<s>
The	O
Machine	O
Operating	B-General_Concept
System	I-General_Concept
(	O
MOS	O
)	O
or	O
OS	O
is	O
a	O
discontinued	O
computer	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
used	O
in	O
Acorn	O
Computers	O
 '	O
BBC	B-Device
computer	I-Device
range	O
.	O
</s>
<s>
It	O
included	O
support	O
for	O
four-channel	O
sound	O
,	O
graphics	O
,	O
file	B-Application
system	I-Application
abstraction	O
,	O
and	O
digital	O
and	O
analogue	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
including	O
a	O
daisy-chained	O
expansion	O
bus	O
.	O
</s>
<s>
The	O
system	O
was	O
single-tasking	O
,	O
monolithic	B-Operating_System
and	O
non-reentrant	O
.	O
</s>
<s>
Versions	O
0.10	O
to	O
1.20	O
were	O
used	O
on	O
the	O
BBC	B-Device
Micro	I-Device
,	O
version	O
1.00	O
on	O
the	O
Electron	B-Device
,	O
version	O
2	O
was	O
used	O
on	O
the	O
B+	O
,	O
and	O
versions	O
3	O
to	O
5	O
were	O
used	O
in	O
the	O
BBC	B-Device
Master	I-Device
series	I-Device
.	O
</s>
<s>
The	O
final	O
BBC	B-Device
computer	I-Device
,	O
the	O
BBC	O
A3000	O
,	O
was	O
32-bit	O
and	O
ran	O
RISC	B-Operating_System
OS	I-Operating_System
,	O
which	O
kept	O
on	O
portions	O
of	O
the	O
Acorn	B-Operating_System
MOS	I-Operating_System
architecture	O
and	O
shared	O
a	O
number	O
of	O
characteristics	O
(	O
e.g.	O
</s>
<s>
"	O
star	O
commands	O
"	O
CLI	B-Application
,	O
"	O
VDU	O
"	O
video	O
control	O
codes	O
and	O
screen	O
modes	O
)	O
with	O
the	O
earlier	O
8-bit	O
MOS	O
.	O
</s>
<s>
Versions	O
0	O
to	O
2	O
of	O
the	O
MOS	O
were	O
16KiB	O
in	O
size	O
,	O
written	O
in	O
6502	B-General_Concept
machine	B-Language
code	I-Language
,	O
and	O
held	O
in	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
on	O
the	O
motherboard	B-Device
.	O
</s>
<s>
The	O
upper	O
quarter	O
of	O
the	O
16-bit	B-Device
address	O
space	O
(	O
0xC000	O
to	O
0xFFFF	O
)	O
is	O
reserved	O
for	O
its	O
ROM	B-Device
code	O
and	O
I/O	B-General_Concept
space	O
.	O
</s>
<s>
Versions	O
3	O
to	O
5	O
were	O
still	O
restricted	O
to	O
a	O
16KiB	O
address	O
space	O
,	O
but	O
managed	O
to	O
hold	O
more	O
code	O
and	O
hence	O
more	O
complex	O
routines	O
,	O
partly	O
because	O
of	O
the	O
alternative	O
65C102	B-General_Concept
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
with	O
its	O
denser	O
instruction	B-General_Concept
set	I-General_Concept
plus	O
the	O
careful	O
use	O
of	O
paging	B-Architecture
.	O
</s>
<s>
The	O
original	O
MOS	O
versions	O
,	O
from	O
0	O
to	O
2	O
,	O
did	O
not	O
have	O
a	O
user	O
interface	O
per	O
se	O
:	O
applications	O
were	O
expected	O
to	O
forward	O
operating	B-General_Concept
system	I-General_Concept
command	B-Application
lines	I-Application
to	O
the	O
OS	O
on	O
its	O
behalf	O
,	O
and	O
the	O
programming	O
