<s>
The	O
LINK	B-Device
480Z	I-Device
was	O
an	O
8-bit	O
microcomputer	B-Architecture
produced	O
by	O
Research	O
Machines	O
Limited	O
in	O
Oxford	O
,	O
England	O
,	O
during	O
the	O
early	O
1980s	O
.	O
</s>
<s>
The	O
480Z	O
used	O
a	O
Z80	B-General_Concept
microprocessor	I-General_Concept
with	O
up	O
to	O
256KB	O
of	O
bank-switched	B-General_Concept
RAM	B-Architecture
.	O
</s>
<s>
The	O
system	O
could	O
be	O
used	O
as	O
a	O
stand-alone	O
unit	O
with	O
cassette-based	O
storage	O
and	O
the	O
BASIC	O
programming	O
language	O
run	O
from	O
ROM	B-Device
,	O
or	O
it	O
could	O
boot	B-Operating_System
CP/NOS	O
(	O
a	O
network	O
version	O
of	O
CP/M	B-Application
)	O
over	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
from	O
a	O
file	B-Application
server	I-Application
.	O
</s>
<s>
When	O
fitted	O
with	O
an	O
optional	O
external	O
floppy	B-Device
disk	I-Device
drive	I-Device
the	O
system	O
could	O
boot	B-Operating_System
the	O
CP/M	B-Application
operating	I-Application
system	I-Application
directly	O
.	O
</s>
<s>
The	O
480Z	O
was	O
sold	O
mainly	O
to	O
the	O
UK	O
educational	O
market	O
as	O
cassette-based	O
system	O
or	O
as	O
a	O
diskless	B-Device
node	I-Device
which	O
could	O
be	O
connected	O
,	O
via	O
the	O
proprietary	O
CHAIN	O
Network	O
,	O
to	O
a	O
Research	B-Device
Machines	I-Device
380Z	I-Device
acting	O
as	O
a	O
file	B-Application
server	I-Application
.	O
</s>
<s>
The	O
LINK	B-Device
480Z	I-Device
was	O
packaged	O
as	O
an	O
integrated	O
keyboard	O
and	O
system	O
unit	O
.	O
</s>
<s>
The	O
optional	O
5¼-inch	O
floppy	B-Device
disk	I-Device
drive	I-Device
unit	O
was	O
external	O
.	O
</s>
<s>
The	O
only	O
microprocessor	B-Device
offered	O
was	O
a	O
4MHz	O
Z80A	B-General_Concept
.	O
</s>
<s>
Although	O
some	O
early	O
systems	O
had	O
only	O
32KB	O
(	O
32×1024	O
bytes	B-Application
)	O
of	O
RAM	B-Architecture
,	O
most	O
480Zs	O
were	O
fitted	O
with	O
at	O
least	O
64KB	O
of	O
memory	O
.	O
</s>
<s>
Bank	B-General_Concept
switching	I-General_Concept
allowed	O
memory	O
to	O
be	O
extended	O
to	O
128KB	O
on	O
the	O
main	B-Device
board	I-Device
,	O
and	O
up	O
to	O
256KB	O
by	O
using	O
the	O
option	O
board	O
(	O
which	O
also	O
included	O
the	O
high	B-Algorithm
resolution	I-Algorithm
graphics	O
hardware	O
)	O
.	O
</s>
<s>
As	O
the	O
Z80	B-General_Concept
processor	O
could	O
directly	O
address	O
only	O
64KB	O
without	O
software	O
support	O
the	O
additional	O
memory	O
was	O
typically	O
used	O
as	O
a	O
RAM	B-Application
disk	I-Application
,	O
specifically	O
the	O
Silicon	B-Device
Disk	I-Device
System	I-Device
.	O
</s>
<s>
The	O
480Z	O
was	O
also	O
fitted	O
with	O
up	O
to	O
32KB	O
of	O
firmware	B-Application
that	O
could	O
also	O
be	O
bank-switched	B-General_Concept
