BBC Micro expansion unit

Interior of the 6502 Second Processor

The 6502 Second Processor (using a 65C02) was clocked at 3 MHz, a full 50% faster than the 6502 inside a BBC Model B, and also had 64 KB of RAM, of which typically 30–44 KB was free for application data (compared to as little as 8.5 KB on an unexpanded Model B in graphics mode, or only 5.75 KB with the disc interface). A version of BBC BASIC II, called Hi-BASIC, was delivered on ROM with this processor together with a DNFS ROM containing the latest versions of the disc filing system (DFS) and Econet network filing system (NFS). The product was launched with a price of £199.[2]

The Bitstik CAD system,[3] originally developed by Robocom for the Apple II,[4] was offered as an accessory for the 6502 Second Processor, also requiring dual 80-track floppy drives. The Bitstik system itself was introduced with a price of around £375, which combined with floppy drives estimated at £500, the second processor at £199, the cost of the BBC Micro itself at £399, and the price of a colour monitor (Acorn recommending their own RGB monitor[3]^(pp2)), the total investment was estimated to be between £1500 to £2000 depending on any particular customer's existing equipment and preferences.[5] Featuring a three-axis joystick, offering the usual two-dimensional navigation plus a knob to control zooming, the software worked in the high-resolution four-colour display mode, providing support for the display and editing of scalable vector graphics. The dual-drive arrangement was necessary to allow the first drive to provide access to the utilities and for the second drive to act as a "drawing buffer".[6]

Various CAD programs were able to take advantage of the 6502 Second Processor, as was the second processor-specific version of Elite. Hi versions of View, WordWise and Intersheet were also produced.

The Z80 Second Processor featured a Z80B CPU running at 6 MHz accessing 64 KB of RAM. It required the floppy disc upgrade and, being aimed at business, enabled the BBC system to run CP/M programs. As noted in one review, with reference to the intended appeal of the BBC Micro to the home, education and business markets, with the Z80 second processor "Acorn have completed the BBC Microcomputer system as originally planned".[5]

The product was launched in mid-1984 at a price of £299 and included an estimated £3000 worth of bundled software that included the CP/M 2.2 operating system itself (with GSX graphics), CIS Cobol and utilities from Microfocus, the Memo Plan, Graph Plan and File Plan office applications from Chang Laboratories, the Accountant and Nucleus packages from Compact Accounting Services, and two BASIC implementations: Z80 BBC BASIC and Mallard Professional BASIC.[7]

Despite "a policy of continuous improvement", Acorn apparently abandoned plans to update the software bundle in mid-1986 due to a review of the CP/M market.[8]

Originally referred to as the Gluon, a National Semiconductor 32016 second processor solution was apparently planned for the BBC Micro and for other 8-bit microcomputers, with the BBC Micro version employing the Tube interface and offering a quarter of a megabyte of RAM, whereas the "Universal Gluon" would be connected to a microcomputer acting as a terminal using a serial or parallel interface, offer up to 1 MB of RAM, up to 5 MB of hard disk storage, and either a minimal operating system or Unix.[9] Subsequent news of the second processor indicated the renaming of the product, dropping the Gluon name, the use of Acorn's own Panos operating system instead of Xenix, with availability in 1985.[10]

The product that was eventually delivered is a sophisticated second processor expansion sometimes branded as "Acorn Cambridge Co-Processor" with an Acorn logo, and sometimes as "BBC Microcomputer System 32016 Second Processor" along with the BBC Micro's owl logo. The device uses the 32016 CPU and 32081 FPU running at 6 MHz. It runs the non-graphical Panos operating system. Various programming languages are available including C, FORTRAN, Lisp, and Pascal, in addition to a version of BBC BASIC. Initially offered as the 32016 Second Processor with 256 KB of RAM,[11] the expansion was subsequently delivered as the Cambridge Co-Processor with 512 KB or 1 MB of RAM as standard.[12]

The 32016 second processor is also present as part of the Acorn Cambridge Workstation using an 8 MHz CPU[13] and 4 MB of RAM, sold as part of the Acorn Business Computer line. Originally, Acorn had apparently sought to use CPUs rated for 10 MHz, but seemed to have settled for available parts as the different products were introduced. The second processor board was also able to use 64-kilobit or 256-kilobit RAM devices, thus allowing the earlier 256 KB specification to be upgraded to 1 MB as the higher-density devices became available and affordable.[14]

