<s>
DOS	B-Operating_System
Plus	I-Operating_System
(	O
erroneously	O
also	O
known	O
as	O
DOS+	B-Operating_System
)	O
was	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
developed	O
by	O
Digital	O
Research	O
's	O
OEM	O
Support	O
Group	O
in	O
Newbury	O
,	O
Berkshire	O
,	O
UK	O
,	O
first	O
released	O
in	O
1985	O
.	O
</s>
<s>
DOS	B-Operating_System
Plus	I-Operating_System
1.0	O
was	O
based	O
on	O
CP/M	B-Operating_System
-86	I-Operating_System
Plus	I-Operating_System
combined	O
with	O
the	O
PCMODE	O
emulator	O
from	O
Concurrent	O
PC	O
DOS	B-Device
4.11	O
.	O
</s>
<s>
While	O
CP/M	B-Operating_System
-86	I-Operating_System
Plus	I-Operating_System
and	O
Concurrent	B-Operating_System
DOS	I-Operating_System
4.1	O
still	O
had	O
been	O
developed	O
in	O
the	O
United	O
States	O
,	O
Concurrent	O
PCDOS	O
4.11	O
was	O
an	O
internationalized	O
and	O
bug-fixed	O
version	O
brought	O
forward	O
by	O
Digital	O
Research	O
UK	O
.	O
</s>
<s>
Later	O
DOSPlus	B-Operating_System
2.x	O
issues	O
were	O
based	O
on	O
Concurrent	O
PC	O
DOS	B-Device
5.0	O
instead	O
.	O
</s>
<s>
In	O
the	O
broader	O
picture	O
,	O
DOS	B-Operating_System
Plus	I-Operating_System
can	O
be	O
seen	O
as	O
an	O
intermediate	O
step	O
between	O
Concurrent	B-Operating_System
CP/M	I-Operating_System
-86	I-Operating_System
and	O
DR-DOS	B-Application
.	O
</s>
<s>
DOS	B-Operating_System
Plus	I-Operating_System
is	O
able	O
to	O
run	O
programs	O
written	O
for	O
either	O
CP/M	B-Operating_System
-86	I-Operating_System
or	O
MS-DOS	O
2.11	O
,	O
and	O
can	O
read	O
and	O
write	O
the	O
floppy	O
formats	O
used	O
by	O
both	O
of	O
these	O
systems	O
.	O
</s>
<s>
Up	O
to	O
four	O
CP/M	B-Operating_System
-86	I-Operating_System
programs	O
can	O
be	O
multitasked	B-Operating_System
,	O
but	O
only	O
one	O
DOS	B-Device
program	O
can	O
be	O
run	O
at	O
a	O
time	O
.	O
</s>
<s>
DOS	B-Operating_System
Plus	I-Operating_System
attempts	O
to	O
present	O
the	O
same	O
command-line	B-Application
interface	I-Application
as	O
MS-DOS	O
.	O
</s>
<s>
Like	O
MS-DOS	O
,	O
it	O
has	O
a	O
command-line	B-Application
interpreter	O
called	O
COMMAND.COM	B-Operating_System
(	O
alternative	O
name	O
DOSPLUS.COM	B-Operating_System
)	O
.	O
</s>
<s>
There	O
is	O
an	O
AUTOEXEC.BAT	O
file	O
,	O
but	O
no	O
CONFIG.SYS	B-Device
(	O
except	O
for	O
FIDDLOAD	O
,	O
an	O
extension	O
to	O
load	O
some	O
field-installable	O
device	O
drivers	O
(	O
FIDD	O
)	O
in	O
some	O
versions	O
of	O
DOS	B-Operating_System
Plus	I-Operating_System
2.1	O
)	O
.	O
</s>
<s>
The	O
left-hand	O
side	O
of	O
the	O
status	O
bar	O
shows	O
running	O
processes	B-Operating_System
.	O
</s>
<s>
