<s>
DOS	O
(	O
,	O
)	O
is	O
a	O
family	O
of	O
disk-based	O
operating	O
systems	O
for	O
IBM	B-Device
PC	I-Device
compatible	O
computers	O
.	O
</s>
<s>
The	O
DOS	O
family	O
primarily	O
consists	O
of	O
Microsoft	O
's	O
MS-DOS	B-Application
and	O
a	O
rebranded	O
version	O
,	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
,	O
both	O
of	O
which	O
were	O
introduced	O
in	O
1981	O
.	O
</s>
<s>
Later	O
compatible	O
systems	O
from	O
other	O
manufacturers	O
include	O
DR	O
DOS	O
(	O
1988	O
)	O
,	O
ROM-DOS	B-Operating_System
(	O
1989	O
)	O
,	O
PTS-DOS	B-Operating_System
(	O
1993	O
)	O
,	O
and	O
FreeDOS	B-Application
(	O
1998	O
)	O
.	O
</s>
<s>
MS-DOS	B-Application
dominated	O
the	O
IBM	B-Device
PC	I-Device
compatible	O
market	O
between	O
1981	O
and	O
1995	O
.	O
</s>
<s>
Although	O
the	O
name	O
has	O
come	O
to	O
be	O
identified	O
specifically	O
with	O
this	O
particular	O
family	O
of	O
operating	O
systems	O
,	O
"	O
DOS	O
"	O
is	O
a	O
platform-independent	O
acronym	O
for	O
"	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
"	O
,	O
whose	O
use	O
predates	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
Dozens	O
of	O
other	O
operating	O
systems	O
also	O
use	O
the	O
acronym	O
,	O
beginning	O
with	O
the	O
mainframe	O
DOS/360	B-Application
from	O
1966	O
.	O
</s>
<s>
Others	O
include	O
Apple	B-Operating_System
DOS	I-Operating_System
,	O
Apple	B-Operating_System
ProDOS	I-Operating_System
,	O
Atari	B-Operating_System
DOS	I-Operating_System
,	O
Commodore	B-Device
DOS	I-Device
,	O
TRSDOS	B-Operating_System
,	O
and	O
AmigaDOS	B-Operating_System
.	O
</s>
<s>
IBM	B-Device
PC	I-Device
DOS	O
(	O
and	O
the	O
separately	O
sold	O
MS-DOS	B-Application
)	O
and	O
its	O
predecessor	O
,	O
86-DOS	B-Operating_System
,	O
ran	O
on	O
Intel	B-General_Concept
8086	I-General_Concept
16-bit	B-Device
processors	I-Device
.	O
</s>
<s>
It	O
was	O
developed	O
to	O
be	O
similar	O
to	O
Digital	O
Research	O
's	O
CP/M	B-Application
—	O
the	O
dominant	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
8-bit	O
Intel	B-General_Concept
8080	I-General_Concept
and	O
Zilog	B-General_Concept
Z80	I-General_Concept
microcomputers	O
—	O
in	O
order	O
to	O
simplify	O
porting	O
CP/M	B-Application
applications	O
to	O
MS-DOS	B-Application
.	O
</s>
<s>
When	O
IBM	O
introduced	O
the	O
IBM	B-Device
PC	I-Device
,	O
built	O
with	O
the	O
Intel	B-Device
8088	I-Device
microprocessor	O
,	O
they	O
needed	O
an	O
operating	O
system	O
.	O
</s>
<s>
Chairman	O
John	O
Opel	O
had	O
a	O
conversation	O
with	O
fellow	O
United	O
Way	O
National	O
Board	O
Executive	O
Committee	O
member	O
Mary	O
Maxwell	O
Gates	O
,	O
who	O
referred	O
Opel	O
to	O
her	O
son	O
Bill	O
Gates	O
for	O
help	O
with	O
an	O
8088-compatible	O
build	O
of	O
CP/M	B-Application
.	O
</s>
<s>
However	O
,	O
initial	O
negotiations	O
for	O
the	O
use	O
of	O
CP/M	B-Application
broke	O
down	O
:	O
Digital	O
Research	O
wished	O
to	O
sell	O
CP/M	B-Application
on	O
a	O
royalty	O
basis	O
,	O
while	O
IBM	O
sought	O
a	O
single	O
license	O
,	O
and	O
to	O
change	O
the	O
name	O
to	O
"	O
PCDOS	B-Operating_System
"	O
.	O
</s>
<s>
There	O
,	O
programmer	O
Tim	O
Paterson	O
had	O
developed	O
a	O
variant	O
of	O
CP/M	B-Application
-80	I-Application
,	O
intended	O
as	O
an	O
internal	O
product	O
for	O
testing	O
SCP	O
's	O
new	O
16-bit	B-Device
Intel	B-General_Concept
8086	I-General_Concept
CPU	B-Device
card	O
for	O
the	O
S-100	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
The	O
system	O
was	O
initially	O
named	O
QDOS	B-Operating_System
(	O
Quick	B-Operating_System
and	I-Operating_System
Dirty	I-Operating_System
Operating	I-Operating_System
System	I-Operating_System
)	O
,	O
before	O
being	O
made	O
commercially	O
available	O
as	O
86-DOS	B-Operating_System
.	O
</s>
<s>
Microsoft	O
purchased	O
86-DOS	B-Operating_System
,	O
allegedly	O
for	O
.	O
</s>
<s>
This	O
became	O
Microsoft	B-Application
Disk	I-Application
Operating	I-Application
System	I-Application
,	O
MS-DOS	B-Application
,	O
introduced	O
in	O
1981	O
.	O
</s>
<s>
Within	O
a	O
year	O
Microsoft	O
licensed	O
MS-DOS	B-Application
to	O
over	O
70	O
other	O
companies	O
,	O
which	O
supplied	O
the	O
operating	O
system	O
for	O
their	O
own	O
hardware	B-Architecture
,	O
sometimes	O
under	O
their	O
own	O
names	O
.	O
</s>
<s>
Microsoft	O
later	O
required	O
the	O
use	O
of	O
the	O
MS-DOS	B-Application
name	O
,	O
with	O
the	O
exception	O
of	O
the	O
IBM	O
variant	O
.	O
</s>
<s>
IBM	O
continued	O
to	O
develop	O
their	O
version	O
,	O
PC	O
DOS	O
,	O
for	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
Digital	O
Research	O
became	O
aware	O
that	O
an	O
operating	O
system	O
similar	O
to	O
CP/M	B-Application
was	O
being	O
sold	O
by	O
IBM	O
(	O
under	O
the	O
same	O
name	O
that	O
IBM	O
insisted	O
upon	O
