<s>
RISC	B-Operating_System
OS	I-Operating_System
is	O
a	O
computer	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
originally	O
designed	O
by	O
Acorn	O
Computers	O
Ltd	O
in	O
Cambridge	O
,	O
England	O
.	O
</s>
<s>
First	O
released	O
in	O
1987	O
,	O
it	O
was	O
designed	O
to	O
run	O
on	O
the	O
ARM	B-Architecture
chipset	O
,	O
which	O
Acorn	O
had	O
designed	O
concurrently	O
for	O
use	O
in	O
its	O
new	O
line	O
of	O
Archimedes	B-Device
personal	B-Device
computers	I-Device
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
takes	O
its	O
name	O
from	O
the	O
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
RISC	B-Architecture
)	O
architecture	O
it	O
supports	O
.	O
</s>
<s>
Between	O
1987	O
and	O
1998	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
was	O
included	O
in	O
every	O
ARM-based	O
Acorn	O
computer	O
model	O
,	O
including	O
the	O
Acorn	B-Device
Archimedes	I-Device
line	O
,	O
Acorn	O
's	O
R	O
line	O
(	O
with	O
RISC	B-Operating_System
iX	I-Operating_System
as	O
a	O
dual-boot	O
option	O
)	O
,	O
RiscPC	B-Device
,	O
A7000	B-Device
,	O
and	O
prototype	O
models	O
such	O
as	O
the	O
Acorn	O
NewsPad	O
and	O
Phoebe	B-Device
computer	I-Device
.	O
</s>
<s>
A	O
version	O
of	O
the	O
OS	O
,	O
named	O
NCOS	B-Operating_System
,	O
was	O
used	O
in	O
Oracle	B-Application
Corporation	I-Application
's	O
Network	B-Operating_System
Computer	I-Operating_System
and	O
compatible	O
systems	O
.	O
</s>
<s>
Since	O
then	O
,	O
it	O
has	O
been	O
bundled	O
with	O
several	O
ARM-based	O
desktop	O
computers	O
such	O
as	O
the	O
Iyonix	B-Device
PC	I-Device
and	O
A9home	B-Device
.	O
</s>
<s>
Most	O
recent	O
stable	O
versions	O
run	O
on	O
the	O
ARMv3/ARMv4	O
RiscPC	B-Device
,	O
the	O
ARMv5	O
Iyonix	B-Device
,	O
ARMv7	O
Cortex-A8	B-Application
processors	O
(	O
such	O
as	O
that	O
used	O
in	O
the	O
BeagleBoard	B-Application
and	O
Touch	B-Application
Book	I-Application
)	O
and	O
Cortex-A9	B-Application
processors	O
(	O
such	O
as	O
that	O
used	O
in	O
the	O
PandaBoard	B-Architecture
)	O
and	O
the	O
low-cost	O
educational	O
Raspberry	B-Operating_System
Pi	I-Operating_System
computer	O
.	O
</s>
<s>
SD	B-Device
card	I-Device
images	O
have	O
been	O
released	O
for	O
downloading	O
free	O
of	O
charge	O
to	O
Raspberry	B-Operating_System
Pi	I-Operating_System
1	O
,	O
2	O
,	O
3	O
,	O
&	O
4	O
users	O
with	O
a	O
full	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
version	O
and	O
a	O
command-line	B-Application
interface	I-Application
only	O
version	O
(	O
RISC	B-Operating_System
OS	I-Operating_System
Pico	O
,	O
at	O
3.8MB	O
)	O
.	O
</s>
<s>
The	O
first	O
version	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
was	O
originally	O
released	O
in	O
1987	O
as	O
Arthur	O
1.20	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
3.00	O
was	O
released	O
with	O
the	O
A5000	O
in	O
1991	O
,	O
and	O
contained	O
many	O
new	O
features	O
.	O
</s>
<s>
By	O
1996	O
,	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>
In	O
March	O
1999	O
a	O
new	O
company	O
,	O
RISCOS	B-Operating_System
Ltd	O
,	O
licensed	O
the	O
rights	O
to	O
develop	O
a	O
desktop	O
version	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