language	O
BBC	B-Language
BASIC	I-Language
ROM	B-Device
,	O
with	O
6502	B-General_Concept
assembler	O
built	O
in	O
,	O
supplied	O
with	O
the	O
BBC	B-Device
Micro	I-Device
is	O
the	O
default	O
application	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
The	O
BBC	B-Device
Micro	I-Device
would	O
halt	O
with	O
a	O
Language	O
?	O
</s>
<s>
error	O
if	O
no	O
ROM	B-Device
is	O
present	O
that	O
advertises	O
to	O
the	O
OS	O
an	O
ability	O
to	O
provide	O
a	O
user	O
interface	O
(	O
called	O
language	O
ROMs	O
)	O
.	O
</s>
<s>
MOS	O
version	O
3	O
onwards	O
did	O
feature	O
a	O
simple	O
command-line	B-Application
interface	I-Application
,	O
normally	O
only	O
seen	O
when	O
the	O
CMOS	B-Device
memory	I-Device
did	O
not	O
contain	O
a	O
setting	O
for	O
the	O
default	O
language	O
ROM	B-Device
.	O
</s>
<s>
Application	O
programs	O
on	O
ROM	B-Device
,	O
and	O
some	O
cassette	O
and	O
disc-based	O
software	O
also	O
,	O
typically	O
provide	O
a	O
command	B-Application
line	I-Application
,	O
useful	O
for	O
working	O
with	O
file	B-Application
storage	I-Application
such	O
as	O
browsing	O
the	O
currently	O
inserted	O
disc	O
.	O
</s>
<s>
Cassette	O
and	O
disc	O
based	O
software	O
typically	O
relies	O
on	O
BBC	B-Language
BASIC	I-Language
's	O
own	O
user	O
interface	O
in	O
order	O
to	O
be	O
loaded	O
,	O
although	O
it	O
is	O
possible	O
to	O
configure	O
a	O
floppy	B-Device
disk	I-Device
to	O
boot	O
up	O
without	O
needing	O
to	O
have	O
BASIC	O
commands	O
executed	O
,	O
this	O
was	O
rarely	O
used	O
in	O
practice	O
.	O
</s>
<s>
In	O
BBC	B-Language
BASIC	I-Language
,	O
OS	O
commands	O
are	O
preceded	O
with	O
an	O
asterisk	O
or	O
passed	O
via	O
the	O
OSCLI	O
keyword	O
,	O
to	O
instruct	O
BASIC	O
to	O
forward	O
that	O
command	O
directly	O
to	O
the	O
OS	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
asterisk	O
being	O
the	O
prompt	O
symbol	O
for	O
any	O
software	O
providing	O
an	O
OS	O
command	B-Application
line	I-Application
;	O
MOS	O
version	O
3	O
onwards	O
officially	O
uses	O
the	O
asterisk	O
as	O
the	O
command	O
prompt	O
symbol	O
.	O
</s>
<s>
Unrecognised	O
commands	O
are	O
offered	O
to	O
any	O
service	O
(	O
extension	O
)	O
ROMs	O
;	O
filing	O
system	O
ROMs	O
will	O
often	O
check	O
to	O
see	O
if	O
a	O
file	O
on	O
disc	O
matches	O
that	O
name	O
,	O
the	O
same	O
most	O
other	O
command-line	B-Application
interfaces	I-Application
do	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
call	O
OSWORD	O
with	O
accumulator	O
=	O
0	O
does	O
however	O
offer	O
programs	O
single	O
line	O
input	O
(	O
with	O
ctrl-U	O
for	O
clear	O
line	O
and	O
the	O
cursor	O
copying	O
keys	O
enabled	O
)	O
with	O
basic	O
character	O
filtering	O
and	O
line	O
length	O
limit	O
.	O
