sidecar

sidecar n.  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.