Ram Extension For Bbc-B Computer

RAM EXTENSION FOR BBC-B COMPUTER P. J. O"Shea The original BBC microcomputer has one serious shortcoming: lack of user RAM. In the highest screen resolution mode, on a disk system, there are not quite 6 Kbytes available for BASIC programs. The RAM extension board described in this article raises this figure to over 25 Kbytes, available to any language, including word processors, independent of screen mode and without reducing processing speed. Driver software is available to support the extension, which can be used as two banks of sideways RAM, into which sideways ROM programs can be loaded without using up a ROM socket inside the machine. To the user of shadow RAM it appears as if the extension memory is the screen memory and external to the microproces- sor memory field. Hence the whole of what used to be the screen memory is freed for use. In reality, the shadow memory appears in the memory map as shown in Fig. 1. The shadow block is sideways to a block of the main memory in th...