<s>
RISC	B-Operating_System
OS	I-Operating_System
,	O
the	O
computer	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
developed	O
by	O
Acorn	O
Computers	O
for	O
their	O
ARM-based	O
Acorn	B-Device
Archimedes	I-Device
range	O
,	O
was	O
originally	O
released	O
in	O
1987	O
as	O
,	O
and	O
soon	O
followed	O
by	O
,	O
and	O
.	O
</s>
<s>
By	O
1996	O
RISC	B-Operating_System
OS	I-Operating_System
had	O
been	O
shipped	O
on	O
over	O
500,000	O
systems	O
.	O
</s>
<s>
was	O
released	O
by	O
RISCOS	B-Operating_System
Ltd	O
(	O
ROL	O
)	O
in	O
July	O
1999	O
,	O
based	O
on	O
the	O
continued	O
development	O
of	O
.	O
</s>
<s>
ROL	O
had	O
in	O
March	O
1999	O
licensed	O
the	O
rights	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
Element	O
14	O
(	O
the	O
renamed	O
Acorn	O
)	O
and	O
eventually	O
from	O
the	O
new	O
owner	O
,	O
Pace	O
Micro	O
Technology	O
.	O
</s>
<s>
According	O
to	O
the	O
company	O
,	O
over	O
6,400	O
copies	O
of	O
on	O
ROM	B-Device
were	O
sold	O
up	O
until	O
production	O
was	O
ceased	O
in	O
mid-2005	O
.	O
</s>
<s>
These	O
upgrades	O
are	O
released	O
as	O
soft-loadable	O
ROM	B-General_Concept
images	I-General_Concept
,	O
separate	O
to	O
the	O
ROM	B-Device
where	O
the	O
boot	O
OS	O
is	O
stored	O
,	O
and	O
are	O
loaded	O
at	O
boot	O
time	O
.	O
</s>
<s>
ROL	O
released	O
the	O
ROM	B-Device
based	O
the	O
same	O
month	O
,	O
dubbed	O
as	O
a	O
play	O
on	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
GUI	B-Application
convention	O
of	O
calling	O
the	O
three	O
mouse	O
buttons	O
'	O
Select	O
 '	O
,	O
'	O
Menu	O
 '	O
and	O
'	O
Adjust	O
 '	O
.	O
</s>
<s>
ROL	O
sold	O
its	O
500th	O
Adjust	O
ROM	B-Device
in	O
early	O
2006	O
.	O
</s>
<s>
was	O
released	O
in	O
October	O
2002	O
on	O
Castle	O
Technology	O
's	O
Acorn	O
clone	O
Iyonix	B-Device
PC	I-Device
.	O
</s>
<s>
is	O
a	O
separate	O
evolution	O
based	O
upon	O
the	O
NCOS	B-Operating_System
work	O
done	O
by	O
Pace	O
for	O
set-top	O
boxes	O
.	O
</s>
<s>
This	O
Shared	O
Source	O
Initiative	O
(	O
SSI	O
)	O
is	O
managed	O
by	O
RISC	B-Operating_System
OS	I-Operating_System
Open	O
Ltd	O
(	O
ROOL	O
)	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
5	O
has	O
since	O
been	O
released	O
under	O
a	O
fully	O
free	B-License
and	I-License
open	I-License
source	I-License
Apache	B-Application
2.0	I-Application
license	I-Application
,	O
while	O
the	O
older	O
no	O
longer	O
maintained	O
RISC	B-Operating_System
OS	I-Operating_System
6	O
older	O
has	O
not	O
.	O
</s>
<s>
This	O
is	O
the	O
next	O
generation	O
of	O
their	O
stream	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
latest	O
release	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
ROL	O
is	O
,	O
shipped	O
in	O
December	O
2009	O
.	O
</s>
<s>
The	O
OS	O
was	O
designed	O
in	O
the	O
United	O
Kingdom	O
by	O
Acorn	O
for	O
the	O
32-bit	O
ARM	B-Architecture
based	O
Acorn	B-Device
Archimedes	I-Device
,	O
and	O
released	O
in	O
its	O
first	O
version	O
in	O
1987	O
,	O
as	O
the	O
Arthur	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
It	O
was	O
bundled	O
with	O
a	O
desktop	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
,	O
which	O
mostly	O
comprises	O
assembly	B-Language
language	I-Language
software	O
modules	O
,	O
and	O
the	O
Desktop	O
module	O
itself	O
being	O
written	O
in	O
.	O
</s>
<s>
The	O
graphical	O
desktop	O
runs	O
on	O
top	O
of	O
a	O
command-line	B-Application
driven	O
operating	B-General_Concept
system	I-General_Concept
which	O
owes	O
much	O
to	O
Acorn	O
's	O
earlier	O
MOS	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
for	O
its	O
BBC	B-Device
Micro	I-Device
range	O
of	O
8-bit	O
microcomputers	O
.	O
</s>
<s>
