if other capabilities were needed, and then reconnected later. Consequently, multi-function expansions offering a combination of different capabilities offered a significant degree of convenience as well as avoiding wear on the expansion connector. Alongside announcements of Acorn's then-unreleased Plus 1, Solidisk previewed a General Purpose Interface for the Electron in early 1984 offering a Centronics printer port, switched joystick port, user port, sideways ROM sockets, and mini-cartridge sockets supported by the 6522 versatile interface adapter (VIA) chip. The Plus 1 itself was released in mid-1984, introducing the influential cartridge format for expansions ultimately used by several other companies. Acorn Plus 1 The Acorn Plus 1 added two ROM cartridge slots, an analogue interface (supporting four channels) and a Centronics parallel port, priced at £59.90. The analogue interface was normally used for joysticks, although trackball and graphics tablet devices were available, and the parallel interface was typically used to connect a printer. Game ROM cartridges would boot automatically. Languages in paged ROM cartridges would take precedence over BASIC. (The slot at the front of the interface took priority if both were populated.) Access to ROM occurred at 2 MHz until RAM access was required, so theoretically programs released on ROM could run up to twice as fast as those released on tape or disc. Despite this, all of the games released on ROM were packaged as ROM filing system cartridges, from which the micro would load programs into main memory in exactly the same way as if it were loading from tape. This meant that programs did not need to be modified for their new memory location and could be written in BASIC but gave no execution speed benefits. Six ROM cartridge titles were announced for the launch of the Plus 1: three arcade games, one adventure game, one educational title, and the Lisp language implementation, the latter being a genuine language ROM that "takes the place of the BASIC ROM" and is instantly available when switching on. The cartridge slots provided additional control lines (compared to the lines available via the edge connector on the rear of the Electron) to ease implementation of ROM cartridges. Acorn described the hardware extension possibilities in promotional literature, giving an RS423 cartridge as an example of this capability of the Plus 1. Additional peripheral cartridges were produced by companies such as Advanced Computer Products (and subsequently PRES) whose Advanced ROM Adaptor (ARA) and Advanced