The new system would also include an ECI port next to the Cartridge port located on the back panel of the computer system.   The ECI Port stood for: Enhanced Cartridge Interface.   This port provided the additional lines that the original Atari Inc PBI provided to the Atari XL line of computers.   PBI stood for Parallel Bus Interface.   This was a high speed direct bus interface for the XL computers that would allow smart expansion devices and memory modules to be plugged into the back of the XL systems to increase memory, provide alternative video cards and even processor cards.

The ECI would provide those very same capabilities to the XE line of computers.   Originally Atari Inc had planned to release a device in the 3rd quarter of 1984 called the Atari 1090 XL Expansion System.  This was a 5 slot PBI card cage and would've allowed Atari to sell numerous expansion cards for its XL line of computers.   The device was canceled and an XE version was never offered.   So without a standardized means of adding expansion devices to the XL or XE series of computers, several 3rd party companies and in later years, hobbyists, began to develop and sell hard drive interfaces, multi-function boxes, memory expanders and even floppy drive controllers.