Arthur	O
,	O
as	O
originally	O
conceived	O
,	O
was	O
intended	O
to	O
deliver	O
similar	O
functionality	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
BBC	B-Device
Master	I-Device
series	I-Device
of	O
computers	O
,	O
MOS	B-Operating_System
,	O
as	O
a	O
reaction	O
to	O
the	O
fact	O
that	O
a	O
more	O
advanced	O
operating	B-General_Concept
system	I-General_Concept
research	O
project	O
(	O
ARX	B-Operating_System
)	O
would	O
not	O
be	O
ready	O
in	O
time	O
for	O
the	O
Archimedes	B-Device
.	O
</s>
<s>
The	O
Arthur	O
project	O
team	O
,	O
led	O
by	O
Paul	O
Fellows	O
,	O
was	O
given	O
just	O
five	O
months	O
to	O
develop	O
it	O
entirely	O
from	O
the	O
ground	O
up	O
—	O
with	O
the	O
directive	O
"	O
just	O
make	O
it	O
like	O
the	O
BBC	B-Device
micro	I-Device
"	O
.	O
</s>
<s>
It	O
was	O
intended	O
as	O
a	O
stop-gap	O
until	O
the	O
operating	B-General_Concept
system	I-General_Concept
which	O
Acorn	O
had	O
under	O
development	O
(	O
ARX	B-Operating_System
)	O
could	O
be	O
completed	O
.	O
</s>
<s>
Also	O
,	O
it	O
was	O
small	O
enough	O
to	O
run	O
on	O
the	O
first	O
512K	O
machines	O
with	O
only	O
a	O
floppy	O
disc	O
,	O
whereas	O
ARX	B-Operating_System
required	O
4	O
megabytes	O
and	O
a	O
hard	B-Device
drive	I-Device
.	O
</s>
<s>
The	O
OS	O
development	O
was	O
carried	O
out	O
using	O
a	O
prototype	O
ARM-based	O
system	O
connected	O
to	O
a	O
BBC	B-Device
computer	I-Device
,	O
before	O
moving	O
onto	O
the	O
prototype	O
Acorn	B-Device
Archimedes	I-Device
the	O
A500	O
.	O
</s>
<s>
Arthur	O
was	O
not	O
a	O
multitasking	O
operating	B-General_Concept
system	I-General_Concept
,	O
but	O
offered	O
support	O
for	O
adding	O
application-level	O
cooperative	B-Operating_System
multitasking	I-Operating_System
.	O
</s>
<s>
No	O
other	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
was	O
released	O
externally	O
,	O
but	O
internally	O
the	O
development	O
of	O
the	O
desktop	O
and	O
window	O
management	O
continued	O
,	O
with	O
the	O
addition	O
of	O
a	O
cooperative	B-Operating_System
multitasking	I-Operating_System
system	O
,	O
implemented	O
by	O
Neil	O
Raine	O
,	O
which	O
used	O
the	O
memory	O
management	O
hardware	O
to	O
swap-out	O
one	O
task	O
,	O
and	O
bring	O
in	O
another	O
between	O
call-and-return	O
from	O
the	O
Wimp_Poll	O
call	O
that	O
applications	O
were	O
obliged	O
to	O
make	O
to	O
get	O
messages	O
under	O
the	O
desktop	O
.	O
</s>
<s>
Reminiscent	O
of	O
a	O
similar	O
technique	O
employed	O
by	O
MultiFinder	O
on	O
the	O
Apple	B-Device
Macintosh	I-Device
,	O
this	O
transformed	O
a	O
single-application-at-a-time	O
system	O
into	O
one	O
that	O
could	O
operate	O
a	O
full	O
multi-tasking	O
desktop	O
.	O
</s>
<s>
This	O
transformation	O
took	O
place	O
at	O
version	O
1.6	O
though	O
it	O
was	O
not	O
made	O
public	O
until	O
released	O
,	O
with	O
the	O
name	O
change	O
from	O
Arthur	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
,	O
as	O
version	O
2.0	O
.	O
</s>
<s>
Most	O
software	O
made	O
for	O
Arthur	O
1.2	O
can	O
be	O
run	O
under	O
RISC	B-Operating_System
OS	I-Operating_System
2	O
and	O
later	O
because	O
,	O
underneath	O
the	O
desktop	O
,	O
the	O
original	O
Arthur	O
OS	O
core	O
,	O
API	O
interfaces	O
and	O
modular	O
structures	O
remain	O
as	O
the	O
heart	O
of	O
all	O
versions	O
.	O
</s>
<s>
In	O
2011	O
,	O
Business	O
Insider	O
listed	O
Arthur	O
as	O
one	O
of	O
ten	O
"	O
operating	B-General_Concept
systems	I-General_Concept
that	O
time	O
forgot	O
"	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
was	O
a	O
rapid	O
development	O
of	O
Arthur	O
1.2	O
after	O
the	O
failure	O
of	O
the	O
ARX	B-Operating_System
project	O
.	O
</s>
<s>
Given	O
growing	O