The	O
right-hand	O
side	O
shows	O
the	O
keyboard	O
layout	O
in	O
use	O
(	O
UK8	O
in	O
the	O
above	O
example	O
)	O
,	O
the	O
printer	O
port	O
assignment	O
,	O
the	O
keyboard	O
Caps	B-Device
Lock	I-Device
and	O
Num	B-Device
Lock	I-Device
status	O
,	O
and	O
the	O
current	O
time	O
.	O
</s>
<s>
If	O
a	O
DOS	B-Device
program	O
is	O
running	O
,	O
the	O
status	O
line	O
is	O
not	O
shown	O
.	O
</s>
<s>
DOS	B-Device
programs	O
cannot	O
be	O
run	O
in	O
the	O
background	O
.	O
</s>
<s>
The	O
keyboard	O
layout	O
in	O
use	O
can	O
be	O
changed	O
by	O
pressing	O
,	O
and	O
one	O
of	O
the	O
function	B-Application
keys	I-Application
–	O
.	O
</s>
<s>
DOSPlus	B-Operating_System
contains	O
a	O
number	O
of	O
extra	O
commands	B-Application
to	O
support	O
its	O
multitasking	B-Operating_System
features	O
:	O
</s>
<s>
BACKG	O
:	O
Allows	O
background	O
processes	B-Operating_System
to	O
be	O
listed	O
and	O
stopped	O
.	O
</s>
<s>
PRINT	B-Device
:	O
Print	B-Device
spooler	O
.	O
</s>
<s>
It	O
also	O
contains	O
subsets	O
of	O
the	O
standard	O
DOS	B-Operating_System
commands	I-Operating_System
and	O
CP/M	O
commands	B-Application
–	O
for	O
example	O
,	O
it	O
has	O
both	O
a	O
built-in	O
COPY	B-Device
command	O
,	O
and	O
a	O
PIP	B-Application
utility	O
,	O
both	O
of	O
which	O
copy	B-Device
files	O
.	O
</s>
<s>
The	O
CD	B-Application
command	O
can	O
assign	O
one	O
of	O
the	O
three	O
drives	O
N	O
:	O
,	O
O	O
:	O
or	O
P	O
:	O
to	O
a	O
directory	O
on	O
a	O
different	O
drive	O
,	O
in	O
a	O
similar	O
manner	O
to	O
the	O
MS-DOS	O
command	O
SUBST	O
.	O
</s>
<s>
This	O
so-called	O
floating	O
drive	O
feature	O
allows	O
old	O
programs	O
which	O
do	O
n't	O
support	O
subdirectories	O
to	O
work	O
under	O
DOS	B-Operating_System
Plus	I-Operating_System
and	O
can	O
be	O
used	O
to	O
make	O
file	O
handling	O
at	O
the	O
command	O
prompt	O
much	O
easier	O
.	O
</s>
<s>
This	O
feature	O
is	O
also	O
present	O
in	O
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
7	O
,	O
and	O
REAL/32	B-Operating_System
,	O
however	O
,	O
these	O
systems	O
extend	O
the	O
concept	O
to	O
all	O
unused	O
drive	O
letters	O
from	O
A	O
:	O
to	O
Z	O
:	O
,	O
except	O
for	O
drive	O
letter	O
L	O
:	O
.	O
</s>
<s>
DR-DOS	B-Application
3.31	O
–	O
6.0	O
(	O
up	O
to	O
the	O
November	O
1992	O
updates	O
with	O
BDOS	B-Operating_System
6.7	O
only	O
)	O
also	O
support	O
this	O
(	O
including	O
drive	O
letter	O
L	O
:	O
)	O
.	O
</s>
<s>
Under	O
the	O
later	O
systems	O
,	O
the	O
4DOS/NDOS	O
command	O
processor	O
supports	O
this	O
features	O
as	O
well	O
.	O
</s>
<s>
Floating	O
drives	O
are	O
implemented	O
in	O
the	O
BDOS	B-Operating_System
