<s>
IBM	B-Device
PC	I-Device
DOS	B-Device
(	O
also	O
known	O
as	O
simply	O
IBM	O
DOS	B-Device
)	O
,	O
an	O
acronym	O
for	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
Disk	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
,	O
is	O
a	O
discontinued	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
,	O
its	O
successors	O
,	O
and	O
IBM	B-Device
PC	I-Device
compatibles	O
.	O
</s>
<s>
Developed	O
by	O
Microsoft	O
,	O
it	O
was	O
also	O
sold	O
by	O
that	O
company	O
as	O
MS-DOS	B-Application
.	O
</s>
<s>
Both	O
operating	O
systems	O
were	O
identical	O
or	O
almost	O
identical	O
until	O
1993	O
,	O
when	O
IBM	O
began	O
selling	O
PC	O
DOS	B-Device
6.1	O
with	O
new	O
features	O
.	O
</s>
<s>
The	O
collective	O
shorthand	O
for	O
PC	O
DOS	B-Device
and	O
MS-DOS	B-Application
was	O
DOS	B-Device
,	O
which	O
is	O
also	O
the	O
generic	O
term	O
for	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
and	O
is	O
shared	O
with	O
dozens	O
of	O
disk	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
called	I-Operating_System
DOS	I-Operating_System
.	O
</s>
<s>
The	O
IBM	O
task	O
force	O
assembled	O
to	O
develop	O
the	O
IBM	B-Device
PC	I-Device
decided	O
that	O
critical	O
components	O
of	O
the	O
machine	O
,	O
including	O
the	O
operating	O
system	O
,	O
would	O
come	O
from	O
outside	O
vendors	O
.	O
</s>
<s>
This	O
radical	O
break	O
from	O
company	O
tradition	O
of	O
in-house	O
development	O
was	O
one	O
of	O
the	O
key	O
decisions	O
that	O
made	O
the	O
IBM	B-Device
PC	I-Device
an	O
industry	O
standard	O
.	O
</s>
<s>
Although	O
IBM	O
expected	O
that	O
most	O
customers	O
would	O
use	O
PCDOS	O
,	O
the	O
IBM	B-Device
PC	I-Device
also	O
supported	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
which	O
became	O
available	O
six	O
months	O
after	O
PCDOS	O
,	O
and	O
UCSD	B-Language
p-System	I-Language
operating	O
systems	O
.	O
</s>
<s>
IBM	O
's	O
expectation	O
proved	O
correct	O
:	O
one	O
survey	O
found	O
that	O
96.3	O
%	O
of	O
PCs	O
were	O
ordered	O
with	O
the	O
PCDOS	O
compared	O
to	O
3.4	O
%	O
with	O
the	O
CP/M	B-Operating_System
-86	I-Operating_System
.	O
</s>
<s>
By	O
the	O
time	B-Device
PCDOS	O
3.0	O
was	O
completed	O
,	O
IBM	O
had	O
a	O
team	O
of	O
developers	O
covering	O
the	O
full	O
OS	O
.	O
</s>
<s>
At	O
that	O
point	O
in	O
time	B-Device
,	O
either	O
IBM	O
or	O
Microsoft	O
completely	O
developed	O
versions	O
of	O
IBM	O
PCDOS	O
going	O
forward	O
.	O
</s>
<s>
Most	O
of	O
the	O
time	B-Device
branded	O
versions	O
were	O
identical	O
,	O
but	O
there	O
were	O
some	O
cases	O
in	O
which	O
each	O
of	O
the	O
companies	O
made	O
minor	O
modifications	O