Element	O
14	O
,	O
and	O
continued	O
the	O
development	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
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>
Meanwhile	O
,	O
Element	O
14	O
had	O
also	O
kept	O
a	O
copy	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
3.8	O
in	O
house	O
,	O
which	O
they	O
developed	O
into	O
NCOS	B-Operating_System
for	O
use	O
in	O
set-top	O
boxes	O
.	O
</s>
<s>
In	O
2000	O
,	O
as	O
part	O
of	O
the	O
acquisition	O
of	O
Acorn	O
Group	O
plc	O
by	O
MSDW	O
Investment	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
was	O
sold	O
to	O
Pace	O
Micro	O
Technology	O
,	O
who	O
later	O
sold	O
it	O
to	O
Castle	O
Technology	O
Ltd	O
.	O
</s>
<s>
In	O
May	O
2001	O
,	O
RISCOS	B-Operating_System
Ltd	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
RISC	B-Operating_System
OS	I-Operating_System
4	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	B-Operating_System
OS	O
is	O
stored	O
,	O
and	O
are	O
loaded	O
at	O
boot	B-Operating_System
time	I-Operating_System
.	O
</s>
<s>
In	O
the	O
same	O
month	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
4.39	O
,	O
dubbed	O
RISC	B-Operating_System
OS	I-Operating_System
Adjust	O
,	O
was	O
released	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
Adjust	O
was	O
a	O
culmination	O
of	O
all	O
the	O
Select	O
Scheme	O
updates	O
to	O
date	O
,	O
released	O
as	O
a	O
physical	O
set	O
of	O
replaceable	O
ROMs	O
for	O
the	O
RiscPC	B-Device
and	O
A7000	B-Device
series	O
of	O
machines	O
.	O
</s>
<s>
Meanwhile	O
,	O
in	O
October	O
2002	O
,	O
Castle	O
Technology	O
released	O
the	O
Acorn	O
clone	O
Iyonix	B-Device
PC	I-Device
.	O
</s>
<s>
This	O
ran	O
a	O
32-bit	O
(	O
in	O
contrast	O
to	O
26-bit	B-Architecture
)	O
variant	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
,	O
named	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
5	O
is	O
a	O
separate	O
evolution	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
based	O
upon	O
the	O
NCOS	B-Operating_System
work	O
done	O
by	O
Pace	O
.	O
</s>
<s>
The	O
following	O
year	O
,	O
Castle	O
Technology	O
bought	O
RISC	B-Operating_System
OS	I-Operating_System
from	O
Pace	O
for	O
an	O
undisclosed	O
sum	O
.	O
</s>
<s>
In	O
October	O
2006	O
,	O
Castle	O
announced	O
a	O
shared	B-License
source	I-License
license	I-License
plan	O
,	O
managed	O
by	O
RISC	B-Operating_System
OS	I-Operating_System
Open	O
Limited	O
,	O
for	O
elements	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
.	O
</s>
<s>
In	O
October	O
2018	O
,	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
was	O
re-licensed	O
under	O
the	O
Apache	O
2.0	O
license	O
.	O
</s>
<s>
In	O
December	O
2020	O
,	O
the	O
source	O
code	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
3.71	O
was	O
leaked	O
to	O
The	O
Pirate	O
Bay	O
.	O
</s>
<s>
Versions	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
run	O
or	O
have	O
run	O
on	O
the	O
following	O
hardware	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
Open	O
Limited	O
adopted	O
the	O
'	O
even	O
numbers	O
are	O
stable	O
 '	O
version	O
numbering	O
scheme	O
post	O
version	O
5.14	O
,	O
hence	O
