<s>
MS-DOS	B-Application
4.0	I-Application
was	O
a	O
multitasking	B-Operating_System
release	O
of	O
MS-DOS	B-Application
developed	O
by	O
Microsoft	O
based	O
on	O
MS-DOS	B-Application
2.0	O
.	O
</s>
<s>
Lack	O
of	O
interest	O
from	O
OEMs	O
,	O
particularly	O
IBM	O
(	O
who	O
previously	O
gave	O
Microsoft	O
multitasking	B-Operating_System
code	O
on	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
included	O
with	O
TopView	B-Operating_System
)	O
,	O
led	O
to	O
it	O
being	O
released	O
only	O
in	O
a	O
scaled-back	O
form	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
referred	O
to	O
as	O
European	B-Application
MS-DOS	I-Application
4.0	O
,	O
as	O
it	O
was	O
primarily	O
used	O
there	O
.	O
</s>
<s>
It	O
should	O
not	O
be	O
confused	O
with	O
PC	B-Operating_System
DOS	I-Operating_System
4.00	O
or	O
MS-DOS	O
4.01	O
and	O
later	O
,	O
which	O
did	O
not	O
contain	O
the	O
multi-tasking	O
features	O
.	O
</s>
<s>
Apricot	O
Computers	O
pre-announced	O
"	O
MS-DOS	B-Application
4.0	I-Application
"	O
in	O
early	O
1986	O
,	O
and	O
Microsoft	O
demonstrated	O
it	O
in	O
September	O
of	O
that	O
year	O
at	O
a	O
Paris	O
trade	O
show	O
.	O
</s>
<s>
In	O
particular	O
,	O
IBM	O
declined	O
the	O
product	O
,	O
concentrating	O
instead	O
on	O
improvements	O
to	O
MS-DOS	B-Application
3.x	O
and	O
their	O
new	O
joint	O
development	O
with	O
Microsoft	O
to	O
produce	O
OS/2	B-Application
.	O
</s>
<s>
In	O
September	O
1987	O
,	O
a	O
version	O
of	O
multi-tasking	B-Application
MS-DOS	I-Application
4.1	O
was	O
reported	O
to	O
be	O
developed	O
for	O
the	O
ICL	O
DRS	O
Professional	O
Workstation	O
(	O
PWS	O
)	O
.	O
</s>
<s>
In	O
July	O
1988	O
,	O
IBM	O
announced	O
"	O
IBM	B-Operating_System
DOS	I-Operating_System
4.0	O
"	O
,	O
an	O
unrelated	O
product	O
continuing	O
from	O
DOS	B-Device
3.3	O
and	O
3.4	O
,	O
leading	O
to	O
initial	O
conjecture	O
that	O
Microsoft	O
might	O
release	O
it	O
under	O
a	O
different	O
version	O
number	O
.	O
</s>
<s>
However	O
,	O
Microsoft	O
eventually	O
released	O
it	O
as	O
"	O
MS-DOS	B-Application
4.0	I-Application
"	O
,	O
with	O
a	O
MS-DOS	O
4.01	O
following	O
quickly	O
to	O
fix	O
issues	O
many	O
had	O
reported	O
.	O
</s>
<s>
As	O
well	O
as	O
minor	O
improvements	O
such	O
as	O
support	O
for	O
the	O
New	O
Executable	O
file	O
format	B-Application
,	O
the	O
key	O
feature	O
of	O
the	O
release	O
was	O
its	O
support	O
for	O
preemptive	O
multitasking	B-Operating_System
.	O
</s>
<s>
This	O
did	O
not	O
use	O
the	O
protected	B-Application
mode	I-Application
available	O
on	O
80386	B-General_Concept
processors	O
,	O
but	O
allowed	O
specially-written	O
programs	O
to	O
continue	O
executing	O
in	O
a	O
"	O
background	O
mode	O
"	O
,	O
where	O
they	O
had	O
no	O
access	O
to	O
user	O
input	O
and	O
output	O
until	O
returned	O
to	O
the	O
foreground	O
.	O
</s>
<s>
The	O
OS	O
was	O
reported	O
to	O
include	O
a	O
time-sliced	O
scheduler	O
and	O
interprocess	B-Operating_System
communication	I-Operating_System
via	O
pipes	B-Operating_System
and	O
shared	B-Operating_System
memory	I-Operating_System
.	O
</s>
<s>
This	O
limited	O
form	O
of	O
multitasking	B-Operating_System
was	O
considered	O
to	O
be	O
more	B-Device
useful	O
in	O
a	O
server	O
rather	O
than	O
workstation	O
environment	O
,	O
particularly	O
coupled	O
with	O
MS-Net	B-Application
2.0	O
,	O
which	O
was	O
released	O
simultaneously	O
.	O
</s>
<s>
Other	O
limitations	O
of	O
MS-DOS	B-Application
3.0	O
remained	O
,	O
including	O
the	O
inability	O
to	O
use	O
memory	O
above	O
640KB	O
,	O
and	O
this	O
contributed	O
to	O
the	O
product	O
's	O
lack	O
of	O
adoption	O
,	O
particularly	O
in	O
light	O
of	O
the	O
need	O
to	O
write	O
programs	O
specifically	O
targeted	O
at	O
the	O
new	O
environment	O
.	O
</s>
<s>
INT	O
21h/AH	O
=	O
87h	O
can	O
be	O
used	O
to	O
distinguish	O
between	O
the	O
multitasking	B-Application
MS-DOS	I-Application
4.x	O
and	O
the	O
later	O
MS-DOS/PC	O
DOS	O
4.x	O
issues	O
.	O
</s>
<s>
Microsoft	O
president	O
Jon	O
Shirley	O
described	O
it	O
as	O
a	O
"	O
specialized	O
version	O
"	O
and	O
went	O
as	O
far	O
as	O
saying	O
"	O
maybe	O
we	O
should	O
n't	O
have	O
called	O
it	O
DOS	B-Device
4.0	O
"	O
,	O
although	O
it	O
's	O
not	O
clear	O
whether	O
this	O
was	O
always	O
the	O
intention	O
,	O
or	O
if	O
a	O
more	B-Device
enthusiastic	O
response	O
from	O
OEMs	O
would	O
have	O
resulted	O
in	O
it	O
being	O
the	O
true	O
successor	O
to	O
DOS	B-Device
3.x	O
.	O
</s>
<s>
The	O
marketing	O
positioned	O
it	O
as	O
an	O
additional	O
option	O
between	O
DOS	B-Device
3.x	O
for	O
workstations	O
,	O
and	O
Xenix	B-Application
for	O
higher-end	O
servers	O
and	O
multiuser	O
systems	O
.	O
</s>
<s>
MS-DOS	B-Application
Version	O
4.10.20	O
supports	O
the	O
following	O
external	O
commands	O
:	O
</s>