for	O
CP/M	B-Application
)	O
,	O
and	O
threatened	O
legal	O
action	O
.	O
</s>
<s>
IBM	O
responded	O
by	O
offering	O
an	O
agreement	O
:	O
they	O
would	O
give	O
PC	O
consumers	O
a	O
choice	O
of	O
PCDOS	B-Operating_System
or	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
Kildall	O
's	O
8086	B-General_Concept
version	O
.	O
</s>
<s>
Side-by-side	O
,	O
CP/M	B-Application
cost	O
more	O
than	O
PCDOS	B-Operating_System
,	O
and	O
sales	O
were	O
low	O
.	O
</s>
<s>
CP/M	B-Application
faded	O
,	O
with	O
MS-DOS	B-Application
and	O
PCDOS	B-Operating_System
becoming	O
the	O
marketed	O
operating	O
system	O
for	O
PCs	O
and	O
PC	O
compatibles	O
.	O
</s>
<s>
Microsoft	O
originally	O
sold	O
MS-DOS	B-Application
only	O
to	O
original	O
equipment	O
manufacturers	O
(	O
OEMs	O
)	O
.	O
</s>
<s>
One	O
major	O
reason	O
for	O
this	O
was	O
that	O
not	O
all	O
early	O
PCs	O
were	O
100%	O
IBM	B-Device
PC	I-Device
compatible	O
.	O
</s>
<s>
DOS	O
was	O
structured	O
such	O
that	O
there	O
was	O
a	O
separation	O
between	O
the	O
system	O
specific	O
device	B-Application
driver	I-Application
code	O
(	O
IO.SYS	O
)	O
and	O
the	O
DOS	O
kernel	B-Operating_System
(	O
MSDOS.SYS	O
)	O
.	O
</s>
<s>
Microsoft	O
provided	O
an	O
OEM	O
Adaptation	O
Kit	O
(	O
OAK	O
)	O
which	O
allowed	O
OEMs	O
to	O
customize	O
the	O
device	B-Application
driver	I-Application
code	O
to	O
their	O
particular	O
system	O
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
most	O
PCs	O
adhered	O
to	O
IBM	B-Device
PC	I-Device
standards	O
so	O
Microsoft	O
began	O
selling	O
a	O
retail	O
version	O
of	O
MS-DOS	B-Application
,	O
starting	O
with	O
MS-DOS	B-Application
5.0	O
.	O
</s>
<s>
In	O
the	O
mid-1980s	O
,	O
Microsoft	O
developed	O
a	O
multitasking	B-Application
version	I-Application
of	I-Application
DOS	I-Application
.	O
</s>
<s>
This	O
version	O
of	O
DOS	O
is	O
generally	O
referred	O
to	O
as	O
"	O
European	B-Application
MS-DOS	I-Application
4	O
"	O
because	O
it	O
was	O
developed	O
for	O
ICL	O
and	O
licensed	O
to	O
several	O
European	O
companies	O
.	O
</s>
<s>
None	O
of	O
these	O
features	O
were	O
used	O
in	O
later	O
versions	O
of	O
DOS	O
,	O
but	O
they	O
were	O
used	O
to	O
form	O
the	O
basis	O
of	O
the	O
OS/2	B-Application
1.0	O
kernel	B-Operating_System
.	O
</s>
<s>
This	O
version	O
of	O
DOS	O
is	O
distinct	O
from	O
the	O
widely	O
released	O
PCDOS	B-Operating_System
4.0	O
which	O
was	O
developed	O
by	O
IBM	O
and	O
based	O
upon	O
DOS	O
3.3	O
.	O
</s>
<s>
Digital	O
Research	O
attempted	O
to	O
regain	O
the	O
market	O
lost	O
from	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
initially	O
with	O
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
FlexOS	B-Operating_System
and	O
DOS	B-Operating_System
Plus	I-Operating_System
(	O
both	O
compatible	O
with	O
both	O
MS-DOS	B-Application
and	O
CP/M	B-Operating_System
-86	I-Operating_System
software	O
)	O
,	O
later	O
with	O
Multiuser	B-Operating_System
DOS	I-Operating_System
(	O
compatible	O
with	O
both	O
MS-DOS	B-Application
and	O
CP/M	B-Operating_System
-86	I-Operating_System
software	O
)	O
and	O
DR	O
DOS	O
(	O
compatible	O
with	O
MS-DOS	B-Application
software	O
)	O
.	O
</s>
<s>
Digital	O
Research	O
was	O
bought	O
by	O
Novell	O
,	O
and	O
DRDOS	B-Application
became	O
PalmDOS	B-Operating_System
and	O
Novell	B-Operating_System
DOS	I-Operating_System
;	O
later	O
,	O
it	O
was	O
part	O
of	O
Caldera	O
(	O
under	O
the	O
names	O
OpenDOS	B-Application
and	O
DR-DOS	B-Application
7.02/7.03	O
)	O
,	O
Lineo	O
,	O
and	O
DeviceLogics	O
.	O
</s>
<s>
Microsoft	O
expected	O
that	O
it	O
would	O
be	O
an	O
interim	O
solution	O
before	O
Xenix	B-Application
.	O
</s>
<s>
The	O
company	O
planned	O
to	O
improve	O
MS-DOS	B-Application
over	O
time	O
,	O
so	O
it	O
would	O
be	O
almost	O
indistinguishable	O
from	O
single-user	O
Xenix	B-Application
,	O
or	O
XEDOS	B-Application
,	O
which	O
would	O
also	O
run	O
on	O
the	O
Motorola	B-Device
68000	I-Device
,	O
Zilog	B-Device
Z-8000	I-Device
,	O
and	O
LSI-11	O
;	O
they	O
would	O
be	O
upwardly	B-General_Concept
compatible	I-General_Concept
with	O
Xenix	B-Application
,	O
which	O
BYTE	B-Application
in	O
1983	O
described	O
as	O
"	O
the	O
multi-user	O
MS-DOS	B-Application
of	O
the	O
future	O
"	O
.	O
</s>
<s>
After	O
AT&T	O
began	O
selling	O
Unix	O
,	O
Microsoft	O
and	O
IBM	O
began	O
developing	O
OS/2	B-Application
as	O
an	O
alternative	O
.	O
</s>
<s>
The	O
two	O
companies	O
later	O
had	O
a	O
series	O
of	O
disagreements	O
over	O
two	O
successor	O
operating	O
systems	O
to	O
DOS	O
,	O
OS/2	B-Application
and	O
Windows	O
.	O
</s>
<s>
The	O
last	O
retail	O
version	O
of	O
MS-DOS	B-Application
was	O
MS-DOS	B-Application
6.22	O
;	O
after	O
this	O
,	O
MS-DOS	B-Application
became	O
part	O
of	O
Windows	B-Application
95	I-Application
