Sibling relationship and block allocation table in file system for smart card operating system

摘要

Smart card operating system has main functions to manage command execution and manage files in memory. To facilitate the file management, a modest file system which has single rooted hierarchy is designed. Sibling relationship, which is a relation between child files under the same directory file, is used to make relation between files. This relation enables parent file to get connected with every child. Memory allocation which uses 1 byte addressing needs a large amount of memory. To reduce memory usage, addressing method with block allocation table (BAT) is used. Using BAT, memory is divided into three main parts: block allocation table which indicates the use of every blocks in memory, file table which contains information about file structure and file relation, and file body which contains information about file type, access condition, and actual data. There are three file types supported by this file system: transparent, fixed-length record, and variable-length record. This file system is tested using file management and file access command. The operating system is written in C language and implemented in FPGA-based smart card with 8051 processor.