The BBC Master is a home computer released by Acorn Computers in early 1986. It was designed and built for the British Broadcasting Corporation (BBC) and was the successor to the BBC Micro Model B. The Master 128 remained in production until 1993.
Design The Master series featured several improvements over earlier BBC Micro models. Rather than the MOS Technology 6502 microprocessor used by the Model B, Master series models used the slightly improved 65C12. Fabricated using CMOS technology, the 65C12 used less power than the 6502 and offered somewhat better performance, reportedly "almost as fast" as the original 3 MHz 6502 second processor for the BBC Micro. The systems had of dynamic RAM as standard, alleviating the shortage of available RAM which had previously discouraged use of the display modes offering the highest quality graphics on earlier models. Of the total 128 KB of RAM, 64 KB was provided as standard RAM, being used for applications, screen memory and system workspace. Another 64 KB was provided in the form of four 16 KB bank-switched pages of sideways RAM.
Of the 64 KB standard RAM, the lower region of 32 KB was employed in a fashion familiar from earlier models, providing workspace for languages, applications and the system, also hosting screen memory for many programs, particularly games. While the 65C12 ensured software compatibility with the Model B, it perpetuated the architectural limitations of the earlier models, with a 16-bit address bus providing direct access to only 64 KB of memory at a time, thus necessitating the use of paging mechanisms to make additional RAM available. Access to the upper 32 KB region of standard RAM was provided by one such mechanism to take over some of the demands made on the lower memory region by the system. It was divided into three separate regions, each with a code-name, following Acorn's architectural traditions:
Codename Size Physical address range Logical address range Description LYNNE 20 KB Shadow RAM (freeing conventional screen memory for use) HAZEL 8 KB Paged ROM workspace (filing system workspace) ANDY 4 KB System workspace (function key, graphics system and character definitions)
20 KB of this upper region could be assigned as shadow RAM to host the screen memory, freeing up the conventional screen memory region for applications. The remaining 12 KB was available to the system for workspace, freeing up memory that would normally be claimed by ROMs such as filing systems. The cumulative effect of enabling shadow RAM and using the upper memory for workspace made almost 29 KB available for normal programs and was said to "transform the machine" from its predecessors.
Use of the 64 KB of sideways RAM favoured the installation of ROM images into each of the 16 KB banks, with Acorn having announced a "ROM licencing scheme" to authorise the use of the company's ROM-based software in RAM. However, a version of BASIC known as BAS128, previously released for the BBC Model B+ 128, was provided on disk and was able to use the full 64 KB of sideways RAM as workspace, thus expanding the memory available to BASIC considerably. Other Acorn languages did not support this arrangement, however.
Although the extra instructions of the 65C12 permitted slightly greater code density, the OS and BBC BASIC ROMs, still limited by the memory architecture to 16 KB each, were augmented by additional ROMs. In total, the updated OS, known as MOS 3.2 occupied 35 KB and incorporated features previously introduced in the Graphics Extension ROM for the BBC Micro, along with additional commands and system calls plus a variety of enhancements. The improved version of BBC Basic was named Basic 4, fixing bugs in the earlier Basic 2 and introducing enhancements and new functionality such as a variable yielding the current date and time in a concise but human-readable format. The inclusion of a real-time clock to keep the date and time was a notable built-in feature of the Master 128 and derived models, together with 50 bytes of battery-backed CMOS RAM to retain details of the machine's configuration while powered off.
To hold the expanded OS and BASIC, the Master 128 was fitted with a ROM device having a capacity of one megabit, or 128 KB. Alongside the OS and BASIC, a text editor suitable for writing programs was included, DFS and ADFS provided filing system support to access files stored on disk, the View and ViewSheet applications respectively offered word processing and spreadsheet functionality. A terminal emulator was also included to support serial communications over the machine's RS423 port or the optional internal modem.
The Master series largely carried forward many of the core architectural features of the earlier BBC Micro models. The sound chip used in earlier models was retained, but the dedicated speech interface was omitted, with a "plug-in speech cartridge" anticipated by one reviewer for the Master 128. Although chips such as the 6522 VIA and 6845 CRTC were retained in the Master series, much of the discrete logic of earlier models was consolidated into CMOS gate array chips to perform tasks such as handling the keyboard, input/output and some display functions. This left an impression of the inside of the Master 128 being "another world" compared to the original BBC Micro, featuring fewer but larger chips.