,	O
98	O
and	O
Me	O
.	O
</s>
<s>
The	O
last	O
retail	O
version	O
of	O
PCDOS	B-Operating_System
was	O
PCDOS	B-Operating_System
2000	O
(	O
also	O
called	O
PCDOS	B-Operating_System
7	O
revision	O
1	O
)	O
,	O
though	O
IBM	O
did	O
later	O
develop	O
PCDOS	B-Operating_System
7.10	O
for	O
OEMs	O
and	O
internal	O
use	O
.	O
</s>
<s>
The	O
FreeDOS	B-Application
project	O
began	O
on	O
26	O
June	O
1994	O
,	O
when	O
Microsoft	O
announced	O
it	O
would	O
no	O
longer	O
sell	O
or	O
support	O
MS-DOS	B-Application
.	O
</s>
<s>
A	O
kernel	B-Operating_System
,	O
the	O
COMMAND.COM	B-Operating_System
command	B-Application
line	I-Application
interpreter	O
(	O
shell	B-Operating_System
)	O
,	O
and	O
core	O
utilities	O
were	O
created	O
by	O
pooling	O
code	O
they	O
had	O
written	O
or	O
found	O
available	O
.	O
</s>
<s>
There	O
were	O
several	O
official	O
pre-release	O
distributions	O
of	O
FreeDOS	B-Application
before	O
the	O
FreeDOS	B-Application
1.0	O
distribution	O
was	O
released	O
on	O
3	O
September	O
2006	O
.	O
</s>
<s>
Made	O
available	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
,	O
FreeDOS	B-Application
does	O
not	O
require	O
license	O
fees	O
or	O
royalties	O
.	O
</s>
<s>
Early	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
ran	O
on	O
MS-DOS	B-Application
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
the	O
Windows	O
graphical	O
shell	B-Operating_System
saw	O
heavy	O
use	O
on	O
new	O
DOS	O
systems	O
.	O
</s>
<s>
In	O
1995	O
,	O
Windows	B-Application
95	I-Application
was	O
bundled	O
as	O
a	O
standalone	O
operating	O
system	O
that	O
did	O
not	O
require	O
a	O
separate	O
DOS	O
license	O
.	O
</s>
<s>
Windows	B-Application
95	I-Application
(	O
and	O
Windows	O
98	O
and	O
ME	O
,	O
that	O
followed	O
it	O
)	O
took	O
over	O
as	O
the	O
default	O
OS	B-Operating_System
kernel	I-Operating_System
,	O
though	O
the	O
MS-DOS	B-Application
component	O
remained	O
for	O
compatibility	O
.	O
</s>
<s>
With	O
Windows	B-Application
95	I-Application
and	O
98	O
,	O
but	O
not	O
ME	O
,	O
the	O
MS-DOS	B-Application
component	O
could	O
be	O
run	O
without	O
starting	O
Windows	O
.	O
</s>
<s>
Available	O
compatible	O
systems	O
in	O
2012	O
are	O
FreeDOS	B-Application
,	O
DR-DOS	B-Application
,	O
ROM-DOS	B-Operating_System
,	O
PTS-DOS	B-Operating_System
,	O
RxDOS	O
and	O
REAL/32	B-Operating_System
.	O
</s>
<s>
Some	O
computer	O
manufacturers	O
,	O
including	O
Dell	O
and	O
HP	O
,	O
sell	O
computers	O
with	O
FreeDOS	B-Application
and	O
DR-DOS	B-Application
as	O
OEM	O
operating	O
systems	O
.	O
</s>
<s>
DOS	O
's	O
structure	O
of	O
accessing	O
hardware	B-Architecture
directly	O
allows	O
it	O
to	O
be	O
used	O
in	O
embedded	B-Architecture
devices	I-Architecture
.	O
</s>
<s>
The	O
final	O
versions	O
of	O
DR-DOS	B-Application
are	O
still	O
aimed	O
at	O
this	O
market	O
.	O
</s>
<s>
ROM-DOS	B-Operating_System
is	O
used	O
as	O
operating	O
system	O
for	O
the	O
Canon	B-Algorithm
PowerShot	I-Algorithm
Pro	I-Algorithm
70	O
.	O
</s>
<s>
On	O
Linux	B-Application
,	O
it	O
is	O
possible	O
to	O
run	O
DOSEMU	B-Application
,	O
a	O
Linux-native	O
virtual	B-Architecture
machine	I-Architecture
for	O
running	O
DOS	O
programs	O
at	O
near	O
native	O
speed	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
other	O
emulators	B-Application
for	O
running	O
DOS	O
on	O
various	O
versions	O
of	O
Unix	O
and	O
Microsoft	B-Application
Windows	I-Application
such	O
as	O
DOSBox	B-Application
.	O
</s>
<s>
DOSBox	B-Application
is	O
designed	O
for	O
legacy	O
gaming	O
(	O
e.g.	O
</s>
<s>
King	B-Application
's	I-Application
Quest	I-Application
,	O
Doom	B-Application
)	O
on	O
modern	O
operating	O
systems	O
.	O
</s>
<s>
MS-DOS	B-Application
and	O
IBM	O
PCDOS	B-Operating_System
related	O
operating	O
systems	O
are	O
commonly	O
associated	O
with	O
machines	O
using	O
the	O
Intel	B-Operating_System
x86	I-Operating_System
or	O
compatible	O
CPUs	B-Device
,	O
mainly	O
IBM	B-Device
PC	I-Device
compatibles	O
.	O
</s>
<s>
Machine-dependent	O
versions	O
of	O
MS-DOS	B-Application
were	O
produced	O
for	O
many	O
non-IBM-compatible	O
x86-based	O
machines	O
,	O
with	O
variations	O
from	O
relabelling	O
of	O
the	O
Microsoft	O
distribution	O
under	O
the	O
manufacturer	O
's	O
name	O
,	O
to	O
versions	O
specifically	O
designed	O
to	O
work	O
with	O
non-IBM-PC-compatible	O
hardware	B-Architecture
.	O
</s>
<s>
As	O
long	O
as	O
application	O
programs	O
used	O
DOS	B-Application
APIs	I-Application
instead	O
of	O
direct	O
hardware	B-Architecture
access	O
,	O
they	O
could	O
run	O
on	O
both	O
IBM-PC-compatible	O
and	O
incompatible	O
machines	O
.	O
</s>
<s>
The	O
original	O
FreeDOS	B-Application
kernel	B-Operating_System
,	O
DOS-C	B-Operating_System
,	O
was	O
derived	O
from	O
DOS/NT	B-Operating_System
for	O
the	O
