<s>
The	O
development	B-Application
of	O
a	O
hobbyist	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
is	O
one	O
of	O
the	O
more	O
involved	O
and	O
technical	O
options	O
for	O
a	O
computer	O
hobbyist	O
.	O
</s>
<s>
The	O
definition	O
of	O
a	O
hobby	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
can	O
sometimes	O
be	O
vague	O
.	O
</s>
<s>
It	O
can	O
be	O
from	O
the	O
developer	B-Application
's	O
view	O
,	O
where	O
the	O
developers	B-Application
do	O
it	O
just	O
for	O
fun	O
or	O
learning	O
;	O
it	O
can	O
also	O
be	O
seen	O
from	O
the	O
user	O
's	O
view	O
,	O
where	O
the	O
users	O
are	O
only	O
using	O
it	O
as	O
a	O
toy	O
;	O
or	O
it	O
can	O
be	O
defined	O
as	O
an	O
operating	B-General_Concept
system	I-General_Concept
which	O
does	O
n't	O
have	O
a	O
very	O
big	O
user	O
base	O
.	O
</s>
<s>
Development	B-Application
can	O
begin	O
from	O
existing	O
resources	O
like	O
a	O
kernel	B-Operating_System
,	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
or	O
a	O
bootloader	B-Application
,	O
or	O
it	O
can	O
also	O
be	O
made	O
completely	O
from	O
scratch	O
.	O
</s>
<s>
The	O
development	B-Application
platform	O
could	O
be	O
a	O
bare	O
hardware	O
machine	O
,	O
which	O
is	O
the	O
nature	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
but	O
it	O
could	O
also	O
be	O
developed	O
and	O
tested	O
on	O
a	O
virtual	O
machine	O
.	O
</s>
<s>
Since	O
the	O
hobbyist	O
must	O
claim	O
more	O
ownership	O
for	O
adapting	O
a	O
complex	O
system	O
to	O
the	O
ever-changing	O
needs	O
of	O
the	O
technical	O
terrain	O
,	O
much	O
enthusiasm	O
is	O
common	O
amongst	O
the	O
many	O
different	O
groups	O
attracted	O
to	O
operating	B-Operating_System
system	I-Operating_System
development	I-Operating_System
.	O
</s>
<s>
Elements	O
of	O
operating	B-Operating_System
system	I-Operating_System
development	I-Operating_System
include	O
:	O
</s>
<s>
Kernel	B-Operating_System
:	O
</s>
<s>
The	O
C	B-Language
programming	I-Language
language	I-Language
is	O
frequently	O
used	O
for	O
hobby	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
programming	O
,	O
as	O
well	O
as	O
assembly	B-Language
language	I-Language
,	O
though	O
other	O
languages	O
can	O
be	O
used	O
as	O
well	O
.	O
</s>
<s>
The	O
use	O
of	O
assembly	B-Language
language	I-Language
is	O
common	O
with	O
small	O
systems	O
,	O
especially	O
those	O
based	O
on	O
eight	O
bit	O
microprocessors	O
such	O
as	O
the	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
family	I-General_Concept
or	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
,	O
or	O
in	O
systems	O
with	O
a	O
lack	O
of	O
available	O
resources	O
because	O
of	O
its	O
small	O
output	O
size	O
and	O
low-level	O
efficiency	O
.	O
</s>
<s>
Most	O
hobby	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
use	O
a	O
command-line	B-Application
interface	I-Application
or	O
a	O
simple	O
text	B-Application
user	I-Application
interface	I-Application
due	O
to	O
ease	O
of	O
development	B-Application
.	O
</s>
<s>
More	O
advanced	O
hobby	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
may	O
have	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
AtheOS	B-Application
was	O
a	O
hobby	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
with	O
a	O
graphical	B-Application
interface	I-Application
written	O
entirely	O
by	O
one	O
programmer	B-Application
.	O
</s>
<s>
This	O
section	O
is	O
predominantly	O
x86	B-Operating_System
oriented	O
.	O
</s>
<s>
The	O
term	O
BIOS	B-Operating_System
(	O
Basic	B-Operating_System
Input/Output	I-Operating_System
System	I-Operating_System
)	O
refers	O
to	O
firmware	B-Application
that	O
initialises	O
computer	O
hardware	O
and	O
has	O
provisions	O
to	O
load	O
an	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
BIOS	B-Operating_System
also	O
sets	O
up	O
a	O
standard	O
interface	O
for	O
several	O
low-level	O
device	B-Application
drivers	I-Application
at	O
boot	O
time	O
.	O
</s>
<s>
BIOS	B-Operating_System
resources	O
are	O
often	O
used	O
by	O
hobbyist	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
especially	O
those	O
written	O
on	O
16-bit	O
x86	B-Operating_System
machines	O
,	O
as	O
many	O
hobby	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
developers	B-Application
lack	O
the	O
time	O
to	O
write	O
complex	O
low	O
level	O
drivers	O
themselves	O
or	O
they	O
simply	O
want	O
to	O
get	O
into	O
writing	O
software	O
for	O
the	O
system	O
as	O
soon	O
as	O
possible	O
.	O
</s>
<s>
The	O
most	O
commonly	O
used	O
BIOS	B-Operating_System
functions	O
are	O
VideoBIOS	B-Device
and	O
Disk	B-Device
services	I-Device
.	O
</s>
<s>
The	O
use	O
of	O
the	O
BIOS	B-Operating_System
is	O
uncommon	O
in	O
operating	B-General_Concept
systems	I-General_Concept
that	O
operate	O
in	O
Protected	B-Application
mode	I-Application
or	O
Long	B-Application
mode	I-Application
,	O
because	O
the	O
system	O
must	O
switch	O
back	O
to	O
real	B-Application
mode	I-Application
which	O
BIOS	B-Operating_System
drivers	O
run	O
in	O
.	O
</s>