dissatisfaction	O
with	O
various	O
bugs	B-Error_Name
and	O
limitations	O
with	O
Arthur	O
,	O
testing	O
of	O
what	O
was	O
then	O
known	O
as	O
was	O
apparently	O
ongoing	O
during	O
1988	O
with	O
selected	O
software	O
houses	O
.	O
</s>
<s>
At	O
this	O
stage	O
,	O
Computer	O
Concepts	O
,	O
who	O
had	O
been	O
prolific	O
developers	O
for	O
the	O
BBC	B-Device
Micro	I-Device
and	O
who	O
had	O
begun	O
software	O
development	O
for	O
the	O
Archimedes	B-Device
,	O
had	O
already	O
initiated	O
a	O
rival	O
operating	B-General_Concept
system	I-General_Concept
project	O
,	O
Impulse	O
,	O
to	O
support	O
their	O
own	O
applications	O
(	O
including	O
the	O
desktop	O
publishing	O
application	O
that	O
would	O
eventually	O
become	O
Impression	B-Device
)	O
,	O
stating	O
that	O
Arthur	O
did	O
not	O
meet	O
the	O
"	O
hundreds	O
of	O
requirements	O
"	O
involved	O
including	O
"	O
true	O
multi-tasking	O
"	O
.	O
</s>
<s>
Such	O
an	O
operating	B-General_Concept
system	I-General_Concept
was	O
to	O
be	O
offered	O
free	O
of	O
charge	O
with	O
the	O
planned	O
application	O
packages	O
,	O
but	O
with	O
the	O
release	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
and	O
Computer	O
Concepts	O
acknowledging	O
that	O
RISC	B-Operating_System
OS	I-Operating_System
"	O
overcomes	O
the	O
old	O
problems	O
with	O
Arthur	O
"	O
,	O
the	O
applications	O
were	O
to	O
be	O
able	O
to	O
run	O
under	O
either	O
RISC	B-Operating_System
OS	I-Operating_System
or	O
Impulse	O
.	O
</s>
<s>
Impression	B-Device
was	O
eventually	O
released	O
as	O
a	O
RISC	B-Operating_System
OS	I-Operating_System
application	O
.	O
</s>
<s>
Ultimately	O
,	O
was	O
renamed	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
,	O
and	O
was	O
first	O
sold	O
as	O
RISC	B-Operating_System
OS	I-Operating_System
2.00	O
in	O
April	O
1989	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
implements	O
co-operative	B-Operating_System
multitasking	I-Operating_System
with	O
some	O
limitations	O
but	O
is	O
not	O
multi-threaded	B-Operating_System
.	O
</s>
<s>
It	O
uses	O
the	O
ADFS	B-Device
file	O
system	O
for	O
both	O
floppy	O
and	O
hard	B-Device
disc	I-Device
access	O
.	O
</s>
<s>
The	O
WIMP	B-Application
interface	I-Application
offers	O
all	O
the	O
standard	O
features	O
and	O
fixes	O
many	O
of	O
the	O
bugs	B-Error_Name
that	O
had	O
hindered	O
Arthur	O
.	O
</s>
<s>
It	O
lacks	O
virtual	B-Architecture
memory	I-Architecture
and	O
extensive	O
memory	B-General_Concept
protection	I-General_Concept
(	O
applications	O
are	O
protected	O
from	O
each	O
other	O
,	O
but	O
many	O
functions	O
have	O
to	O
be	O
implemented	O
as	O
'	O
modules	O
 '	O
which	O
have	O
full	O
access	O
to	O
the	O
memory	O
)	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
release	O
,	O
the	O
main	O
advantage	O
of	O
the	O
OS	O
was	O
its	O
ROM	B-Device
;	O
it	O
booted	O
very	O
quickly	O
and	O
while	O
it	O
was	O
easy	O
to	O
crash	O
,	O
it	O
was	O
impossible	O
to	O
permanently	O
break	O
the	O
OS	O
from	O
software	O
.	O
</s>
<s>
Its	O
high	O
performance	O
was	O
due	O
to	O
much	O
of	O
the	O
system	O
being	O
written	O
in	O
ARM	B-Architecture
assembly	B-Language
language	I-Language
.	O
</s>
<s>
Much	O
of	O
the	O
system	O
's	O
functionality	O
is	O
implemented	O
in	O
modules	O
coded	O
in	O
the	O
ROM	B-Device
,	O
though	O
these	O
can	O
be	O
supplanted	O
by	O
more	O
evolved	O
versions	O
loaded	O
into	O
RAM	B-Architecture
.	O
</s>
<s>
This	O
facility	O
is	O
used	O
by	O
a	O
module	O
forming	O
part	O
of	O
the	O
standard	O
editor	O
program	O
to	O
provide	O
a	O
terminal	B-Application
emulator	I-Application
window	O
for	O
console	O
applications	O
.	O
</s>
<s>