Motorola	B-Device
68000	I-Device
series	O
of	O
CPUs	B-Device
in	O
the	O
early	O
1990s	O
.	O
</s>
<s>
While	O
these	O
systems	O
loosely	O
resembled	O
the	O
DOS	O
architecture	O
,	O
applications	O
were	O
not	O
binary	O
compatible	O
due	O
to	O
the	O
incompatible	O
instruction	O
sets	O
of	O
these	O
non-x86-CPUs	O
.	O
</s>
<s>
DOS	O
is	O
a	O
single-user	O
,	O
single-tasking	O
operating	O
system	O
with	O
basic	O
kernel	B-Operating_System
functions	O
that	O
are	O
non-reentrant	B-Operating_System
:	O
only	O
one	O
program	O
at	O
a	O
time	O
can	O
use	O
them	O
,	O
and	O
DOS	O
itself	O
has	O
no	O
functionality	O
to	O
allow	O
more	O
than	O
one	O
program	O
to	O
execute	O
at	O
a	O
time	O
.	O
</s>
<s>
The	O
DOS	O
kernel	B-Operating_System
provides	O
various	B-Application
functions	I-Application
for	I-Application
programs	I-Application
(	O
an	O
application	O
program	O
interface	O
)	O
,	O
like	O
character	O
I/O	O
,	O
file	O
management	O
,	O
memory	O
management	O
,	O
program	O
loading	O
and	O
termination	O
.	O
</s>
<s>
DOS	O
provides	O
the	O
ability	O
for	O
shell	B-Language
scripting	I-Language
via	O
batch	O
files	O
(	O
with	O
the	O
filename	O
extension	O
.BAT	O
)	O
.	O
</s>
<s>
Batch	O
files	O
can	O
also	O
make	O
use	O
of	O
internal	O
commands	O
,	O
such	O
as	O
GOTO	B-Application
and	O
conditional	B-Language
statements	I-Language
.	O
</s>
<s>
The	O
operating	O
system	O
offers	O
an	O
application	O
programming	O
interface	O
that	O
allows	O
development	O
of	O
character-based	B-Application
applications	O
,	O
but	O
not	O
for	O
accessing	O
most	O
of	O
the	O
hardware	B-Architecture
,	O
such	O
as	O
graphics	B-Device
cards	I-Device
,	O
printers	O
,	O
or	O
mice	B-Device
.	O
</s>
<s>
This	O
required	O
programmers	O
to	O
access	O
the	O
hardware	B-Architecture
directly	O
,	O
usually	O
resulting	O
in	O
each	O
application	O
having	O
its	O
own	O
set	O
of	O
device	B-Application
drivers	I-Application
for	O
each	O
hardware	B-Architecture
peripheral	O
.	O
</s>
<s>
Hardware	B-Architecture
manufacturers	O
would	O
release	O
specifications	O
to	O
ensure	O
device	B-Application
drivers	I-Application
for	O
popular	O
applications	O
were	O
available	O
.	O
</s>
<s>
The	O
bootstrap	B-Operating_System
loader	I-Operating_System
on	O
PC-compatible	O
computers	O
,	O
the	O
master	B-Device
boot	I-Device
record	I-Device
,	O
is	O
located	O
beginning	O
at	O
the	O
boot	B-Device
sector	I-Device
,	O
the	O
first	O
sector	O
on	O
the	O
first	O
track	O
(	O
track	B-Application
zero	I-Application
)	O
,	O
of	O
the	O
boot	B-Operating_System
disk	O
.	O
</s>
<s>
The	O
ROM	B-Operating_System
BIOS	I-Operating_System
will	O
load	O
this	O
sector	O
into	O
memory	O
at	O
address	O
:	O
,	O
and	O
typically	O
check	O
for	O
a	O
signature	O
""	O
at	O
offset	O
.	O
</s>
<s>
If	O
the	O
sector	O
is	O
not	O
considered	O
to	O
be	O
valid	O
,	O
the	O
ROM	B-Operating_System
BIOS	I-Operating_System
will	O
try	O
the	O
next	O
physical	O
disk	O
in	O
the	O
row	O
,	O
otherwise	O
it	O
will	O
jump	O
to	O
the	O
load	O
address	O
with	O
certain	O
registers	O
set	O
up	O
.	O
</s>
<s>
If	O
the	O
loaded	O
boot	B-Device
sector	I-Device
happens	O
to	O
be	O
a	O
Master	B-Device
Boot	I-Device
Record	I-Device
(	O
MBR	O
)	O
,	O
as	O
found	O
on	O
partitioned	O
media	O
,	O
it	O
will	O
relocate	O
itself	O
to	O
:	O
in	O
memory	O
,	O
otherwise	O
this	O
step	O
is	O
skipped	O
.	O
</s>
<s>
The	O
MBR	O
code	O
will	O
scan	O
the	O
partition	O
table	O
,	O
which	O
is	O
located	O
within	O
this	O
sector	O
,	O
for	O
an	O
active	O
partition	O
(	O
modern	O
MBRs	O
check	O
if	O
bit	O
7	O
is	O
set	O
at	O
offset	O
,	O
whereas	O
old	O
MBRs	O
simply	O
check	O
for	O
a	O
value	O
of	O
)	O
,	O
and	O
,	O
if	O
found	O
,	O
load	O
the	O
first	O
sector	O
of	O
the	O
corresponding	O
partition	O
,	O
which	O
holds	O
the	O
Volume	B-Device
Boot	I-Device
Record	I-Device
(	O
VBR	O
)	O
of	O
that	O
volume	O
,	O
into	O
memory	O
at	O
:	O
in	O
the	O
similar	O
fashion	O
as	O
if	O
it	O
had	O
been	O
loaded	O
by	O
the	O
ROM	B-Operating_System
BIOS	I-Operating_System
itself	O
.	O
</s>
<s>
In	O
very	O
old	O
versions	O
of	O
DOS	O
such	O
as	O
DOS	O
1.x	O
,	O
the	O
VBR	O
would	O
load	O
the	O
whole	O
IO.SYS/IBMBIO.COM	O
file	O
into	O
memory	O
at	O
:	O
.	O
</s>
<s>
In	O
later	O
issues	O
,	O
it	O
would	O
locate	O
and	O
store	O
the	O
contents	O
of	O
the	O
first	O
two	O
entries	O
in	O
the	O
root	O
directory	O
at	O
:	O
and	O
if	O
they	O
happen	O
to	O
reflect	O
the	O
correct	O
boot	B-Operating_System
files	O
as	O
recorded	O
in	O
the	O
VBR	O
,	O
the	O
VBR	O
would	O
load	O
the	O
first	O
3	O
consecutive	O
sectors	O
of	O
the	O
IO.SYS/IBMBIO.COM	O
file	O
into	O
memory	O
at	O
:	O
.	O
</s>
<s>
In	O
later	O
DOS	O
versions	O
,	O
where	O
the	O
VBR	O
has	O
loaded	O
only	O
the	O
first	O