kernel	B-Operating_System
,	O
not	O
in	O
the	O
command	B-Application
line	I-Application
shell	O
,	O
thus	O
this	O
feature	O
can	O
also	O
be	O
used	O
from	O
within	O
DOS	B-Device
applications	O
when	O
entering	O
directory	O
paths	O
for	O
as	O
long	O
as	O
the	O
application	O
does	O
not	O
parse	O
and	O
split	O
the	O
dirspec	O
for	O
further	O
processing	O
.	O
</s>
<s>
Using	O
a	O
similar	O
feature	O
,	O
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
and	O
REAL/32	B-Operating_System
will	O
dynamically	O
assign	O
a	O
floating	O
drive	O
L	O
:	O
to	O
the	O
load	O
path	O
of	O
a	O
loaded	O
application	O
,	O
thereby	O
allowing	O
applications	O
to	O
refer	O
to	O
files	O
residing	O
in	O
their	O
load	O
directory	O
under	O
a	O
standardized	O
drive	O
letter	O
instead	O
of	O
under	O
a	O
fixed	O
absolute	O
path	O
.	O
</s>
<s>
(	O
For	O
similar	O
reasons	O
,	O
the	O
appendage	O
to	O
the	O
environment	O
block	O
associated	O
with	O
loaded	O
applications	O
under	O
MS-DOS/PCDOS	O
3.0	O
(	O
and	O
higher	O
)	O
contains	O
a	O
reference	O
to	O
the	O
load	O
path	O
of	O
the	O
executable	O
,	O
however	O
,	O
this	O
consumes	O
more	O
resident	O
memory	O
,	O
and	O
to	O
take	O
advantage	O
of	O
it	O
,	O
support	O
for	O
it	O
must	O
be	O
coded	O
into	O
the	O
executable	O
,	O
whereas	O
DRI	O
's	O
solutions	O
transparently	O
works	O
with	O
any	O
kind	O
of	O
application	O
.	O
)	O
</s>
<s>
Another	O
feature	O
resulting	O
from	O
the	O
BDOS	B-Operating_System
 '	O
internal	O
organization	O
of	O
current	O
working	O
directories	O
as	O
relative	O
links	O
to	O
parent	O
directories	O
is	O
the	O
theoretically	O
unlimited	O
directory	O
depth	O
supported	O
by	O
all	O
those	O
above	O
mentioned	O
operating	B-General_Concept
systems	I-General_Concept
–	O
in	O
contrast	O
to	O
MS-DOS/PC	O
DOS	B-Device
(	O
and	O
DR-DOS	B-Application
since	O
1992	O
)	O
,	O
where	O
an	O
MS-DOS	O
compatible	O
internal	O
data	O
structure	O
named	O
Current	O
Directory	O
Structure	O
(	O
CDS	B-Application
)	O
limits	O
directory	O
depths	O
to	O
a	O
maximum	O
of	O
66	O
characters	O
.	O
</s>
<s>
These	O
features	O
can	O
be	O
attributed	O
to	O
the	O
fact	O
that	O
CP/M	O
itself	O
did	O
not	O
have	O
a	O
concept	O
of	O
subdirectories	O
,	O
and	O
DOS	B-Device
was	O
emulated	O
under	O
these	O
operating	B-General_Concept
systems	I-General_Concept
,	O
so	O
directories	O
had	O
to	O
be	O
translated	O
to	O
internal	O
CP/M	O
structures	O
in	O
some	O
intelligent	O
way	O
.	O
</s>
<s>
DOS	B-Operating_System
Plus	I-Operating_System
boots	O
from	O
a	O
single	O
file	O
called	O
either	O
DOSPLUS.SYS	B-Operating_System
or	O
