<s>
Multiuser	O
DOS	B-Device
is	O
a	O
real-time	B-Operating_System
multi-user	O
multi-tasking	O
operating	B-General_Concept
system	I-General_Concept
for	O
IBM	O
PC-compatible	O
microcomputers	O
.	O
</s>
<s>
An	O
evolution	O
of	O
the	O
older	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
Concurrent	O
DOS	B-Device
and	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
operating	B-General_Concept
systems	I-General_Concept
,	O
it	O
was	O
originally	O
developed	O
by	O
Digital	O
Research	O
and	O
acquired	O
and	O
further	O
developed	O
by	O
Novell	O
in	O
1991	O
.	O
</s>
<s>
Its	O
ancestry	O
lies	O
in	O
the	O
earlier	O
Digital	O
Research	O
8-bit	O
operating	B-General_Concept
systems	I-General_Concept
CP/M	B-Application
and	O
MP/M	B-Operating_System
,	O
and	O
the	O
16-bit	B-Device
single-tasking	O
CP/M	B-Operating_System
-86	I-Operating_System
which	O
evolved	O
from	O
CP/M	B-Application
.	O
</s>
<s>
When	O
Novell	O
abandoned	O
Multiuser	O
DOS	B-Device
in	O
1992	O
,	O
the	O
three	O
master	O
value-added	O
resellers	O
(	O
VARs	O
)	O
DataPac	O
Australasia	O
,	O
Concurrent	O
Controls	O
and	O
Intelligent	O
Micro	O
Software	O
were	O
allowed	O
to	O
take	O
over	O
and	O
continued	O
independent	O
development	O
into	O
Datapac	O
Multiuser	O
DOS	B-Device
and	O
System	O
Manager	O
,	O
CCI	O
Multiuser	O
DOS	B-Device
,	O
and	O
IMS	O
Multiuser	O
DOS	B-Device
and	O
REAL/32	O
.	O
</s>
<s>
The	O
FlexOS	B-Operating_System
line	O
,	O
which	O
evolved	O
from	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
and	O
Concurrent	B-Operating_System
DOS	I-Operating_System
68K	I-Operating_System
,	O
was	O
sold	O
off	O
to	O
Integrated	O
Systems	O
,	O
Inc	O
.	O
(	O
ISI	O
)	O
in	O
July	O
1994	O
.	O
</s>
<s>
The	O
initial	O
version	O
of	O
CP/M	B-Operating_System
-86	I-Operating_System
1.0	O
(	O
with	O
BDOS	B-Operating_System
2.x	O
)	O
was	O
adapted	O
and	O
became	O
available	O
to	O
the	O
IBM	B-Device
PC	I-Device
in	O
1982	O
.	O
</s>
<s>
It	O
was	O
commercially	O
unsuccessful	O
as	O
IBM	O
's	O
PC	O
DOS	B-Device
1.0	O
offered	O
much	O
the	O
same	O
facilities	O
for	O
a	O
considerably	O
lower	O
price	O
.	O
</s>
<s>
Neither	O
PCDOS	B-Operating_System
nor	O
CP/M	B-Operating_System
-86	I-Operating_System
could	O
fully	O
exploit	O
the	O
power	O
and	O
capabilities	O
of	O
the	O
new	O
16-bit	B-Device
machine	O
.	O
</s>
<s>
It	O
was	O
soon	O
supplemented	O
by	O
an	O
implementation	O
of	O
CP/M	B-Application
'	O
s	O
multitasking	B-Operating_System
'	O
big	O
brother	O
 '	O
,	O
MP/M	B-Operating_System
-86	I-Operating_System
2.0	O
,	O
since	O
September	O
1981	O
.	O
</s>
<s>
This	O
turned	O
a	O
PC	O
into	O
a	O
multiuser	O
machine	O
capable	O
of	O
supporting	O
multiple	O
concurrent	B-License
users	I-License
using	O
dumb	O
terminals	O
attached	O
by	O
serial	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
CP/M	B-Operating_System
-86	I-Operating_System
1.1	O
(	O
with	O
BDOS	B-Operating_System
2.2	O
)	O
and	O
MP/M	B-Operating_System
-86	I-Operating_System
2.1	O
were	O
merged	O
to	O
create	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
3.0	O
(	O
also	O
known	O
as	O
CCP/M	O
-86	O
)	O
with	O