</s>
<s>
The	O
MOS	O
command	B-Application
line	I-Application
interpreter	O
features	O
a	O
rather	O
unusual	O
idea	O
:	O
abbreviation	O
of	O
commands	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
MOS	O
would	O
prioritise	O
the	O
command	O
from	O
the	O
ROM	B-Device
in	O
the	O
higher	O
numbered	O
ROM	B-Device
slot	O
,	O
e.g.	O
,	O
7	O
has	O
precedence	O
over	O
6	O
.	O
</s>
<s>
The	O
lower	O
16KiB	O
of	O
the	O
ROM	B-Device
map	O
(	O
0x8000	O
to	O
0xBFFF	O
)	O
is	O
reserved	O
for	O
the	O
active	O
Sideways	B-General_Concept
address	I-General_Concept
space	I-General_Concept
paged	O
bank	O
.	O
</s>
<s>
The	O
Sideways	O
system	O
on	O
the	O
BBC	B-Device
Micro	I-Device
allows	O
for	O
one	O
ROM	B-Device
at	O
a	O
time	O
from	O
sockets	O
on	O
the	O
motherboard	B-Device
(	O
or	O
expansion	O
boards	O
)	O
to	O
be	O
switched	O
into	O
the	O
main	O
memory	O
map	O
.	O
</s>
<s>
Software	O
can	O
be	O
run	O
from	O
ROM	B-Device
this	O
way	O
(	O
leaving	O
the	O
RAM	O
free	O
of	O
user	O
program	O
code	O
,	O
for	O
more	O
workspace	O
)	O
and	O
the	O
OS	O
can	O
be	O
extended	O
by	O
way	O
of	O
such	O
ROMs	O
.	O
</s>
<s>
The	O
most	O
prevalent	O
sideways	O
ROM	B-Device
after	O
BASIC	O
is	O
the	O
Acorn	B-Application
Disc	I-Application
Filing	I-Application
System	I-Application
used	O
to	O
provide	O
floppy	B-Device
disc	I-Device
support	O
to	O
the	O
machine	O
.	O
</s>
<s>
During	O
a	O
reset	O
,	O
every	O
paged	O
ROM	B-Device
is	O
switched	O
in	O
and	O
asked	O
how	O
much	O
public	O
and	O
private	O
workspace	O
it	O
needs	O
.	O
</s>
<s>
Each	O
ROM	B-Device
is	O
allocated	O
a	O
chunk	O
of	O
private	O
workspace	O
that	O
remains	O
allocated	O
at	O
all	O
times	O
,	O
and	O
a	O
single	O
block	O
of	O
public	O
workspace	O
,	O
equal	O
to	O
the	O
size	O
of	O
the	O
largest	O
request	O
,	O
is	O
made	O
available	O
to	O
the	O
active	O
ROM	B-Device
.	O
</s>
<s>
During	O
operation	O
,	O
the	O
paged	O
area	O
is	O
rapidly	O
switched	O
between	O
ROMs	O
when	O
file	B-Application
system	I-Application
commands	O
are	O
issued	O
and	O
unrecognised	O
commands	O
are	O
put	O
to	O
the	O
OS	O
.	O
</s>
<s>
MOS	O
allocates	O
a	O
3.5KiB	O
block	O
of	O
memory	O
(	O
0x0000	O
to	O
0x0DFF	O
)	O
from	O
the	O
bottom	O
of	O
the	O
memory	O
map	O
for	O
operating	B-General_Concept
system	I-General_Concept
and	O
language	O
ROM	B-Device
workspace	O
:	O
</s>
<s>
Address	O
Use	O
0x0000-0x00FF	O
Current	O
language	O
workspace	O
,	O
misc	O
system	O
workspace	O
0x0100-0x01FF	O
CPU	O
stack	O
0x0200-0x02FF	O
OS	O
vectors	O
,	O
system	O
variables	O
,	O
other	O
workspace	O
0x0300-0x03FF	O
VDU	O
driver	O
workspace	O
,	O
cassette	O
system	O
workspace	O
,	O
keyboard	O
input	O
buffer	O
0x0400-0x07FF	O
Allocated	O