The	O
same	O
approach	O
made	O
it	O
possible	O
for	O
advanced	O
users	O
to	O
implement	O
modules	O
giving	O
RISC	B-Operating_System
OS	I-Operating_System
the	O
ability	O
to	O
do	O
pre-emptive	O
multitasking	O
.	O
</s>
<s>
A	O
slightly	O
updated	O
version	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
2.01	O
,	O
was	O
released	O
later	O
to	O
support	O
the	O
ARM3	O
processor	O
,	O
larger	O
memory	O
capacities	O
,	O
and	O
the	O
VGA	B-Protocol
and	O
SVGA	O
modes	O
provided	O
by	O
the	O
Acorn	B-Device
Archimedes	I-Device
540	O
and	O
Acorn	O
R225/R260	O
.	O
</s>
<s>
introduced	O
a	O
number	O
of	O
new	O
features	O
,	O
including	O
multitasking	O
Filer	O
operations	O
,	O
applications	O
and	O
fonts	O
in	O
ROM	B-Device
,	O
no	O
limit	O
on	O
number	O
of	O
open	O
windows	O
,	O
ability	O
to	O
move	O
windows	O
off	O
screen	O
,	O
safe	O
shutdown	B-Device
,	O
the	O
Pinboard	O
,	O
grouping	O
of	O
icon	O
bar	O
icons	O
,	O
up	O
to	O
128	O
tasks	O
,	O
native	O
ability	O
to	O
read	O
MS-DOS	B-Application
format	O
discs	O
and	O
use	O
named	O
hard	B-Device
discs	I-Device
.	O
</s>
<s>
Improved	O
configuration	B-Protocol
was	O
also	O
included	O
,	O
by	O
way	O
of	O
multiple	O
windows	O
to	O
change	O
the	O
settings	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.00	O
was	O
released	O
with	O
the	O
very	O
earliest	O
version	O
of	O
the	O
A5000	O
in	O
1991	O
;	O
it	O
is	O
almost	O
four	O
times	O
the	O
size	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
2	O
and	O
runs	O
from	O
a	O
2MB	O
ROM	B-Device
.	O
</s>
<s>
It	O
improves	O
multitasking	O
and	O
also	O
places	O
some	O
of	O
the	O
more	O
popular	O
base	O
applications	O
in	O
the	O
ROM	B-Device
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.00	O
had	O
several	O
bugs	B-Error_Name
and	O
was	O
replaced	O
by	O
RISC	B-Operating_System
OS	I-Operating_System
3.1	O
a	O
few	O
months	O
later	O
;	O
the	O
upgraded	O
ROMs	O
were	O
supplied	O
for	O
the	O
cost	O
of	O
postage	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.1	O
was	O
released	O
later	O
and	O
sold	O
built	O
into	O
the	O
A3010	O
,	O
A3020	B-Device
,	O
A4000	O
,	O
A4	O
and	O
later	O
A5000	O
models	O
.	O
</s>
<s>
It	O
was	O
also	O
made	O
available	O
as	O
replacement	O
ROMs	O
for	O
the	O
A5000	O
and	O
earlier	O
Archimedes	B-Device
machines	O
(	O
this	O
is	O
the	O
last	O
RISC	B-Operating_System
OS	I-Operating_System
version	O
suitable	O
for	O
those	O
machines	O
)	O
.	O
</s>
<s>
Three	O
variants	O
were	O
released	O
:	O
RISC	B-Operating_System
OS	I-Operating_System
3.10	O
the	O
base	O
version	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
3.11	O
which	O
included	O
a	O
slight	O
update	O
that	O
fixes	O
some	O
serial	O
port	O
issues	O
and	O
RISC	B-Operating_System
OS	I-Operating_System
3.19	O
which	O
was	O
a	O
German	O
translation	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.50	O
was	O
sold	O
from	O
1994	O
with	O
the	O
first	O
Risc	B-Device
PCs	I-Device
.	O
</s>
<s>
Due	O
to	O
the	O
very	O
different	O
hardware	O
architecture	O
of	O
the	O
Risc	B-Device
PC	I-Device
,	O
including	O
an	O
ARM	B-Architecture
6	O
processor	O
,	O
16	O
-	O
and	O
24-bit	O
colour	O
and	O
a	O
different	O
IO	O
chip	O
(	O
IOMD	O
)	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
3.50	O
was	O
not	O
made	O
available	O
for	O
the	O
older	O
Archimedes	B-Device
and	O
A	O
Series	O
ARM2	O
and	O
3	O
machines	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.5	O
was	O
somewhat	O
shoehorned	O
into	O
the	O
2MB	O
footprint	O
,	O
and	O
moved	O
the	O
ROM	B-Device
applications	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
3.1	O
onto	O
the	O
hard	B-Device