BDOS	B-Operating_System
3.0	O
in	O
late	O
1982	O
.	O
</s>
<s>
Kathryn	O
Strutynski	O
,	O
the	O
project	O
manager	O
for	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
was	O
also	O
the	O
project	O
manager	O
for	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
.	O
</s>
<s>
Initially	O
,	O
this	O
was	O
a	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
supporting	O
true	O
multi-tasking	O
of	O
up	O
to	O
four	O
(	O
in	O
its	O
default	O
configuration	O
)	O
CP/M	B-Operating_System
-86	I-Operating_System
compatible	O
programs	O
.	O
</s>
<s>
Like	O
its	O
predecessors	O
it	O
could	O
be	O
configured	O
for	O
multi-processor	B-Operating_System
support	O
(	O
see	O
e.g.	O
</s>
<s>
Concurrent	B-Operating_System
CP/M-86/80	I-Operating_System
)	O
and	O
also	O
added	O
"	O
virtual	O
screens	O
"	O
letting	O
an	O
operator	O
switch	O
between	O
the	O
interactions	O
of	O
multiple	O
programs	O
.	O
</s>
<s>
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
3.1	O
(	O
BDOS	B-Operating_System
3.1	O
)	O
shipped	O
on	O
21	O
February	O
1984	O
.	O
</s>
<s>
In	O
February	O
1984	O
Digital	O
Research	O
also	O
offered	O
a	O
version	O
of	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
with	O
windowing	O
capabilities	O
named	O
Concurrent	O
CP/M	B-Application
with	O
Windows	O
for	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
and	O
Personal	O
Computer	O
XT	O
.	O
</s>
<s>
This	O
was	O
an	O
adaptation	O
of	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
for	O
the	O
LSI-M4	O
,	O
LSI	O
Octopus	O
and	O
CAL	O
PC	O
computers	O
.	O
</s>
<s>
These	O
machines	O
had	O
both	O
16-bit	B-Device
and	O
8-bit	O
processors	O
,	O
because	O
in	O
the	O
early	O
days	O
of	O
16-bit	B-Device
personal	O
computing	O
,	O
8-bit	O
software	O
was	O
more	O
available	O
and	O
often	O
ran	O
faster	O
than	O
the	O
corresponding	O
16-bit	B-Device
software	O
.	O
</s>
<s>
Concurrent	B-Operating_System
CP/M-86/80	I-Operating_System
allowed	O
users	O
to	O
run	O
both	O
CP/M	B-Application
(	O
8-bit	O
)	O
and	O
CP/M	B-Operating_System
-86	I-Operating_System
(	O
16-bit	B-Device
)	O
applications	O
.	O
</s>
<s>
When	O
a	O
command	O
was	O
entered	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
ran	O
the	O
corresponding	O
application	O
on	O
either	O
the	O
8-bit	O
or	O
the	O
16-bit	B-Device
processor	I-Device
,	O
depending	O
on	O
whether	O
the	O
executable	O
file	O
had	O
a	O
.COM	O
or	O
.CMD	O
extension	O
.	O
</s>
<s>
It	O
emulated	O
a	O
CP/M	B-Application
environment	O
for	O
8-bit	O
programs	O
by	O
translating	O
CP/M	B-Application
system	O
calls	O
into	O
CP/M	B-Operating_System
-86	I-Operating_System
system	O
calls	O
,	O
which	O
were	O
then	O
executed	O
by	O
the	O
16-bit	B-Device
processor	I-Device
.	O
</s>
<s>
In	O
August	O
1983	O
,	O
Bruce	O
Skidmore	O
,	O
Raymond	O
D	O
.	O
Pedrizetti	O
,	O
Dave	O
Brown	O
and	O
Gordon	O
Edmonds	O
teamed	O
up	O
to	O
create	O
PC-MODE	O
,	O
an	O
optional	O
module	O
for	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
3.1	O
(	O
with	O
BDOS	B-Operating_System
3.1	O
)	O
to	O
provide	O
basic	O
compatibility	O
with	O
PC	B-Operating_System
DOS	I-Operating_System
