File Management
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This document summarizes a lecture on file management. It discusses how files provide data storage and ensure data validity. It also covers file concepts like access methods and directory structure. File protection and different file structures are described. The key components of a file like name, location, and protection attributes are defined. Common file operations such as create, read, and delete are listed. Directory structure and how it organizes and locates files is explained. The importance of file sharing and protection schemes is highlighted.
File Management
- 1. Sir Kashif Lecture 2: File Management
- 2. provides the file abstraction for data storage guarantees data validity (most of the time) performance: throughput and response time enforces protection
- 3. File Concept Access Methods Directory Structure File-System Mounting //skip File Sharing //skip Protection
- 4. None - sequence of words, bytes Simple record structure ◦ Lines ◦ Fixed length ◦ Variable length Complex Structures ◦ Formatted document ◦ Relocatable load file Can simulate last two with first method by inserting appropriate control characters Who decides: ◦ Operating system ◦ Program
- 5. Name – only information kept in human-readable form Identifier – unique tag (number) identifies file within file system Type – needed for systems that support different types Location – pointer to file location on device Size – current file size Protection – controls who can do reading, writing, executing Time, date, and user identification – data for protection, security, and usage monitoring Information about files are kept in the directory structure, which is maintained on the disk
- 6. Create Write Read Reposition within file Delete Truncate //roundup/skip# Open(Fi) –open read/write session for Fi ◦ File pointer: pointer to last read/write location, Close (Fi) – close read/write session
- 7. Set of files Used to organize files Translates external file names to internal file names (file labels, i-nodes, file control blocks) Treated as a file but with special operations
- 8. Search for a file Create a file Delete a file List a directory Rename a file Traverse the file system
- 9. Efficiency – locating a file quickly Naming – convenient to users ◦ Two users can have same name for different files ◦ The same file can have several different names Grouping – logical grouping of files by properties, (e.g., all Java programs, all games, …)
- 10. Sharing of files on multi-user systems is desirable Sharing may be done through a protection scheme On distributed systems, files may be shared across a network Network File System (NFS) is a common distributed file- sharing method
- 11. User IDs identify users, allowing permissions and protections to be per-user Group IDs allow users to be in groups, permitting group access rights
- 12. File owner/creator should be able to control: ◦ what can be done ◦ by whom Types of access ◦ Read ◦ Write ◦ Execute ◦ Append ◦ Delete ◦ List
Editor's Notes
- #13: A read-only file is any file with the read-only attribute turned on. Some common files that are read-only by default in Windows include boot.ini, io.sys, msdos.sys and others. Append: In general, to append is to join or add on to the end of something. For example, an appendix is a section appended (added to the end) of a document. (append '(1 2 3) '(a b) '() '(6)) ;Output: (1 2 3 a b 6)