NETPLUS.SYS	B-Operating_System
(	O
rather	O
than	O
the	O
IO.SYS	O
/	O
MSDOS.SYS	O
combination	O
of	O
MS-DOS	O
)	O
.	O
</s>
<s>
This	O
file	O
is	O
in	O
the	O
CP/M	B-Operating_System
-86	I-Operating_System
CMD	O
format	O
,	O
and	O
is	O
structured	O
internally	O
as	O
a	O
number	O
of	O
modules	O
:	O
</s>
<s>
The	O
BDOS	B-Operating_System
basic	B-Operating_System
disk	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
kernel	B-Operating_System
,	O
which	O
handles	O
multitasking	B-Operating_System
and	O
implements	O
the	O
CP/M	O
API	O
.	O
</s>
<s>
The	O
XIOS	B-Architecture
extended	O
input/output	O
system	O
,	O
which	O
is	O
the	O
machine-dependent	O
component	O
that	O
performs	O
low-level	O
disc	O
and	O
character	O
I/O	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
NETPLUS.SYS	B-Operating_System
with	O
DR	O
Net	O
support	O
.	O
</s>
<s>
The	O
DOS	B-Device
emulator	O
(	O
internally	O
named	O
PCMODE	O
)	O
,	O
which	O
converts	O
each	O
MS-DOS	O
function	O
call	O
into	O
one	O
or	O
more	O
CP/M	O
calls	O
.	O
</s>
<s>
A	O
stub	O
which	O
loads	O
COMMAND.COM	B-Operating_System
(	O
or	O
DOSPLUS.COM	B-Operating_System
)	O
when	O
required	O
.	O
</s>
<s>
This	O
stub	O
contains	O
the	O
string	O
"	O
OS	O
=	O
CPCDOS	O
"	O
,	O
suggesting	O
that	O
it	O
is	O
based	O
on	O
the	O
Concurrent	O
PC	O
DOS	B-Device
codebase	O
.	O
</s>
<s>
DOSPlus	B-Operating_System
was	O
the	O
main	O
operating	B-General_Concept
system	I-General_Concept
in	O
ROM	O
for	O
the	O
Philips	B-Device
:YES	I-Device
,	O
for	O
which	O
it	O
was	O
originally	O
developed	O
.	O
</s>
<s>
The	O
non-IBM	O
PC	O
compatible	O
BBC	B-Device
Master	I-Device
512	I-Device
,	O
came	O
with	O
DOS	B-Operating_System
Plus	I-Operating_System
1.2	O
,	O
1.2a	O
or	O
2.1	O
,	O
also	O
in	O
conjunction	O
with	O
Solidisk	O
's	O
PCPlus	O
memory	O
expansion	O
.	O
</s>
<s>
There	O
were	O
DOSPlus	B-Operating_System
2.1e/g	O
adaptations	O
for	O
the	O
Apricot	O
ACT	O
series	O
 '	O
non-standard	O
315	O
KB	O
and	O
720	O
KB	O
FAT12	B-Application
floppy	O
formats	O
.	O
</s>
<s>
The	O
logical	B-Application
sectored	I-Application
FAT	I-Application
hard	O
disk	O
format	O
(	O
partition	O
type	O
)	O
of	O
Sperry	O
IT	O
PCs	O
,	O
and	O
the	O
80186	B-Device
co-processor	O
boards	O
for	O
the	O
Acorn	O
Archimedes	O
A300	O
and	O
A310	O
as	O
well	O
as	O
Acorn	O
286	O
prototypes	O
were	O
supported	O
as	O
well	O
.	O
</s>
<s>
Known	O
operating	B-General_Concept
system	I-General_Concept
versions	O
include	O
:	O
</s>
<s>
DOSPlus	B-Operating_System
1.0	O
(	O
ROMed	O
in	O
Philips	B-Device
:YES	I-Device
)	O
(	O
with	O
BDOS	B-Operating_System
4.1	O
)	O
.	O
</s>
