<s>
CONFIG.SYS	O
is	O
the	O
primary	O
configuration	B-Protocol
file	I-Protocol
for	O
the	O
DOS	B-Device
and	O
OS/2	B-Application
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
It	O
is	O
a	O
special	O
ASCII	B-Protocol
text	I-Protocol
file	I-Protocol
that	O
contains	O
user-accessible	O
setup	O
or	O
configuration	O
directives	O
evaluated	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
DOS	B-Device
BIOS	B-Operating_System
(	O
typically	O
residing	O
in	O
IBMBIO.COM	O
or	O
IO.SYS	O
)	O
during	O
boot	O
.	O
</s>
<s>
CONFIG.SYS	O
was	O
introduced	O
with	O
DOS	B-Device
2.0	O
.	O
</s>
<s>
The	O
directives	O
in	O
this	O
file	O
configure	O
DOS	B-Device
for	O
use	O
with	O
devices	O
and	O
applications	O
in	O
the	O
system	O
.	O
</s>
<s>
After	O
processing	O
the	O
CONFIG.SYS	O
file	O
,	O
DOS	B-Device
proceeds	O
to	O
load	O
and	O
execute	O
the	O
command	O
shell	O
specified	O
in	O
the	O
SHELL	O
line	O
of	O
CONFIG.SYS	O
,	O
or	O
COMMAND.COM	B-Operating_System
if	O
there	O
is	O
no	O
such	O
line	O
.	O
</s>
<s>
In	O
fact	O
,	O
these	O
will	O
either	O
define	O
some	O
tunable	O
parameters	O
often	O
resulting	O
in	O
reservation	O
of	O
memory	O
,	O
or	O
load	O
files	O
,	O
mostly	O
device	B-Application
drivers	I-Application
and	O
terminate-and-stay-resident	O
programs	O
(	O
TSRs	O
)	O
,	O
into	O
memory	O
.	O
</s>
<s>
In	O
DOS	B-Device
,	O
CONFIG.SYS	O
is	O
located	O
in	O
the	O
root	B-Application
directory	I-Application
of	O
the	O
drive	O
from	O
which	O
the	O
system	O
was	O
booted	O
.	O
</s>
<s>
The	O
filename	O
is	O
also	O
used	O
by	O
(	O
DCP	O
)	O
,	O
an	O
MS-DOS	O
derivative	O
by	O
the	O
former	O
East-German	O
VEB	O
Robotron	O
.	O
</s>
<s>
Some	O
versions	O
of	O
DOS	B-Device
will	O
probe	O
for	O
alternative	O
filenames	O
taking	O
precedence	O
over	O
the	O
default	O
CONFIG.SYS	O
filename	O
if	O
they	O
exist	O
:	O
</s>
<s>
While	O
older	O
versions	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
3.2	O
to	O
4.1	O
did	O
not	O
support	O
CONFIG.SYS	O
files	O
at	O
all	O
,	O
later	O
versions	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
and	O
Concurrent	B-Operating_System
DOS	I-Operating_System
XM	I-Operating_System
,	O
as	O
well	O
as	O
Multiuser	B-Operating_System
DOS	I-Operating_System
,	O
System	O
Manager	O
and	O
REAL/32	B-Operating_System
will	O
probe	O
for	O
CCONFIG.SYS	O
(	O
with	O
"	O
C	O
"	O
derived	O
from	O
"	O
Concurrent	O
"	O
)	O
instead	O
of	O
CONFIG.SYS	O
.	O
</s>
<s>
Some	O
versions	O
of	O
MultiuserDOS	O
use	O
a	O
filename	O
of	O
CCONFIG.INI	O
instead	O
,	O
whereas	O
REAL/32	B-Operating_System
is	O
known	O
to	O
look	O
for	O
MCONFIG.SYS	O