3	O
sectors	O
of	O
the	O
IO.SYS/IBMBIO.COM	O
file	O
into	O
memory	O
,	O
the	O
loaded	O
portion	O
contains	O
another	O
boot	B-Operating_System
loader	O
,	O
which	O
will	O
then	O
load	O
the	O
remainder	O
of	O
itself	O
into	O
memory	O
,	O
using	O
the	O
root	O
directory	O
information	O
stored	O
at	O
:	O
.	O
</s>
<s>
The	O
DOS	O
system	O
initialization	O
code	O
will	O
initialize	O
its	O
built-in	O
device	B-Application
drivers	I-Application
and	O
then	O
load	O
the	O
DOS	O
kernel	B-Operating_System
,	O
located	O
in	O
MSDOS.SYS	O
on	O
MS-DOS	B-Application
systems	O
,	O
into	O
memory	O
as	O
well	O
.	O
</s>
<s>
In	O
Windows	O
9x	O
,	O
the	O
DOS	O
system	O
initialization	O
code	O
and	O
built-in	O
device	B-Application
drivers	I-Application
and	O
the	O
DOS	O
kernel	B-Operating_System
are	O
combined	O
into	O
a	O
single	O
IO.SYS	O
file	O
while	O
MSDOS.SYS	O
is	O
used	O
as	O
a	O
text	O
configuration	O
file	O
.	O
</s>
<s>
The	O
CONFIG.SYS	B-Device
file	O
is	O
then	O
read	O
to	O
parse	O
configuration	O
parameters	O
.	O
</s>
<s>
The	O
variable	O
specifies	O
the	O
location	O
of	O
the	O
shell	B-Operating_System
which	O
defaults	O
to	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
The	O
shell	B-Operating_System
is	O
loaded	O
and	O
executed	O
.	O
</s>
<s>
The	O
startup	O
batch	O
file	O
AUTOEXEC.BAT	O
is	O
then	O
run	O
by	O
the	O
shell	B-Operating_System
.	O
</s>
<s>
The	O
DOS	O
system	O
files	O
loaded	O
by	O
the	O
boot	B-Device
sector	I-Device
must	O
be	O
contiguous	B-Architecture
and	O
be	O
the	O
first	O
two	O
directory	O
entries	O
.	O
</s>
<s>
It	O
is	O
,	O
however	O
,	O
possible	O
to	O
replace	O
the	O
shell	B-Operating_System
at	O
will	O
,	O
a	O
method	O
that	O
can	O
be	O
used	O
to	O
start	O
the	O
execution	O
of	O
dedicated	O
applications	O
faster	O
.	O
</s>
<s>
This	O
limitation	O
does	O
not	O
apply	O
to	O
any	O
version	O
of	O
DRDOS	B-Application
,	O
where	O
the	O
system	O
files	O
can	O
be	O
located	O
anywhere	O
in	O
the	O
root	O
directory	O
and	O
do	O
not	O
need	O
to	O
be	O
contiguous	B-Architecture
.	O
</s>
<s>
Therefore	O
,	O
system	O
files	O
can	O
be	O
simply	O
copied	O
to	O
a	O
disk	O
provided	O
that	O
the	O
boot	B-Device
sector	I-Device
is	O
DRDOS	B-Application
compatible	O
already	O
.	O
</s>
<s>
In	O
PCDOS	B-Operating_System
and	O
DRDOS	B-Application
5.0	O
and	O
above	O
,	O
the	O
DOS	O
system	O
files	O
are	O
named	O
IBMBIO.COM	O
instead	O
of	O
IO.SYS	O
and	O
IBMDOS.COM	O
instead	O
of	O
MSDOS.SYS	O
.	O
</s>
<s>
Older	O
versions	O
of	O
DRDOS	B-Application
used	O
DRBIOS.SYS	O
and	O
DRBDOS.SYS	O
instead	O
.	O
</s>
<s>
Starting	O
with	O
MS-DOS	B-Application
7.0	I-Application
the	O
binary	O
system	O
files	O
IO.SYS	O
and	O
MSDOS.SYS	O
were	O
combined	O
into	O
a	O
single	O
file	O
IO.SYS	O
whilst	O
MSDOS.SYS	O
became	O
a	O
configuration	O
file	O
similar	O
to	O
CONFIG.SYS	B-Device
and	O
AUTOEXEC.BAT	O
.	O
</s>
<s>
If	O
the	O
MSDOS.SYS	O
BootGUI	O
directive	O
is	O
set	O
to	O
0	O
,	O
the	O
boot	B-Operating_System
process	I-Operating_System
will	O
stop	O
with	O
the	O
command	O
processor	O
(	O
typically	O
COMMAND.COM	B-Operating_System
)	O
loaded	O
,	O
instead	O
of	O
executing	O
WIN.COM	O
automatically	O
.	O
</s>
<s>
Including	O
the	O
drive	O
name	O
,	O
the	O
maximum	O
length	O
of	O
a	O
fully	O
qualified	O
filename	O
that	O
DOS	O
supports	O
is	O
80	O
characters	O
using	O
the	O
format	O
drive	O
:	O
\path\filename.ext	O
followed	O
by	O
a	O
null	O
byte	B-Application
.	O
</s>
<s>
DOS	O
uses	O
the	O
File	B-Application
Allocation	I-Application
Table	I-Application
(	O
FAT	O
)	O
filesystem	O
.	O
</s>
<s>
This	O
was	O
originally	O
FAT12	B-Application
which	O
supported	O
up	O
to	O
4078	O
clusters	O
per	O
drive	O
.	O
</s>
<s>
DOS	O
3.0	O
added	O
support	O
for	O
FAT16	B-Application
which	O
used	O
16-bit	B-Device
allocation	O
entries	O
and	O
supported	O
up	O
to	O
65518	O
clusters	O
per	O
drive	O
.	O
</s>
<s>
Compaq	O
MS-DOS	B-Application
3.31	O
added	O
support	O
for	O
FAT16B	B-Application
which	O
removed	O
the	O
32‑MiB	O
drive	O
limit	O
and	O
could	O
support	O
up	O
to	O
512MiB	O
.	O
</s>
<s>
Finally	O
MS-DOS	B-Application
7.1	I-Application
(	O
the	O
DOS	O
component	O
of	O
Windows	O
9x	O
)	O
added	O
support	O
for	O
FAT32	B-Application
which	O
used	O
32-bit	O
allocation	O
entries	O
and	O
could	O
support	O
hard	B-Device
drives	I-Device
up	O
to	O
137	O
GiB	O
and	O
beyond	O
.	O
</s>
<s>
This	O
was	O
initially	O
used	O
to	O
support	O
networking	O
but	O
was	O
later	O
used	O
to	O
support	O
CD-ROM	O
drives	O
with	O
MSCDEX	O
.	O
</s>
<s>
IBM	O
PCDOS	B-Operating_System
4.0	O
also	O
had	O
preliminary	O
installable	O
file	O
system	O
(	O
IFS	O
)	O
support	O
but	O
this	O
was	O
unused	O
and	O
removed	O
in	O
DOS	O
5.0	O
.	O
</s>
<s>
DOS	O
also	O
supported	O
