<s>
IBMBIO.COM	O
is	O
a	O
system	B-General_Concept
file	I-General_Concept
in	O
many	O
DOS	B-Device
operating	O
systems	O
.	O
</s>
<s>
It	O
contains	O
the	O
system	O
initialization	O
code	O
and	O
all	O
built-in	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
It	O
also	O
loads	O
the	O
DOS	B-Device
kernel	O
(	O
IBMDOS.COM	O
)	O
and	O
optional	O
pre-loadable	O
system	O
components	O
(	O
like	O
for	O
disk	B-General_Concept
compression	I-General_Concept
or	O
security	O
)	O
,	O
displays	O
boot	B-Operating_System
menus	I-Operating_System
,	O
processes	O
configuration	O
files	O
(	O
like	O
CONFIG.SYS	B-Device
)	O
and	O
launches	O
the	O
shell	O
(	O
like	O
COMMAND.COM	B-Operating_System
)	O
.	O
</s>
<s>
The	O
file	O
is	O
part	O
of	O
IBM	O
's	O
PC	O
DOS	B-Device
(	O
all	O
versions	O
)	O
as	O
well	O
as	O
of	O
DR	O
DOS	B-Device
5.0	O
and	O
higher	O
(	O
with	O
the	O
exception	O
of	O
DR-DOS	B-Application
7.06	O
)	O
.	O
</s>
<s>
It	O
serves	O
the	O
same	O
purpose	O
as	O
the	O
file	O
IO.SYS	O
in	O
MS-DOS	B-Application
,	O
or	O
DRBIOS.SYS	O
in	O
DR	O
DOS	B-Device
3.31	O
to	O
3.41	O
.	O
</s>
<s>
(	O
For	O
compatibility	O
purposes	O
with	O
some	O
DOS	B-Device
applications	O
the	O
IBMBIO.COM	O
file	O
name	O
was	O
briefly	O
also	O
used	O
by	O
the	O
IBM	O
version	O
of	O
OS/2	O
1.0	O
,	O
where	O
it	O
resembled	O
the	O
OS2BIO.COM	B-Device
file	O
as	O
used	O
by	O
Microsoft	O
.	O
)	O
</s>
<s>
The	O
file	O
is	O
located	O
in	O
the	O
root	B-Application
directory	I-Application
of	O
the	O
bootable	B-Operating_System
FAT-formatted	O
drive/partition	O
(	O
typically	O
C:\	O
)	O
and	O
typically	O
has	O
the	O
system	O
,	O
hidden	O
,	O
and	O
(	O
since	O
DOS	B-Device
2.0	O
also	O
the	O
)	O
read-only	O
file	B-Application
attributes	I-Application
set	O
.	O
</s>
<s>
Under	O
DR-DOS	B-Application
the	O
file	O
may	O
be	O
optionally	O
password-protected	O
as	O
well	O
.	O
</s>
<s>
Under	O
PCDOS	B-Operating_System
,	O
the	O
system	O
attribute	O
is	O
set	O
in	O
order	O
to	O
mark	O
the	O
file	O
as	O
non-movable	O
,	O
a	O
restriction	O
technically	O
not	O
necessary	O
under	O
DR-DOS	B-Application
.	O
</s>
<s>
This	O
is	O
no	O
longer	O
necessary	O
for	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
,	O
because	O
under	O
these	O
systems	O
the	O
file	O
is	O
a	O
fat	B-Application
binary	O
also	O
containing	O
a	O
tiny	O
COM-style	O
stub	O
just	O
displaying	O
some	O
version	O
info	O
and	O
exiting	O
gracefully	O
when	O
not	O
being	O
loaded	O
by	O
a	O
boot	B-Device
sector	I-Device
.	O
</s>
<s>
In	O
the	O
PC	O
bootup	B-Operating_System
sequence	O
,	O
the	O
first	O
sector	O
of	O
the	O
boot	B-Operating_System
volume	O
contains	O
a	O
boot	B-Application
loader	I-Application
called	O
the	O
volume	B-Device
boot	I-Device
record	I-Device
(	O
VBR	B-Device
)	O
and	O
is	O
loaded	O
into	O
memory	O
and	O
executed	O
.	O
</s>
<s>
If	O
this	O
is	O
a	O
VBR	B-Device
of	O
PCDOS	B-Operating_System
before	O
3.3	O
it	O
would	O
load	O
both	O
system	B-General_Concept
files	I-General_Concept
into	O
memory	O
by	O
itself	O
.	O
</s>
<s>
As	O
the	O
PCDOS	B-Operating_System
VBR	B-Device
cannot	O
mount	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
,	O
the	O
system	B-General_Concept
files	I-General_Concept
have	O
to	O
be	O
stored	O
in	O
the	O
first	O
directory	O
entries	O
on	O
the	O
disk	O
and	O
be	O
located	O
at	O
fixed	O
physical	O
positions	O
on	O
the	O
disk	O
stored	O
in	O
consecutive	O
sectors	O
,	O
conditions	O
of	O
which	O
the	O
SYS	B-Language
utility	O
must	O
take	O
care	O
of	O
.	O
</s>
<s>
If	O
the	O
loaded	O
boot	B-Device
sector	I-Device
is	O
a	O
PC	O
DOS	B-Device
3.3	O
(	O
or	O
newer	O
)	O
VBR	B-Device
,	O
the	O
requirements	O
are	O
slightly	O
relaxed	O
.	O
</s>
<s>
The	O
