The BBC and Master Computer Public Domain Library
Acorn 8 Bit History
This text is copied faithfully from Robert
McMordie's website here
Thanks to Robert McMordie
1978 December Acorn formed by Herman Hauser.
1979 March System One launched.
1979 to 1980 Systems Two, Three and Four launched.
1980 System Five launched.
1980 Acorn Atom launched.
1981 November BBC Micro Models A and B launched.
1983 August Acorn Electron launched.
1984 BBC Model B+ launched.
1984 Acorn Business Machine range launched, including Acorn Cambridge Workstation.
1986 January BBC Master 128 launched.
1986 September BBC Master Compact launched.
The beginings - The founding of Acorn and the System x machines (1978
Acorn Computers Ltd were founded in December 1978 in Cambridge, England, as
Cambridge Processor Unit. The founders, Chris Curry and Herman Hauser, came
from Sinclair Research and Cambridge University respectively. Their first
contact was with Ace Coin Equipment, to provide fruit machines.
In 1979, Curry and Hauser were approached by Roger Wilson, who had developed
a machine but had no OS ROM for it. The software had been written but not
tested. Acorn's facilities were used to blow the operating system software
in to a PROM. The PROM was plugged in and the machine switched on - and booted
first time. It turned out that there were only two minor bugs in the software,
both to do with LED configurations. This machine became known as the System
The System 1 was based on the 8-bit Mostek 6502 processor and was supplied
with 256 bytes of RAM, a 512 byte monitor in ROM, a keypad and a cassette
interface. The System 1 was sold as a self assembly kit for £69. A variety
of add-ons were produced for this machine, with one of the more interesting
ones being a device that, when connected up and switched on, would play "God
Save The Queen".
Systems 2, 3 and 4 followed in from the System 1, and were enhancements of
the basic machine with up to 32 Kb of RAM, a variety of different computers
and a selection of additional interfaces, including a VDU, analogue and disc
interfaces. The System x range reached a peak in 1980, with the System 5.
This was a rack-based modular system, based on a slightly faster version of
the 6502 than the previous models in the range.
The entry into the home market - The Acorn Atom (1980).
The Atom was Acorn's first attempt to break into the home market. Released
in 1980, it continued Acorn's association with the 6502 processor, with the
1 MHz 6502A used in the Atom. The operating system and an integer-only version
of BBC BASIC were provided in 8 Kb of ROM and 2 Kb of RAM (expandable to 12
Kb) was available.
The Atom was a highly expandable machine, with UHF TV and tape connectors
provided as standard, as well as two expansion ports. A wide range of peripherals
could be added using these ports, including a floppy drive, using an early
version of Acorn's DFS (Disc Filing System), and Econet (a networking system
devised by Acorn and the University of Cambridge). A high resolution video
graphics card and floating point extension ROM for BASIC could also be added.
The graphics system was capable of 32 by 24 and 16 by 12 character text modes
and 128 by 96 and 256 by 192 pixel graphics modes, with four colours available
simultaneously from a total palette of 8. The video controller selected was
the 6847, which was the most advanced available at the time, but was slightly
flawed in that it was basically designed for an NTSC display, and could only
produce a signal at 60 Hz, rather than the 50 Hz required by PAL. As a result
it was incompatible with about 20% of TVs. A multiple channel sound system
was also supplied.
The Atom was sold in a ready made form, for £170, or in self-assembly
form for £120.
The BBC Computer Literacy Project - The BBC Micro (1981).
The BBC Microcomputer is perhaps the best known of all Acorn's computers.
The design was originally developed during 1980 under the name Proton. Acorn
had decided to stick with the 6502 processor as the basis for the new machine
but, in an attempt to mininise the risk associated with making a bad choice,
developed an interface port that allowed the simple connection of a second
Around this time the BBC were launching their Computer Literacy Project,
and were looking for a machine to link it with. An outline specification was
sent out to a number of manufacturers, including Acorn, Sinclair and Dragon.
The outline specification matched the specification Acorn had developed for
the Proton, and the BBC arranged to come and see the machine in operation.