Block	O
Devices	O
(	O
"	O
Disk	O
Drive	O
"	O
devices	O
)	O
loaded	O
from	O
CONFIG.SYS	B-Device
that	O
could	O
be	O
used	O
under	O
the	O
DOS	B-Application
file	I-Application
system	I-Application
to	O
support	O
network	O
devices	O
.	O
</s>
<s>
Standard	O
practice	O
is	O
to	O
reserve	O
"	O
A	O
"	O
and	O
"	O
B	O
"	O
for	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
On	O
systems	O
with	O
only	O
one	O
floppy	B-Device
drive	I-Device
DOS	O
assigns	O
both	O
letters	O
to	O
the	O
drive	O
,	O
prompting	O
the	O
user	O
to	O
swap	O
disks	O
as	O
programs	O
alternate	O
access	O
between	O
them	O
.	O
</s>
<s>
This	O
facilitates	O
copying	O
from	O
floppy	B-Device
to	O
floppy	B-Device
or	O
having	O
a	O
program	O
run	O
from	O
one	O
floppy	B-Device
while	O
accessing	O
its	O
data	O
on	O
another	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
were	O
originally	O
assigned	O
the	O
letters	O
"	O
C	O
"	O
and	O
"	O
D	O
"	O
.	O
</s>
<s>
As	O
support	O
for	O
more	O
hard	B-Device
drives	I-Device
became	O
available	O
,	O
this	O
developed	O
into	O
first	O
assigning	O
a	O
drive	O
letter	O
to	O
each	O
drive	O
's	O
active	O
primary	O
partition	O
,	O
then	O
making	O
a	O
second	O
pass	O
over	O
the	O
drives	O
to	O
allocate	O
letters	O
to	O
logical	O
drives	O
in	O
the	O
extended	B-Application
partition	I-Application
,	O
then	O
a	O
third	O
pass	O
to	O
give	O
any	O
other	O
non-active	O
primary	O
partitions	O
their	O
names	O
(	O
where	O
such	O
additional	O
partitions	O
existed	O
and	O
contained	O
a	O
DOS-supported	O
file	O
system	O
)	O
.	O
</s>
<s>
Lastly	O
,	O
DOS	O
allocates	O
letters	O
for	O
optical	O
disc	O
drives	O
,	O
RAM	B-Application
disks	I-Application
,	O
and	O
other	O
hardware	B-Architecture
.	O
</s>
<s>
Because	O
DOS	O
applications	O
use	O
these	O
drive	O
letters	O
directly	O
(	O
unlike	O
the	O
/dev	O
directory	O
in	O
Unix-like	B-Operating_System
systems	I-Operating_System
)	O
,	O
they	O
can	O
be	O
disrupted	O
by	O
adding	O
new	O
hardware	B-Architecture
that	O
needs	O
a	O
drive	O
letter	O
.	O
</s>
<s>
An	O
example	O
is	O
the	O
addition	O
of	O
a	O
new	O
hard	B-Device
drive	I-Device
having	O
a	O
primary	O
partition	O
where	O
a	O
pre-existing	O
hard	B-Device
drive	I-Device
contains	O
logical	O
drives	O
in	O
extended	B-Application
partitions	I-Application
;	O
the	O
new	O
drive	O
will	O
be	O
assigned	O
a	O
letter	O
that	O
was	O
previously	O
assigned	O
to	O
one	O
of	O
the	O
extended	B-Application
partition	I-Application
logical	O
drives	O
.	O
</s>
<s>
Moreover	O
,	O
even	O
adding	O
a	O
new	O
hard	B-Device
drive	I-Device
having	O
only	O
logical	O
drives	O
in	O
an	O
extended	B-Application
partition	I-Application
would	O
still	O
disrupt	O
the	O
letters	O
of	O
RAM	B-Application
disks	I-Application
and	O
optical	O
drives	O
.	O
</s>
<s>
Under	O
some	O
versions	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
as	O
well	O
as	O
under	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
and	O
REAL/32	B-Operating_System
,	O
the	O
reserved	O
drive	O
letter	O
L	O
:	O
will	O
automatically	O
be	O
assigned	O
to	O
the	O
corresponding	O
load	O
drive	O
whenever	O
an	O
application	O
starts	O
.	O
</s>
<s>
NUL	B-Operating_System
,	O
for	O
null	B-Operating_System
devices	I-Operating_System
;	O
added	O
in	O
86-DOS	B-Operating_System
1.10	O
and	O
PC	B-Operating_System
DOS	I-Operating_System
1.0	O
.	O
</s>
<s>
These	O
names	O
(	O
except	O
for	O
NUL	B-Operating_System
)	O
have	O
continued	O
to	O
be	O
supported	O
in	O
all	O
versions	O
of	O
MS-DOS	B-Application
,	O
PCDOS	B-Operating_System
and	O
DR-DOS	B-Application
ever	O
since	O
.	O
</s>
<s>
LST	O
was	O
also	O
available	O
in	O
some	O
OEM	O
versions	O
of	O
MS-DOS	B-Application
1.25	O
,	O
whereas	O
other	O
OEM	O
versions	O
of	O
MS-DOS	B-Application
1.25	O
already	O
used	O
LPT1	O
(	O
first	O
line	B-Device
printer	I-Device
)	O
and	O
COM1	B-Architecture
(	O
first	O
serial	B-Architecture
communication	I-Architecture
device	I-Architecture
)	O
instead	O
,	O
as	O
introduced	O
with	O
PCDOS	B-Operating_System
.	O
</s>
<s>
In	O
addition	O
to	O
LPT1	O
and	O
LPT2	O
as	O
well	O
as	O
COM1	B-Architecture
to	O
COM3	O
,	O
Hewlett-Packard	O
'	O
s	O
MS-DOS	B-Application
2.11	O
for	O
the	O
HP	O
Portable	O
Plus	O
also	O
supported	O
LST	O
as	O
alias	O
for	O
LPT2	O
and	O
82164A	O
as	O
alias	O
for	O
COM2	O
;	O
it	O
also	O
supported	O
PLT	O
for	O
plotters	B-Operating_System
.	O
</s>
<s>
Otherwise	O
,	O
COM2	O
,	O
LPT2	O
,	O
LPT3	O
and	O
the	O
CLOCK$	O
(	O
still	O
named	O
CLOCK	O
in	O
some	O
issues	O
of	O
MS-DOS	B-Application
2.11	O
)	O
clock	O
device	O
were	O
introduced	O
with	O
DOS	O
2.0	O
,	O
and	O
COM3	O
and	O
COM4	O
were	O
added	O
with	O
DOS	O
3.3	O
.	O
</s>
<s>
Only	O
the	O
multitasking	B-Application
MS-DOS	I-Application
