Tony Saxby reports:
I was the product manager at RM looking after network
products. The 480Z was designed to offer a lower cost computer to schools.
It was primarily designed as a network station. The network interface
was based on Zilog's Z-NET a 1 (later enhanced to 2) Mb/s CSMA/CD system,
not unlike ethernet (but in thoose days much cheaper!).
The system was origionally designed to go into
a plastic "Structural foam" case, but just before production
started the tool for the case was 'dropped' and damaged. A short term
solution was to us a welded steel case - thus the black 480Z was born.
We had quite a few prototypes made, which were painted different colours.
It was somewhat of a status symbol to have one of these on your desk.
I guess 'black' was choosen because it was the house colour at the time.
It took over a year to get the plastic case on line, at which time we
moved over to the more common cream colour.
The 480Z was a twin board system. There was the
main logic board and then an option board that plugged in above the main
one. This provided high res graphics (sorry can't remember the resolution).
It also had an IEE488 intrumentation bus option as well. Thought to be
honest I don't think we sold that many of those. The board had this option
in order for RM to
qualify for a DTI (Department of trade and Industry) grant towards its
development! If memory serves me right this was in the order of £200K
- which was a considerable sum in those days.
The system was sold in two versions - the cheaper
40 Character wide video mode and the 80 character wide one. The price
difference was about £150 .. the only difference was the rom chip
and a link! Later on everything went onto 80 character as standard (about
the time the plastic case came out).
The system ran CP/M and the network was based on
CP/NET. Very basic by todays standards, but fully workable and reliable.
Most problems were simply cable faults.
The 380Z and 480Z family has a BIOS written by
David Small (who later setup a company in the UK called High-level Hardware).
It had a full Z-80 debugger which could be used to single step through
code - looking at all the internal registers. It was called the 'Front
Panel'. It also had a really neat feature that enabled BIOS routines to
be simply accessed - the op-code F7 followed by an argument could call
up any of the BIOS routines. The FF op-code was the BREAK into debugger.
It made writing and degugging z-80 code a real breeze.
RM was unique in that it published the full source
code for the BIOS.
The 480Z was never designed for floppy disks and
as such didn't have any hardware in them for that purpose. The floppy
drives were an 'after thought'. These were commonally known as the 'Toaster'
because of the shape of the case. The drives had a rather expensive controller
inside and communicated with the host using nothing more complicated as
a high speed serial interface. It did the job, but was slow and very expensive
The 480Z was superceeded by the Nimbus PC-186 -
it was at this stage we ditched CP/M and moved over to MS products. But
that is a different story.