The only problem was that the machine didn't at that time exist. The meeting
had been arranged on a Monday for the following Friday - Curry and Hauser,
assisted by Steve Furbur and Roger Wilson, spent Monday, Tuesday and Wednesday
assembling the machine, and the first test took place on the Wedneday evening,
and the machine didn't work. Finally, at 7am on Friday morning, it was found
that the problem was due to timing differences between the prototype machine
and the development kit. The meeting with the BBC took place at 10am, and
the people from the BBC were impressed with what they saw and awarded Acorn
a contract for 12,000 machines. The Proton was renamed the BBC Microcomputer
To enable the BBC Micro to be so fast, a large amount of the computer circuity
was bundled up in to two Uncommitted Logic Arrays (ULAs), of which 10,000
were ordered from Ferranti. When the completed chips were delivered, it turned
out that only 3%, those at the top end of the specified speed range, would
work. Fortunately, Ferranti were able to manufacture new versions and get
the revised chips back to Acorn in just three days.
Initially two versions of the BBC Micro were launched, known as the Model
A and the Model B. Both were based around a 2 MHz 6502 processor and featured
the same operating system and language, BBC BASIC I (later BBC BASIC II),
housed in 32 Kb of ROM. Both machines also had standard TV, cassette, RGB
monitor, RS423 serial and analogue ports and three special Acorn-designed
ports, the User Port, 1 MHz Bus and the Tube. The User Port was designed to
allow peripherals such as turtles to be attached, the 1 MHz Bus for peripherals
that needed direct system bus access and the Tube allowed the easy connection
of a second processor. The main differences between the two systems were the
amount of RAM (the Model A had 16 Kb and the Model B had 32 Kb) and the number
of interfaces (the Model B was supplied with two additional interfaces, allowing
a disc drive and a printer to be added). The BBC Micro could also be networked,
with the addition of an optional Acorn Econet adapter.
There was also a variant released for the US and Canadian market. This was
based on the BBC Model B, but included a speech synthesiser system and Econet
interface as standard, and was fitted with BBC BASIC III (based on BBC BASIC
II, but with a number of bug fixed and the addition of the COLOR keyword).
However, problems gaining FCC approval delayed the introduction of the US
variant, and it never gained the same degree of popularity that it did in
The original BBC Micro cost £235 or £335 (for the Model A and
Model B, respectively), but this was later increased to £299 and £399.
The Beeb turned out to be incredibly popular, and sold in excess of 1,000,000
units worldwide before it was discontinued in 1986. At one point it was the
computer of choice in seven out of ten schools, and enjoyed a 60% market share.
Acorn needed to produce something fairly spectactular to live up to the success
of the BBC Micro.
After the Beeb - the Electron and the Acorn Business Computer (1983 to
Despite the popularity of the Beeb, it was a relatively expensive machine
to buy. To address this problem, Acorn introduced a cut-down version of the
Model B. This machine was the Acorn Electron.
The Electron was developed by Acorn during 1983, with the aim of releasing
it in time for the Christmas rush. In terms of hardware it was similar to
the Beeb, and used the same processor, the 6502A, operating system and BASIC
variant (BBC BASIC II). However, much of the functionality of the Electron
was contained in a single ULA, thus cutting down manufacturing costs. The
other main difference between the BBC Micro and the Electron was that the
Electron did not have the extra circuitry to display the Beeb's teletext mode.
There were also a number of other hardware differences.
Although the basic Electron only came with six ports (power supply in, TV
out, video out, RGB monitor out, cassette interface and expansion connector)
it was relatively easy to expand, mainly due to Acorn's Plus 1 and Plus 3
add-ons. The Plus 1 plugged in to the expansion connector and added two cartridge
slots, a printer interface and the ability to add extra ROMs to the system.
The Plus 3 was a complete 3.5" disc drive system that also plugged directly
in to the expansion slot. A Plus 1 could then be added using an expansion
slot on the back of the Plus 3. This device also came with an uprated power
supply unit, to cope with the extra demands made by the floppy drive. Even
after the original Plus 1 and Plus 3 were no longer available, a number of
other companies, particularly Slogger and PRES, were still manufacturing peripherals
that made use of the expansion connector.
In the end, however, the ULA took too long to develop, and the Electron was
released too late to take full advantage of Christmas 1983. By Christmas 1984,
the Electron has been largely superseded, and it never enjoyed the popularity
of its larger brother, although a number of enhanced Electrons did find their
way in to Interflora shops, as the "Interflora Messenger".
Following the problems with the Electron, Acorn was in serious financial
trouble, and in 1984 the company was rescued by Olivetti. To help revive flagging
sales of the BBC Micro a new stop-gap revision was introduced, known as the
Model B+. This was basically a BBC Model B with a number of glitches cured
and 64 Kb or 128 Kb of RAM. While this machine was not at popular as the original
machines, it still managed to sell somewhere in the region of 28,000 units.
