<s>
The	O
Sophisticated	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
,	O
or	O
SOS	B-Operating_System
(	O
)	O
,	O
is	O
the	O
primary	O
operating	B-General_Concept
system	I-General_Concept
of	O
the	O
Apple	B-Device
III	I-Device
computer	O
.	O
</s>
<s>
SOS	B-Operating_System
was	O
developed	O
by	O
Apple	O
Computer	O
and	O
released	O
in	O
October	O
1980	O
.	O
</s>
<s>
In	O
1985	O
,	O
Steve	O
Wozniak	O
,	O
while	O
critical	O
of	O
the	O
Apple	B-Device
III	I-Device
's	O
hardware	O
flaws	O
,	O
called	O
SOS	B-Operating_System
"	O
the	O
finest	O
operating	B-General_Concept
system	I-General_Concept
on	O
any	O
microcomputer	O
ever	O
"	O
.	O
</s>
<s>
SOS	B-Operating_System
is	O
a	O
single-tasking	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
It	O
makes	O
the	O
resources	O
of	O
the	O
Apple	B-Device
III	I-Device
available	O
in	O
the	O
form	O
of	O
a	O
menu-driven	O
utility	O
program	O
as	O
well	O
as	O
a	O
programming	O
application	B-General_Concept
programming	I-General_Concept
interface	I-General_Concept
(	O
API	B-General_Concept
)	O
.	O
</s>
<s>
Once	O
loaded	O
,	O
the	O
interpreter	O
can	O
then	O
use	O
the	O
SOS	B-Operating_System
API	B-General_Concept
to	O
make	O
requests	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
SOS	B-Operating_System
API	B-General_Concept
is	O
divided	O
into	O
four	O
main	O
areas	O
:	O
</s>
<s>
The	O
Apple	B-Device
III	I-Device
System	O
Utilities	O
program	O
shipped	O
with	O
each	O
Apple	B-Device
III	I-Device
computer	O
.	O
</s>
<s>
It	O
provides	O
the	O
user	O
interface	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
itself	O
,	O
for	O
system	O
configuration	O
and	O
file	O
management	O
.	O
</s>
<s>
System	O
Configuration	O
Program	O
(	O
SCP	O
)	O
:	O
configure	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
SOS	B-Operating_System
has	O
two	O
types	O
of	O
devices	O
it	O
communicates	O
with	O
via	O
device	B-Application
drivers	I-Application
:	O
character	O
devices	O
and	O
block	O
devices	O
.	O
</s>
<s>
Examples	O
of	O
SOS	B-Operating_System
character	O
devices	O
are	O
keyboards	O
and	O
serial	O
ports	O
.	O
</s>
<s>
When	O
powered	O
on	O
,	O
the	O
Apple	B-Device
III	I-Device
runs	O
through	O
system	O
diagnostics	O
,	O
then	O
reads	O
block	O
number	O
zero	O
from	O
the	O
built-in	O
diskette	O
drive	O
into	O
memory	O
and	O
executes	O
it	O
.	O
</s>
<s>
SOS-formatted	O
diskettes	O
place	O
a	O
loader	O
program	O
in	O
block	O
zero	O
.	O
</s>
<s>
That	O
loader	O
program	O
searches	O
for	O
,	O
loads	O
,	O
and	O
executes	O
a	O
file	O
named	O
SOS.KERNEL	O
,	O
which	O
is	O
the	O
kernel	B-Operating_System
and	O
API	B-General_Concept
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
kernel	B-Operating_System
,	O
in	O
turn	O
,	O
searches	O
for	O
and	O
loads	O
a	O
file	O
named	O
SOS.INTERP	O
(	O
the	O
interpreter	O
,	O
or	O
program	O
,	O
to	O
run	O
)	O
and	O
SOS.DRIVER	O
,	O
the	O
set	O
of	O
device	B-Application
drivers	I-Application
to	O
use	O
.	O
</s>
<s>
Once	O
all	O
files	O
are	O
loaded	O
,	O
control	O
is	O
passed	O
to	O
the	O
SOS.INTERP	O
program	O
.	O
</s>
<s>
Apple	B-Operating_System
ProDOS	I-Operating_System
uses	O
the	O
same	O
file	O
system	O
as	O
SOS	B-Operating_System
.	O
</s>
<s>
On	O
a	O
disk	O
formatted	O
by	O
ProDOS	B-Operating_System
,	O
the	O
ProDOS	B-Operating_System
loader	O
and	O
SOS	B-Operating_System
loader	O
are	O
written	O
to	O
blocks	O
zero	O
and	O
one	O
,	O
respectively	O
.	O
</s>
<s>
The	O
ProDOS	B-Operating_System
loader	O
includes	O
code	O
that	O
can	O
execute	O
on	O
an	O
Apple	B-Device
III	I-Device
,	O
and	O
which	O
will	O
chainload	O
the	O
SOS	B-Operating_System
loader	O
from	O
block	O
one	O
,	O
so	O
SOS	B-Operating_System
and	O
ProDOS	B-Operating_System
can	O
co-exist	O
on	O
the	O
same	O
volume	O
.	O
</s>
<s>
Some	O
software	O
,	O
such	O
as	O
ADTPro	O
,	O
makes	O
use	O
of	O
this	O
to	O
store	O
Apple	O
II	O
and	O
Apple	B-Device
III	I-Device
versions	O
of	O
a	O
program	O
on	O
the	O
same	O
disk	O
,	O
which	O
is	O
then	O
bootable	O
on	O
both	O
systems	O
.	O
</s>