out	O
of	O
the	O
normal	O
address	O
space	O
when	O
not	O
in	O
use	O
,	O
leaving	O
a	O
total	O
of	O
58KB	O
of	O
RAM	B-Architecture
directly	O
available	O
to	O
the	O
user	O
,	O
with	O
2KB	O
of	O
RAM	B-Architecture
reserved	O
for	O
system	O
use	O
and	O
4KB	O
inaccessible	O
because	O
of	O
the	O
firmware	B-Application
ROM	B-Device
.	O
</s>
<s>
All	O
480Zs	O
,	O
with	O
the	O
exception	O
of	O
some	O
very	O
early	O
units	O
,	O
were	O
fitted	O
with	O
software-switchable	O
40×24	O
or	O
80×24	O
character	O
text-only	B-Application
monochrome	O
video	B-Device
hardware	I-Device
.	O
</s>
<s>
The	O
text-mode	B-Application
display	O
had	O
its	O
own	O
dedicated	O
memory	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
text-mode	B-Application
video	O
interface	O
the	O
system	O
could	O
be	O
enhanced	O
with	O
an	O
option	O
board	O
providing	O
a	O
high-resolution	B-Algorithm
graphics	O
capability	O
and	O
an	O
additional	O
TTL	B-General_Concept
RGB	O
interface	O
for	O
a	O
colour	O
monitor	O
.	O
</s>
<s>
Extra	O
high	B-Algorithm
resolution	I-Algorithm
:	O
640×192	O
pixels	B-Algorithm
,	O
1	O
bit	O
per	O
pixel	B-Algorithm
,	O
1	O
page	B-General_Concept
.	O
</s>
<s>
High	B-Algorithm
resolution	I-Algorithm
:	O
320×192	O
pixels	B-Algorithm
,	O
2	O
bits	O
per	O
pixel	B-Algorithm
,	O
1	O
page	B-General_Concept
.	O
</s>
<s>
Medium	O
resolution	O
:	O
160×96	O
pixels	B-Algorithm
,	O
4	O
bits	O
per	O
pixel	B-Algorithm
,	O
2	O
pages	O
.	O
</s>
<s>
A	O
programmable	O
lookup	B-Data_Structure
table	I-Data_Structure
with	O
an	O
8-bit	O
output	O
mapped	O
the	O
pixel	B-Algorithm
value	O
to	O
one	O
of	O
256	O
different	O
intensities	O
(	O
composite	O
video	O
)	O
or	O
one	O
of	O
8	O
colours	O
(	O
TTL	B-General_Concept
RGB	O
output	O
)	O
.	O
</s>
<s>
Output	O
from	O
the	O
graphics	B-Device
board	I-Device
was	O
mixed	O
with	O
output	O
from	O
the	O
text-only	B-Application
video	O
interface	O
,	O
allowing	O
text	O
and	O
graphics	O
to	O
be	O
easily	O
overlaid	O
.	O
</s>
<s>
Memory	O
in	O
both	O
the	O
text	O
and	O
graphics	O
video	O
interfaces	O
was	O
accessed	O
by	O
the	O
processor	O
using	O
port-mapped	B-General_Concept
I/O	I-General_Concept
and	O
therefore	O
did	O
not	O
consume	O
memory	O
address	O
space	O
.	O
</s>
<s>
Mass	B-Device
storage	I-Device
was	O
either	O
via	O
cassette	B-Device
tape	I-Device
,	O
floppy	B-Device
disk	I-Device
,	O
or	O
an	O
external	O
file	B-Application
server	I-Application
.	O
</s>
<s>
ROS	O
1.2	O
(	O
see	O
below	O
)	O
and	O
later	O
systems	O
could	O
be	O
connected	O
via	O
a	O
serial	O
interface	O
to	O
an	O
external	O
single	O
or	O
dual	O
5¼-inch	B-Device
disk	I-Device
drive	O
unit	O
with	O
a	O
built-in	O
double	B-Device
density	I-Device
Intelligent	O