4	O
supported	O
KEYBD$	O
and	O
SCREEN$	O
.	O
</s>
<s>
DR	B-Application
DOS	I-Application
5.0	O
and	O
higher	O
and	O
Multiuser	B-Operating_System
DOS	I-Operating_System
support	O
an	O
$IDLE$	O
device	O
for	O
dynamic	O
idle	O
detection	O
to	O
saving	O
power	O
and	O
improve	O
multitasking	O
.	O
</s>
<s>
LPT4	O
is	O
an	O
optional	O
built-in	O
driver	O
for	O
a	O
fourth	O
line	B-Device
printer	I-Device
supported	O
in	O
some	O
versions	O
of	O
DR-DOS	B-Application
since	O
7.02	O
.	O
</s>
<s>
CONFIG$	O
constitutes	O
the	O
real	B-Application
mode	I-Application
PnP	B-Device
manager	O
in	O
MS-DOS	B-Application
7.0	I-Application
–	O
8.0	O
.	O
</s>
<s>
AUX	O
typically	O
defaults	O
to	O
COM1	B-Architecture
,	O
and	O
PRN	O
to	O
LPT1	O
(	O
LST	O
)	O
,	O
but	O
these	O
defaults	O
can	O
be	O
changed	O
in	O
some	O
versions	O
of	O
DOS	O
to	O
point	O
to	O
other	O
serial	O
or	O
parallel	O
devices	O
.	O
</s>
<s>
Filenames	O
ended	O
with	O
a	O
colon	O
(	O
)	O
such	O
as	O
NUL	B-Operating_System
:	I-Operating_System
conventionally	O
indicate	O
device	O
names	O
,	O
but	O
the	O
colon	O
is	O
not	O
actually	O
a	O
part	O
of	O
the	O
name	O
of	O
the	O
built-in	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
DOS	O
was	O
designed	O
for	O
the	O
Intel	B-Device
8088	I-Device
processor	O
,	O
which	O
can	O
only	O
directly	O
access	O
a	O
maximum	O
of	O
1MiB	O
of	O
RAM	O
.	O
</s>
<s>
Both	O
IBM	O
and	O
Microsoft	O
chose	O
640	O
kibibytes	O
(	O
KiB	O
)	O
as	O
the	O
maximum	O
amount	O
of	O
memory	O
available	O
to	O
programs	O
and	O
reserved	O
the	O
remaining	O
384KiB	O
for	O
video	O
memory	O
,	O
the	O
read-only	B-Device
memory	I-Device
of	O
adapters	O
on	O
some	O
video	O
and	O
network	O
peripherals	O
,	O
and	O
the	O
system	O
's	O
BIOS	B-Operating_System
.	O
</s>
<s>
The	O
first	O
was	O
the	O
Expanded	B-Device
Memory	I-Device
Specification	I-Device
(	O
EMS	O
)	O
was	O
designed	O
to	O
allow	O
memory	O
on	O
an	O
add-on	O
card	O
to	O
be	O
accessed	O
via	O
a	O
64KiB	O
page	O
frame	O
in	O
the	O
reserved	O
upper	B-Device
memory	I-Device
area	I-Device
.	O
</s>
<s>
80386	B-General_Concept
and	O
later	O
systems	O
could	O
use	O
a	O
virtual	B-Application
8086	I-Application
mode	I-Application
(	O
V86	B-Application
)	O
mode	O
memory	O
manager	O
like	O
EMM386	B-Device
to	O
create	O
expanded	O
memory	O
from	O
extended	O
memory	O
without	O
the	O
need	O
of	O
an	O
add-on	O
card	O
.	O
</s>
<s>
This	O
provided	O
a	O
way	O
to	O
copy	O
data	O
to	O
and	O
from	O
extended	O
memory	O
,	O
access	O
to	O
the	O
65,520	O
-byte	O
high	B-Device
memory	I-Device
area	I-Device
directly	O
above	O
the	O
first	O
megabyte	O
of	O
memory	O
and	O
the	O
upper	B-Device
memory	I-Device
block	I-Device
area	O
.	O
</s>
<s>
Generally	O
XMS	O
support	O
was	O
provided	O
by	O
HIMEM.SYS	O
or	O
a	O
V86	B-Application
mode	I-Application
memory	O
manager	O
like	O
QEMM	B-Device
or	O
386MAX	B-Device
which	O
also	O
supported	O
EMS	O
.	O
</s>
<s>
Starting	O
with	O
DOS	O
5	O
,	O
DOS	O
could	O
directly	O
take	O
advantage	O
of	O
the	O
HMA	O
by	O
loading	O
its	O
kernel	B-Operating_System
code	O
and	O
disk	O
buffers	O
there	O
via	O
the	O
DOS	O
=	O
HIGH	O
statement	O
in	O
CONFIG.SYS	B-Device
.	O
</s>
<s>
DOS	O
5+	O
also	O
allowed	O
the	O
use	O
of	O
available	O
upper	B-Device
memory	I-Device
blocks	I-Device
via	O
the	O
DOS	O
=	O
UMB	O
statement	O
in	O
CONFIG.SYS	B-Device
.	O
</s>
<s>
The	O
DOS	O
emulation	B-Application
in	O
OS/2	B-Application
and	O
Windows	O
runs	O
in	O
much	O
the	O
same	O
way	O
as	O
native	O
applications	O
do	O
.	O
</s>
<s>
Because	O
the	O
drivers	O
for	O
file	O
systems	O
and	O
such	O
forth	O
reside	O
in	O
the	O
host	O
system	O
,	O
the	O
DOS	O
emulation	B-Application
needs	O
only	O
provide	O
a	O
DOS	B-Application
API	I-Application
translation	O
layer	O
which	O
converts	O
DOS	O
calls	O
to	O
OS/2	B-Application
or	O
Windows	O
system	O
calls	O
.	O
</s>
<s>
The	O
translation	O
layer	O
generally	O
also	O
converts	O
BIOS	B-Operating_System
calls	O
and	O
virtualizes	O
common	O
I/O	O
port	O
accesses	O
which	O
many	O
DOS	O
programs	O
commonly	O
use	O
.	O
</s>
<s>
In	O
Windows	O
3.1	O
and	O
9x	O
,	O
the	O
DOS	O
virtual	B-Architecture
machine	I-Architecture
is	O
provided	O
by	O
WINOLDAP	O
.	O
</s>
<s>
WinOldAp	O
creates	O
a	O
virtual	B-Architecture
machine	I-Architecture
based	O
on	O
the	O
program	O
's	O
PIF	O
file	O
,	O
and	O
the	O
system	O
state	O
when	O
Windows	O
was	O
loaded	O
.	O
</s>
<s>
The	O
emulated	B-Application
DOS	O
in	O
OS/2	B-Application
and	O
Windows	O
NT	O
is	O
based	O
upon	O
DOS	O
5	O
.	O
</s>
<s>
Although	O
there	O
is	O
a	O
default	O
configuration	O
(	O
config.sys	B-Device
and	O
autoexec.bat	O
)	O
,	O
one	O
can	O
use	O
alternate	O
files	O
on	O
a	O
session-by-session	O
basis	O
.	O
</s>
