Simple plastic card, just at the size of a credit card, with a microprocessor and memory embedded inside is a smart card. Beside its tiny little structure it has many uses and wide variety of applications ranging from phone cards to digital identification of the individuals.
These application could be; identity of the customer, library card, e-wallet, keys to various doors, etc... And only one card can be issued to an end-entity for all these applications. Smart cards hold these data within different files, and , as you will read, these data is only visible to its program depending on the operating system of the card. These data files are arranged in a file system much like a Linux directory structure.
MF (Master File)
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-------------+--------------
| | |
EF (Elementary File) EF DF (Dedicated File)
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---------+--------
| | |
EF DF EF
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EF |
MF (Master File), can be seen as the root directory where the headers of elementary files and dedicated files are contained. Dedicated files are like the ordinary directories and elementary files are just data files. The PIN is also stored in an EF but only the card has access permission to this file. The attributes of the files on UNIX environments are changed to access conditions. Many cards have access condition lists which must be fulfilled before accessing the data.
With the file system, access conditions, a microcomputer, RAM, ROM, EEPROM a smart card is just a computer running its own operating system inside your wallet.