to	O
the	O
current	O
language	O
ROM	B-Device
,	O
or	O
to	O
the	O
Tube	B-Device
.	O
</s>
<s>
BASIC	O
uses	O
0x0400-0x046B	O
for	O
the	O
single-letter	O
integer	O
variables	O
@%	O
through	O
Z%	O
(	O
4	O
bytes	O
per	O
letter	O
)	O
,	O
which	O
are	O
thus	O
accessed	O
faster	O
than	O
are	O
variables	O
on	O
the	O
heap	B-General_Concept
.	O
</s>
<s>
0x0800-0x08FF	O
Sound	O
system	O
(	O
stores	O
ADSR	O
envelopes	O
and	O
the	O
tone	O
buffer	O
;	O
if	O
sound	O
is	O
not	O
in	O
use	O
then	O
a	O
small	O
amount	O
of	O
user	O
data	O
can	O
be	O
stored	O
here	O
)	O
,	O
printer	O
buffer	O
,	O
ENVELOPE	O
definitions	O
0x0900-0x09FF	O
Cassette	O
and	O
serial	O
input	O
buffers	O
(	O
user	O
data	O
can	O
be	O
placed	O
here	O
if	O
cassette	O
is	O
not	O
in	O
use	O
,	O
so	O
many	O
small	O
machine	B-Language
code	I-Language
utilities	O
were	O
assembled	O
into	O
page	O
9	O
)	O
0x0A00-0x0AFF	O
Cassette	O
and	O
serial	O
output	O
buffers	O
,	O
also	O
used	O
for	O
small	O
machine	B-Language
code	I-Language
utilities	O
.	O
</s>
<s>
On	O
a	O
cassette-only	O
machine	O
,	O
0x0E00	O
is	O
the	O
start	O
of	O
user	O
program	B-Device
memory	I-Device
.	O
</s>
<s>
With	O
OS	O
extension	O
ROMs	O
fitted	O
such	O
as	O
the	O
a	O
filing	O
system	O
ROM	B-Device
,	O
more	O
memory	O
is	O
allocated	O
above	O
this	O
point	O
;	O
DFS	O
ROMs	O
generally	O
use	O
another	O
2.75KiB	O
to	O
cache	O
the	O
disc	O
catalogue	O
and	O
manage	O
random	O
access	O
buffers	O
.	O
</s>
<s>
A	O
network	O
filing	O
system	O
ROM	B-Device
(	O
for	O
Econet	B-Device
)	O
allocates	O
another	O
0.5KiB	O
on	O
top	O
of	O
this	O
.	O
</s>
<s>
This	O
is	O
a	O
serious	O
problem	O
because	O
MOS	O
does	O
not	O
support	O
relocation	O
of	O
machine	B-Language
code	I-Language
,	O
which	O
must	O
be	O
run	O
from	O
the	O
address	O
at	O
which	O
it	O
was	O
assembled	O
,	O
so	O
some	O
programs	O
which	O
assumed	O
a	O
fixed	O
start	O
of	O
user	O
program	B-Device
memory	I-Device
could	O
overwrite	O
MOS	O
workspace	O
.	O
</s>
<s>
The	O
ASCII	B-Protocol
control	O
characters	O
are	O
almost	O
entirely	O
given	O
new	O
significance	O
under	O
MOS	O
:	O
known	O
as	O
the	O
"	O
VDU	O
drivers	O
"	O
,	O
because	O
the	O
documentation	O
described	O
them	O
in	O
relation	O
to	O
the	O
VDU	O
statement	O
in	O
BBC	B-Language
BASIC	I-Language
,	O
they	O
are	O
interpreted	O
as	O
video	O
control	O
characters	O
.	O
</s>
<s>
ASCII	B-Protocol
30	O
)	O
moves	O
the	O
cursor	O
to	O
(	O
0	O
,	O
0	O
)	O
,	O
VDU	O
4	O
and	O
5	O
select	O
whether	O
text	O
should	O
be	O
drawn	O
at	O
the	O
graphics	O
or	O
text	O
cursor	O
,	O
VDU	O
12	O
clears	O
the	O
screen	O
and	O
VDU	O
14	O
and	O
15	O
turn	O
scroll	O
lock	O
on	O
and	O
off	O
.	O
</s>
<s>
The	O
BBC	B-Language
