Page 207 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes Objectives

After studying this unit, you will be able to:

• Explain file concepts
• Understand file access
• Discuss access methods
• Explain directories for languages

• Understand file sharing
• Discuss protection mechanisms

• Explain allocation methods
• Understand free-space management
• Discuss directory implementation

Introduction

A file is a collection of related information defined by its creator. Computer can store files on
the disk (secondary storage), which provide long term storage. Some examples of storage media
are magnetic tape, magnetic disk and optical disk. Each of these media has its own properties
like speed, capacity, data transfer rate and access methods.

Drive: The piece of hardware that holds and runs disks; used as a top-level location criterion
for a file. Your “hard disk” or “hard drive” is usually designated with the letter “C,” while your
floppy disk/drive is usually named “A.”
File: One document, one image, one something. In the world of computing, the terms “folder”
and “file” are entirely separate, distinct, and no interchangeable. Folders contain files; files
cannot contain folders. Files are represented by various icons that indicate which program is
used to open them:
File extension: The two or three or four letters after the dot in a filename. The file extension
indicates what kind of file it is: its “format” or “type.” For instance, the file extension .exe refers

to an “executable” file-in other words, an application. The file extension .html indicates a
Hypertext Markup Language file—in other words, a web page. In My Computer or Windows
Explorer, double-clicking on a file will open it if the file extension is correct. Some common file
extensions:.
doc – Microsoft Word document

wpd – WordPerfect Document
txt – Plain text document
htm, .html – A plain text document with added code that enables it to be read on the World
Wide Web
jpg – An image file
gif – An image file

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