1.1	O
(	O
and	O
MS-DOS	B-Application
1.1	O
)	O
.	O
</s>
<s>
This	O
was	O
shown	O
publicly	O
at	O
COMDEX	O
in	O
December	O
1983	O
and	O
shipped	O
in	O
March	O
1984	O
as	O
Concurrent	O
DOS	B-Device
3.1	O
(	O
a.k.a.	O
</s>
<s>
CDOS	O
with	O
BDOS	B-Operating_System
3.1	O
)	O
to	O
hardware	O
vendors	O
.	O
</s>
<s>
Simple	O
DOS	B-Device
applications	O
,	O
which	O
did	O
not	O
directly	O
access	O
the	O
screen	O
or	O
other	O
hardware	O
,	O
could	O
be	O
run	O
.	O
</s>
<s>
For	O
example	O
,	O
although	O
a	O
console	B-Application
program	O
such	O
as	O
PKZIP	B-Application
worked	O
perfectly	O
and	O
offered	O
more	O
facilities	O
than	O
the	O
CP/M	B-Application
-native	O
ARC	B-Application
archiver	O
,	O
applications	O
which	O
performed	O
screen	O
manipulations	O
,	O
such	O
as	O
the	O
WordStar	B-Application
word	B-General_Concept
processor	I-General_Concept
for	O
DOS	B-Device
,	O
would	O
not	O
,	O
and	O
native	O
Concurrent	O
CP/M	B-Application
(	O
or	O
CP/M	B-Operating_System
-86	I-Operating_System
)	O
versions	O
were	O
required	O
.	O
</s>
<s>
While	O
Concurrent	O
DOS	B-Device
3.1	O
up	O
to	O
4.1	O
had	O
been	O
developed	O
in	O
the	O
US	O
,	O
OEM	O
adaptations	O
and	O
localizations	O
were	O
carried	O
out	O
by	O
DR	O
Europe	O
's	O
OEM	O
Support	O
Group	O
in	O
Newbury	O
,	O
UK	O
,	O
since	O
1983	O
.	O
</s>
<s>
Digital	O
Research	O
positioned	O
Concurrent	O
DOS	B-Device
4.1	O
with	O
GEM	B-Application
as	O
alternative	O
for	O
IBM	O
's	O
TopView	B-Operating_System
in	O
1985	O
.	O
</s>
<s>
Concurrent	O
DOS	B-Device
3.2	O
(	O
with	O
BDOS	B-Operating_System
3.2	O
)	O
in	O
1984	O
was	O
compatible	O
with	O
applications	O
for	O
CP/M	B-Operating_System
-86	I-Operating_System
1.x	O
,	O
Concurrent	O
CP/M	B-Operating_System
-86	I-Operating_System
3.x	O
and	O
PC	B-Operating_System
DOS	I-Operating_System
2.0	O
.	O
</s>
<s>
The	O
version	O
with	O
an	O
IBM	B-Device
PC	I-Device
compatible	O
BIOS/XIOS	O
was	O
named	O
Concurrent	O
PC	B-Operating_System
DOS	I-Operating_System
3.2	O
.	O
</s>
<s>
Kathryn	O
Strutynski	O
was	O
the	O
product	O
manager	O
for	O
Concurrent	O
PC	B-Operating_System
DOS	I-Operating_System
.	O
</s>
<s>
Efforts	O
being	O
part	O
of	O
a	O
cooperation	O
with	O
Motorola	O
since	O
1984	O
led	O
to	O
the	O
development	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
68K	I-Operating_System
in	O
Austin	O
,	O
Texas	O
,	O
as	O
a	O
successor	O
to	O
CP/M	B-Operating_System
-68K	I-Operating_System
written	O
in	O
C	B-Language
.	O
One	O
of	O
its	O
main	O
architects	O
was	O
Francis	O
"	O
Frank	O
"	O
R	O
.	O
Holsworth	O
(	O
using	O
siglum	O
FRH	O
)	O
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
68K	I-Operating_System
1.0	O
became	O
available	O
for	O
OEM	O
evaluation	O
in	O
early	O
1985	O
.	O
</s>
<s>
The	O
effort	O
received	O
considerable	O
funding	O
worth	O
several	O
million	O
dollars	O
from	O
Motorola	O
and	O
was	O
designed	O
for	O
their	O
68000/68010	O
processors	O
.	O
</s>
<s>
Like	O
the	O
earlier	O
GEMDOS	B-Operating_System
system	O
for	O
68000	B-Device
processors	O
it	O
initially	O
ran	O
on	O
the	O
Motorola	O
VME/10	O
development	O
system	O
