of memory for the display, with the expansion listening to display memory write accesses and buffering the data in its own memory. A ROM was included to extend the operating system to allow activation of Mode 7 as a genuine screen mode and to provide extra commands and to support keyboard shortcuts used on the BBC Micro to emit Teletext control sequences. To support the output of both the Mode 7 display and the existing video output, a lead connected the Electron's RGB output to the expansion, with the expansion providing only RF (television) output. Conscious of the relatively high price of the Mark 1 unit, John Wike of Jafa devised and, at the end of 1988, introduced a software-based Mode 7 Simulator, priced at £25, supplied on a ROM cartridge that rendered the Mode 7 display in a low-resolution, 8-colour graphics mode. Although cheap and effective in enabling use of some software that only used official operating system routines for text output, this solution proved very slow because the Electron had to be placed into the high-bandwidth Mode 2 display to be able to show eight colours at once. In doing so, the CPU spent a lot of time drawing representations of Mode 7 characters and graphics that in a hardware solution would be achieved without any demand on the CPU. It also used up 20 KB of RAM for the graphics display rather than the 1000 bytes of a hardware Mode 7. A conceptually similar predecessor to the software-based simulator was published by Electron User in early 1987, offering a monochrome Mode 4 simulation of the Teletext display, using the lower 25 character lines of the screen to show the Teletext output, reserving several lines at the top of the screen for a representation of Mode 7 used to prepare the eventual visual output. However, the program did not support direct access to Mode 7 memory locations. The author noted that a Mode 2 version would have been possible but would have required a redesigned character set and "too much memory". A further refinement of the hardware solution was introduced in 1989 with the Mode 7 Mark 2 Display Unit, which retained the SAA5050 character generator but omitted the 6845 display controller, and was fitted internally in the Electron itself instead of being housed in an external unit, although some kind of ROM expansion unit was needed to