BASIC	I-Language
VDU	O
statement	O
is	O
equivalent	O
to	O
the	O
conventional	O
BASIC	O
and	O
many	O
of	O
the	O
control	O
codes	O
(	O
such	O
as	O
12	O
for	O
"	O
clear	O
screen	O
"	O
and	O
7	O
for	O
"	O
beep	O
"	O
)	O
have	O
the	O
same	O
functions	O
as	O
on	O
other	O
contemporary	O
machines	O
.	O
</s>
<s>
BBC	B-Language
BASIC	I-Language
contained	O
aliases	O
for	O
the	O
commonly	O
used	O
VDU	O
codes	O
(	O
such	O
as	O
GCOL	O
for	O
VDU	O
18	O
or	O
PLOT	O
for	O
VDU	O
25	O
)	O
.	O
</s>
<s>
This	O
allowed	O
a	O
programmer	O
to	O
allocate	O
a	O
block	O
of	O
memory	O
from	O
BASIC	O
for	O
example	O
to	O
load	O
machine	B-Language
code	I-Language
routines	O
into	O
by	O
lowering	O
the	O
value	O
of	O
HIMEM	O
at	O
the	O
start	O
of	O
a	O
program	O
,	O
and	O
still	O
be	O
free	O
to	O
switch	O
screen	O
modes	O
without	O
deallocating	O
it	O
as	O
a	O
side	O
effect	O
.	O
</s>
<s>
There	O
is	O
one	O
operating	B-General_Concept
system	I-General_Concept
command	O
to	O
write	O
a	O
character	O
,	O
OSWRCH	O
,	O
which	O
is	O
responsible	O
for	O
all	O
text	O
and	O
graphics	O
.	O
</s>
<s>
For	O
example	O
,	O
to	O
move	O
the	O
cursor	O
to	O
(	O
10	O
,	O
15	O
)	O
,	O
needed	O
,	O
in	O
6502	B-General_Concept
assembler	O
:	O
</s>
<s>
BBC	B-Language
BASIC	I-Language
allows	O
performing	O
the	O
above	O
as	O
any	O
of	O
the	O
following	O
:	O
</s>
<s>
Graphics	O
in	O
the	O
Acorn	B-Operating_System
MOS	I-Operating_System
use	O
a	O
virtual	O
graphics	O
resolution	O
of	O
1280×1024	O
,	O
with	O
pixel	O
positions	O
mapped	O
to	O
the	O
nearest	O
equivalent	O
pixel	O
in	O
the	O
current	O
graphics	O
mode	O
.	O
</s>
<s>
The	O
precise	O
code	O
for	O
OSASCI	O
and	O
OSNEWL	O
five	O
lines	O
of	O
6502	B-General_Concept
assembler	O
is	O
documented	O
in	O
the	O
BBC	B-Device
Micro	I-Device
User	O
Guide	O
.	O
</s>
<s>
There	O
are	O
four	O
buffered	O
sound	O
channels	O
three	O
melodic	O
and	O
one	O
noise-based	O
on	O
the	O
sound	O
chip	O
found	O
in	O
the	O
BBC	B-Device
Micro	I-Device
.	O
</s>
<s>
The	O
BBC	B-Device
Micro	I-Device
had	O
support	O
for	O
a	O
second	O
processor	O
connected	O
via	O
the	O
Tube	B-Device
,	O
which	O
allowed	O
direct	O
access	O
to	O
the	O
system	O
bus	O
.	O
</s>
<s>
The	O
driver	O
code	O
for	O
the	O
Tube	B-Device
interface	O
is	O
not	O
held	O
in	O
the	O
MOS	O
,	O
usually	O
being	O
supplied	O
by	O
an	O
external	O
service	O
ROM	B-Device
.	O
</s>
<s>
The	O
OS	O
has	O
calls	O
to	O
handle	O
reading	O
and	O
writing	O
to	O
all	O
I/O	B-General_Concept
(	O
ports	O
and	O
screen	O
memory	O
)	O
and	O
programmers	O
are	O
strongly	O
advised	O
to	O
use	O
these	O
by	O
the	O
Acorn	O
documentation	O
.	O
</s>
<s>
The	O
reason	O
for	O
this	O
is	O
that	O
when	O
a	O
second	O
processor	O