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
68K	I-Operating_System
1.20/1.21	O
was	O
available	O
in	O
April	O
1986	O
,	O
offered	O
for	O
about	O
to	O
OEMs	O
.	O
</s>
<s>
This	O
system	O
evolved	O
into	O
FlexOS	B-Operating_System
68K	I-Operating_System
in	O
late	O
1986	O
.	O
</s>
<s>
In	O
parallel	O
to	O
the	O
Concurrent	B-Operating_System
DOS	I-Operating_System
68K	I-Operating_System
effort	O
,	O
Digital	O
Research	O
also	O
previewed	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
in	O
cooperation	O
with	O
Intel	O
in	O
January	O
1985	O
.	O
</s>
<s>
This	O
was	O
based	O
on	O
MP/M	B-Operating_System
-286	I-Operating_System
and	O
Concurrent	O
CP/M	B-Application
-286	O
,	O
on	O
which	O
Digital	O
Research	O
had	O
worked	O
since	O
1982	O
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
was	O
a	O
complete	O
rewrite	O
in	O
the	O
C	B-Language
language	I-Language
based	O
on	O
a	O
new	O
system	O
architecture	O
with	O
dynamically	O
loadable	O
device	B-Application
drivers	I-Application
instead	O
of	O
a	O
static	O
BIOS	O
or	O
XIOS	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
would	O
function	O
strictly	O
in	O
80286	B-General_Concept
native	O
mode	O
,	O
allowing	O
protected	O
mode	O
multi-user	O
,	O
multitasking	B-Operating_System
operation	O
while	O
running	O
8086	B-Operating_System
emulation	I-Operating_System
.	O
</s>
<s>
While	O
this	O
worked	O
on	O
the	O
B-1	O
step	B-General_Concept
of	O
prototype	O
chip	O
samples	O
,	O
Digital	O
Research	O
,	O
with	O
evaluation	O
copies	O
of	O
their	O
operating	B-General_Concept
system	I-General_Concept
already	O
shipping	O
in	O
April	O
,	O
discovered	O
problems	O
with	O
the	O
emulation	O
on	O
the	O
production	O
level	O
C-1	O
step	B-General_Concept
of	O
the	O
processor	O
in	O
May	O
,	O
which	O
would	O
not	O
allow	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
to	O
run	O
8086	B-General_Concept
software	O
in	O
protected	O
mode	O
.	O
</s>
<s>
The	O
release	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
had	O
been	O
scheduled	O
for	O
late	O
May	O
,	O
but	O
was	O
delayed	O
until	O
Intel	O
could	O
develop	O
a	O
new	O
version	O
of	O
the	O
chip	O
.	O
</s>
<s>
In	O
August	O
,	O
after	O
extensive	O
testing	O
E-1	O
step	B-General_Concept
samples	O
of	O
the	O
80286	B-General_Concept
,	O
Digital	O
Research	O
said	O
that	O
Intel	O
had	O
corrected	O
all	O
documented	O
286	B-General_Concept
errata	O
,	O
but	O
that	O
there	O
were	O
still	O
undocumented	O
chip	O
performance	O
problems	O
with	O
the	O
prerelease	O
version	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
running	O
on	O
the	O
E-1	O
step	B-General_Concept
.	O
</s>
<s>
Intel	O
said	O
that	O
the	O
approach	O
Digital	O
Research	O
wished	O
to	O
take	O
in	O
emulating	O
8086	B-General_Concept
software	O
in	O
protected	O
mode	O
differed	O
from	O
the	O
original	O
specifications	O
;	O
nevertheless	O
they	O
incorporated	O
into	O
the	O
E-2	O
step	B-General_Concept
minor	O
changes	O
in	O
the	O
microcode	B-Device
that	O
allowed	O
Digital	O
Research	O
to	O
run	O
emulation	O
mode	O
much	O
faster	O
(	O
see	O
LOADALL	B-Device
)	O
.	O
</s>
<s>
These	O
same	O
limitations	O