system	B-General_Concept
files	I-General_Concept
still	O
have	O
to	O
be	O
stored	O
in	O
the	O
first	O
two	O
root	B-Application
directory	I-Application
entries	O
on	O
the	O
disk	O
,	O
but	O
the	O
VBR	B-Device
will	O
use	O
only	O
the	O
first	O
entry	O
to	O
load	O
the	O
first	O
three	O
sectors	O
of	O
IBMBIO.COM	O
into	O
memory	O
and	O
transfer	O
control	O
to	O
it	O
.	O
</s>
<s>
This	O
part	O
of	O
IBMBIO.COM	O
then	O
contains	O
a	O
somewhat	O
larger	O
boot	B-Application
loader	I-Application
which	O
:	O
</s>
<s>
Before	O
PC	O
DOS	B-Device
5.0	O
the	O
system	B-General_Concept
files	I-General_Concept
still	O
had	O
to	O
be	O
stored	O
at	O
fixed	O
physical	O
positions	O
on	O
the	O
disk	O
and	O
stored	O
in	O
consecutive	O
sectors	O
.	O
</s>
<s>
Loads	O
the	O
DOS	B-Device
kernel	O
.	O
</s>
<s>
Initializes	O
each	O
default	O
device	B-Application
driver	I-Application
in	O
turn	O
(	O
console	B-Device
,	O
disk	O
,	O
serial	B-Protocol
port	I-Protocol
,	O
et	O
cetera	O
)	O
.	O
</s>
<s>
Calls	O
the	O
DOS	B-Device
kernel	O
's	O
initialization	O
routine	O
.	O
</s>
<s>
Under	O
DR	O
DOS	B-Device
5.0	O
and	O
higher	O
,	O
the	O
first	O
step	O
is	O
skipped	O
,	O
since	O
a	O
DR-DOS	B-Application
VBR	B-Device
is	O
capable	O
of	O
mounting	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
,	O
locate	O
the	O
IBMBIO.COM	O
(	O
or	O
DRBIOS.SYS	O
)	O
file	O
anywhere	O
in	O
the	O
root	B-Application
directory	I-Application
and	O
load	O
it	O
into	O
memory	O
by	O
itself	O
.	O
</s>
<s>
The	O
filename	O
of	O
the	O
IBMBIO.COM	O
file	O
to	O
be	O
loaded	O
by	O
the	O
boot	B-Device
sector	I-Device
is	O
stored	O
in	O
the	O
boot	B-Device
sector	I-Device
rather	O
than	O
necessarily	O
in	O
the	O
first	O
root	B-Application
directory	I-Application
entry	O
,	O
likewise	O
the	O
filename	O
of	O
the	O
IBMDOS.COM	O
file	O
to	O
be	O
loaded	O
by	O
IBMBIO.COM	O
is	O
stored	O
in	O
IBMBIO.COM	O
itself	O
rather	O
than	O
necessarily	O
in	O
the	O
second	O
directory	O
entry	O
on	O
the	O
disk	O
.	O
</s>
<s>
Also	O
,	O
similar	O
to	O
the	O
IBMBIO.COM	O
loader	O
in	O
the	O
VBR	B-Device
,	O
the	O
IBMDOS.COM	O
loader	O
in	O
IBMBIO.COM	O
is	O
capable	O
of	O
rudimentarily	O
mounting	O
the	O
filesystem	O
as	O
well	O
,	O
therefore	O
it	O
is	O
not	O
necessary	O
for	O
the	O
system	B-General_Concept
files	I-General_Concept
to	O
be	O
stored	O
in	O
the	O
first	O
two	O
directory	O
entries	O
,	O
to	O
reside	O
at	O
fixed	O
physical	O
positions	O
or	O
be	O
stored	O
in	O
consecutive	O
sectors	O
.	O
</s>
<s>
Instead	O
,	O
the	O
system	B-General_Concept
files	I-General_Concept
can	O
be	O
simply	O
copied	O
to	O
the	O
disk	O
(	O
without	O
SYS	B-Language
)	O
,	O
given	O
a	O
DR-DOS	B-Application
boot	B-Device
sector	I-Device
already	O
resides	O
on	O
the	O
disk	O
.	O
</s>
<s>
Microsoft	O
sometimes	O
calls	O
this	O
component	O
the	O
I/O	O
system	O
,	O
but	O
it	O
is	O
generally	O
known	O
as	O
DOS	B-Device
BIOS	B-Operating_System
(	O
the	O
DOS-related	O
part	O
of	O
the	O
Basic	B-Operating_System
Input/Output	I-Operating_System
System	I-Operating_System
)	O
.	O
</s>
<s>
The	O
term	O
BIOS	B-Operating_System
was	O
originally	O
coined	O
by	O
Gary	O
Kildall	O
in	O
1975	O
for	O
CP/M	B-Application
,	O
but	O
is	O
also	O
used	O
to	O
describe	O
a	O
similar	O
component	O
or	O
layer	O
in	O
other	O
operating	O
systems	O
by	O
Digital	O
Research	O
,	O
IBM	O
,	O
Microsoft	O
and	O
many	O
others	O
.	O
</s>
<s>
In	O
a	O
more	O
generic	O
sense	O
,	O
some	O
vendors	O
refer	O
to	O
this	O
portion	O
as	O
the	O
RAM	O
BIOS	B-Operating_System
of	O
operating	O
systems	O
such	O
as	O
DOS	B-Device
or	O
CP/M	B-Application
in	O
order	O
to	O
contrast	O
it	O
with	O
the	O
built-in	O
ROM	B-Operating_System
BIOS	I-Operating_System
of	O
a	O
machine	O
.	O
</s>