.	O
</s>
<s>
These	O
operating	B-General_Concept
systems	I-General_Concept
support	O
many	O
additional	O
and	O
different	O
configuration	O
settings	O
(	O
like	O
INIT_INSTALL	O
)	O
not	O
known	O
under	O
MS-DOS/PCDOS	O
,	O
but	O
they	O
are	O
stored	O
in	O
the	O
binary	O
repository	O
named	O
CCONFIG.BIN	O
rather	O
than	O
in	O
CCONFIG.INI	O
.	O
</s>
<s>
Since	O
DRDOS6.0	O
this	O
was	O
used	O
in	O
conjunction	O
with	O
disk	O
compression	O
software	O
,	O
where	O
the	O
original	O
boot	O
driveC	O
:	O
would	O
become	O
driveD	O
:	O
after	O
loading	O
the	O
compression	O
driver	O
(	O
and	O
the	O
"	O
D	O
"	O
in	O
the	O
file	O
name	O
came	O
in	O
handy	O
as	O
well	O
)	O
,	O
but	O
it	O
is	O
commonly	O
used	O
to	O
help	O
maintain	O
multiple	O
configuration	B-Protocol
files	I-Protocol
in	O
multi-boot	O
scenarios	O
.	O
</s>
<s>
For	O
example	O
,	O
with	O
SYS	O
/L	O
/DR:703	O
the	O
written	O
Volume	B-Device
Boot	I-Device
Record	I-Device
would	O
look	O
for	O
a	O
renamed	O
and	O
modified	O
IBMBIO.703	O
system	O
file	O
(	O
instead	O
of	O
the	O
default	O
IBMBIO.COM	O
)	O
and	O
the	O
IBMBIO.703	O
would	O
look	O
for	O
IBMDOS.703	O
and	O
[D]CONFIG.703	O
(	O
instead	O
of	O
IBMDOS.COM	O
and	O
[D]CONFIG.SYS	O
)	O
,	O
so	O
that	O
multiple	O
parallel	O
sets	O
of	O
files	O
can	O
coexist	O
in	O
the	O
same	O
root	B-Application
directory	I-Application
and	O
be	O
selected	O
via	O
a	O
boot-loader	O
like	O
LOADER	O
,	O
supplied	O
with	O
Multiuser	B-Operating_System
DOS	I-Operating_System
and	O
DR-DOS	O
7.02/7.03	O
.	O
</s>
<s>
The	O
SHELL	O
directive	O
is	O
enhanced	O
to	O
provide	O
means	O
to	O
specify	O
alternative	O
AUTOEXEC.BAT	O
files	O
via	O
/P[:filename.ext]	O
and	O
in	O
this	O
specific	O
scenario	O
,	O
COMMAND.COM	B-Operating_System
will	O
accept	O
file	O
extensions	O
other	O
than	O
"	O
.BAT	O
"	O
as	O
well	O
(	O
both	O
features	O
are	O
also	O
supported	O
by	O
4DOS	B-Application
)	O
.	O
</s>
<s>
Under	O
DRDOS6.0	O
and	O
higher	O
,	O
the	O
CONFIG.SYS	O
directive	O
CHAIN	O
=	O
filespec	O
can	O
be	O
used	O
to	O
continue	O
processing	O
in	O
the	O
named	O
file	O
,	O
which	O
does	O
not	O
necessarily	O
need	O
to	O
reside	O
in	O
the	O
root	B-Application
directory	I-Application
of	O
the	O
boot	O
drive	O
.	O
</s>
<s>
DR-DOS	O
7.03	O
and	O
higher	O
support	O
a	O
new	O
SYS	O
/A	O
parameter	O
in	O
order	O
to	O
copy	O
the	O
corresponding	O
CONFIG.SYS	O
and	O
AUTOEXEC.BAT	O
files	O
along	O
with	O
the	O
system	O
files	O
.	O
</s>
<s>
FreeDOS	B-Application
implements	O
a	O
similar	O
feature	O
with	O
its	O
FDCONFIG.SYS	O
configuration	B-Protocol
file	I-Protocol
.	O
</s>
<s>