affected	O
FlexOS	B-Operating_System
286	I-Operating_System
version	O
1.x	O
,	O
a	O
reengineered	O
derivation	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
,	O
which	O
was	O
developed	O
by	O
Digital	O
Research	O
's	O
new	O
Flexible	O
Automation	O
Business	O
Unit	O
in	O
Monterey	O
,	O
California	O
,	O
since	O
1986	O
.	O
</s>
<s>
Later	O
versions	O
added	O
compatibility	O
with	O
PC	B-Operating_System
DOS	I-Operating_System
2.x	O
and	O
3.x	O
.	O
</s>
<s>
The	O
OEM	O
Support	O
Group	O
was	O
relocated	O
into	O
Digital	O
Research	O
's	O
newly	O
created	O
European	O
Development	O
Centre	O
(	O
EDC	O
)	O
in	O
Hungerford	O
,	O
UK	O
in	O
1986	O
,	O
which	O
started	O
to	O
take	O
over	O
further	O
development	O
of	O
the	O
Concurrent	O
DOS	B-Device
family	O
since	O
Concurrent	O
DOS	B-Device
4.11	O
,	O
including	O
siblings	O
like	O
DOS	B-Operating_System
Plus	I-Operating_System
and	O
successors	O
.	O
</s>
<s>
Developed	O
in	O
Hungerford	O
,	O
UK	O
,	O
versions	O
5	O
and	O
6	O
(	O
Concurrent	O
DOS	B-Device
XM	O
,	O
with	O
XM	O
standing	O
for	O
Expanded	B-Device
Memory	I-Device
)	O
could	O
bank	B-General_Concept
switch	I-General_Concept
up	O
to	O
8MB	O
of	O
EEMS	B-Device
to	O
provide	O
a	O
real-mode	O
environment	O
to	O
run	O
multiple	O
CP/M	B-Operating_System
-86	I-Operating_System
and	O
DOS	B-Device
programs	O
concurrently	O
and	O
support	O
up	O
to	O
three	O
users	O
(	O
one	O
local	O
and	O
up	O
to	O
two	O
hooked	O
up	O
via	O
serial	O
terminals	O
)	O
.	O
</s>
<s>
In	O
1987	O
,	O
Concurrent	O
DOS	B-Device
86	O
was	O
rewritten	O
to	O
become	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
,	O
still	O
a	O
continuation	O
of	O
the	O
classical	O
XIOS	O
&	O
BDOS	B-Operating_System
architecture	O
.	O
</s>
<s>
This	O
ran	O
on	O
machines	O
equipped	O
with	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
and	O
later	O
processors	O
,	O
using	O
the	O
386	B-General_Concept
's	O
hardware	O
facilities	O
for	O
virtualizing	B-General_Concept
the	O
hardware	O
,	O
allowing	O
most	O
DOS	B-Device
applications	O
to	O
run	O
unmodified	O
under	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
,	O
even	O
on	O
terminals	O
.	O
</s>
<s>
The	O
OS	O
supported	O
concurrent	O
multiuser	O
file	O
access	O
,	O
allowing	O
multiuser	O
applications	O
to	O
run	O
as	O
if	O
they	O
were	O
on	O
individual	O
PCs	O
attached	O
to	O
a	O
network	B-Application
server	I-Application
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
allowed	O
a	O
single	O
server	B-Application
to	O
support	O
a	O
number	O
of	O
users	O
on	O
dumb	O
terminals	O
or	O
inexpensive	O
low-specification	O
PCs	O
running	O
terminal	O
emulation	O
software	O
,	O
without	O
the	O
need	O
for	O
expensive	O
workstations	O
and	O
then-expensive	O
network	O
cards	O
.	O
</s>
<s>
It	O
was	O
a	O
true	O
multiuser	O
system	O
;	O
several	O
users	O
could	O
use	O
a	O
single	O
database	O
with	O
record	B-Operating_System
locking	I-Operating_System
to	O
prevent	O
mutual	O
interference	O
.	O
</s>
<s>
Concurrent	O
DOS	B-Device
6.0	O
represented	O
also	O
the	O
starting	O
point	O
for	O
the	O
DR	B-Application
DOS	I-Application
family	O
,	O
which	O