to	O
their	O
version	O
of	O
DOS	B-Device
.	O
</s>
<s>
In	O
the	O
fall	O
of	O
1984	O
,	O
IBM	O
gave	O
all	O
the	O
source	O
code	O
and	O
documentation	O
of	O
the	O
internally	O
developed	O
IBM	B-Operating_System
TopView	I-Operating_System
for	O
DOS	B-Device
to	O
Microsoft	O
so	O
that	O
Microsoft	O
could	O
more	O
fully	O
understand	O
how	O
to	O
develop	O
an	O
object-oriented	B-Language
operating	B-Application
environment	I-Application
,	O
overlapping	O
windows	O
(	O
for	O
its	O
development	O
of	O
Windows	B-Application
2.0	I-Application
)	O
and	O
multitasking	B-Operating_System
.	O
</s>
<s>
Microsoft	O
first	O
licensed	O
,	O
then	O
purchased	O
86-DOS	B-Operating_System
from	O
Seattle	O
Computer	O
Products	O
(	O
SCP	O
)	O
,	O
which	O
was	O
modified	O
for	O
the	O
IBM	B-Device
PC	I-Device
by	O
Microsoft	O
employee	O
Bob	O
O'Rear	O
with	O
assistance	O
from	O
SCP	O
(	O
later	O
Microsoft	O
)	O
employee	O
Tim	O
Paterson	O
.	O
</s>
<s>
O'Rear	O
got	O
86-DOS	B-Operating_System
to	O
run	O
on	O
the	O
prototype	O
PC	O
in	O
February	O
1981	O
.	O
</s>
<s>
86-DOS	B-Operating_System
had	O
to	O
be	O
converted	O
from	O
8-inch	O
to	O
5.25-inch	O
floppy	B-Device
disks	I-Device
and	O
integrated	O
with	O
the	O
BIOS	B-Operating_System
,	O
which	O
Microsoft	O
was	O
helping	O
IBM	O
to	O
write	O
.	O
</s>
<s>
Perhaps	O
the	O
first	O
public	O
mention	O
of	O
the	O
operating	O
system	O
was	O
in	O
July	O
1981	O
,	O
when	O
Byte	O
discussed	O
rumors	O
of	O
a	O
forthcoming	O
personal	O
computer	O
with	O
"	O
a	O
CP/M	B-Application
-like	I-Application
DOS	B-Device
...	O
to	O
be	O
called	O
,	O
simply	O
,	O
'	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
DOS	B-Device
.	O
</s>
<s>
86-DOS	B-Operating_System
was	O
rebranded	O
IBM	O
PCDOS	O
1.0	O
for	O
its	O
August	O
1981	O
release	O
with	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
The	O
initial	O
version	O
of	O
DOS	B-Device
was	O
largely	O
based	O
on	O
CP/M	B-Application
-80	I-Application
1.x	O
and	O
most	O
of	O
its	O
architecture	O
,	O
function	O
calls	O
and	O
file-naming	O
conventions	O
were	O
copied	O
directly	O
from	O
the	O
older	O
OS	O
.	O
</s>
<s>
The	O
most	O
significant	O
difference	O
was	O
the	O
fact	O
that	O
it	O
introduced	O
a	O
different	O
file	O
system	O
,	O
FAT12	B-Application
.	O
</s>
<s>
Unlike	O
all	O
later	O
DOS	B-Device
versions	O
,	O
the	O
and	O
commands	O
were	O
separate	O
executables	O
rather	O
than	O
part	O
of	O
.	O
</s>
<s>
Single-sided	O
160	O
kilobyte	O
(	O
KB	O
)	O
5.25-inch	O
floppies	B-Device
were	O
the	O
only	O
disk	O
format	O
supported	O
.	O
</s>
<s>
It	O
debuted	O
in	O