drive	I-Device
;	O
this	O
proved	O
so	O
unpopular	O
that	O
they	O
were	O
later	O
moved	O
back	O
into	O
ROM	B-Device
.	O
</s>
<s>
This	O
version	O
introduced	O
issues	O
of	O
backward	B-General_Concept
compatibility	I-General_Concept
,	O
particularly	O
with	O
games	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.60	O
followed	O
in	O
1995	O
.	O
</s>
<s>
The	O
OS	O
features	O
much	O
improved	O
hard	B-Device
disk	I-Device
access	O
and	O
its	O
networking	B-Architecture
was	O
enhanced	O
to	O
include	O
TCP/IP	B-Protocol
as	O
standard	O
in	O
addition	O
to	O
Acorn	O
's	O
existing	O
proprietary	O
Econet	B-Device
system	O
.	O
</s>
<s>
The	O
hardware	O
support	O
was	O
also	O
improved	O
;	O
Risc	B-Device
PCs	I-Device
could	O
now	O
use	O
ARM7	O
processors	O
.	O
</s>
<s>
Acorn	O
's	O
A7000	B-Device
machine	O
with	O
its	O
ARM7500	O
processor	O
was	O
also	O
supported	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.6	O
was	O
twice	O
the	O
size	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
3.5	O
,	O
shipping	O
on	O
4MB	O
in	O
two	O
ROM	B-Device
chips	I-Device
;	O
components	O
that	O
had	O
been	O
moved	O
onto	O
disk	O
in	O
3.5	O
(	O
the	O
standard	O
application	O
suite	O
and	O
networking	B-Architecture
)	O
were	O
now	O
moved	O
back	O
into	O
ROM	B-Device
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.70	O
was	O
released	O
in	O
1996	O
.	O
</s>
<s>
The	O
primary	O
changes	O
in	O
the	O
OS	O
was	O
support	O
for	O
the	O
StrongARM	B-Device
processor	O
that	O
was	O
made	O
available	O
as	O
an	O
upgrade	O
for	O
the	O
Risc	B-Device
PC	I-Device
.	O
</s>
<s>
This	O
required	O
extensive	O
code	O
changes	O
due	O
to	O
StrongARM	B-Device
's	I-Device
split	O
data	O
and	O
instruction	O
cache	O
(	O
Harvard	B-Architecture
architecture	I-Architecture
)	O
and	O
32-bit	O
interrupt	O
modes	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.71	O
is	O
a	O
small	O
update	O
released	O
to	O
support	O
the	O
hardware	O
in	O
the	O
Acorn	O
A7000+	O
with	O
its	O
ARM7500FE	O
processor	O
.	O
</s>
<s>
The	O
FE	O
offered	O
hardware	O
support	O
for	O
floating	O
point	O
mathematics	O
,	O
which	O
until	O
then	O
was	O
usually	O
emulated	O
in	O
one	O
of	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
Software	O
modules	O
)	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.60	O
also	O
formed	O
the	O
foundation	O
of	O
NCOS	B-Operating_System
,	O
as	O
shipped	O
in	O
the	O
Acorn	O
NetChannel	O
NCs	O
.	O
</s>
<s>
Acorn	O
officially	O
halted	O
work	O
in	O
all	O
areas	O
except	O
set-top	O
boxes	O
in	O
January	O
1999	O
and	O
the	O
company	O
was	O
renamed	O
Element	O
14	O
(	O
the	O
14th	O
element	O
of	O
the	O
periodic	O
table	O
being	O
silicon	O
)	O
with	O
a	O
new	O
goal	O
to	O
become	O
purely	O
a	O
Silicon	O
design	O
business	O
(	O
like	O
the	O
previous	O
very	O
successful	O
spin	O
off	O
of	O
ARM	B-Architecture
from	O
Acorn	O
in	O
1990	O
)	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
development	O
was	O
halted	O
during	O
the	O
development	O
of	O
OS	O
4.0	O
for	O
the	O
RiscPC	B-Device
2	I-Device
(	O
"	O
Phoebe	B-Device
2100	I-Device
"	O
)	O
,	O
whose	O
completion	O
was	O
also	O
cancelled	O
.	O
</s>
<s>
A	O
beta	O
version	O
,	O
OS	O
3.8	O
(	O
"	O
Ursula	O
"	O
)	O
for	O
the	O
original	O
RiscPC	B-Device
,	O
had	O
previously	O
been	O
released	O
to	O
developers	O
.	O
</s>
<s>
The	O
project	O
code	O
names	O
of	O
Phoebe	B-Device
(	O
for	O
the	O
hardware	O
)	O
,	O
Ursula	O
(	O
for	O
the	O
software	O
)	O
and	O
Chandler	O
(	O
for	O
the	O
graphics	O
processor	O
chip	O
)	O
were	O
taken	O
from	O
the	O
names	O
of	O
characters	O
in	O
the	O
TV	O
series	O
Friends	O