PTS-DOS	B-Operating_System
uses	O
CONFIG.PTS	O
.	O
</s>
<s>
Both	O
CONFIG.SYS	O
and	O
AUTOEXEC.BAT	O
can	O
be	O
found	O
included	O
in	O
the	O
root	B-Application
folder	I-Application
of	O
Windows	O
95	O
,	O
and	O
Windows	O
98	O
boot	O
drives	O
,	O
as	O
they	O
are	O
based	O
on	O
DOS	B-Device
.	O
</s>
<s>
Windows	O
ME	O
does	O
not	O
even	O
parse	O
the	O
CONFIG.SYS	O
file	O
during	O
the	O
Windows	O
boot	O
process	O
,	O
loading	O
environment	O
variables	O
from	O
the	O
Windows	B-Protocol
Registry	I-Protocol
instead	O
:	O
</s>
<s>
Under	O
FlexOS	B-Operating_System
,	O
CONFIG.SYS	O
is	O
a	O
binary	O
file	O
defining	O
the	O
resource	O
managers	O
and	O
device	B-Application
drivers	I-Application
loaded	O
.	O
</s>
<s>
(	O
Under	O
MS-DOS/PCDOS	O
the	O
inline-comment	O
is	O
not	O
ignored	O
if	O
put	O
in	O
double-quotes	O
.	O
)	O
</s>
<s>
(	O
FreeDOS	B-Application
does	O
not	O
support	O
optional	O
messages	O
,	O
but	O
optional	O
conditions	O
in	O
conjunction	O
with	O
boot	O
menus	O
defined	O
with	O
and	O
.	O
)	O
</s>
<s>
(	O
DOS	B-Device
6.0	O
and	O
higher	O
supports	O
a	O
similar	O
feature	O
by	O
adding	O
a	O
after	O
the	O
corresponding	O
CONFIG.SYS	O
directive	O
,	O
f.e.	O
</s>
<s>
Configures	O
which	O
drives	O
should	O
store	O
file	O
access	O
date	O
stamps	O
in	O
the	O
reserved	O
area	O
of	O
directory	O
entries	O
in	O
FAT	B-Application
file	I-Application
systems	I-Application
.	O
</s>
<s>
Changes	O
internal	O
default	O
serial	O
device	B-Application
driver	I-Application
(	O
to	O
)	O
for	O
device	O
.	O
</s>
<s>
Loads	O
base	O
device	B-Application
driver	I-Application
into	O
memory	O
.	O
</s>
<s>
Specifies	O
operating	B-General_Concept
system	I-General_Concept
to	O
be	O
booted	O
.	O
</s>
<s>
Same	O
as	O
,	O
but	O
explicitly	O
loads	O
buffers	O
into	O
HMA	O
or	O
UMB	O
(	O
like	O
under	O
DR	O
DOS	B-Device
6.0	O
and	O
higher	O
)	O
.	O
</s>
<s>
Similar	O
to	O
under	O
DOS	B-Device
,	O
loads	O
programs	O
in	O
CONFIG.SYS	O
.	O
</s>
<s>
Similar	O
to	O
under	O
OS/2	B-Application
,	O
but	O
runs	O
in	O
foreground	O
and	O
halts	O
CONFIG.SYS	O
processing	O
until	O
return	O
.	O
</s>
<s>
Specifies	O
the	O
name	O
of	O
the	O
CD-ROM	O
hardware	B-Application
driver	I-Application
.	O
</s>
<s>
Continues	O
CONFIG.SYS	O
processing	O
in	O
new	O
file	O
and	O
(	O
since	O
DR-DOS	O
7.02	O
)	O
at	O
optional	O
label	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
COM1	B-Architecture
:	O
device	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
COM2	B-Device
:	O
device	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
COM3	B-Device
:	O
device	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