Disc	O
Controller	O
(	O
IDC	O
)	O
.	O
</s>
<s>
Disk	O
capacity	O
was	O
180KB	O
(	O
48	O
TPI	B-Device
drives	O
)	O
or	O
360KB	O
(	O
96	O
TPI	B-Device
drives	O
)	O
per	O
side	O
.	O
</s>
<s>
Research	O
Machines	O
also	O
offered	O
plug-in	O
ROM	B-Device
Packs	O
,	O
containing	O
up	O
to	O
64KB	O
of	O
ROM	B-Device
.	O
</s>
<s>
These	O
connected	O
via	O
the	O
parallel	O
interface	O
allowing	O
applications	O
to	O
be	O
quickly	O
loaded	O
into	O
RAM	B-Architecture
.	O
</s>
<s>
The	O
LINK	B-Device
480Z	I-Device
supported	O
a	O
proprietary	O
800kbit/s	O
CHAIN	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
that	O
ran	O
over	O
a	O
coaxial	O
cable	O
in	O
a	O
similar	O
manner	O
to	O
10BASE2	O
Ethernet	O
.	O
</s>
<s>
Using	O
the	O
built-in	O
Z-Net	O
firmware	B-Application
a	O
diskless	B-Device
480Z	O
could	O
be	O
directly	O
booted	O
from	O
a	O
network	O
file	B-Application
server	I-Application
(	O
typically	O
a	O
Research	B-Device
Machines	I-Device
380Z	I-Device
)	O
.	O
</s>
<s>
The	O
480Z	O
motherboard	B-Device
contained	O
the	O
processor	O
and	O
up	O
to	O
128KB	O
of	O
RAM	B-Architecture
as	O
well	O
as	O
most	O
of	O
the	O
external	O
interfaces	O
:	O
</s>
<s>
Parallel	O
I/O	B-General_Concept
–	O
used	O
either	O
as	O
a	O
high-speed	O
link	O
for	O
the	O
external	O
disk	O
drives	O
or	O
ROM	B-Device
Packs	O
,	O
or	O
as	O
a	O
Centronics	B-Device
printer	I-Device
port	I-Device
.	O
</s>
<s>
The	O
high	B-Algorithm
resolution	I-Algorithm
graphics	O
and	O
memory	O
option	O
board	O
allowed	O
an	O
extra	O
128KB	O
of	O
RAM	B-Architecture
to	O
be	O
added	O
and	O
included	O
a	O
TTL	B-General_Concept
RGB	O
monitor	O
output	O
.	O
</s>
<s>
The	O
option	O
board	O
could	O
also	O
be	O
fitted	O
with	O
an	O
IEEE-488	O
interface	O
and	O
an	O
AMD	O
9511	O
or	O
9512	O
floating	B-Algorithm
point	I-Algorithm
coprocessor	B-General_Concept
.	O
</s>
<s>
The	O
480Z	O
was	O
fitted	O
with	O
up	O
to	O
32KB	O
of	O
firmware	B-Application
:	O
</s>
<s>
ROM	B-Device
monitor	O
(	O
ROS	O
)	O
–	O
8KB	O
.	O
</s>
<s>
Z-Net	O
network	O
firmware	B-Application
–	O
4KB	O
.	O
</s>
<s>
BASIC	O
in	O
ROM	B-Device
–	O
20KB	O
.	O
</s>
<s>
ROS	O
(	O
standing	O
for	O
Resident	O
Operating	B-General_Concept
System	I-General_Concept
)	O
provided	O
a	O
monitor	O
program	O
and	O
a	O
set	O
of	O
basic	O
system	O
services	O
.	O
</s>
<s>
The	O
monitor	O
could	O
be	O
used	O
to	O
start	O
BASIC	O
from	O
ROM	B-Device
,	O
load	O
application	O
programs	O
from	O
cassette	O
,	O
or	O
boot	B-Operating_System
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
ROS	O
also	O
provided	O
a	O
software	O
front	B-Device
panel	I-Device
allowing	O
a	O
display	O
of	O
registers	O
and	O
memory	O
,	O
and	O
supporting	O
breakpoints	O
and	O
