O
)	O
for	O
the	O
SCP	B-Operating_System
Gazelle	I-Operating_System
computer	O
with	O
SCP	O
controller	O
or	O
Cromemco	O
16FDC	O
controller	O
(	O
by	O
default	O
,	O
this	O
version	O
only	O
supported	O
the	O
MS-DOS-compatible	O
variants	O
of	O
the	O
8.0in	O
formats	O
with	O
a	O
single	O
reserved	O
sector	O
but	O
it	O
could	O
be	O
built	O
to	O
provide	O
two	O
extra	O
drive	O
letters	O
to	O
read	O
and	O
write	O
floppies	B-Device
in	O
the	O
previous	O
SCP	B-Operating_System
86-DOS	I-Operating_System
8.0in	O
disk	O
formats	O
since	O
0.42	O
as	O
well	O
)	O
:	O
</s>
<s>
In	O
1984	O
Seattle	O
Computer	O
Products	O
released	O
an	O
OEM	O
version	O
of	O
MS-DOS	B-Operating_System
2.0	I-Operating_System
for	O
the	O
SCP	O
S-100	B-Architecture
computer	I-Architecture
with	O
SCP-500	O
Disk	O
Master	O
Floppy	B-Device
controller	O
.	O
</s>
<s>
It	O
added	O
support	O
for	O
5.25in	O
DD/1S	O
(	O
180KB	O
)	O
and	O
DD/2S	O
(	O
360KB	O
)	O
FAT12	B-Application
formats	O
and	O
supported	O
the	O
older	O
formats	O
as	O
well	O
,	O
although	O
possibly	O
with	O
some	O
of	O
the	O
parameters	O
modified	O
compared	O
to	O
MS-DOS	B-Operating_System
1.25	I-Operating_System
.	O
</s>
