Boulder-based ProStor Systems, a developer of removable disk drive cartridges targeted at the backup market, reported today that it has increased the capacity of its removable disk cartridges to 640GB. The firm said that the new, upgraded disks are fully read- and write- compatible with its prior line of products. ProStor develops the RDX removable disk format, and licenses that to others. The firm is looking to displace tape drive technology with its removable cartridges, which use hard disk drive technology instead of tape backup. The firm's technology has been licensed to companies such as Dell, Fujitsu, HP, IBM, Imation, Maxell, NEC and Tandberg Data. ProStor said the new, upgraded cartdiges will begin shipping this month.