This unit was designed to provide the Atari XL series of home computers: 600XL, 800XL (Unreleased 1400XL & 1450XLD) with expansion slots. The XL Expansion System contained 5 8-bit PBI (Parallel Bus Interface) slots which could accommodate a variety of expansion options. Also a control line was added to the PBI to allow a "BUS MASTERING" card such as an alternative CPU card to take over the Bus and in effect, take over the computer. This would have allowed for alternative CPU configurations like an Intel 8086 processor for IBM compatibility or the 65816 processor which was the 16-bit version of the 6502 processor used in all of the Atari 8-bit series computers.

          The XL Expansion system appears to have been in a finished and completed form.   The case was complete and although they are scarce for one reason or another the top covers were also completed.   Several cards were completed or near completion and data on the product was delivered to all Atari dealers.   The XL Expansion system would have opened the doors for the Atari 8-bits and allowed them to grow in all new ways. However in 1984 Atari, Inc was acquired by Jack Trameil and like so many innovative Atari projects, the 1090 XL Expansion system made it to the garbage dumpster and not the Atari Retailers shelves.