May	O
1982	O
along	O
with	O
the	O
RevisionB	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
Completely	O
rewritten	O
,	O
DOS	B-Device
2.0	O
added	O
subdirectories	O
and	O
hard	O
disk	O
support	O
for	O
the	O
new	O
IBM	B-Device
XT	I-Device
,	O
which	O
debuted	O
in	O
March	O
1983	O
.	O
</s>
<s>
A	O
new	O
9-sector	O
format	O
bumped	O
the	O
capacity	O
of	O
floppy	B-Device
disks	I-Device
to	O
360KB	O
.	O
</s>
<s>
The	O
Unix-inspired	O
kernel	O
featured	O
file	B-Application
handles	I-Application
in	O
place	O
of	O
the	O
CP/M	B-Application
-derivative	O
file	O
control	O
blocks	O
and	O
loadable	O
device	O
drivers	O
could	O
now	O
be	O
used	O
for	O
adding	O
hardware	O
beyond	O
that	O
which	O
the	O
IBM	B-Operating_System
PC	I-Operating_System
BIOS	I-Operating_System
supported	O
.	O
</s>
<s>
BASIC	O
and	O
most	O
of	O
the	O
utilities	O
provided	O
with	O
DOS	B-Device
were	O
substantially	O
upgraded	O
as	O
well	O
.	O
</s>
<s>
A	O
major	O
undertaking	O
that	O
took	O
almost	O
10	O
months	O
of	O
work	O
,	O
DOS	B-Device
2.0	O
was	O
more	O
than	O
twice	O
as	O
big	O
as	O
DOS	B-Device
1.x	O
,	O
occupying	O
around	O
28KB	O
of	O
RAM	O
compared	O
to	O
the	O
12KB	O
of	O
its	O
predecessor	O
.	O
</s>
<s>
It	O
would	O
form	O
the	O
basis	O
for	O
all	O
Microsoft	O
consumer-oriented	O
OSes	O
until	O
2001	O
,	O
when	O
Windows	B-Application
XP	I-Application
(	O
based	O
on	O
Windows	B-Device
NT	I-Device
)	O
was	O
released	O
.	O
</s>
<s>
In	O
October	O
1983	O
(	O
officially	O
1	O
November	O
1983	O
)	O
DOS	B-Device
2.1	O
debuted	O
.	O
</s>
<s>
It	O
fixed	O
some	O
bugs	O
and	O
added	O
support	O
for	O
half-height	O
floppy	B-Device
drives	I-Device
and	O
the	O
new	O
IBM	B-Device
PCjr	I-Device
.	O
</s>
<s>
In	O
1983	O
,	O
Compaq	O
released	O
the	O
Compaq	B-Device
Portable	I-Device
,	O
the	O
first	O
100%	O
IBM	B-Device
PC	I-Device
compatible	O
and	O
licensed	O
their	O
own	O
OEM	O
version	O
of	O
DOS	B-Device
1.10	O
(	O
quickly	O
replaced	O
by	O
DOS	B-Device
2.00	O
)	O
from	O
Microsoft	O
.	O
</s>
<s>
Other	O
PC	O
compatibles	O
followed	O
suit	O
,	O
most	O
of	O
which	O
included	O
hardware-specific	O
DOS	B-Device
features	O
,	O
although	O
some	O
were	O
generic	O
.	O
</s>
<s>
In	O
August	O
1984	O
,	O
IBM	O
introduced	O
the	O
Intel	O
80286-derived	O
IBM	B-Operating_System
PC/AT	I-Operating_System
,	O
its	O
next-generation	O
machine	O
.	O
</s>
<s>
Along	O
with	O
this	O
was	O
DOS	B-Device
3.00	O
.	O
</s>
<s>
Despite	O
jumping	O
a	O
whole	O
version	O
number	O
,	O
it	O
again	O
proved	O
little	O
more	O
than	O
an	O
incremental	O
upgrade	O
,	O
adding	O
nothing	O
more	O
substantial	O
