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Background for Relevant Application Specific Functions

Techniques are known in the art for making and using systems that download or capture compressed digital audio for storage and later playback using dedicated removable media. For example, U.S. Pat. No. 5,676,734 ('734), SYSTEM FOR TRANSMITTINGDESIRED DIGITAL VIDEO OR AUDIO SIGNALS, assigned to Parsec Sight/Sound, and hereby incorporated by reference, teaches a system for transmitting digital video or audio signals over a telecommunications link from a first to a second party. In addition,U.S. Pat. No. 5,579,430 ('430), DIGITAL ENCODING PROCESS, assigned to Fraunhofer Gesellschaft zur Foerderung der angewandten Forschung e.V., and hereby incorporated by reference, teaches processes for encoding digitized analog signals. Such processesare useful for insuring high-quality reproduction while reducing transmission bandwidth and data storage requirements.

Techniques are also known in the art for making and using record and playback portable host devices based on a dedicated flash memory. For example, see U.S. Pat. No. 5,491,774 ('774), HANDHELD RECORD AND PLAYBACK DEVICE WITH FLASH MEMORY,assigned to Comp General Corporation, and hereby incorporated by reference, and U.S. Pat. No. 5,839,108 ('108), FLASH MEMORY FILE SYSTEM IN A HANDHELD RECORD AND PLAYBACK DEVICE, assigned to Norris Communications, also hereby incorporated by reference.

SUMMARY OF THE INVENTION

The utility of computer hosts, including portable computer hosts, such as PDAs (or handhelds), is enhanced by methods and apparatus for removable expansion modules (cards) having application specific circuitry, a second-level-removable memory,and optional I/O, in a number of illustrative embodiments. The term "second-level" is intended to emphasize that while the expansion module is removable from a computer host at a first-level of functionality, the expansion memory is independentlyremovable from the expansion module, providing a second-level of functionality. In addition to providing greater expansion utility in a compact and low profile industrial design, the present invention permits memory configuration versatility forapplication specific expansion modules, permitting easy user field selection and upgrades of the memory used in conjunction with the expansion module. Finally, from a system perspective, the present invention enables increased parallelism andfunctionality previously not available to portable computer devices.