COM4	B-Device
:	O
device	O
.	O
</s>
<s>
Loads	O
a	O
device	B-Application
driver	I-Application
into	O
memory	O
.	O
</s>
<s>
Loads	O
a	O
device	B-Application
driver	I-Application
into	O
upper	O
memory	O
.	O
</s>
<s>
Configures	O
country	O
and	O
codepage	O
information	O
for	O
KBD	O
,	O
SCR	O
,	O
LPT1	B-Device
,	O
LPT2	B-Device
,	O
LPT3	B-Device
devices	O
.	O
</s>
<s>
Specifies	O
whether	O
to	O
load	O
DOS	B-Device
into	O
the	O
high	O
memory	O
area	O
and/or	O
use	O
upper	O
memory	O
.	O
</s>
<s>
Specifies	O
whether	O
to	O
load	O
DOS	B-Device
tables	O
(	O
,	O
,	O
,	O
,	O
)	O
into	O
upper	O
memory	O
.	O
</s>
<s>
Specifies	O
alternative	O
path	O
to	O
search	O
for	O
DOS	B-Device
files	O
.	O
</s>
<s>
Works	O
considerably	O
differently	O
from	O
the	O
external	O
MS-DOS/PCDOS	O
FASTOPEN	B-Application
driver	O
.	O
</s>
<s>
Specifies	O
the	O
number	O
of	O
cached	O
FCBs	B-Operating_System
that	O
can	O
be	O
opened	O
at	O
once	O
.	O
</s>
<s>
(	O
Under	O
DR-DOS	O
,	O
and	O
dynamically	O
share	O
the	O
same	O
internal	O
buffer	O
.	O
)	O
</s>
<s>
Same	O
as	O
,	O
but	O
explicitly	O
loads	O
FCBs	B-Operating_System
into	O
upper	O
memory	O
.	O
</s>
<s>
Waits	O
for	O
key	O
(	O
or	O
timeout	O
)	O
and	O
sets	O
error	O
level	O
to	O
its	O
ASCII	B-Protocol
code	I-Protocol
(	O
or	O
1024	O
on	O
timeout	O
)	O
.	O
</s>
<s>
Installs	O
a	O
TSR	O
program	O
into	O
memory	O
,	O
like	O
,	O
but	O
installs	O
after	O
the	O
DOS	B-Device
data	O
segment	O
relocation	O
.	O
</s>
<s>
Loads	O
installable	B-Application
file	I-Application
systems	I-Application
.	O
</s>
<s>
Specifies	O
programs	O
(	O
which	O
would	O
normally	O
run	O
at	O
the	O
CPU	O
's	O
IOPL	B-Device
ring	B-Operating_System
3	I-Operating_System
)	O
which	O
should	O
be	O
allowed	O
to	O
run	O
at	O
ring	B-Operating_System
2	I-Operating_System
in	O
order	O
to	O
directly	O
access	O
the	O
hardware	O
for	O
I/O	O
.	O
</s>
<s>
(	O
Can	O
be	O
emulated	O
using	O
and	O
under	O
DR-DOS	O
.	O
)	O
</s>
<s>
(	O
Same	O
as	O
in	O
DR	O
DOS	B-Device
5.0	O
.	O
)	O
</s>
<s>
Installs	O
a	O
TSR	O
program	O
into	O
memory	O
,	O
like	O
,	O
but	O
installs	O
after	O
the	O
DOS	B-Device
data	O
segment	O
relocation	O
.	O
</s>
<s>
Configures	O
boot	O
logo	O
support	O
under	O
MS-DOS	O
.	O
</s>
<s>
Allows	O
to	O
display	O
startup	O
message	O
in	O
conjunction	O
with	O
PTS-DOS	B-Operating_System
boot	O
manager	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
LPT1	B-Device
:	O
device	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
LPT2	B-Device
:	O
device	O
.	O
</s>
<s>
Defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