The Universal Second Processor Unit was an adapter for BBC Master internal co-processor boards, to allow them to be used as external co-processors. It comprised a power supply, interface logic and a connector that matched the internal co-processor connector built into the BBC Master main board. This allowed the BBC B and B+ to use the Turbo board (4 MHz 65C102 with 64 KB of RAM) and the Master 512 board (10 MHz 80186 with 512 kKB of RAM), by fitting them into this expansion unit. It also allowed the BBC Master to have two internal co-processor boards connected, only one of which could be enabled through software.[15]

As one of the first production RISC processors, the ARM Evaluation System was part of the development programme leading to the Acorn Archimedes and its early Arthur operating system. It was not branded "BBC", but it is physically contained within the family's "cheese wedge" case. The ARM 1 processor was clocked at 8 MHz, and was fitted with 2 MB or 4 MB of RAM.

In 2006, a new ARM processor board using an ARM7TDMI processor was designed and sold, without an enclosure but able to fit within the original case.[16]

Several other second processor solutions were produced by third party suppliers, typically employing a different style of casing than the standard expansion unit profile, with some using the 1 MHz bus instead of the Tube connector, and with others merely providing a conventional serial link.

Z80 second processors offering 64 KB of RAM and CP/M-compatible operating systems included the Multiform Z80 from Technomatic, priced at £299,[17] and several products from Torch Computers such as the Z80 Disc Pack (ZDP) and ZEP, the latter priced at around £340.[18]

Torch also offered the Intel 8088-based Graduate running MS-DOS and having 256 KB of RAM and dual floppy drives, priced at £1000 plus VAT,[19] and the Z80- and 68000-based HDP68K or Unicorn, the latter running Unix and having 256 KB of RAM or more, floppy drive and 20 MB hard drive.[20]

Various other 68000-based second processor solutions were offered, such as the Casper by CA Special Products,[21] the Cambridge Microprocessor Systems 68000 second processor,[22] the Flight Electronics 68000 processor board,[23] and the Micro Developments MD512k Universal Second Processor System.[24]

Cumana chose to produce a 68008 second processor running the OS-9 operating system that was installed into the 6502 CPU socket, relocating the 6502 to the second processor board itself, and providing 512 KB RAM and its own disk controller. It was priced at £695 plus VAT.[25]

Cambridge Microprocessor Systems and Control Universal both offered 6809 second processor solutions supporting the FLEX operating system.[26]

Permanent Memory Systems produced a 6502 second processor, the B2P 6502, employing a 2 MHz 65C02 processor - as opposed to the faster 6502 device used by the Acorn 6502 Second Processor unit - together with 64 KB of RAM. Connecting to the Tube and 1 MHz bus connectors, the expansion did not use Acorn's Tube ULA and thus risked incompatibility with some software written for the Acorn unit, but the benefit of this approach was the B2P's more competitive price of around £100.[27]

The teletext-like "Mode 7" display mode inside the 8-bit BBC Micros made a broadcast teletext adapter an obvious expansion, and the BBC would broadcast telesoftware free over Ceefax. The hardware and software design was created by Graham Toal.[28] The initial software to use the adapter was quite basic but the BBC decided to rewrite it and produced the Advanced Teletext System. This new ROM added several new features including support for the new Fastext system, which introduced the four coloured buttons subsequently found almost ubiquitously on European remote controls, including the "red button" which remains a feature of digital television broadcasting.

The adapter itself was mains powered with its own power switch matching the one on the BBC microcomputer. Connection to the computer was via a ribbon cable and the only other connector on the adapter was a female 75ohm TV aerial (in) connector. The adapter contained four manual tuning wheels to receive signals from four different broadcast channels. Rear view of the adapter. Once tuned, use of the adapter, including switching channels, was controlled via the computer. Teletext pages were displayed on the computer monitor.

The Prestel adapter was essentially a modem fitted into the "cheese wedge"-shaped case. It enabled the user to connect to Prestel viewdata services over a telephone line.

Allowed the BBC Micro to talk over an IEEE-488 bus to specialised equipment. "Acorn" rather than "BBC" branded.

• BeebMaster's Cheese Wedges
• Chris' Acorns

• Binary Dinosaurs 32016 co-processor
• BeebMaster's 32016
• Acorn Cambridge Co-Processor @ The Centre for Computing History

• Acorn Business Computer

• ARM Processor types
• ARM Evaluation System pictures
• ARM Evaluation System software
• Acorn ARM Evaluation System @ The Centre for Computing History