single-stepping	O
of	O
machine	O
code	O
.	O
</s>
<s>
ROS	O
provided	O
a	O
number	O
of	O
basic	O
hardware	O
control	O
functions	O
,	O
such	O
as	O
keyboard	O
input	O
,	O
writing	O
text	O
to	O
the	O
video	O
memory	O
and	O
disk	O
input/output	B-General_Concept
.	O
</s>
<s>
ROS	O
functions	O
were	O
called	O
by	O
means	O
of	O
the	O
Emulator	O
Trap	B-Application
(	O
EMT	O
)	O
pseudo-opcode	O
,	O
which	O
used	O
the	O
Z80	B-General_Concept
RST30H	O
instruction	O
to	O
call	O
the	O
EMT	O
handler	O
function	O
.	O
</s>
<s>
The	O
EMT	O
handler	O
read	O
the	O
first	O
byte	B-Application
following	O
the	O
RST30H	O
instruction	O
to	O
determine	O
which	O
EMT	O
function	O
was	O
being	O
requested	O
;	O
all	O
parameters	O
were	O
passed	O
in	O
registers	O
.	O
</s>
<s>
A	O
call-relative	O
pseudo-opcode	O
was	O
also	O
implemented	O
using	O
RST28H	O
.	O
</s>
<s>
ROS	O
services	O
were	O
largely	O
compatible	O
with	O
the	O
COS	O
services	O
provided	O
on	O
the	O
earlier	O
Research	B-Device
Machines	I-Device
380Z	I-Device
.	O
</s>
<s>
The	O
Z-Net	O
firmware	B-Application
was	O
used	O
to	O
allow	O
the	O
system	O
to	O
network	B-Device
boot	I-Device
from	O
a	O
file	B-Application
server	I-Application
over	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Research	O
Machines	O
provided	O
a	O
full	O
version	O
of	O
their	O
BASIC	O
interpreter	B-Application
as	O
part	O
of	O
the	O
standard	O
firmware	B-Application
.	O
</s>
<s>
ROS	O
1.2	O
–	O
added	O
floppy	B-Device
disk	I-Device
support	O
.	O
</s>
<s>
The	O
main	O
operating	B-General_Concept
systems	I-General_Concept
were	O
CP/M	B-Application
2.2	O
if	O
booted	O
from	O
disk	O
or	O
CP/NOS	O
(	O
a	O
network-only	O
version	O
of	O
CP/M	B-Application
)	O
if	O
booted	O
from	O
a	O
file	B-Application
server	I-Application
.	O
</s>
<s>
Systems	O
running	O
CP/M	B-Application
could	O
access	O
network	O
services	O
using	O
CP/NET	O
.	O
</s>
<s>
Many	O
standard	O
CP/M	B-Application
applications	O
were	O
available	O
,	O
such	O
as	O
WordStar	B-Application
.	O
</s>
<s>
Research	O
Machines	O
also	O
produced	O
their	O
own	O
assembler	B-Language
(	O
ZASM	O
)	O
,	O
text	B-Application
editor	I-Application
(	O
TXED	O
)	O
and	O
BASIC	O
interpreter	B-Application
.	O
</s>
<s>
Programs	O
for	O
the	O
earlier	O
Research	B-Device
Machines	I-Device
380Z	I-Device
written	O
in	O
high-level	O
languages	O
,	O
such	O
as	O
BASIC	O
,	O
or	O
using	O
only	O
basic	O
CP/M	B-Application
and	O
standard	O
firmware	B-Application
functions	O
,	O
could	O
be	O
run	O
directly	O
on	O
the	O
480Z	O
.	O
</s>
<s>
Programs	O
that	O
wrote	O
directly	O
to	O
hardware	O
such	O
as	O
the	O
high-resolution	B-Algorithm
graphics	B-Device
cards	I-Device
were	O
generally	O
incompatible	O
.	O
</s>