LPT3	B-Device
:	O
device	O
.	O
</s>
<s>
Enables	O
,	O
defines	O
count	O
and	O
logical	O
order	O
and	O
configures	O
I/O	B-Architecture
address	I-Architecture
and	O
timeout	O
for	O
LPT4	B-Device
:	O
device	O
.	O
</s>
<s>
Specifies	O
the	O
default	O
DOS	B-Device
memory	O
allocation	O
strategy	O
.	O
</s>
<s>
(	O
Can	O
be	O
emulated	O
using	O
under	O
DR-DOS	O
.	O
)	O
</s>
<s>
(	O
Can	O
be	O
emulated	O
using	O
and	O
under	O
DR-DOS	O
.	O
)	O
</s>
<s>
(	O
Can	O
be	O
emulated	O
using	O
and	O
under	O
DR-DOS	O
.	O
)	O
</s>
<s>
Continues	O
CONFIG.SYS	O
processing	O
in	O
new	O
file	O
(	O
similar	O
to	O
DR-DOS	O
CHAIN	O
)	O
and	O
optionally	O
after	O
loading	O
a	O
specific	O
device	B-Application
driver	I-Application
and	O
setting	O
%NEWFILE%	O
environment	O
variable	O
.	O
</s>
<s>
Similar	O
to	O
and	O
under	O
DR-DOS	O
,	O
displays	O
a	O
text	O
and	O
waits	O
for	O
a	O
key	O
press	O
.	O
</s>
<s>
Configures	O
buffer	O
size	O
for	O
LPT1	B-Device
,	O
LPT2	B-Device
,	O
LPT3	B-Device
.	O
</s>
<s>
Changes	O
internal	O
default	O
printer	O
device	B-Application
driver	I-Application
(	O
to	O
,	O
or	O
even	O
)	O
for	O
PRN	O
device	O
.	O
</s>
<s>
Specifies	O
if	O
DOS	B-Device
programs	O
can	O
be	O
run	O
or	O
not	O
.	O
</s>
<s>
Conditional	O
execution	O
on	O
PS/1	B-Device
-compatible	O
machines	O
only	O
.	O
</s>
<s>
Conditional	O
execution	O
on	O
PS/2	B-Device
-compatible	O
machines	O
only	O
.	O
</s>
<s>
Specifies	O
a	O
drive	O
letter	O
not	O
to	O
be	O
used	O
up	O
for	O
local	O
block	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
Similar	O
to	O
under	O
DOS	B-Device
and	O
under	O
OS/2	B-Application
,	O
but	O
loads	O
programs	O
in	O
background	O
concurrently	O
.	O
</s>
<s>
Specifies	O
,	O
if	O
the	O
first	O
character	O
of	O
deleted	O
files	O
should	O
be	O
stored	O
in	O
the	O
reserved	O
area	O
of	O
directory	O
entries	O
in	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
Similar	O
to	O
under	O
PTS-DOS	B-Operating_System
,	O
specifies	O
the	O
video	O
mode	O
to	O
be	O
used	O
under	O
FreeDOS	B-Application
.	O
</s>
<s>
Under	O
PTS-DOS	B-Operating_System
,	O
does	O
not	O
specify	O
the	O
video	O
mode	O
but	O
screen	O
access	O
methods	O
.	O
</s>
<s>
Same	O
as	O
,	O
but	O
supports	O
an	O
additional	O
parameter	O
to	O
define	O
the	O
size	O
of	O
the	O
pre-allocation	O
for	O
COMMAND.COM	B-Operating_System
to	O
relocate	O
its	O
resident	O
portion	O
into	O
the	O
HMA	O
(	O
with	O
/MH	O
)	O
.	O
</s>
<s>
SHELLHIGH	O
under	O
PTS-DOS	B-Operating_System
tries	O
to	O
load	O
the	O
shell	O
into	O
UMBs	O
instead	O
.	O
)	O
</s>
<s>
Specifies	O
the	O
state	O
of	O
the	O
keyboard	O
modifiers	O
