BeebMaster - BBC Microcomputer




BBC Microcomputer Model B+

In 1984, Acorn switched production to the BBC Model B+ which came in two forms, the 64K machine and the 128K machine.

The B+ looked almost identical to the earlier BBC micro from the outside but contained a redesigned circuit board layout. The 6502 was replaced with the newer 65C12 and there was provision for both 8271 and 1770 disc interfaces to be fitted (although not at the same time).

Acorn cleverly moved the sideways ROM sockets to make them accessible without removing the keyboard. BASIC II was supplied as before along with a new edition, version 2.00, of the Operating System. A combined ROM provided both BASIC and OS in a single chip.

Never again would "BBC Computer" appear in the start-up message for an Acorn machine; instead the user was greeted with the message "Acorn OS" after switch-on.

32K of additional RAM was provided for the BBC Model B+. This took the form of 20K shadow screen RAM and 12K of extra workspace memory. Using the shadow RAM to hold the screen memory map meant that all the memory previously only available in Teletext mode 7 was available to the high resolution graphics modes.

In its 128K form, the Model B+ had a 64K sideways RAM daughter board fitted which was allowed the contents of ROMs to be stored on disc and loaded into memory when required as if they were present as ROMs inside the computer. This would reduce the need for opening up the computer to change ROMs and having to store languages and applications on EPROM chips. Sideways RAM became invaluable to ROM developers who could now try out their efforts without having to blow an EPROM every time a test was needed.