was	O
carved	O
out	O
of	O
it	O
.	O
</s>
<s>
Concurrent	O
PC	B-Operating_System
DOS	I-Operating_System
XM	O
5.0	O
emulated	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
2.10	O
,	O
whereas	O
Concurrent	O
DOS	B-Device
XM	O
6.0	O
and	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
2.0	O
were	O
compatible	O
with	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
3.30	O
.	O
</s>
<s>
Known	O
CCI	O
Concurrent	O
DOS	B-Device
adaptations	O
by	O
Concurrent	O
Controls	O
,	O
Inc	O
.	O
include	O
:	O
</s>
<s>
Later	O
versions	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
incorporated	O
some	O
of	O
the	O
enhanced	O
functionality	O
of	O
DR	O
's	O
later	O
single-user	O
PC	B-Operating_System
DOS	I-Operating_System
clone	O
DR	B-Application
DOS	I-Application
5.0	O
,	O
after	O
which	O
the	O
product	O
was	O
given	O
the	O
more	O
explanatory	O
name	O
"	O
Multiuser	O
DOS	B-Device
"	O
(	O
a.k.a.	O
</s>
<s>
MDOS	O
)	O
,	O
starting	O
with	O
version	O
5.0	O
(	O
with	O
BDOS	B-Operating_System
6.5	O
)	O
in	O
1991	O
.	O
</s>
<s>
Multiuser	O
DOS	B-Device
suffered	O
from	O
several	O
technical	O
limitations	O
that	O
restricted	O
its	O
ability	O
to	O
compete	O
with	O
LANs	B-General_Concept
based	O
on	O
PC	B-Operating_System
DOS	I-Operating_System
.	O
</s>
<s>
It	O
required	O
its	O
own	O
special	O
device	B-Application
drivers	I-Application
for	O
much	O
common	O
hardware	O
,	O
as	O
PC	B-Operating_System
DOS	I-Operating_System
drivers	O
were	O
not	O
multiuser	O
or	O
multi-tasking	O
aware	O
.	O
</s>
<s>
Driver	O
installation	O
was	O
more	O
complex	O
than	O
the	O
simple	O
PC	B-Operating_System
DOS	I-Operating_System
method	O
of	O
copying	O
the	O
files	O
onto	O
the	O
boot	O
disk	O
and	O
modifying	O
CONFIG.SYS	O
appropriately	O
it	O
was	O
necessary	O
to	O
relink	O
the	O
Multiuser	O
DOS	B-Device
kernel	B-Operating_System
(	O
known	O
as	O
a	O
nucleus	B-Operating_System
)	O
using	O
the	O
SYSGEN	B-Application
command	O
.	O
</s>
<s>
Multiuser	O
DOS	B-Device
was	O
also	O
unable	O
to	O
use	O
many	O
common	O
PC	B-Operating_System
DOS	I-Operating_System
additions	O
such	O
as	O
network	B-Protocol
stacks	I-Protocol
,	O
and	O
it	O
was	O
limited	O
in	O
its	O
ability	O
to	O
support	O
later	O
developments	O
in	O
the	O
PC-compatible	O
world	O
,	O
such	O
as	O
graphics	B-Device
adaptors	I-Device
,	O
sound	B-Device
cards	I-Device
,	O
CD-ROM	B-Device
drives	O
and	O
mice	O
.	O
</s>
<s>
Although	O
many	O
of	O
these	O
were	O
soon	O
rectified	O
for	O
example	O
,	O
graphical	O
terminals	O
were	O
developed	O
,	O
allowing	O
users	O
to	O
use	O
CGA	B-Device
,	O
EGA	B-Device
and	O
VGA	B-Protocol
software	O
it	O
was	O
less	O
flexible	O
in	O
this	O
regard	O
than	O
a	O
network	O
of	O
individual	O
PCs	O
,	O
and	O
as	O
the	O
prices	O
of	O
these	O
fell	O
,	O
it	O
became	O
less	O
and	O
less	O
competitive	O
,	O
although	O
it	O
still	O
offered	O
benefits	O
in	O
terms	O
of	O
management	O
and	O
lower	O
total	O
cost	O
of	O
ownership	O
.	O
</s>
<s>
As	O
a	O
multi-user	O
operating	B-General_Concept
system	I-General_Concept
its	O
price	O
was	O
higher	O
than	O
a	O
single-user	O
system	O
,	O
of	O
course	O
,	O
