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CHAPTER 3 - Coggle Diagram
CHAPTER 3
3.1 Type of Protection
Read
Write
Read
Append
List Folder
Contents
Full Control
3.1 Concept of the File
term file is used for anything that is stored in the secondary storage
file could be a program
files differs in the kind of information they hold and also the way in which the information is stored.
define as a system that an operating system uses to keep track of different files
file management aims to provide a convenient programming environment for the users
Free space lists
manage records all free disk blocks.
not allocated to some file or directory
Low overhead to perform free list maintenance operations
Files are likely to be allocated in non contiguous blocks
Increases file access time
3.1 Goal of Protection
to prevent malicious misuse of the system by users or programs
To ensure that each shared resource is used only in accordance with system policies
To ensure that errant programs cause the minimal amount of damage possible.
only provide the mechanisms for enforcing policies and ensuring reliable systems.
3.1 Types of Directory Structure
Storage structure
Directory structure
Single-level directory
Two-level directory
3.1 File Access Techniques
Sequential
Implemented by the file system
accessed one record right after the last
Read cause pointer to be moved ahead by one.
allocate space for the record and move the pointer to the new end of file
reasonable for tape.
Easiest to implement because records are stored
Indexed
logically the same as sequential organization
combine the advantages of a sequential file with the possibility of direct access using the primary key
Direct
Uses direct access files
no restrictions on which blocks are read/written in any order
Method useful for disks
Give users flexibility of accessing any record
Records are identified by their relative addresses
3.1 Methods of File Allocation
many files are stored on the same disk.
Three major methods of allocating disk space are in wide use
Contiguous file allocation
Linked file allocation
Indexed file allocation
3.1 Free Space Management
Need to reuse the space from deleted files for new files
Free space management is implemented by this technique
Using bitmaps
Linked List