like	O
Shift	O
Lock	O
,	O
Num	B-Device
Lock	I-Device
,	O
Scroll	B-Device
Lock	I-Device
or	O
Insert	O
mode	O
.	O
</s>
<s>
Specifies	O
if	O
POST	B-Device
should	O
be	O
skipped	O
on	O
reboots	O
.	O
</s>
<s>
Compatibility	O
dummy	O
-	O
DR	O
DOS	B-Device
3.31	O
-	O
6.0	O
were	O
mostly	O
reentrant	O
and	O
had	O
a	O
different	O
stacks	B-Device
layout	O
.	O
</s>
<s>
Specifies	O
the	O
number	O
of	O
stacks	B-Device
for	O
hardware	O
interrupts	O
.	O
</s>
<s>
Default	O
stack	B-Device
size	O
allocated	O
for	O
new	O
threads	O
.	O
</s>
<s>
(	O
Can	O
be	O
emulated	O
using	O
,	O
and	O
under	O
DR-DOS	O
.	O
)	O
</s>
<s>
Defines	O
the	O
default	O
SwitChar	B-Device
used	O
by	O
the	O
system	O
(	O
either	O
'	O
/	O
'	O
or	O
'	O
-	O
'	O
)	O
.	O
</s>
<s>
Specifies	O
file	O
name	O
of	O
alternative	O
DOS	B-Device
operating	B-General_Concept
systems	I-General_Concept
to	O
boot	O
.	O
</s>
<s>
Configures	O
the	O
location	O
of	O
the	O
various	O
DOS	B-Device
parts	O
in	O
memory	O
.	O
</s>
<s>
Specifies	O
if	O
DOS	B-Device
data	O
and	O
code	O
should	O
be	O
loaded	O
into	O
UMBs	O
.	O
</s>
<s>
PTS-DOS	B-Operating_System
only	O
supports	O
the	O
timeout	O
value	O
.	O
</s>
<s>
The	O
functionality	O
under	O
OS/2	B-Application
differs	O
significantly	O
from	O
that	O
under	O
DOS	B-Device
.	O
</s>
<s>
Configures	O
DOS	B-Device
management	O
to	O
use	O
a	O
specific	O
segment	O
as	O
UMB	O
memory	O
.	O
</s>
<s>
Specifies	O
the	O
DOS	B-Device
version	O
(	O
and	O
optionally	O
the	O
true	O
DOS	B-Device
version	O
)	O
to	O
be	O
reported	O
to	O
programs	O
.	O
</s>
<s>
Similar	O
to	O
under	O
FreeDOS	B-Application
,	O
specifies	O
current	O
video	O
mode	O
.	O
</s>
<s>
Configures	O
the	O
built-in	O
Year	B-Error_Name
2000	I-Error_Name
support	O
.	O
</s>
<s>
However	O
,	O
this	O
file	O
,	O
along	O
with	O
AUTOEXEC.BAT	O
,	O
is	O
essential	O
for	O
the	O
complete	O
bootup	O
process	O
to	O
occur	O
with	O
the	O
DOS	B-Device
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
These	O
files	O
contain	O
information	O
that	O
is	O
used	O
to	O
customize	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
personal	O
use	O
.	O
</s>
<s>
A	O
DOS	B-Device
system	O
would	O
require	O
troubleshooting	O
if	O
either	O
of	O
these	O
files	O
became	O
damaged	O
or	O
corrupted	O
.	O
</s>
<s>
If	O
CONFIG.SYS	O
does	O
not	O
contain	O
a	O
SHELL	O
directive	O
(	O
or	O
the	O
file	O
is	O
corrupt	O
or	O
missing	O
)	O
,	O
DOS	B-Device
typically	O
searches	O
for	O
COMMAND.COM	B-Operating_System
in	O
the	O
root	B-Application
directory	I-Application
of	O
the	O
boot	O
drive	O
.	O
</s>
<s>
If	O
this	O
is	O
not	O
found	O
,	O
