Operating System and File System - Practices

A New Breed of Operating Systems

The commonly used smart card operating system supports a file system as specified in ISO 7816-4. Although the may pose a little resemblance to the commonly employed operating systems such as windows, UNIX etc.

APDUs, which are specified under ISO 7816-4 are generally file system oriented commands. It contains a user application that mainly compromise of data file that are used for storing application specific information. Operating system is used implement semantics and instruction for accessing the data file.

Since, the old system does not have a well defined separation between the operating system and the application. So, newer operating system, which support a better system layer and downloading of custom application code are now in wider use.

A File System Too

File system used for the smart card have a hierarchical file system and supports three types of file:

1. Master file (MF): this single file is the root of the file system and contains dedicated file and elementary files.
   
   
2. Dedicated file (DF): it is the directory of the smart card and holds all files like dedicated and elementary files.
   
   
3. Elementary file (EF): it is a file which contains other files. It can be further categorized into:
   1. Transparent file: this file consists of structured sequence of data bytes.
   2. Other’s : these files consist of sequence of individually identifiable records
      1. Linear fixed file: it contains records of fixed size.
      2. Variable: It contains records of variable size.
      3. Cyclic file: it consists of files organized as ring structure.

An operation on any file is done after opening it; some of the cards in use open the master file as soon as the powered is on. Access condition allows the access to file system, and it can be easily specified distinctive for distinct read and write operation.