The BBC Master 128 was the standard machine in the Master Series. This was an enhanced and expanded version of the BBC Model B with a 65C12 microprocessor at its heart, a later version of the 6502 used in the Model A and B.
The Master 128 was supplied with a 1 Mega-Bit ROM containing the Acorn operating system, Terminal, Edit, View, Viewsheet, ADFS, DFS and BASIC all in a single ROM.
A 1770 series disc interface was provided as standard and 128K RAM made up of 32K user RAM, 20K shadow screen RAM, 12K private RAM and 64K sideways RAM usable either as a continuous block of memory or as 4 16K segments designed to take ROM images loaded from disc.
The Master 128 came in a number of variations. There are two motherboard issues with various different forms of MOS ROM. Most are in a standard 28-pin ROM package but some are mounted on a little carrier board. Some machines reportedly have the MOS ROM soldered onto the board. The connector at PL12 is either a plug, a socket or missing altogether.
Click here to see the Master 128 issue 1