At around this time, Acorn started looking at a previously unknown market
- that of business machines. The result was the introduction of the Acorn
Business Computer range in 1984 and 1985. These machines were based on the
Model B+, housed in a different case with an integral monitor and separate
keyboard. What made them different was the inclusion of a variety of second
processors and associated operating systems. There were a total of eight machines
in the range, both discless and hard disc based, and with between 64 Kb and
4096 Kb of RAM. All machines consisted of a 6502 processor with a "parasite"
second processor. The available second processors and operating systems were
a 32016 running PANOS, an 80286 running various versions of DOS and a Z80
running CP/M. The most successful machine in the range was the 32016-based
Model 210, later known as the Cambridge Workstation. This contained 4096 Kb
of RAM, and was supplied with a 10 Mb hard disc. By default it was supplied
with PANOS, but Xenix was also used on this machine. Eventually some of the
second processors used in the ABC range were released as second processors
for the existing range of BBC Micros. Of these the Z80-based solution became
the most popular.
At the end of 1985 Acorn were in serious need of a new machine. The BBC Micro
range was looking dated, and the Electron and ABC range was not selling as
they perhaps had hoped. Fortunately, a new 6502-based machine was in development,
that it was hoped would revive Acorn's fortunes - the BBC Master.
The next generation - The BBC Master series (1986).
The BBC Master 128 was released in January 1986, as a replacement for
the highly successful BBC Micro range. It used the same basic architecture
as the earlier system, and was backward compatible with it, but contained
many enhancements and improvements. The BBC Master was based on the 8-bit
65C02 processor, a later revision of the 6502A used in the earlier Acorn systems,
and was provided with four times the memory, 128 Kb. To allow existing peripherals
to be used with the new system, it came with the same range of interfaces
as the BBC Model B, including the Tube and the user port. Two cartridge slots,
similar to those provided with the Plus 1, were also added to the system,
as well as a numeric keypad. It could also be used with the Acorn Econet network
system, and contained a space inside the case intended for an internal modem.
In addition to the hardware improvements, there were numerous software improvements.
The operating system was enhanced, and additional software was provided in
ROM, including an updated version of BBC BASIC (BBC BASIC IV) and Acorn's
wordprocessor and spreadsheet, View and Viewsheet. The existing Disc Filing
System (DFS), originally supplied with the BBC Model B, was supplemented by
an updated version of the Advanced Disc Filing System (ADFS), originally supplied
with the Electron's Plus 3, allowing better use to be made of 3.5" discs.
(DFS was traditionally used with 5.25" discs.)
The BBC Master was released in a number of different varients. As well as
the BBC Master 128, the Master Compact, Master ET, Master 512 and Master Turbo
models were also released. The Master Compact (released in September 1986)
was a standard BBC Master 128 fitted in to a three-box case along the same
lines as the later Archimedes, with an integral 3.5" disc drive and lacking
some of the interfaces (although an add-on was available which provided some
of the missing interfaces). The Master ET was a Master 128 provided with an
Econet interface, but without the disc drive and printer interfaces, and was
intended as a network terminal. The Master 512 was a standard Master 128 with
an internal 80186 coprocessor system, and 512 Kb of memory, running DOS. Finally,
the Master Turbo was a BBC Master 128 with an internal 65C02 second procesor.
The basic BBC Master 128 sold for £499, and the Master Compact sold
for £599. The BBC Master and its varients proved to be almost as popular
as the original BBC Micro - by 1989 over 200,000 Master 128s and 70,000 Master
Compacts had been sold.
In my opinion, one of the most interesting applications of the BBC Master
was in connection with the BBC Domesday Project. The hardware, consisting
of a specially enhanced BBC Master Turbo (the enhancement consisting of an
internal SCSI interface and a Videodisc Filing System ROM) fitted with a laser
disc player and trackerball, released in November 1986, was used to display
facts about modern life in the U.K. Schools and members of the public all
over Great Britain contributed to the project, by compiling information about
their local area.
While Acorn was developing and marketing the BBC Master, the PC world was
moving on from 8-bit processors to the 16-bit 80x86-class chips. Acorn had
already realised that sooner or later the 6502 chip, and all 8- and 16-bit
chips, would eventually become obsolete, and had already started developing
their own 32-bit chip - the Acorn RISC Machine, or ARM.
Hinted, less than 10,000 System 1, System 2 and System 3 combined
Over 10,000 Acorn Atom computers
Over 1,000,000 BBC Micro Models A and B, perhaps over 1,500,000
About 30,000 Electron computers
Over 28,000 BBC B+ computers
Over 200,000 BBC Master 128
Over 70,000 Master Compact