and	O
it	O
required	O
special	O
device	B-Application
drivers	I-Application
,	O
unlike	O
single-user	O
multitasking	B-Operating_System
DOS	B-Device
add-ons	O
such	O
as	O
Quarterdeck	O
's	O
DESQview	B-Operating_System
.	O
</s>
<s>
Unlike	O
MP/M	B-Operating_System
,	O
it	O
never	O
became	O
popular	O
for	O
single-user	O
but	O
multitasking	B-Operating_System
use	O
.	O
</s>
<s>
When	O
Novell	O
acquired	O
Digital	O
Research	O
in	O
1991	O
and	O
abandoned	O
Multiuser	O
DOS	B-Device
in	O
1992	O
,	O
the	O
three	O
Master	O
VARs	O
DataPac	O
Australasia	O
,	O
Concurrent	O
Controls	O
and	O
Intelligent	O
Micro	O
Software	O
were	O
allowed	O
to	O
license	O
the	O
source	O
code	O
of	O
the	O
system	O
to	O
take	O
over	O
and	O
continue	O
independent	O
development	O
of	O
their	O
derivations	O
in	O
1994	O
.	O
</s>
<s>
All	O
versions	O
of	O
Digital	O
Research	O
and	O
Novell	O
DR	O
Multiuser	O
DOS	B-Device
reported	O
themselves	O
as	O
"	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
"	O
version	O
3.31	O
.	O
</s>
<s>
In	O
2002	O
the	O
Sydney-based	O
unit	O
was	O
spun	O
out	O
into	O
Citrix	B-Application
 '	O
Advanced	O
Products	O
Group	O
.	O
</s>
<s>
Known	O
CCI	O
Multiuser	O
DOS	B-Device
versions	O
by	O
Concurrent	O
Controls	O
,	O
Inc	O
.	O
(	O
CCI	O
)	O
include	O
:	O
</s>
<s>
All	O
versions	O
of	O
CCI	O
Multiuser	O
DOS	B-Device
report	O
themselves	O
as	O
"	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
"	O
version	O
3.31	O
.	O
</s>
<s>
Similar	O
to	O
SETVER	B-Operating_System
under	O
DOS	B-Device
,	O
this	O
can	O
be	O
changed	O
using	O
the	O
Multiuser	O
DOS	B-Device
utility	O
.	O
</s>
<s>
Known	O
adaptations	O
of	O
IMS	O
Multiuser	O
DOS	B-Device
include	O
:	O
</s>
<s>
All	O
versions	O
of	O
IMS	O
Multiuser	O
DOS	B-Device
report	O
themselves	O
as	O
"	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
"	O
version	O
3.31	O
.	O
</s>
<s>
Intelligent	O
Micro	O
Software	O
Ltd	O
.	O
(	O
IMS	O
)	O
of	O
Thatcham	O
,	O
UK	O
,	O
acquired	O
a	O
license	O
to	O
further	O
develop	O
Multiuser	O
DOS	B-Device
from	O
Novell	O
in	O
1994	O
and	O
renamed	O
their	O
product	O
REAL/32	O
in	O
1995	O
.	O
</s>
<s>
Similar	O
to	O
FlexOS/4690	O
OS	O
before	O
,	O
IBM	O
in	O
1995	O
licensed	O
REAL/32	O
7.50	O
to	O
bundle	O
it	O
with	O
their	O
4695	O
POS	O
terminals	O
.	O
</s>
<s>
REAL/32	O
7.50	O
to	O
7.74	O
report	O
themselves	O
as	O
"	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
"	O
version	O
3.31	O
,	O
whereas	O
7.80	O
and	O
higher	O
report	O
a	O
version	O
of	O
6.20	O
.	O
</s>
<s>
LBA	B-Device
and	O
FAT32	B-Application
support	O
was	O
added	O
with	O
REAL/32	O
7.90	O
in	O
1999	O
.	O
</s>
<s>
REAL/NG	O
promised	O
"	O
increased	O
range	O
of	O
hardware	O
from	O
PCs	O
to	O
x86	B-Operating_System
multi-processor	B-Operating_System
server	B-Application
systems	O
"	O
.	O
</s>
<s>
While	O
the	O
various	O
releases	O
of	O
this	O
operating	B-General_Concept
system	I-General_Concept
had	O
increasing	O
ability	O
to	O
run	O
DOS	B-Device
programs	O
,	O
software	O
written	O
for	O
the	O
platform	O
could	O
take	O
advantage	O
of	O
its	O
features	O
by	O
using	O
function	O
calls	O
specifically	O
suitable	O