some	O
table	O
entries	O
above	O
include	O
two	O
latest	O
releases	O
–	O
the	O
last	O
stable	O
one	O
and	O
the	O
more	O
recent	O
development	O
one	O
.	O
</s>
<s>
A	O
special	O
cut	O
down	O
RISC	B-Operating_System
OS	I-Operating_System
Pico	O
(	O
for	O
16MiB	O
cards	O
and	O
larger	O
)	O
styled	O
to	O
start	O
up	O
like	O
a	O
BBC	B-Device
Micro	I-Device
was	O
released	O
for	O
BASIC	O
's	O
50th	O
anniversary	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
has	O
also	O
been	O
used	O
by	O
both	O
Acorn	O
and	O
Pace	O
Micro	O
Technology	O
in	O
various	O
TV	O
connected	O
set-top	O
boxes	O
,	O
sometimes	O
referred	O
to	O
instead	O
as	O
NCOS	B-Operating_System
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
can	O
also	O
run	O
on	O
a	O
range	O
of	O
computer	O
system	O
emulators	O
that	O
emulate	O
the	O
earlier	O
Acorn	O
machines	O
listed	O
above	O
.	O
</s>
<s>
The	O
OS	O
is	O
single-user	B-Operating_System
and	O
employs	O
cooperative	B-Operating_System
multitasking	I-Operating_System
(	O
CMT	O
)	O
.	O
</s>
<s>
While	O
most	O
current	O
desktop	O
OSes	O
use	O
preemptive	B-Operating_System
multitasking	B-Operating_System
(	O
PMT	O
)	O
and	O
multithreading	B-Operating_System
,	O
remains	O
with	O
a	O
CMT	O
system	O
.	O
</s>
<s>
The	O
OS	O
memory	B-General_Concept
protection	I-General_Concept
is	O
not	O
comprehensive	O
.	O
</s>
<s>
The	O
core	O
of	O
the	O
OS	O
is	O
stored	O
in	O
ROM	B-Device
,	O
giving	O
a	O
fast	O
bootup	B-Operating_System
time	O
and	O
safety	O
from	O
operating	B-General_Concept
system	I-General_Concept
corruption	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
4	O
and	O
5	O
are	O
stored	O
in	O
of	O
flash	B-Device
memory	I-Device
,	O
or	O
as	O
a	O
ROM	B-General_Concept
image	I-General_Concept
on	O
SD	B-Device
Card	I-Device
on	O
single	O
board	O
computers	O
such	O
as	O
the	O
Beagleboard	B-Application
or	O
Raspberry	B-Operating_System
Pi	I-Operating_System
,	O
allowing	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
be	O
updated	O
without	O
having	O
to	O
replace	O
the	O
ROM	B-Device
chip	I-Device
.	O
</s>
<s>
The	O
OS	O
is	O
made	O
up	O
of	O
several	O
modules	B-Application
.	O
</s>
<s>
These	O
can	O
be	O
added	O
to	O
and	O
replaced	O
,	O
including	O
soft-loading	O
of	O
modules	B-Application
not	O
present	O
in	O
ROM	B-Device
at	O
run	O
time	O
and	O
on-the-fly	O
replacement	O
.	O
</s>
<s>
This	O
design	O
has	O
led	O
to	O
OS	O
developers	O
releasing	O
rolling	O
updates	O
to	O
their	O
versions	O
of	O
the	O
OS	O
,	O
while	O
third	O
parties	O
are	O
able	O
to	O
write	O
OS	O
replacement	O
modules	B-Application
to	O
add	O
new	O
features	O
.	O
</s>
<s>
OS	O
modules	B-Application
are	O
accessed	O
via	O
software	O
interrupts	B-Application
(	O
SWIs	O
)	O
,	O
similar	O
to	O
system	B-Operating_System
calls	I-Operating_System
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Most	O
of	O
the	O
OS	O
has	O
defined	O
application	B-Operating_System
binary	I-Operating_System
interfaces	I-Operating_System
(	O
ABIs	O
)	O
to	O
handle	O
filters	O
and	O
vectors	O
.	O
</s>
<s>
This	O
simplifies	O
the	O
task	O
of	O
modifying	O
its	O
behaviour	O
,	O