is	O
installed	O
,	O
user	O
software	O
is	O
run	O
from	O
the	O
separate	O
memory	O
map	O
on	O
the	O
far	O
side	O
of	O
the	O
Tube	B-Device
processor	O
bus	O
,	O
and	O
direct	O
access	O
to	O
memory-mapped	O
I/O	B-General_Concept
registers	O
and	O
video	O
memory	O
is	O
impossible	O
.	O
</s>
<s>
However	O
,	O
for	O
the	O
sake	O
of	O
performance	O
,	O
many	O
apps	O
including	O
many	O
games	O
,	O
write	O
directly	O
to	O
main	O
address	O
space	O
for	O
I/O	B-General_Concept
,	O
and	O
hence	O
crash	O
or	O
give	O
a	O
blank	O
screen	O
if	O
a	O
6502	B-General_Concept
second	O
processor	O
is	O
attached	O
.	O
</s>
<s>
One	O
such	O
performance-critical	O
area	O
is	O
sprite	O
support	O
:	O
BBC	B-Device
Micro	I-Device
hardware	O
does	O
not	O
support	O
sprites	O
,	O
and	O
games	O
must	O
implement	O
sprites	O
in	O
software	O
.	O
</s>
<s>
The	O
MOS	O
contains	O
two	O
built-in	O
file	B-Application
systems	I-Application
:	O
cassette	O
and	O
ROM	B-Device
.	O
</s>
<s>
These	O
are	O
quite	O
similar	O
(	O
try	O
,	O
,	O
with	O
a	O
suitable	O
ROM	B-Device
installed	O
)	O
and	O
share	O
a	O
great	O
deal	O
of	O
code	O
.	O
</s>
<s>
They	O
feature	O
a	O
rudimentary	B-Operating_System
copy	I-Operating_System
protection	I-Operating_System
mechanism	I-Operating_System
where	O
a	O
file	O
with	O
a	O
certain	O
flag	O
set	O
cannot	O
be	O
loaded	O
except	O
to	O
execute	O
it	O
.	O
</s>
<s>
The	O
Advanced	O
Disc	B-Application
Filing	I-Application
System	I-Application
(	O
ADFS	O
)	O
,	O
installed	O
as	O
standard	O
in	O
the	O
Master	O
series	O
,	O
has	O
a	O
similar	O
mechanism	O
.	O
</s>
<s>
Versions	O
for	O
the	O
BBC	B-Device
Micro	I-Device
family	O
,	O
starting	O
at	O
0.10	O
and	O
finishing	O
at	O
1.20	O
.	O
</s>
<s>
Confusingly	O
the	O
Electron	B-Device
shipped	O
with	O
version	O
1.00	O
despite	O
being	O
released	O
after	O
the	O
BBC	B-Device
Micro	I-Device
's	O
version	O
1.20	O
,	O
because	O
it	O
was	O
the	O
first	O
release	O
of	O
a	O
ROM	B-Device
for	O
the	O
electron	B-Device
.	O
</s>
<s>
The	O
MOS	O
version	O
number	O
was	O
not	O
intended	O
as	O
an	O
API	O
definition	O
:	O
the	O
Electron	B-Device
ROM	B-Device
was	O
not	O
"	O
based	O
on	O
"	O
the	O
BBC	B-Device
Micro	I-Device
ROM	B-Device
version	O
1.0	O
in	O
any	O
sense	O
.	O
</s>
<s>
MOS	O
3	O
to	O
MOS	O
5	O
shipped	O
with	O
the	O
BBC	B-Device
Master	I-Device
Series	I-Device
systems	O
,	O
in	O
the	O
Master	O
128	O
,	O
Master	O
ET	O
,	O
and	O
Master	O
Compact	O
models	O
respectively	O
.	O
</s>
<s>
The	O
initial	O
release	O
of	O
MOS	O
3	O
expanded	O
upon	O
the	O
facilities	O
provided	O
in	O
MOS	O
2	O
on	O
the	O
B+	O
to	O
support	O
additional	O
hardware	O
,	O
provide	O
a	O
command	B-Application
line	I-Application
facility	O
