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TOPIC 3: FILE MANAGEMENT, Access Method, Also known as relative access.
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TOPIC 3: FILE MANAGEMENT
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THE DIRECTORY STRUCTURE includes storage structure, directory structure, single-level structure, two-level structure
(nur athirah)
INTRODUCTION
- The file systems of computers, can be extensive.
- Some systems store millions of files on terabytes of disk.
- To manage all these data, we need to organize them.
- This organization involves the use of directories.
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A Typical File-system Organization
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- Also known as relative access.
- A file is made up of fixed length logical records
- The file is viewed as a numbered sequence of blocks or records.
-Databases are often of this type.
Scenario Example
3.To store information about a larger set, such as people, we might compute a hash function on the people's names or search a small in-memory index to determine a block to read and search.
1.On an airline-reservation system, we might store all the information about a particular flight (for example, flight 713) in the block identified by the flight number.
2.Thus, the number of available seats for flight 713 is stored in block 713 of the reservation file.
- Information in the file is processed in order, one record after the other.
- The most common.
- For example, editors and compilers usually access files in this method.
- Most operations on a file are read and write.
- A read operation—read next—reads the next portion of the file and automatically advances a file pointer, which tracks the I/O location.
- The write operation—write next—appends to the end of the file and advances to the end of the newly written material (the new end of file).
- With large files, the index file itself may become too large to be kept in memory.
- One solution is to create an index for the index file.
- The primary index file would contain pointers to secondary index files, which would point to the actual data items.
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- contains pointers to the various blocks.
- search the index(find a record in file) and use the pointer(access file)