<s>
The	O
DOS	B-Application
API	I-Application
is	O
an	O
API	B-Application
which	O
originated	O
with	O
86-DOS	B-Operating_System
and	O
is	O
used	O
in	O
MS-DOS/PC	O
DOS	B-Device
and	O
other	O
DOS-compatible	O
operating	O
systems	O
.	O
</s>
<s>
Most	O
calls	O
to	O
the	O
DOS	B-Application
API	I-Application
are	O
invoked	O
using	O
software	O
interrupt	O
21h	O
(	O
INT	B-Application
21h	I-Application
)	O
.	O
</s>
<s>
By	O
calling	O
INT	B-Application
21h	I-Application
with	O
a	O
subfunction	O
number	O
in	O
the	O
AH	O
processor	B-General_Concept
register	I-General_Concept
and	O
other	O
parameters	O
in	O
other	O
registers	O
,	O
various	O
DOS	B-Device
services	O
can	O
be	O
invoked	O
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
DOS	B-Device
extenders	I-Device
along	O
with	O
the	O
DOS	B-Device
Protected	B-Application
Mode	I-Application
Interface	O
(	O
DPMI	O
)	O
allow	O
the	O
programs	O
to	O
run	O
in	O
either	O
16-bit	O
or	O
32-bit	O
protected	B-Application
mode	I-Application
and	O
still	O
have	O
access	O
to	O
the	O
DOS	B-Application
API	I-Application
.	O
</s>
<s>
The	O
original	O
DOS	B-Application
API	I-Application
in	O
86-DOS	B-Operating_System
and	O
MS-DOS	B-Application
1.0	O
was	O
designed	O
to	O
be	O
functionally	O
compatible	O
with	O
CP/M	B-Application
.	O
</s>
<s>
Files	O
were	O
accessed	O
using	O
file	B-Operating_System
control	I-Operating_System
blocks	I-Operating_System
(	O
FCBs	O
)	O
.	O
</s>
<s>
The	O
DOS	B-Application
API	I-Application
was	O
greatly	O
extended	O
in	O
MS-DOS	B-Application
2.0	O
with	O
several	O
Unix	B-Application
concepts	O
,	O
including	O
file	O
access	O
using	O
file	B-Application
handles	I-Application
,	O
hierarchical	B-Application
directories	I-Application
and	O
device	O
I/O	O
control	O
.	O
</s>
<s>
In	O
DOS	B-Device
3.1	O
,	O
network	B-Operating_System
redirector	I-Operating_System
support	O
was	O
added	O
.	O
</s>
<s>
In	O
MS-DOS	B-Application
3.31	O
,	O
the	O
INT	B-Device
25h/26h	O
functions	O
were	O
enhanced	O
to	O
support	O
hard	O
disks	O
greater	O
than	O
32	O
MB	O
.	O
</s>
<s>
MS-DOS	B-Application
5	O
added	O
support	O
for	O
using	O
upper	B-Device
memory	I-Device
blocks	I-Device
(	O
UMBs	O
)	O
.	O
</s>
<s>
After	O
MS-DOS	B-Application
5	O
,	O
the	O
DOS	B-Application
API	I-Application
was	O
unchanged	O
for	O
the	O
successive	O
standalone	O
releases	O
of	O
DOS	B-Device
.	O
</s>
<s>
In	O
Windows	O
9x	O
,	O
DOS	B-Device
loaded	O
the	O
protected-mode	B-Application
system	O
and	O
graphical	O
shell	O
.	O
</s>
<s>
DOS	B-Device
was	O
usually	O
accessed	O
from	O
a	O
virtual	O
DOS	B-Device
machine	O
(	O
VDM	O
)	O
but	O
it	O
was	O
also	O
possible	O
to	O
boot	O
directly	O
to	O
real	B-Application
mode	I-Application
MS-DOS	B-Application
7.0	I-Application
without	O
loading	O
Windows	O
.	O
</s>
<s>
The	O
DOS	B-Application
API	I-Application
was	O
extended	O
with	O
enhanced	O
internationalization	O
support	O
and	O
long	O
filename	O
support	O
,	O
though	O
the	O
long	O
filename	O
support	O
was	O
only	O
available	O
in	O
a	O
VDM	O
.	O
</s>
<s>
With	O
Windows	B-Application
95	I-Application
OSR2	O
,	O
DOS	B-Device
was	O
updated	O
to	O
7.1	O
,	O
which	O
added	O
FAT32	B-Application
support	O
,	O
and	O
functions	O
were	O
added	O
to	O
the	O
DOS	B-Application
API	I-Application
to	O
support	O
this	O
.	O
</s>
<s>
Windows	B-Device
98	I-Device
and	O
Windows	B-Device
ME	I-Device
also	O
implement	O
the	O