and	O
extend	O
the	O
VDU	O
driver	O
code	O
with	O
enhanced	O
graphics	O
plotting	O
abilities	O
.	O
</s>
<s>
With	O
the	O
exception	O
of	O
MOS	O
3.50	O
where	O
the	O
space	O
was	O
reclaimed	O
for	O
more	O
code	O
,	O
the	O
area	O
normally	O
hidden	O
by	O
the	O
input/output	B-General_Concept
memory	O
locations	O
(	O
the	O
768	O
bytes	O
from	O
0xFC00-0xFEFF	O
inclusive	O
)	O
in	O
the	O
MOS	O
ROM	B-Device
contained	O
a	O
list	O
of	O
names	O
of	O
contributors	O
to	O
the	O
system	O
.	O
</s>
<s>
This	O
could	O
be	O
recovered	O
by	O
extracting	O
the	O
ROM	B-Device
and	O
reading	O
its	O
contents	O
in	O
an	O
EPROM	O
programmer	O
.	O
</s>
<s>
Those	O
who	O
did	O
not	O
have	O
such	O
a	O
device	O
could	O
access	O
the	O
ROM	B-Device
on	O
a	O
Master	O
by	O
setting	O
a	O
test	O
bit	O
of	O
an	O
access	O
control	O
register	O
,	O
then	O
using	O
a	O
machine-code	O
program	O
to	O
copy	O
the	O
ROM	B-Device
directly	O
to	O
text-mode	O
screen	O
memory	O
.	O
</s>
<s>
"	O
(	O
C	O
)	O
1981	O
Acorn	O
Computers	O
Ltd.Thanks	O
are	O
due	O
to	O
the	O
following	O
contributors	O
to	O
the	O
development	O
of	O
the	O
BBC	B-Device
Computer	I-Device
(	O
among	O
others	O
too	O
numerous	O
to	O
mention	O
)	O
:	O
-	O
David	O
Allen	O
,	O
Bob	O
Austin	O
,	O
Ram	O
Banerjee	O
,	O
Paul	O
Bond	O
,	O
Allen	O
Boothroyd	O
,	O
Cambridge	O
,	O
Cleartone	O
,	O
John	O
Coll	O
,	O
John	O
Cox	O
,	O
Andy	O
Cripps	O
,	O
Chris	O
Curry	O
,	O
6502	B-General_Concept
designers	O
,	O
Jeremy	O
Dion	O
,	O
Tim	O
Dobson	O
,	O
Joe	O
Dunn	O
,	O
Paul	O
Farrell	O
,	O
Ferranti	O
,	O
Steve	O
Furber	O
,	O
Jon	O
Gibbons	O
,	O
Andrew	O
Gordon	O
,	O
Lawrence	O
Hardwick	O
,	O
Dylan	O
Harris	O
,	O
Hermann	O
Hauser	O
,	O
Hitachi	O
,	O
Andy	O
Hopper	O
,	O
ICL	O
,	O
Martin	O
Jackson	O
,	O
Brian	O
Jones	O
,	O
Chris	O
Jordan	O
,	O
David	O
King	O
,	O
David	O
Kitson	O
,	O
Paul	O
Kriwaczek	O
,	O
Computer	O
Laboratory	O
,	O
Peter	O
Miller	O
,	O
Arthur	O
Norman	O
,	O
Glyn	O
Phillips	O
,	O
Mike	O
Prees	O
,	O
John	O
Radcliffe	O
,	O
Wilberforce	O
Road	O
,	O
Peter	O
Robinson	O
,	O
Richard	O
Russell	O
,	O
Kim	O
Spence-Jones	O
,	O
Graham	O
Tebby	O
,	O
Jon	O
Thackray	O
,	O
Chris	O
Turner	O
,	O
Adrian	O
Warner	O
,	O
Roger	O
Wilson	O
,	O
Alan	O
Wright.	O
"	O
</s>
<s>
In	O
interviews	O
in	O
1993	O
and	O
2001	O
,	O
Acorn	O
cofounder	O
Hermann	O
Hauser	O
recounted	O
that	O
Microsoft	O
's	O
Bill	O
Gates	O
,	O
having	O
noticed	O
that	O
1.5	O
million	O
BBC	B-Device
Micros	I-Device
were	O
sold	O
,	O
tried	O
to	O
sell	O
MS-DOS	B-Application
to	O
Acorn	O
,	O
but	O
Hauser	O
considered	O
that	O
adopting	O
MS-DOS	B-Application
would	O
have	O
been	O
a	O
"	O
retrograde	O
step	O
"	O
compared	O
to	O
retaining	O
Acorn	O
's	O
system	O
.	O
</s>
