OS - File Management

File Manager

- also called the File Management System

File Manager

- responsible for creating, deleting, modifying, controlling access to files

File Manager

- provides support for libraries of programs to online users, for spooling operation, and for interactive computing.

Files

- the building blocks of any operation system.

- represent program and data.

executable file

- output of program

File access mechanism

- refers to the manner in which the records of a file may be accessed.

• Sequential File Access

• Direct File Access

• Indexed File Access

- FILE ACCESS METHODS (3) -

Sequential File Access

- a method of accessing data sequentially/one record at a time by starting from the beginning of the file to its end.

- most primitive and straightforward method of accessing files

Direct File Access

- Also known as Random file access.

- Allows users to access data directly from any location within the file without the need to read/write all the records that come before it.

Indexed File Access

- method that incorporates the benefits of both sequential and direct file access.

- creating an index file that maps logical keys or data elements to their corresponding physical addresses within the file.

- Index is searched sequentially and its pointer is used to access the file directly.

File types

refers to the ability of the operating system to distinguish different types of file such as text files, source files, and binary files etc.

• Ordinary files

• Directory files

• Special files

- FILE TYPES (3) -

Ordinary Files

- files that contains user information

- may have text, databases or executable program

- user can apply various operations on such files like - add, modify, delete or even remove the entire file.

Directory files

- contains list of file and other related information to those files.

- Also known as "FOLDERS" in other operating systems.

- Folders that holds and organize multiple files

Special files

- these files are also known as device files.

- represents physical devices

• Character special files

• Block special files

- TYPES OF SPECIAL FILES (2) -

Character special files

− data is handled character by character as in case of terminals or printers.

Block special files

− data is handled in blocks as in the case of disks and tapes

• Create - file created with no data

• Delete - no longer needed, free up

• Open - open before using

• Close - free up internal table space

• Read - read stored data in file

• Write - write the to file, again

• Append - only add at the end

• Seek - where to take data

• Rename - changing name

- FILE OPERATIONS (9) -

Directory

- is a list of FILES that stores all the related information about the file it holds with the contents.

1. Single-level directory structure

2. Two-level directory structure

3. Tree-structured directory structure

- TYPES OF DIRECTORY STRUCTURE (3) - *

Single-level directory structure

- all the files are placed in one directory

Two-level directory structure

- the system maintains a master block that has one entry for each user

Tree-structured directory structure

- the directory themselves are files.

- this files to the possibility of having sub-directories that can contain files and sub-subdirectories

• Application Program Layer

• Logical File System Layer

• File Organization Module Layer

• Basic File System Layer

• I/O Control Interface Layer

• Physical Hardware Device Layer

- FILE MANAGEMENT SYSTEM STRUCTURE (6) -

Application Program Layer

- user creates application program

Logical File System Layer

- manages the meta data information

File Organization Module Layer

- maintain information about file

Basic File System Layer

- generate command for device driver

- also manage buffer memory and cache

I/O Control Interface Layer

- it consists of device driver & interrupt handler

- transfer data: between main memory to disk system.

Physical Hardware Device Layer

- contain actual hardware device

Data Compression

- reduction in the amount of bits required to represent data is known as

- save storage capacity, speed up file transfer and decrease costs for storage hardware and network bandwidth.