either	O
in	O
the	O
GUI	B-Application
,	O
or	O
deeper	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
there	O
are	O
several	O
third-party	O
programs	O
which	O
allow	O
customising	O
the	O
OS	O
look	B-Application
and	I-Application
feel	I-Application
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
is	O
volume-oriented	O
:	O
the	O
top	O
level	O
of	O
the	O
file	O
hierarchy	O
is	O
a	O
volume	O
(	O
disc	O
,	O
network	O
share	O
)	O
prefixed	O
by	O
the	O
file	B-Application
system	I-Application
type	O
.	O
</s>
<s>
Colons	O
are	O
used	O
to	O
separate	O
the	O
file	B-Application
system	I-Application
from	O
the	O
rest	O
of	O
the	O
path	O
;	O
the	O
root	O
is	O
represented	O
by	O
a	O
dollar	O
( $	O
)	O
sign	O
and	O
directories	O
are	O
separated	O
by	O
a	O
full	O
stop	O
(	O
.	O
)	O
.	O
</s>
<s>
Extensions	O
from	O
foreign	O
file	B-Application
systems	I-Application
are	O
shown	O
using	O
a	O
slash	O
(	O
example.txt	O
becomes	O
example/txt	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
ADFS::HardDisc4.	O
$	O
is	O
the	O
root	O
of	O
the	O
disc	O
named	O
HardDisc4	O
using	O
the	O
Advanced	B-Device
Disc	I-Device
Filing	I-Device
System	I-Device
(	O
ADFS	O
)	O
file	B-Application
system	I-Application
.	O
</s>
<s>
When	O
using	O
cross-platform	B-Operating_System
software	I-Operating_System
,	O
filetypes	O
can	O
be	O
invoked	O
on	O
other	O
systems	O
by	O
naming	O
appending	O
'/[extension]'	O
to	O
the	O
filename	O
under	O
.	O
</s>
<s>
A	O
file	B-Application
system	I-Application
can	O
present	O
a	O
file	O
of	O
a	O
given	O
type	O
as	O
a	O
volume	O
of	O
its	O
own	O
,	O
similar	O
to	O
a	O
loop	B-Application
device	I-Application
.	O
</s>
<s>
It	O
is	O
not	O
necessary	O
for	O
the	O
archive	O
to	O
contain	O
the	O
data	O
it	O
refers	O
to	O
:	O
some	O
symbolic	O
link	O
and	O
network	O
share	O
file	B-Application
systems	I-Application
put	O
a	O
reference	O
inside	O
the	O
image	O
file	O
and	O
go	O
elsewhere	O
for	O
the	O
data	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
abstraction	O
layer	O
API	B-Application
uses	O
32-bit	O
file	O
offsets	O
,	O
making	O
the	O
largest	O
single	O
file	O
4GiB	O
(	O
minus	O
1	O
byte	O
)	O
long	O
.	O
</s>
<s>
However	O
,	O
prior	O
to	O
RISC	B-Operating_System
OS	I-Operating_System
5.20	O
the	O
file	B-Application
system	I-Application
abstraction	O
layer	O
and	O
many	O
RISC	O
OS-native	O
file	B-Application
systems	I-Application
limited	O
support	O
to	O
31bits	O
(	O
just	O
under	O
2GiB	O
)	O
to	O
avoid	O
dealing	O
with	O
apparently	O
negative	O
file	O
extents	O
when	O
expressed	O
in	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
notation	I-General_Concept
.	O
</s>
<s>
Some	O
common	O
file	O
formats	O
from	O
other	O
systems	O
are	O
mapped	O
to	O
filetypes	O
by	O
the	O
MimeMap	O
module	B-Application
.	O
</s>
<s>
The	O
RISC	B-Operating_System
OS	I-Operating_System
kernel	O
is	O
single-tasking	O
and	O
controls	O
handling	O
of	O
interrupts	B-Application
,	O
DMA	B-General_Concept
services	O
,	O
memory	O
allocation	O
and	O
the	O
video	O
display	O
;	O
the	O
cooperative	O
multi-tasking	O
is	O
provided	O
by	O
the	O
WindowManager	O
