How to Store Data in Disk?

Data is stored on a hard disk drive in binary code, using 1s and 0s. The information is spread out on the magnetic layer of the disk(s) and is read or written by the read heads that ‘float’ above the surface thanks to the layer of air produced by the ultra-fast rotation of the disk.

In writing mode, an electrical current travels via the heads and modifies the surface of the electric field by inscribing a 0 or a 1. In read mode, the process is reversed: the magnetic field transmits an electrical current to the read head, and this signal is then translated into a digital signal readable by the computer.

To store data on a magnetic hard disk drive, the disk is divided into tracks, which are circular paths on the disk surface. Each track is further divided into sectors. Sectors are the smallest physical storage units on a disk. They are the unit of information transfer and are mapped with a logical block on the disk. A group of sectors makes a cluster, also known as a block.

Clusters are used by the operating system to read and write data. The low-level format or physical format divides the disk into sectors before storing data so that the disk controller can read and write. The logical format or “Create File System” stores the data structure of the first file system on the disk and contains free space and allocated space. For efficiency, most file systems group blocks into clusters.

Disk Structure in OS

Hard disk is organized into two different ways like as physical structure and logical structure; below shown each one in detail, you can check them:

Physical Structure of Hard Disk

The physical division of a hard disk refers to the way data is stored on the disk at a low level. Here are the main parts of the physical structure of hard disk, including:

Platters: The disks that make up the hard disk drive. Each platter has an upper and lower oxide-coated surface.

Read/Write Heads: The heads that float above the surface of the platters and read and write data as the platters spin around. There is at least one head per surface.

Tracks: The concentric circles on the surface of the platters. Each track is divided into sectors.

Sectors: The smallest physical storage units on the disk. Sectors are the unit of information transfer and are mapped with a logical block on the disk.

Cylinders: The set of tracks that have the same track value on all platters. A cylinder is made up of rings on the upper and lower surfaces of all of the platters.

Spindle: Help to connects all the platters and is connected to a motor. The motor of the spindle rotates with a constant speed, causing the disk platter to spin at a constant speed.

Arm Assembly: It holds the read/write heads. The arm assembly is moved in or out to position a head on a desired track.

Logical Structure of Hard Disk

The logical division of a hard disk refers to the way data is organized and stored on the disk. Here are the main components of the logical structure of hard disk, as following them:

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Master Boot Record (MBR): The MBR contains a small program to load and start the active (or bootable) partition from the hard disk drive. The MBR contains information about all four primary partitions on the hard disk drive such as the starting sector, ending sector, size of the partition, etc.

DOS Boot Record (DBR): The DBR is the first sector of a partition and contains the boot loader code that is executed when the partition is booted.

File Allocation Table (FAT): The FAT is a table that keeps track of which clusters are free and which are in use. It is used by the file system to locate files on the disk.

Root Directory: The root directory is the top-level directory on a disk. It contains all the files and directories that are stored directly on the disk.

Clusters: A cluster is a group of sectors that are allocated to a file. Clusters are used by the file system to read and write data.

Difference Between Logical and Physical Structure of Disk

Here is a tabular comparison of the physical and logical structure of a hard disk:

 Disk Performance Parameters

Disk performance parameters are most helpful for getting to assess the overall performance of disk and understand their capabilities in the respect of data transfer rates, access times, and throughput. Here are some of the key disk performance parameters, including:

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Capacity: The total amount of data that can be stored on the disk, typically measured in bytes (e.g., terabytes or petabytes).

Rotational Speed: For hard disk drives (HDDs), this parameter indicates how quickly the disk platters rotate, usually measured in revolutions per minute (RPM). A higher rotational speed generally leads to faster data access times.

Latency: The average time it takes for the desired data sector to rotate under the read/write heads after the seek operation is completed. It is determined by the rotational speed of the disk and is measured in milliseconds (ms).

Input/Output Operations per Second (IOPS): The number of reads or write operations that can be performed by the disk in one second. IOPS is an important measure of disk performance for tasks involving small, random access operations.

Buffer Size/Cache: The amount of high-speed memory (cache) present on the disk itself, used to temporarily store frequently accessed data. A larger cache can improve disk performance by reducing the need to access the physical disk for data.

Access Time: The time it takes for the disk to locate and retrieve data. Access time is the sum of seek time and rotational latency time.

Seek Time: The time it takes for the read/write head to move to the desired track on the disk.

Data Transfer Rate: The speed at which data can be read from or written to the disk, typically measured in megabytes per second (MB/s).

Reliability: The ability of the disk to operate without failure over time.

FAQs (Frequently Asked Questions)

What are the main components of a disk structure?

The major components of disk structure typically the boot sector, file system, partition table, and data blocks. These components work together to keep manage and store data on the hard disk.

What is the purpose of the boot sector?

The boot sector is small portion of the disk that consists the essential information for getting to boot the operating system.

What is a file system, and how does it relate to disk structure?

A file system is set of rules and data structures that help to organize and manage files and directories on the disk. It defines about how data is stored, named, and accessed. The file system is a crucial component of disk structure.

What is a partition table, and why is it important?

Partition table is a data structure that keeps record information about the partitions on a disk. It assists the operating system locate and manage data on different partitions and makes ensuring that they do not overlap.

How are data blocks organized on a disk?

Data blocks are typically organized into clusters or sectors that are the smallest addressable units on the disk. These clusters or sectors are grouped together into tracks and cylinders on older hard drives.

What is fragmentation, and how does it affect disk structure?

Fragmentation happens when files are split into non-contiguous parts on the disk, making to lead the inefficient storage and slower access times. File systems must manage fragmentation to optimize disk usage and performance.

Summing Up

Through this blog post, you have been completely aware about what is disk structure in OS and its diagram with ease. If this content is valuable for you, then please share it along with your friends, family members or relatives over social media platforms like as Facebook, Instagram, Linked In, Twitter, and more.

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