The Scalar i6000 supports a capacity-on-demand model. Physical slot capacity is sold separately from licensed slot capacity. Customers must purchase expansion modules, tape drives, slot licenses, and other options as required. With a single robot, the library can support up to 16 modules (Control Module plus 15 expansion modules). With dual robots, library can support up to 17 modules (Control Module plus 16 expansion modules, one of which will function as the Left Parking Module and one of which will function as the Right Parking Module). Library can also support up to 12,006 cartridge slots, 192 tape drives, 16 I/E Stations (with 24 to 1,104 slots) and two robots. There is a tradeoff between number of slots and drives. As drives are added, the maximum number of slots may decrease and vice versa, so it is not possible to have both a maximum of 12,006 cartridge slots AND 192 tape drives.