for	O
multiuser	O
operation	O
.	O
</s>
<s>
It	O
used	O
pre-emptive	O
multitasking	B-Operating_System
,	O
preventing	O
badly-written	O
applications	O
from	O
delaying	O
other	O
processes	O
by	O
retaining	O
control	O
of	O
the	O
processor	O
.	O
</s>
<s>
To	O
this	O
day	O
,	O
Multiuser	O
DOS	B-Device
is	O
supported	O
by	O
popular	O
SSL/TLS	B-Protocol
libraries	O
such	O
as	O
wolfSSL	B-Protocol
.	O
</s>
<s>
The	O
API	B-General_Concept
provided	O
support	O
for	O
blocking	O
and	O
non-blocking	O
message	B-Operating_System
queues	I-Operating_System
,	O
mutual-exclusion	O
queues	O
,	O
the	O
ability	O
to	O
create	O
sub-process	O
threads	B-Operating_System
which	O
executed	O
independently	O
from	O
the	O
parent	O
,	O
and	O
a	O
method	O
of	O
pausing	O
execution	O
which	O
did	O
not	O
waste	O
processor	O
cycles	O
,	O
unlike	O
idle	O
loops	O
used	O
by	O
single-user	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Applications	O
were	O
started	O
as	O
"	O
attached	O
"	O
to	O
a	O
console	B-Application
.	O
</s>
<s>
However	O
,	O
if	O
an	O
application	O
did	O
not	O
need	O
user	O
interaction	O
it	O
could	O
"	O
detach	O
"	O
from	O
the	O
console	B-Application
and	O
run	O
as	O
a	O
background	B-Operating_System
process	I-Operating_System
,	O
later	O
reattaching	O
to	O
a	O
console	B-Application
if	O
needed	O
.	O
</s>
<s>
Another	O
key	O
feature	O
was	O
that	O
the	O
memory	B-General_Concept
management	I-General_Concept
supported	O
a	O
"	O
shared	O
"	O
memory	B-General_Concept
model	I-General_Concept
for	O
processes	O
(	O
in	O
addition	O
to	O
the	O
usual	O
models	O
available	O
to	O
normal	O
DOS	B-Device
programs	O
)	O
.	O
</s>
<s>
In	O
the	O
shared	O
memory	B-General_Concept
model	I-General_Concept
the	O
"	O
code	O
"	O
and	O
"	O
data	O
"	O
sections	O
of	O
a	O
program	O
were	O
isolated	O
from	O
each	O
other	O
.	O
</s>
<s>
Programs	O
written	O
,	O
or	O
adapted	O
,	O
for	O
any	O
multitasking	B-Operating_System
platform	O
need	O
to	O
avoid	O
the	O
technique	O
used	O
by	O
single-tasking	O
systems	O
of	O
going	O
into	O
endless	O
loops	O
until	O
interrupted	O
when	O
,	O
for	O
example	O
,	O
waiting	O
for	O
a	O
user	O
to	O
press	O
a	O
key	O
;	O
this	O
wasted	O
processor	O
time	O
that	O
could	O
be	O
used	O
by	O
other	O
processes	O
.	O
</s>
<s>
Instead	O
,	O
Concurrent	O
DOS	B-Device
provided	O
an	O
API	B-General_Concept
call	O
which	O
a	O
process	O
could	O
call	O
to	O
"	O
sleep	O
"	O
for	O
a	O
period	O
of	O
time	O
.	O
</s>
<s>
Later	O
versions	O
of	O
the	O
Concurrent	O
DOS	B-Device
kernel	B-Operating_System
included	O
Idle	O
Detection	O
,	O
which	O
monitored	O
DOS	B-Application
API	I-Application
calls	O
to	O
determine	O
whether	O
the	O
application	O
was	O
doing	O
useful	O
work	O
or	O
in	O
fact	O
idle	O
,	O
in	O
which	O
case	O
the	O
process	O
was	O
suspended	O
allowing	O
other	O
processes	O
to	O
run	O
.	O
</s>
<s>
Idle	O
Detection	O
was	O
the	O
catalyst	O
for	O
the	O
patented	O
DR-DOS	B-Application
Dynamic	O
Idle	O
Detection	O
power	O
management	O
feature	O
invented	O
in	O
1989	O
by	O
Roger	O
Alan	O
Gross	O
and	O
John	O
P	O
.	O
Constant	O
and	O
marketed	O
as	O
BatteryMAX	O
.	O
</s>