module	B-Application
.	O
</s>
<s>
The	O
WIMP	B-Application
interface	I-Application
is	O
based	O
on	O
a	O
stacking	B-Device
window	I-Device
manager	I-Device
and	O
incorporates	O
three	O
mouse	O
buttons	O
(	O
named	O
Select	O
,	O
Menu	O
and	O
Adjust	O
)	O
,	O
context-sensitive	B-Application
menus	O
,	O
window	O
order	O
control	O
(	O
i.e.	O
</s>
<s>
send	O
to	O
back	O
)	O
and	O
dynamic	O
window	O
focus	B-Application
(	O
a	O
window	O
can	O
have	O
input	O
focus	B-Application
at	O
any	O
position	O
on	O
the	O
stack	O
)	O
.	O
</s>
<s>
The	B-Device
icon	I-Device
bar	I-Device
(	O
Dock	O
)	O
holds	O
icons	O
which	O
represent	O
mounted	O
disc	O
drives	O
,	O
RAM	O
discs	O
,	O
running	O
applications	O
,	O
system	O
utilities	O
and	O
docked	O
:	O
files	O
,	O
directories	O
or	O
inactive	O
applications	O
.	O
</s>
<s>
These	O
icons	O
have	O
context-sensitive	B-Application
menus	O
and	O
support	O
drag-and-drop	O
operation	O
.	O
</s>
<s>
They	O
represent	O
the	O
running	O
application	O
as	O
a	O
whole	O
,	O
irrespective	O
of	O
whether	O
it	O
has	O
open	O
windows	B-Application
.	O
</s>
<s>
The	O
GUI	B-Application
functions	O
on	O
the	O
concept	O
of	O
files	O
.	O
</s>
<s>
Application	B-Application
directories	I-Application
are	O
used	O
to	O
store	O
applications	O
.	O
</s>
<s>
The	O
Style	O
Guide	O
encourages	O
a	O
consistent	O
look	B-Application
and	I-Application
feel	I-Application
across	O
applications	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
was	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
to	O
provide	O
scalable	O
anti-aliased	O
fonts	O
.	O
</s>
<s>
Anti-aliased	O
fonts	O
were	O
already	O
familiar	O
from	O
Arthur	O
,	O
and	O
their	O
presence	O
in	O
RISC	B-Operating_System
OS	I-Operating_System
was	O
confirmed	O
in	O
an	O
early	O
1989	O
preview	O
,	O
featuring	O
in	O
the	O
final	O
RISC	B-Operating_System
OS	I-Operating_System
2	O
product	O
,	O
launched	O
in	O
April	O
1989	O
.	O
</s>
<s>
A	O
new	O
version	O
of	O
the	O
font	O
manager	O
employing	O
"	O
new-style	O
outline	O
fonts	O
"	O
was	O
made	O
available	O
after	O
the	O
release	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
,	O
offering	O
full	O
support	O
for	O
the	O
printing	O
of	O
scalable	O
fonts	O
,	O
and	O
was	O
provided	O
with	O
Acorn	O
Desktop	O
Publisher	O
.	O
</s>
<s>
This	O
outline	O
font	O
manager	O
provides	O
support	O
for	O
the	O
rendering	O
of	O
font	O
outlines	O
to	O
bitmaps	O
for	O
screen	O
and	O
printer	O
use	O
,	O
employing	O
anti-aliasing	B-Algorithm
for	O
on-screen	O
fonts	O
,	O
utilising	O
sub-pixel	O
anti-aliasing	B-Algorithm
and	O
caching	O
for	O
small	O
font	O
sizes	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
the	O
introduction	O
of	O
Acorn	O
's	O
outline	O
font	O
manager	O
,	O
the	O
developers	O
of	O
rival	O
desktop	B-General_Concept
systems	I-General_Concept
were	O
either	O
contemplating	O
or	O
promising	O
outline	O
font	O
support	O
for	O
still-unreleased	O
products	O
such	O
as	O
Macintosh	B-Operating_System
System	I-Operating_System
7	I-Operating_System
and	O
OS/2	B-Application
version	O
2	O
.	O
</s>
<s>
Since	O
1994	O
,	O
in	O
RISC	B-Operating_System
