Various terms in File System

Prerequisite - File Systems in Operating System First Understand the structure of storage device HDD: Terminology:

(i). Sector
(ii). Track
(iii). Track-Sector
(iv). Cluster or Block 

Figure - Terminology in diskThese are explained as following below in brief.

• (i). Sector: This is a pie like structure from center of disk to circumference, the time require by read/write head to move from center of disk to circumference is called latency time.
• (ii). Track: It is the circular path which is covered and tracked by r/w head.Its width depends on the head size of r/w head.
• (iii). Track-Sector: This is the intersection of sector and the track, you can refer to the image to understand it better.
• (iv). Cluster: Two or more track-sector are called clusters. It is the minimum unit used by OS to store data. Size of each cluster varies with its location in disk.All the clusters are not used to store a file.

Building Concept and Visualization:

1. Tommy and Jonny: Let’s assume we want a book called Data Structure and Algorithm from college library. Now you go to library computer (let’s name it Tommy) and find if this book really present in library or not. If this is in library then tell me the shelf-number where to find the book. And suppose you are with your friend (let’s name him Jonny) and if book exist you pass the shelf-number to your friend and ask him to bring the book for you. Similarly, HDD also have Tommy known as BUFFER, this stores all the addresses and other attributes of different files and folders. Buffer helps you find anything on HDD with the help of Jonny that is read/write head. This proves that we can’t interact directly to disk but indirectly using buffer. Figure - HDD Structure
2. Project Colleague: Suppose you and your colleague are working on a project, you have a windows laptop and your colleague has mac book. He copied some project files in a pen drive and shared to you. But problem is that you are unable to see data on the pen drive.
   • How is it possible ?
   • What could possibly be wrong ?
   • Is it a virus ?
   • Pen drive is corrupted ?