Article Directory
1. The logical structure of the file
1. Unstructured documents
The data inside the file is a series of binary streams or character streams, also known as stream files .
2. Structured documents
Structured files are divided into three categories: sequential files, index files, and index sequential files
Sequential file
Index file
Index file
Note: The search efficiency of multi-level index table is high
2. File directory
1. File control block
2. Directory structure
Single-level directory structure
Two-level directory structure
Multi-level directory structure
Multi-level directory structure is not easy to share files, then we introduce acyclic graph directory structure
3. Improvement of index nodes
Summary of file directory
Three, file distribution method
File block, disk block
1. Sequential distribution
Advantages: When disk blocks are read sequentially, the speed is the fastest when continuously allocated
Disadvantages:
- Files stored in sequence are not convenient for expansion
- Physically uses continuous allocation, low storage space utilization, and hard-to-use disk fragments
2. Link Assignment
Implicit link
Explicit link
3. Index allocation
When the file is expanded , just add a row of data to the index table
When a disk block cannot fit the index table of a file, we have the following three methods:
- Link scheme
- Multi-level index
- Mixed index
Link scheme
Multi-level index
Mixed index
Index method summary
4. File storage space management
1. Free list method
2. Free linked list method
3. Bitmap method
4. Group link method
Allocate 100 free blocks
When all the packets are full, another disk block needs to be reclaimed
Five, file sharing
1. Sharing method based on index node (hard link)
2. Sharing mode based on symbolic chain (soft link)
Six, file protection
1. Password protection
2. Encryption protection
What is saved in the system is the result of data encryption, and the original data can be seen only after decryption with a password.
Advantages: strong confidentiality, no need to store passwords in the system
Disadvantages: encryption and decryption takes time
3. Access Control
When the user of the computer a lot, you need to set the unit for access control