(	O
Phoebe	B-Device
and	O
Ursula	O
were	O
twin	O
sisters	O
in	O
the	O
series	O
)	O
.	O
</s>
<s>
Acorn	O
held	O
discussions	O
with	O
many	O
interested	O
parties	O
,	O
and	O
eventually	O
agreed	O
to	O
exclusively	O
licence	O
RISC	B-Operating_System
OS	I-Operating_System
to	O
RISCOS	B-Operating_System
Ltd	O
,	O
which	O
was	O
formed	O
from	O
a	O
consortium	O
of	O
dealers	O
,	O
developers	O
and	O
end-users	O
.	O
</s>
<s>
Pace	O
purchased	O
the	O
rights	O
to	O
use	O
and	O
develop	O
NCOS	B-Operating_System
.	O
</s>
<s>
There	O
were	O
also	O
a	O
number	O
of	O
projects	O
to	O
bring	O
the	O
advantages	O
of	O
the	O
RISC	O
Operating	B-General_Concept
System	I-General_Concept
to	O
other	O
platforms	O
by	O
the	O
creation	O
of	O
the	O
ROX	B-Language
Desktop	I-Language
to	O
provide	O
a	O
RISC	O
OS-like	O
interface	O
on	O
Unix	B-Application
and	O
Linux	B-Application
systems	O
.	O
</s>
<s>
The	O
separate	O
work	O
by	O
and	O
Pace	O
resulted	O
in	O
a	O
code	B-Application
fork	I-Application
.	O
</s>
<s>
In	O
March	O
1999	O
,	O
a	O
new	O
company	O
called	O
RISCOS	B-Operating_System
Ltd	O
was	O
founded	O
.	O
</s>
<s>
They	O
licensed	O
the	O
rights	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
Element	O
14	O
(	O
and	O
eventually	O
from	O
the	O
new	O
owner	O
,	O
Pace	O
Micro	O
Technology	O
)	O
and	O
continued	O
the	O
development	O
of	O
OS	O
3.8	O
,	O
releasing	O
it	O
as	O
RISC	B-Operating_System
OS	I-Operating_System
4	O
in	O
July	O
1999	O
.	O
</s>
<s>
Whilst	O
the	O
hardware	O
support	O
for	O
Phoebe	B-Device
was	O
not	O
needed	O
,	O
the	O
core	O
improvements	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
3.80	O
could	O
be	O
finished	O
and	O
released	O
.	O
</s>
<s>
According	O
to	O
the	O
company	O
,	O
over	O
6,400	O
copies	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
4.02	O
on	O
ROM	B-Device
were	O
sold	O
up	O
until	O
production	O
was	O
ceased	O
in	O
mid-2005	O
.	O
</s>
<s>
During	O
1999	O
and	O
2000	O
,	O
RISCOS	B-Operating_System
Ltd	O
also	O
released	O
versions	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
4	O
to	O
support	O
several	O
additional	O
hardware	O
platforms	O
,	O
the	O
MicroDigital	O
Mico	O
,	O
MicroDigital	B-Device
Omega	I-Device
,	O
RiscStation	O
R7500	O
and	O
the	O
Castle	O
Kinetic	O
RiscPC	B-Device
.	O
</s>
<s>
In	O
2003	O
a	O
version	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
4	O
was	O
released	O
with	O
support	O
for	O
the	O
Millipede	O
Graphics	O
AlphaLock	O
podule	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
4	O
is	O
also	O
available	O
for	O
various	O
hardware	O
emulators	O
for	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
In	O
September	O
2003	O
VirtualAcorn	B-Operating_System
released	O
the	O
commercial	O
emulator	O
VirtualRPC	B-Operating_System
which	O
included	O
a	O
copy	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
4.02	O
.	O
</s>
<s>
In	O
December	O
2008	O
RISCOS	B-Operating_System
Ltd	O
made	O
4.02	O
available	O
for	O
non-commercial	O
emulators	O
for	O
£5	O
in	O
a	O
product	O
called	O
Virtually	O
Free	O
.	O
</s>
<s>
In	O
May	O
2001	O
,	O
the	O
company	O
launched	O
RISC	B-Operating_System
OS	I-Operating_System
Select	O
,	O
a	O
subscription	O
scheme	O
allowing	O
users	O
access	O
to	O
the	O
latest	O
OS	O
updates	O
.	O
</s>
<s>
These	O
upgrades	O
are	O
released	O
as	O
soft-loadable	O
ROM	B-General_Concept
images	I-General_Concept
,	O
separate	O
to	O
the	O
ROM	B-Device
where	O
the	O
boot	O
OS	O
is	O
stored	O
,	O
and	O
are	O
loaded	O
at	O
boot	O
time	O
.	O
</s>
<s>
By	O
providing	O
soft-loads	O
,	O
physical	O
ROM	B-Device
costs	O
are	O
eliminated	O
and	O