versions	O
of	O
DOS	B-Device
before	O
6.0	O
will	O
not	O
start	O
up	O
.	O
</s>
<s>
MS-DOS	O
6.0/PCDOS	O
6.1	O
and	O
Novell	O
DOS	B-Device
7	O
and	O
higher	O
will	O
instead	O
display	O
a	O
prompt	O
to	O
enter	O
the	O
path	O
and	O
filename	O
of	O
a	O
command	O
processor	O
.	O
</s>
<s>
(	O
In	O
the	O
case	O
of	O
COMMAND.COM	B-Operating_System
,	O
the	O
internal	O
EXIT	O
command	O
is	O
disabled	O
only	O
when	O
the	O
shell	O
was	O
started	O
with	O
/P	O
.	O
)	O
</s>
<s>
This	O
also	O
provides	O
limited	O
means	O
to	O
replace	O
the	O
shell	O
at	B-Library
runtime	I-Library
without	O
having	O
to	O
reboot	O
the	O
system	O
.	O
</s>
<s>
Since	O
the	O
MS-DOS	B-Application
7.0	I-Application
and	O
higher	O
COMMAND.COM	B-Operating_System
executable	O
is	O
incompatible	O
with	O
DR-DOS	O
,	O
but	O
typically	O
resides	O
in	O
the	O
root	O
of	O
drive	O
C	O
:	O
in	O
dual-boot	O
scenarios	O
with	O
DR-DOS	O
,	O
DR-DOS	O
7.02	O
and	O
higher	O
no	O
longer	O
allow	O
to	O
bypass	O
SHELL	O
directives	O
in	O
( +	O
)	O
//	O
"	O
skip	O
"	O
/	O
"	O
trace	O
"	O
/	O
"	O
step	O
"	O
modes	O
.	O
</s>
<s>
Also	O
,	O
if	O
no	O
SHELL	O
directive	O
could	O
be	O
found	O
when	O
skipping	O
CONFIG.SYS	O
processing	O
via	O
( +	O
)	O
(	O
and	O
also	O
with	O
( +	O
)	O
/	O
,	O
when	O
the	O
default	O
file	O
extension	O
has	O
been	O
changed	O
with	O
SYS	O
/DR:ext	O
)	O
,	O
the	O
user	O
is	O
prompted	O
to	O
enter	O
a	O
valid	O
shell	O
file	O
name	O
before	O
trying	O
to	O
load	O
COMMAND.COM	B-Operating_System
from	O
the	O
root	O
.	O
</s>
<s>
Depending	O
on	O
the	O
version	O
,	O
the	O
size	O
of	O
the	O
CONFIG.SYS	O
file	O
is	O
limited	O
to	O
a	O
few	O
kilobytes	O
under	O
MS-DOS/PCDOS	O
(	O
up	O
to	O
64KB	O
in	O
most	O
recent	O
versions	O
)	O
,	O
whereas	O
the	O
file	O
's	O
size	O
is	O
unlimited	O
under	O
DR-DOS	O
.	O
</s>
<s>
This	O
is	O
because	O
the	O
former	O
operating	B-General_Concept
systems	I-General_Concept
(	O
since	O
DOS	B-Device
3.0	O
)	O
will	O
compile	O
the	O
file	O
into	O
some	O
tokenized	O
in-memory	O
representation	O
before	O
they	O
sort	O
and	O
regroup	O
the	O
directives	O
to	O
be	O
processed	O
in	O
a	O
specific	O
order	O
(	O
with	O
device	B-Application
drivers	I-Application
always	O
being	O
loaded	O
before	O
TSRs	O
)	O
,	O
whereas	O
DR-DOS	O
interprets	O
the	O
file	O
and	O
executes	O
most	O
directives	O
line-by-line	O
,	O
thereby	O
giving	O
full	O
control	O
over	O
the	O
load	O
order	O
of	O
drivers	O
and	O
TSRs	O
via	O
DEVICE	O
and	O
INSTALL	O
(	O
for	O
example	O
to	O
solve	O
load	O
order	O
conflicts	O
or	O
to	O
load	O
a	O
program	O
debugger	O
before	O
a	O
device	B-Application
