1. Syn. slap on the side. Esp. used of add-ons for the late and unlamented IBM PCjr. 2. The IBM PC compatibility box that could be bolted onto the side of an Amiga. Designed and produced by Commodore, it broke all of the company's own design rules. If it worked with any other peripherals, it was by magic. 3. More generally, any of various devices designed to be connected to the expansion slot on the left side of the Amiga 500 (and later, 600 & 1200), which included a hard drive controller, a hard drive, and additional memory.