OS	I-Operating_System
3.5	O
,	O
it	O
has	O
been	O
possible	O
to	O
use	O
an	O
outline	O
anti-aliased	O
font	O
in	O
the	O
WindowManager	O
for	O
UI	O
elements	O
,	O
rather	O
than	O
the	O
bitmap	O
system	O
font	O
from	O
previous	O
versions	O
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
4	O
does	O
not	O
support	O
Unicode	O
but	O
"	O
RISC	B-Operating_System
OS	I-Operating_System
5	O
provides	O
a	O
Unicode	O
Font	O
Manager	O
which	O
is	O
able	O
to	O
display	O
Unicode	O
characters	O
and	O
accept	O
text	O
in	O
UTF-8	O
,	O
UTF-16	O
and	O
UTF-32	O
.	O
</s>
<s>
Other	O
parts	O
of	O
the	O
RISC	B-Operating_System
OS	I-Operating_System
kernel	O
and	O
core	O
modules	B-Application
support	O
text	O
described	O
in	O
UTF-8.	O
"	O
</s>
<s>
Support	O
for	O
the	O
characters	O
of	O
RISC	B-Operating_System
OS	I-Operating_System
(	O
and	O
some	O
other	O
historic	O
computers	O
)	O
was	O
added	O
to	O
Unicode	O
13.0	O
(	O
in	O
2020	O
)	O
.	O
</s>
<s>
is	O
available	O
in	O
several	O
distributions	O
,	O
all	O
of	O
which	O
include	O
a	O
small	O
standard	O
set	O
of	O
desktop	B-Application
applications	I-Application
,	O
but	O
some	O
of	O
which	O
also	O
include	O
a	O
much	O
wider	O
set	O
of	O
useful	O
programs	O
.	O
</s>
<s>
Limited	O
software	B-Architecture
portability	I-Architecture
exists	O
with	O
subsequent	O
versions	O
of	O
the	O
OS	O
and	O
hardware	O
.	O
</s>
<s>
Single-tasking	O
BBC	B-Language
BASIC	I-Language
applications	O
often	O
require	O
only	O
trivial	O
changes	O
,	O
if	O
any	O
.	O
</s>
<s>
Successive	O
OS	O
upgrades	O
have	O
raised	O
more	O
serious	O
issues	O
of	O
backward	B-General_Concept
compatibility	I-General_Concept
for	O
desktop	B-Application
applications	I-Application
and	O
games	O
.	O
</s>
<s>
The	O
introduction	O
of	O
the	O
RiscPC	B-Device
in	O
1994	O
and	O
its	O
later	O
StrongARM	B-Device
upgrade	O
raised	O
issues	O
of	O
incompatible	O
code	O
sequences	O
and	O
proprietary	B-Application
squeezing	O
(	O
data	B-General_Concept
compression	I-General_Concept
)	O
.	O
</s>
<s>
Patching	O
of	O
applications	O
for	O
the	O
StrongARM	B-Device
was	O
facilitated	O
and	O
Acorn	O
's	O
UnsqueezeAIF	O
software	O
unsqueezed	O
images	O
according	O
to	O
their	O
AIF	O
header	O
.	O
</s>
<s>
The	O
incompatibilities	O
prompted	O
release	O
by	O
The	O
ARM	B-Architecture
Club	O
of	O
its	O
Game	O
On	O
!	O
</s>
<s>
The	O
version	O
of	O
the	O
OS	O
for	O
the	O
A9home	B-Device
prevented	O
the	O
running	O
of	O
software	O
without	O
an	O
AIF	O
header	O
(	O
in	O
accord	O
with	O
Application	O
Note	O
295	O
)	O
to	O
stop	O
"	O
trashing	O
the	O
desktop	O
"	O
.	O
</s>
<s>
The	O
Iyonix	B-Device
PC	I-Device
(	O
)	O
and	O
A9home	B-Device
(	O
custom	O
)	O
saw	O
further	O
software	O
incompatibility	O
because	O
of	O
the	O
deprecated	O
addressing	O
modes	O
.	O
</s>
<s>
Some	O
older	O
26-bit	B-Architecture
software	O
can	O
be	O
run	O
without	O
modification	O
using	O
the	O
Aemulor	B-Device
emulator	O
.	O
</s>
<s>
Additional	O
incompatibilities	O
were	O
introduced	O
with	O
newer	O
ARM	B-Architecture
cores	O
,	O
such	O
as	O
ARMv7	O
in	O
the	O
BeagleBoard	B-Application
and	O
ARMv8	O
in	O
the	O
.	O
</s>