than	O
support	O
for	O
the	O
AT	O
's	O
new	O
1.2	O
megabyte	O
(	O
MB	O
)	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
Planned	O
networking	O
capabilities	O
in	O
DOS	B-Device
3.00	O
were	O
judged	O
too	O
buggy	O
to	O
be	O
usable	O
and	O
Microsoft	O
disabled	O
them	O
prior	O
to	O
the	O
OS	O
's	O
release	O
.	O
</s>
<s>
PCDOS	O
3.1	O
(	O
released	O
March	O
1985	O
)	O
fixed	O
the	O
bugs	O
in	O
DOS	B-Device
3.00	O
and	O
supported	O
IBM	O
's	O
Network	O
Adapter	O
card	O
on	O
the	O
IBM	B-General_Concept
PC	I-General_Concept
Network	I-General_Concept
.	O
</s>
<s>
PCDOS	O
3.2	O
added	O
support	O
for	O
-inch	O
double-density	O
720KB	O
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
supporting	O
the	O
IBM	B-Device
PC	I-Device
Convertible	I-Device
,	O
IBM	O
's	O
first	O
computer	O
to	O
use	O
-inch	O
floppy	B-Device
disks	I-Device
,	O
released	O
April	O
1986	O
,	O
and	O
later	O
the	O
IBM	B-Device
Personal	I-Device
System/2	I-Device
in	O
1987	O
.	O
</s>
<s>
In	O
June	O
1985	O
,	O
IBM	O
and	O
Microsoft	O
signed	O
a	O
long-term	O
Joint	O
Development	O
Agreement	O
to	O
share	O
specified	O
DOS	B-Device
code	O
and	O
create	O
a	O
new	O
operating	O
system	O
from	O
scratch	O
,	O
known	O
at	O
the	O
time	B-Device
as	O
Advanced	O
DOS	B-Device
.	O
</s>
<s>
On	O
2	O
April	O
1987	O
OS/2	B-Application
was	O
announced	O
as	O
the	O
first	O
product	O
produced	O
under	O
the	O
agreement	O
.	O
</s>
<s>
At	O
the	O
same	O
time	B-Device
,	O
IBM	O
released	O
its	O
next	O
generation	O
of	O
personal	O
computers	O
,	O
the	O
IBM	B-Device
Personal	I-Device
System/2	I-Device
(	O
PS/2	B-Device
)	O
.	O
</s>
<s>
PCDOS	O
3.3	O
,	O
released	O
with	O
the	O
PS/2	B-Device
line	O
,	O
added	O
support	O
for	O
high	O
density	O
-inch	O
1.44MB	O
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
which	O
IBM	O
introduced	O
in	O
its	O
80286-based	O
and	O
higher	O
PS/2	B-Device
models	O
.	O
</s>
<s>
The	O
upgrade	O
from	O
DOS	B-Device
3.2	O
to	O
3.3	O
was	O
completely	O
written	O
by	O
IBM	O
,	O
with	O
no	O
development	O
effort	O
on	O
the	O
part	O
of	O
Microsoft	O
,	O
who	O
were	O
working	O
on	O
"	O
Advanced	O
DOS	B-Device
1.0	O
"	O
.	O
</s>
<s>
DOS	B-Device
3.30	O
was	O
the	O
last	O
version	O
designed	O
with	O
the	O
IBM	B-Device
XT	I-Device
and	O
floppy-only	O
systems	O
in	O
mind	O
;	O
it	O
became	O
one	O
of	O
the	O
most	O
popular	O
versions	O
and	O
many	O
users	O
preferred	O
it	O
to	O
its	O
buggy	O
successor	O
.	O
</s>
<s>
PCDOS	O
4.0	O
(	O
internally	O
known	O
as	O
DOS	B-Device
3.4	O
originally	O
)	O
,	O
shipped	O
July	O
1988	O
.	O
</s>
<s>
DOS	B-Device
4.0	O
had	O
some	O