<s>
Under	O
OS/2	B-Application
2.x	O
and	O
later	O
,	O
the	O
DOS	O
emulation	B-Application
is	O
provided	O
by	O
DOSKRNL	O
.	O
</s>
<s>
This	O
is	O
a	O
file	O
that	O
represents	O
the	O
combined	O
IBMBIO.COM	O
and	O
IBMDOS.COM	O
,	O
the	O
system	O
calls	O
are	O
passed	O
through	O
to	O
the	O
OS/2	B-Application
windowing	O
services	O
.	O
</s>
<s>
DOS	O
programs	O
run	O
in	O
their	O
own	O
environment	O
,	O
the	O
bulk	O
of	O
the	O
DOS	O
utilities	O
are	O
provided	O
by	O
bound	O
DOS	O
/	O
OS2	B-Application
applications	O
in	O
the	O
\OS2	O
directory	O
.	O
</s>
<s>
OS/2	B-Application
can	O
run	O
Windows	O
3.1	O
applications	O
by	O
using	O
a	O
modified	O
copy	O
of	O
Windows	O
(	O
Win-OS/2	B-Application
)	O
.	O
</s>
<s>
The	O
modifications	O
allow	O
Windows	O
3.1	O
programs	O
to	O
run	O
seamlessly	O
on	O
the	O
OS/2	B-Application
desktop	O
,	O
or	O
one	O
can	O
start	O
a	O
WinOS/2	B-Application
desktop	O
,	O
similar	O
to	O
starting	O
Windows	O
from	O
DOS	O
.	O
</s>
<s>
OS/2	B-Application
allows	O
for	O
'	O
DOS	O
from	O
Drive	O
A	O
:	O
'	O
,	O
(	O
VMDISK	O
)	O
.	O
</s>
<s>
This	O
is	O
a	O
real	O
DOS	O
,	O
like	O
MS-DOS	B-Application
6.22	O
or	O
PCDOS	B-Operating_System
5.00	O
.	O
</s>
<s>
One	O
makes	O
a	O
bootable	B-Operating_System
floppy	B-Device
disk	I-Device
of	O
the	O
DOS	O
,	O
adds	O
a	O
number	O
of	O
drivers	O
from	O
OS/2	B-Application
,	O
and	O
then	O
creates	O
a	O
special	O
image	O
.	O
</s>
<s>
The	O
DOS	O
booted	O
this	O
way	O
has	O
full	O
access	O
to	O
the	O
system	O
,	O
but	O
provides	O
its	O
own	O
drivers	O
for	O
hardware	B-Architecture
.	O
</s>
<s>
One	O
can	O
use	O
such	O
a	O
disk	O
to	O
access	O
cdrom	O
drives	O
for	O
which	O
there	O
is	O
no	O
OS/2	B-Application
driver	O
.	O
</s>
<s>
In	O
all	O
32-bit	O
(	O
IA-32	O
)	O
editions	O
of	O
the	O
Windows	O
NT	O
family	O
since	O
1993	O
,	O
DOS	O
emulation	B-Application
is	O
provided	O
by	O
way	O
of	O
a	O
virtual	O
DOS	O
machine	O
(	O
NTVDM	O
)	O
.	O
</s>
<s>
64-bit	O
(	O
IA-64	O
)	O
versions	O
of	O
Windows	O
do	O
not	O
support	O
NTVDM	O
and	O
cannot	O
run	O
16-bit	B-Device
DOS	O
applications	O
directly	O
;	O
third-party	O
emulators	B-Application
such	O
as	O
DOSbox	B-Application
can	O
be	O
used	O
to	O
run	O
DOS	O
programs	O
on	O
those	O
machines	O
.	O
</s>
<s>
DOS	O
systems	O
use	O
a	O
command-line	B-Application
interface	I-Application
.	O
</s>
<s>
In	O
an	O
attempt	O
to	O
provide	O
a	O
more	O
user-friendly	O
environment	O
,	O
numerous	O
software	O
manufacturers	O
wrote	O
file	B-Application
management	I-Application
programs	I-Application
that	O
provided	O
users	O
with	O
menu	O
-	O
and/or	O
icon-based	O
interfaces	O
.	O
</s>
<s>
Text	B-Application
user	I-Application
interface	I-Application
programs	O
included	O
Norton	B-Application
Commander	I-Application
,	O
DOS	B-Application
Navigator	I-Application
,	O
Volkov	B-Application
Commander	I-Application
,	O
Quarterdesk	O
DESQview	B-Operating_System
,	O
and	O
Sidekick	B-Application
.	O
</s>
<s>
Graphical	B-Application
user	I-Application
interface	I-Application
programs	O
included	O
Digital	O
Research	O
's	O
GEM	B-Application
(	O
originally	O
written	O
for	O
CP/M	B-Application
)	O
and	O
GEOS	B-Application
.	O
</s>
<s>
MS-DOS/IBM	O
DOS	O
4	O
included	O
DOS	B-Application
Shell	I-Application
;	O
DR	B-Application
DOS	I-Application
5.0	O
,	O
released	O
the	O
following	O
year	O
,	O
included	O
ViewMAX	B-Application
,	O
based	O
upon	O
GEM	B-Application
.	O
</s>
<s>
The	O
DOS	O
PRINT	B-Device
command	O
does	O
this	O
to	O
implement	O
background	O
print	B-Device
spooling	O
.	O
</s>
<s>
Borland	B-Application
Sidekick	I-Application
,	O
a	O
popup	O
personal	B-Application
information	I-Application
manager	I-Application
(	O
PIM	O
)	O
,	O
also	O
uses	O
this	O
technique	O
.	O
</s>
<s>
Programs	O
like	O
CED	O
and	O
DOSKEY	B-Device
provide	O
command-line	B-Application
editing	O
facilities	O
beyond	O
what	O
is	O
available	O
in	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
Programs	O
like	O
the	O
Microsoft	O
CD-ROM	O
Extensions	O
(	O
MSCDEX	O
)	O
provide	O
access	O
to	O
files	O
on	O
CD-ROM	O
disks	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
shareware	B-License
program	O
Back	O
and	O
Forth	O
(	O
1990	O
)	O
has	O
a	O
hotkey	O
to	O
save	O
the	O
state	O
of	O
the	O
currently-running	O
program	O
to	O
disk	O
,	O
load	O
another	O
program	O
,	O
and	O
switch	O
to	O
it	O
,	O
making	O
it	O
possible	O
to	O
switch	O
"	O
back	O
and	O
forth	O
"	O
between	O
programs	O
(	O
albeit	O
slowly	O
,	O
due	O
to	O
the	O
disk	O
access	O
required	O
)	O
.	O
</s>
<s>
Back	O
and	O
Forth	O
could	O
not	O
enable	O
background	O
processing	O
however	O
;	O
that	O
needed	O
DESQview	B-Operating_System
(	O
on	O
at	O
least	O
a	O
386	B-General_Concept
)	O
.	O
</s>