updates	O
are	O
able	O
to	O
be	O
delivered	O
with	O
accelerated	O
speed	O
and	O
frequency	O
.	O
</s>
<s>
It	O
has	O
also	O
allowed	O
the	O
company	O
to	O
subsidise	O
the	O
retail	O
price	O
of	O
ROM	B-Device
releases	O
,	O
which	O
are	O
generally	O
a	O
culmination	O
of	O
the	O
last	O
few	O
Select	O
upgrades	O
with	O
a	O
few	O
extra	O
minor	O
changes	O
.	O
</s>
<s>
Also	O
in	O
June	O
2004	O
,	O
RISCOS	B-Operating_System
Ltd	O
released	O
the	O
ROM	B-Device
based	O
version	O
4.39	O
,	O
being	O
dubbed	O
RISC	B-Operating_System
OS	I-Operating_System
Adjust	O
.	O
</s>
<s>
(	O
The	O
name	O
was	O
a	O
play	O
on	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
GUI	B-Application
convention	O
of	O
calling	O
the	O
three	O
mouse	O
buttons	O
'	O
Select	O
 '	O
,	O
'	O
Menu	O
 '	O
and	O
'	O
Adjust	O
 '	O
.	O
)	O
</s>
<s>
RISCOS	B-Operating_System
Ltd	O
sold	O
its	O
500th	O
Adjust	O
ROM	B-Device
in	O
early	O
2006	O
.	O
</s>
<s>
Features	O
introduced	O
in	O
4.39	O
include	O
user	O
customization	O
of	O
the	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
Further	O
release	O
under	O
the	O
Select	O
scheme	O
were	O
made	O
under	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
Six	O
branding	O
,	O
mentioned	O
below	O
.	O
</s>
<s>
This	O
was	O
developed	O
by	O
and	O
supports	O
32-bit	O
addressing	O
modes	O
found	O
on	O
later	O
ARM	B-Architecture
architectures	I-Architecture
.	O
</s>
<s>
In	O
October	O
2006	O
,	O
shortly	O
after	O
Castle	O
Technology	O
announced	O
the	O
Shared	O
Source	O
Initiative	O
,	O
RISCOS	B-Operating_System
Ltd	O
announced	O
RISC	B-Operating_System
OS	I-Operating_System
Six	O
,	O
the	O
next	O
generation	O
of	O
their	O
stream	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
first	O
product	O
to	O
be	O
launched	O
under	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
Six	O
name	O
,	O
was	O
the	O
continuation	O
of	O
the	O
Select	O
scheme	O
,	O
Select	O
4	O
.	O
</s>
<s>
A	O
beta-version	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
6	O
,	O
Preview	O
1	O
(	O
Select	O
4i1	O
)	O
,	O
was	O
available	O
in	O
2007	O
as	O
a	O
free	O
download	O
to	O
all	O
subscribers	O
to	O
the	O
Select	O
scheme	O
,	O
both	O
present	O
subscribers	O
and	O
those	O
whose	O
subscription	O
was	O
renewed	O
after	O
30	O
May	O
2004	O
but	O
has	O
since	O
lapsed	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
Six	O
brought	O
portability	O
,	O
stability	O
and	O
internal	O
structure	O
improvements	O
,	O
including	O
full	O
26/32	O
-bit	O
neutrality	O
.	O
</s>
<s>
Teletext	O
support	O
,	O
device	O
interrupt	O
handler	O
,	O
software-based	O
graphics	O
operations	O
,	O
the	O
real-time	O
clock	O
,	O
the	O
mouse	O
pointer	O
,	O
CMOS	O
RAM	B-Architecture
support	O
,	O
and	O
hardware	O
timer	O
support	O
have	O
been	O
abstracted	O
out	O
of	O
the	O
kernel	O
and	O
into	O
their	O
own	O
separate	O
modules	O
.	O
</s>
<s>
Legacy	O
components	O
,	O
like	O
the	O
VIDC	O
driver	O
,	O
and	O
obsolete	O
functionality	O
for	O
the	O
BBC	B-Device
Micro	I-Device
have	O
been	O
abstracted	O
too	O
.	O
</s>
<s>
Select	O
4	O
releases	O
are	O
initially	O
compatible	O
with	O
only	O
Acorn	B-Device
Risc	I-Device
PC	I-Device
and	O
A7000	B-Device
machines	O
.	O
</s>
<s>
RiscStation	O
R7500	O
,	O
MicroDigital	B-Device
Omega	I-Device
and	O
Mico	O
computers	O
will	O
not	O
officially	O
be	O
supported	O
,	O
as	O
the	O
company	O
does	O
not	O
have	O
test	O
machines	O
available	O
and	O
requires	O
proprietary	O
software	O
code	O
to	O
which	O
they	O
do	O
not	O
have	O
the	O
rights	O
.	O
</s>
<s>
Lack	O
of	O
detailed	O
technical	O
information	O
about	O
the	O
MicroDigital	B-Device