compatibility	O
issues	O
with	O
low-level	O
disk	O
utilities	O
due	O
to	O
some	O
internal	O
data	O
structure	O
changes	O
.	O
</s>
<s>
DOS	B-Device
4.0	O
used	O
more	O
memory	O
than	O
DOS	B-Device
3.30	O
and	O
it	O
also	O
had	O
a	O
few	O
glitches	O
.	O
</s>
<s>
DOS	B-Device
4.0	O
is	O
also	O
notable	O
for	O
including	O
the	O
first	O
version	O
of	O
the	O
DOS	B-Application
Shell	I-Application
,	O
a	O
full-screen	O
utility	O
designed	O
to	O
make	O
the	O
command-line	B-Application
OS	O
more	O
user-friendly	O
.	O
</s>
<s>
Microsoft	O
took	O
back	O
control	O
of	O
development	O
and	O
released	O
a	O
bug-fixed	O
DOS	B-Device
4.01	O
.	O
</s>
<s>
DOS	B-Device
5	O
debuted	O
in	O
June	O
1991	O
.	O
</s>
<s>
DOS	B-Device
5	O
supported	O
the	O
use	O
of	O
the	O
High	B-Device
Memory	I-Device
Area	I-Device
(	O
HMA	O
)	O
and	O
Upper	B-Device
Memory	I-Device
Blocks	I-Device
(	O
UMBs	O
)	O
on	O
80286	B-General_Concept
and	O
later	O
systems	O
to	O
reduce	O
its	O
conventional	B-Device
memory	I-Device
usage	O
.	O
</s>
<s>
Also	O
all	O
DOS	B-Operating_System
commands	I-Operating_System
now	O
supported	O
the	O
option	O
to	O
display	O
command	O
syntax	O
.	O
</s>
<s>
Aside	O
from	O
IBM	O
's	O
PCDOS	O
,	O
MS-DOS	B-Application
was	O
the	O
only	O
other	O
version	O
available	O
as	O
OEM	O
editions	O
vanished	O
since	O
by	O
this	O
time	B-Device
PCs	O
were	O
100%	O
compatible	O
so	O
customizations	O
for	O
hardware	O
differences	O
were	O
no	O
longer	O
necessary	O
.	O
</s>
<s>
This	O
was	O
the	O
last	O
version	O
of	O
DOS	B-Device
that	O
IBM	O
and	O
Microsoft	O
shared	O
the	O
full	O
code	O
for	O
,	O
and	O
the	O
DOS	B-Device
that	O
was	O
integrated	O
into	O
OS/2	B-Application
2.0	O
'	O
s	O
,	O
and	O
later	O
Windows	B-Device
NT	I-Device
's	O
,	O
virtual	O
DOS	B-Device
machine	O
.	O
</s>
<s>
PCDOS	O
remained	O
a	O
rebranded	O
version	O
of	O
MS-DOS	B-Application
until	O
1993	O
.	O
</s>
<s>
IBM	O
and	O
Microsoft	O
parted	O
waysMS-DOS	O
6	O
was	O
released	O
in	O
March	O
,	O
and	O
PCDOS	O
6.1	O
(	O
separately	O
developed	O
)	O
followed	O
in	O
June	O
.	O
</s>
<s>
Most	O
of	O
the	O
new	O
features	O
from	O
MS-DOS	B-Application
6.0	O
appeared	O
in	O
PCDOS	O
6.1	O
including	O
the	O
new	O
boot	O
menu	O
support	O
and	O
the	O
new	O
commands	O
,	O
,	O
and	O
.	O
</s>
<s>
QBasic	B-Language
was	O
dropped	O
and	O
the	O
MS-DOS	B-Application
Editor	I-Application
was	O
replaced	O
with	O
the	O
IBM	O
E	B-Application
Editor	I-Application
.	O
</s>
<s>
PCDOS	O
6.1	O
reports	O
itself	O
as	O
DOS	B-Device
6.00	O
.	O
</s>
<s>
PCDOS	O
6.3	O
was	O
also	O
used	O
in	O
OS/2	B-Application
for	O
the	O
