<s>
The	O
Acorn	O
Eurocard	O
systems	O
were	O
a	O
series	O
of	O
modular	O
microcomputer	B-Architecture
systems	O
based	O
on	O
rack-mounted	O
Eurocards	O
developed	O
by	O
Acorn	O
Computers	O
from	O
1979	O
to	O
1982	O
,	O
aimed	O
primarily	O
at	O
industrial	O
and	O
laboratory	O
use	O
,	O
but	O
also	O
home	O
enthusiasts	O
.	O
</s>
<s>
The	O
experience	O
gained	O
in	O
developing	O
this	O
modular	O
system	O
strongly	O
influenced	O
the	O
design	O
of	O
Acorn	O
's	O
first	O
all-in-one	O
home	O
computer	O
,	O
the	O
Acorn	B-Device
Atom	I-Device
,	O
released	O
in	O
March	O
1980	O
;	O
and	O
also	O
much	O
of	O
the	O
circuitry	O
in	O
its	O
successor	O
,	O
the	O
BBC	B-Device
Micro	I-Device
,	O
first	O
shown	O
in	O
late	O
1981	O
.	O
</s>
<s>
Placing	O
the	O
two	O
Eurocards	O
from	O
the	O
original	O
Acorn	B-Device
Microcomputer	I-Device
onto	O
a	O
backplane	B-Architecture
made	O
the	O
system	O
straightforward	O
to	O
expand	O
in	O
a	O
modular	O
way	O
.	O
</s>
<s>
The	O
original	O
I/O	O
card	O
,	O
minus	O
its	O
keypad	O
and	O
LED	O
display	O
,	O
became	O
the	O
cassette	O
interface	O
card	O
;	O
while	O
the	O
original	O
6502	B-General_Concept
CPU	O
card	O
,	O
slightly	O
adapted	O
with	O
the	O
addition	O
of	O
a	O
keyboard	O
interface	O
,	O
became	O
the	O
basic	O
CPU	O
card	O
of	O
the	O
system	O
.	O
</s>
<s>
A	O
series	O
of	O
interchangeable	O
expansion	O
cards	O
were	O
then	O
developed	O
:	O
additional	O
RAM	O
cards	O
;	O
a	O
card	O
containing	O
the	O
Acorn	O
System	O
BASIC	O
interpreter	O
on	O
ROM	O
;	O
a	O
40×25	O
character	O
VDU	O
card	O
,	O
and	O
a	O
UHF	O
adaptor	O
for	O
it	O
;	O
interface	O
cards	O
;	O
a	O
floppy	B-Device
disk	I-Device
controller	I-Device
;	O
Econet	B-Device
network	O
cards	O
;	O
an	O
80×25	O
character	O
VDU	O
card	O
;	O
and	O
later	O
also	O
alternate	O
processor	O
cards	O
,	O
offering	O
a	O
6809	B-Device
or	O
a	O
faster	O
6502	B-General_Concept
.	O
</s>
<s>
It	O
was	O
the	O
successor	O
to	O
the	O
Acorn	B-Device
Microcomputer	I-Device
(	O
renamed	O
the	O
Acorn	B-Device
System	I-Device
1	I-Device
)	O
.	O
</s>
<s>
The	O
system	O
comprised	O
four	O
Eurocard-sized	O
printed	O
circuit	O
boards	O
mounted	O
in	O
a	O
19inch	O
sub-rack	O
frame	O
on	O
an	O
8-slot	O
backplane	B-Architecture
,	O
plus	O
a	O
(	O
separately	O
supplied	O
)	O
additional	O
external	O
keyboard	O
.	O
</s>
<s>
a	O
CPU	O
card	O
,	O
containing	O
a	O
1MHz	O
6502	B-General_Concept
microprocessor	I-General_Concept
,	O
the	O
keyboard	O
interface	O
,	O
and	O
a	O
2K	O
ROM	O
with	O
the	O
cassette	O
operating	O
system	O
(	O
The	O
6502	B-General_Concept
card	O
could	O
be	O
swapped	O
for	O
a	O
6809	B-Device
.	O
)	O
</s>
<s>
a	O
VDU	O
card	O
,	O
providing	O
a	O
40×25	O
character	O
teletext-standard	O
display	O
,	O
based	O
on	O
an	O
MC6845	B-General_Concept
CRT	O
controller	O
and	O
an	O
SAA5050	B-General_Concept
teletext	O
character	O
generator	O
,	O
</s>
<s>
The	O
CPU	O
card	O
and	O
cassette	O
interface	O
card	O
were	O
the	O
same	O
cards	O
as	O
used	O
the	O
System	B-Device
1	I-Device
,	O
but	O
with	O
the	O
keypad	O
and	O
LED	O
display	O
of	O
the	O
latter	O
left	O
unused	O
.	O
</s>
<s>
The	O
Acorn	O
System	O
3	O
added	O
a	O
floppy	B-Device
disk	I-Device
controller	I-Device
card	O
,	O
floppy	O
disk	O
drive	O
,	O
and	O
disk	O
operating	O
system	O
ROM	O
,	O
replacing	O
the	O
cassette	O
interface	O
card	O
and	O
cassette	O
operating	O
system	O
of	O
the	O
System	O
2	O
machine	O
.	O
</s>
<s>
The	O
System	O
3	O
became	O
the	O
standard	O
workhorse	O
for	O
development	O
in	O
the	O
Acorn	O
lab	O
:	O
the	O
Acorn	B-Device
Atom	I-Device
has	O
been	O
called	O
a	O
cut-down	O
version	O
of	O
the	O
System	O
3	O
;	O
and	O
it	O
was	O
based	O
on	O
the	O
System	O
3	O
that	O
much	O
of	O
the	O
development	O
work	O
for	O
the	O
BBC	B-Device
Micro	I-Device
was	O
done	O
.	O
</s>
<s>
The	O
Acorn	B-Device
System	I-Device
5	I-Device
was	O
the	O
final	O
Acorn	O
rack-mounted	O
system	O
,	O
released	O
in	O
1983	O
.	O
</s>
<s>
As	O
standard	O
it	O
had	O
a	O
1MHz	O
6502	B-General_Concept
,	O
32K	O
DRAM	O
,	O
a	O
disk	O
controller	O
,	O
and	O
either	O
the	O
80×25	O
or	O
the	O
Teletext	O
40×25	O
VDU	O
cards	O
.	O
</s>
<s>
Customers	O
could	O
choose	O
which	O
cards	O
to	O
install	O
in	O
the	O
remaining	O
slots	O
,	O
including	O
interface	O
cards	O
,	O
an	O
additional	O
16K	O
DRAM	O
card	O
,	O
and/or	O
an	O
Econet	B-Device
network	O
adapter	O
;	O
they	O
could	O
also	O
choose	O
to	O
upgrade	O
the	O
processor	O
board	O
to	O
a	O
faster	O
2MHz	O
6502	B-General_Concept
board	O
.	O
</s>
