computer hosts , such as pdas , are customized for use in bar code scanner applications through use of a first - level removable expansion module having bar code related circuitry and a slot and internal connector for a second - level removable memory . in combination with a connected or attached i / o device for scanning bar codes , these modules provide embedded bar code scanning i / o adapter and / or application - specific functions as well as second - level removable memory functions . the removable memory may be used to store a backup copy of the scanned data for restoration in the event the original scan data is lost or corrupted . restoration may occur using any interface compatible with the removable memory . the removable memory may also be used by the bar code scanner application specific circuitry within the first - level removable expansion module . in illustrative embodiments , an industry standard physical and electrical interface couples the application specific module to the computer host , which provides user interface functions for the application .