In terms of expansion ports, the Master 128 retained all of the standard interfaces of the BBC Micro. One notable addition to the Master 128 was that of an internal modem socket permitting the installation of a modem without occupying the machine's RS423 serial port. An Econet interface could also be fitted internally at a relatively low cost of £49 including VAT. However, the main addition to the Master 128's expansion capabilities was the inclusion of an internal connector for second processor expansions employing Acorn's Tube interface. The first of such internally connected second processors, known as co-processors, was the Turbo co-processor featuring a 4 MHz 65C102 and 64 KB of RAM, later followed by the Master 512 upgrade board featuring a 10 MHz 80186 and 512 KB of RAM.
Outwardly, the Master series models added a numeric keypad alongside the familiar keyboard, and the Master 128 and its variants incorporated two cartridge slots behind the keypad, these employing sockets that provided a superset of the Acorn Electron Plus 1 cartridge interface capabilities, supporting the use of physically compatible Electron cartridges, but also supporting enhanced electrical characteristics for some of the cartridge connector pins.
Although the Master series was intended to be compatible with "legally written" software for the older models, there were some problems running older programs, particularly games. Conversely, although few programs were ever targeted specifically at Master series machines (except the Master 512), many later BBC games (and Master versions of earlier classics such as Elite) included enhanced features which took advantage of the extra memory.
ROM upgrade An upgrade to the Master 128 operating system ROM was released by Acorn in early 1990, providing bug fixes and some performance and functionality enhancements, with the filing systems benefiting in particular. View, Viewsheet and Edit applications all saw various levels of enhancement. One notable feature was the introduction of "relocatable" language (or application) ROM support, permitting appropriately written ROM-based software to automatically take advantage of a second processor, if fitted. Priced at around £45, it was noted that since the copyright message in the ROM was dated 1988 and the manual dated October 1989, such an upgrade might have been more widely adopted by users (and the relocatable ROM feature adopted by software producers) had it been released earlier, with the Master Compact ROM having already benefited from some of the featured improvements, such as direct entry of "foreign characters" or "top-bit-set characters" from the keyboard.
Battery charging hazard
Acorn issued a safety warning for the Master 128 and ET models in 1986 regarding the battery installed in the machine. This battery was in a circuit that would charge the battery "contrary to the recommendations of the battery manufacturer". Due to the risk of combustion with this particular lithium battery arrangement, Acorn introduced a remedy involving its replacement with a different solution using three alkaline batteries fitted next to the power supply.
Models
The Master series consisted of several different models, all of which apart from the Master Compact were variants of the same basic design.
Master 128 This was the "foundation of the new BBC range" when launched. The 128 in the name referred to its 128 KB of RAM, though it also featured 128 KB ROM. A disc interface was fitted, but the drives themselves were not included in the base product, these being offered by third parties and by Acorn as an official expansion. The machine was introduced at a price of £499.
Master Turbo This was a Master 128 with 4 MHz 65C102 co-processor card (which could be either bought with the machine or added to an existing Master 128). This upgrade cost £125 when introduced.
Master AIV
The Master AIV (Advanced Interactive Videodisc) was essentially a Master Turbo model with a SCSI interface and a VFS (Videodisc Filing System) ROM added, and formed the basis of the BBC Domesday System. Although normally supplied as part of a Domesday System, with LaserVision player, Domesday videodiscs, monitor and trackball included, an upgrade kit was also available to turn a normal BBC Master into a Domesday System.
Master ET The ET (Econet Terminal) system was designed for use in a network and as such had no interfaces except RGB and Composite video, plus an Econet interface module and ANFS fitted as standard (it was usually an option). It used the same main circuit board as the Master 128, but the components for missing interfaces were simply not fitted (though there was nothing stopping them being added later by someone with appropriate soldering skills). The internal ROM also contained much less software than that of the Master 128. This reduced configuration allowed the machine to be priced somewhat cheaper than the Master 128, being introduced at £399.
Master 512 This system boasted a co-processor card with a 10 MHz Intel 80186 and 512 KB memory. It also had the ability to run DOS Plus and the GEM graphical user interface. The co-processor card was introduced at £499 as an upgrade to the Master 128, but its price was subsequently reduced to £399.
The competitiveness of the Master 512 was constrained by its compatibility with various DOS applications, with this being limited by "protection and direct use of IBM hardware" by some applications. The additional memory requirements of DOS Plus, when compared to those of PC DOS, and the requirements of the GEM desktop caused potential problems when running some applications, although memory expansions existed to mitigate such problems. System call compatibility was only assured for MS-DOS and PC DOS 2.1, but other DOS versions were not supported, and undocumented system call usage ("fairly rare, but does include some Microsoft packages") could cause applications to run incorrectly. Software written for later GEM versions would also not necessarily run correctly.