MS-DOS	B-Application
7.1	I-Application
API	B-Application
,	O
though	O
Windows	B-Device
ME	I-Device
reports	O
itself	O
as	O
MS-DOS	B-Application
8.0	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
and	O
the	O
systems	O
based	O
on	O
it	O
(	O
e.g.	O
</s>
<s>
Windows	B-Application
XP	I-Application
and	O
Windows	B-Application
Vista	I-Application
)	O
are	O
not	O
based	O
on	O
MS-DOS	B-Application
,	O
but	O
use	O
a	O
virtual	B-Architecture
machine	I-Architecture
,	O
NTVDM	O
,	O
to	O
handle	O
the	O
DOS	B-Application
API	I-Application
.	O
</s>
<s>
NTVDM	O
works	O
by	O
running	O
a	O
DOS	B-Device
program	O
in	O
virtual	B-Application
8086	I-Application
mode	I-Application
(	O
an	O
emulation	O
of	O
real	B-Application
mode	I-Application
within	O
protected	B-Application
mode	I-Application
available	O
on	O
80386	B-General_Concept
and	O
higher	O
processors	O
)	O
.	O
</s>
<s>
NTVDM	O
supports	O
the	O
DOS	B-Device
5.0	O
API	B-Application
.	O
</s>
<s>
DOSEMU	B-Application
for	O
Linux	B-Application
uses	O
a	O
similar	O
approach	O
.	O
</s>
<s>
The	O
following	O
is	O
the	O
list	O
of	O
interrupt	O
vectors	O
used	O
by	O
programs	O
to	O
invoke	O
the	O
DOS	B-Application
API	I-Application
functions	O
.	O
</s>
<s>
Interrupt	O
vectorDescriptionVersionNotesTerminate	O
program1.0	O
+Implemented	O
in	O
DOS	B-Device
kernelMain	O
DOS	B-Device
API1.0	O
+Implemented	O
in	O
DOS	B-Device
kernelProgram	O
terminate	O
address1.0	O
+Return	O
address	O
in	O
calling	O
programControl-C	O
handler	O
address1.0	O
+Default	O
handler	O
is	O
in	O
the	O
command	O
shell	O
(	O
usually	O
COMMAND.COM	B-Operating_System
)	O
Critical	O
error	O
handler	O
address1.0	O
+Default	O
handler	O
is	O
in	O
the	O
command	O
shell	O
(	O
usually	O
COMMAND.COM	B-Operating_System
)	O
Absolute	O
disk	O
read1.0	O
+Implemented	O
in	O
DOS	B-Device
kernel	O
,	O
enhanced	O
in	O
DOS	B-Device
3.31	O
to	O
support	O
up	O
to	O
2	O
GB	O
partitionsAbsolute	O
disk	O
write1.0	O
+Implemented	O
in	O
DOS	B-Device
kernel	O
,	O
enhanced	O
in	O
DOS	B-Device
3.31	O
to	O
support	O
up	O
to	O
2	O
GB	O
partitionsTerminate	O
and	O
stay	O
resident1.0	O
+Implemented	O
in	O
COMMAND.COM	B-Operating_System
in	O
DOS	B-Device
1.0	O
,	O
DOS	B-Device
kernel	O
in	O
DOS	B-Device
2.0	O
+Idle	O
callout2.0	O
+Called	O
by	O
DOS	B-Device
kernel	O
when	O
waiting	O
for	O
inputFast	O
console	O
output2.0	O
+Implemented	O
by	O
the	O
built-in	O
console	O
device	O
driver	O
or	O
a	O
replacement	O
driver	O
like	O
ANSI.SYSNetworking	O
and	O
critical	O
section3.0	O
+Called	O
by	O
DOS	B-Device
kernel	O
to	O
interface	O
with	O
networking	O
softwareUnusedUnusedUnusedReload	O
transient2.0	O
+Implemented	O
in	O
COMMAND.COMMultiplex3.0	O
+Implemented	O
in	O
DOS	B-Device
kernel	O
and	O
various	O
programs	O
(	O
PRINT	O
,	O
MSCDEX	O
,	O
DOSKEY	O
,	O
APPEND	O
,	O
etc	O
.	O
)	O
</s>
<s>
The	O
following	O
is	O
the	O
list	O
of	O
functions	O
provided	O
via	O
the	O
DOS	B-Application
API	I-Application
primary	O
software	O
interrupt	O
vector	O
.	O
</s>
<s>
DR-DOS	B-Application
–	O
Digital	O
Research	O
DOS	B-Device
family	O
,	O
including	O
Novell	B-Operating_System
DOS	I-Operating_System
,	O
PalmDOS	B-Operating_System
,	O
OpenDOS	B-Application
,	O
etc	O
.	O
</s>
<s>
Multiuser	B-Operating_System
DOS	I-Operating_System
–	O
Digital	O
Research/Novell	O
MDOS	O
family	O
including	O
Datapac	O
System	O
Manager	O
,	O
IMS	O
REAL/32	O
,	O
etc	O
.	O
</s>