driver	I-Application
to	O
be	O
debugged	O
)	O
and	O
allowing	O
to	O
adapt	O
the	O
user	O
interaction	O
and	O
change	O
the	O
flow	O
through	O
the	O
file	O
based	O
on	O
conditions	O
like	O
processor	O
types	O
installed	O
,	O
any	O
type	O
of	O
keys	O
pressed	O
,	O
load	O
or	O
input	O
errors	O
occurring	O
,	O
or	O
return	O
codes	O
given	O
by	O
loaded	O
software	O
.	O
</s>
<s>
This	O
becomes	O
particularly	O
useful	O
since	O
INSTALL	O
can	O
also	O
be	O
used	O
to	O
run	O
non-resident	O
software	O
under	O
DR-DOS	O
,	O
so	O
that	O
temporary	O
external	O
programs	O
can	O
be	O
integrated	O
into	O
the	O
CONFIG.SYS	O
control	O
flow	O
.	O
</s>
<s>
In	O
MS-DOS/PCDOS	O
2.0	O
through	O
4.01	O
,	O
the	O
length	O
of	O
the	O
SHELL	O
line	O
was	O
limited	O
to	O
31	O
characters	O
,	O
whereas	O
up	O
to	O
128	O
characters	O
are	O
possible	O
in	O
later	O
versions	O
.	O
</s>
<s>
DR-DOS	O
even	O
accepts	O
up	O
to	O
255	O
characters	O
.	O
</s>
<s>
When	O
installing	O
Windows	O
95	O
over	O
a	O
preexisting	O
DOS/Windows	O
install	O
,	O
CONFIG.SYS	O
and	O
AUTOEXEC.BAT	O
are	O
renamed	O
to	O
CONFIG.DOS	O
and	O
AUTOEXEC.DOS	O
.	O
</s>
<s>
This	O
is	O
intended	O
to	O
ease	O
dual	O
booting	O
between	O
Windows9x	O
and	O
DOS	B-Device
.	O
</s>
<s>
When	O
booting	O
into	O
DOS	B-Device
,	O
they	O
are	O
temporarily	O
renamed	O
CONFIG.SYS	O
and	O
AUTOEXEC.BAT	O
.	O
</s>
<s>
Backups	O
of	O
the	O
Windows95	B-Application
versions	O
are	O
made	O
as	O
CONFIG.W40	O
and	O
AUTOEXEC.W40	O
files	O
.	O
</s>
<s>
When	O
Caldera	O
DR-DOS	O
7.02/7.03	O
is	O
installed	O
on	O
a	O
system	O
already	O
containing	O
Windows95	B-Application
,	O
Windows	O
 '	O
CONFIG.SYS	O
and	O
AUTOEXEC.BAT	O
retain	O
those	O
names	O
.	O
</s>
<s>
DR-DOS	O
'	O
startup	O
files	O
are	O
installed	O
as	O
DCONFIG.SYS	O
(	O
a	O
name	O
already	O
used	O
in	O
earlier	O
versions	O
of	O
DR	O
DOS	B-Device
)	O
and	O
AUTODOS7.BAT	O
.	O
</s>
<s>
OS/2	B-Application
uses	O
the	O
CONFIG.SYS	O
file	O
extensively	O
for	O
setting	O
up	O
its	O
configuration	O
,	O
drivers	O
and	O
environment	O
before	O
the	O
graphical	O
part	O
of	O
the	O
system	O
loads	O
.	O
</s>
<s>
In	O
the	O
OS/2	B-Application
subsystem	O
of	O
Windows	B-Device
NT	I-Device
,	O
what	O
appeared	O
as	O
CONFIG.SYS	O
to	O
OS/2	B-Application
programs	O
was	O
actually	O
stored	O
in	O
the	O
registry	O
.	O
</s>
<s>
There	O
are	O
many	O
undocumented	O
or	O
poorly	O
documented	O
CONFIG.SYS	O
directives	O
used	O
by	O
OS/2	B-Application
.	O
</s>
<s>
CONFIG.SYS	O
continues	O
to	O
be	O
used	O
by	O
the	O
OS/2	B-Application
derivatives	O
eComStation	B-Device
and	O
ArcaOS	B-Device
.	O
</s>