Omega	I-Device
has	O
also	O
been	O
cited	O
as	O
being	O
another	O
reason	O
why	O
support	O
of	O
that	O
hardware	O
is	O
difficult	O
.	O
</s>
<s>
The	O
final	O
release	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
RISCOS	B-Operating_System
Ltd	O
was	O
Select	O
6i1	O
,	O
shipped	O
in	O
December	O
2009	O
,	O
it	O
includes	O
;	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
5	O
is	O
a	O
separate	O
evolution	O
by	O
Castle	O
Technology	O
Ltd	O
based	O
upon	O
work	O
done	O
by	O
Pace	O
for	O
their	O
NCOS	B-Operating_System
based	O
set	O
top	O
boxes	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
5	O
was	O
written	O
to	O
support	O
Castle	O
's	O
Iyonix	B-Device
PC	I-Device
Acorn-compatible	O
,	O
which	O
runs	O
on	O
the	O
Intel	B-Application
XScale	I-Application
ARM	B-Architecture
processor	I-Architecture
.	O
</s>
<s>
Although	O
a	O
wealth	O
of	O
software	O
has	O
now	O
been	O
updated	O
,	O
a	O
few	O
older	O
applications	O
can	O
only	O
be	O
run	O
on	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
via	O
an	O
emulator	O
called	O
Aemulor	O
,	O
since	O
the	O
ARMv5	O
XScale	B-Application
processor	O
does	O
not	O
support	O
26-bit	B-Architecture
addressing	O
modes	O
.	O
</s>
<s>
Likewise	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
itself	O
had	O
to	O
be	O
ported	O
to	O
run	O
properly	O
on	O
the	O
new	O
CPU	O
,	O
and	O
abstraction	O
of	O
the	O
graphics	O
and	O
other	O
hardware	O
interfaces	O
created	O
,	O
to	O
allow	O
it	O
,	O
for	O
example	O
,	O
to	O
use	O
standard	O
graphics	O
cards	O
,	O
instead	O
of	O
Acorn	O
's	O
own	O
VIDC	O
chip	O
.	O
</s>
<s>
In	O
July	O
2003	O
,	O
Castle	O
Technology	O
Ltd	O
bought	O
the	O
head	O
licence	O
for	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
Pace	O
Micro	O
.	O
</s>
<s>
In	O
October	O
2006	O
,	O
Castle	O
Technology	O
Ltd	O
announced	O
a	O
plan	O
to	O
release	O
elements	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
under	O
a	O
source	O
sharing	O
license	O
.	O
</s>
<s>
The	O
Shared	O
Source	O
Initiative	O
(	O
SSI	O
)	O
was	O
a	O
joint	O
venture	O
between	O
Castle	O
and	O
RISC	B-Operating_System
OS	I-Operating_System
Open	O
Limited	O
(	O
ROOL	O
)	O
,	O
a	O
newly	O
formed	O
software	O
development	O
company	O
,	O
which	O
aimed	O
to	O
accelerate	O
development	O
and	O
encourage	O
uptake	O
of	O
the	O
OS	O
.	O
</s>
<s>
By	O
October	O
2008	O
,	O
enough	O
source	O
was	O
released	O
to	O
build	O
an	O
almost	O
complete	O
Iyonix	B-Device
ROM	B-General_Concept
image	I-General_Concept
.	O
</s>
<s>
By	O
late	O
2011	O
,	O
it	O
was	O
possible	O
to	O
build	O
complete	O
ROM	B-General_Concept
images	I-General_Concept
from	O
the	O
published	O
sources	O
;	O
with	O
the	O
full	O
source	O
code	O
available	O
as	O
tarballs	B-Application
,	O
CVS	B-Application
,	O
or	O
a	O
web	O
interface	O
to	O
the	O
CVS	B-Application
archive	O
.	O
</s>
<s>
In	O
October	O
2018	O
,	O
the	O
rights	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
were	O
acquired	O
by	O
RISC	B-Operating_System
OS	I-Operating_System
Developments	O
,	O
and	O
re-licensed	O
under	O
the	O
Apache	B-Application
2.0	I-Application
license	I-Application
.	O
</s>
<s>
Ports	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
are	O
available	O
for	O
the	O
A7000/A7000	B-Device
+	I-Device
,	O
RiscPC	B-Device
,	O
RPCemu	O
,	O
the	O
OMAP3	O
BeagleBoard	B-Application
and	O
derivatives	B-Device
,	O
OMAP4	O
PandaBoard	B-Architecture
and	O
PandaBoard	B-Architecture
ES	I-Architecture
,	O
AM5728	B-Device
Titanium	O
,	O
the	O
Raspberry	B-Operating_System
Pi	I-Operating_System
,	O
and	O
the	O
XScale	B-Application
Iyonix	B-Device
.	O
</s>