PowerPC	B-Architecture
.	O
</s>
<s>
PCDOS	O
7	O
was	O
released	O
in	O
April	O
1995	O
and	O
was	O
the	O
last	O
release	O
of	O
DOS	B-Device
before	O
IBM	O
software	O
development	O
(	O
other	O
than	O
the	O
development	O
IBM	B-Application
ViaVoice	I-Application
)	O
moved	O
to	O
Austin	O
.	O
</s>
<s>
The	O
REXX	B-Language
programming	I-Language
language	I-Language
was	O
added	O
,	O
as	O
well	O
as	O
support	O
for	O
a	O
new	O
floppy	B-Device
disk	I-Device
format	O
,	O
XDF	B-Device
,	O
which	O
extended	O
a	O
standard	O
1.44MB	O
floppy	B-Device
disk	I-Device
to	O
1.86MB	O
.	O
</s>
<s>
SuperStor	O
disk	O
compression	O
technology	O
was	O
replaced	O
with	O
Stac	O
Electronics	O
 '	O
STACKER	B-Application
.	O
</s>
<s>
An	O
algebraic	O
command	B-Application
line	I-Application
calculator	O
and	O
a	O
utility	O
program	O
to	O
load	O
device	O
drivers	O
from	O
the	O
command	B-Application
line	I-Application
were	O
added	O
.	O
</s>
<s>
The	O
most	O
recent	O
retail	O
release	O
was	O
PCDOS	O
2000	O
released	O
from	O
Austin	O
in	O
1998	O
which	O
found	O
its	O
niche	O
in	O
the	O
embedded	B-Application
software	I-Application
market	O
and	O
elsewhere	O
.	O
</s>
<s>
PCDOS	O
2000	O
is	O
a	O
slipstream	O
of	O
7.0	O
with	O
Y2K	B-Error_Name
and	O
other	O
fixes	O
applied	O
.	O
</s>
<s>
ThinkPad	B-Operating_System
products	O
had	O
a	O
copy	O
of	O
the	O
latest	O
version	O
of	O
PCDOS	O
in	O
their	O
Rescue	O
and	O
Recovery	O
partition	O
.	O
</s>
<s>
PCDOS	O
7.1	O
added	O
support	O
for	O
Logical	B-Device
Block	I-Device
Addressing	I-Device
(	O
LBA	O
)	O
and	O
FAT32	B-Application
partitions	O
.	O
</s>
<s>
A	O
build	O
of	O
this	O
version	O
of	O
DOS	B-Device
appeared	O
in	O
Norton	B-Application
Ghost	I-Application
from	O
Symantec	O
.	O
</s>
<s>
Version	O
7.1	O
indicates	O
support	O
for	O
FAT32	B-Application
also	O
in	O
MS-DOS	B-Application
.	O
</s>
<s>
Most	O
builds	O
of	O
this	O
version	O
of	O
DOS	B-Device
are	O
limited	O
to	O
the	O
kernel	O
files	O
,	O
,	O
and	O
.	O
</s>
<s>
The	O
updated	O
programs	O
and	O
allow	O
one	O
to	O
prepare	O
FAT32	B-Application
disks	O
.	O
</s>
<s>
In	O
1986	O
,	O
IBM	O
announced	O
PCDOS	O
support	O
for	O
client	O
access	O
to	O
the	O
file	O
services	O
defined	O
by	O
Distributed	B-Operating_System
Data	I-Operating_System
Management	I-Operating_System
Architecture	I-Operating_System
(	O
DDM	O
)	O
.	O
</s>
<s>
This	O
enabled	O
programs	O
on	O
PCs	O
to	O
create	O
,	O
manage	O
,	O
and	O
access	O
record-oriented	O
files	O
available	O
on	O
IBM	O
System/36	O
,	O
IBM	O
System/38	O
and	O
IBM	O
mainframe	O
computers	O
running	O
CICS	B-Application
.	O
</s>
