Boot Block and Bad Block in Operating System

In a computer system, the operating system (OS) is an essential part that performs several functions like disk management, security management, resource management, etc. In this article, we will explore the boot block and the bad block in detail. Both bad block and boot block are two important features of disk management in an operating system.

  • Boot block is an important component of an operating system which resides in a region of a hard disk or any other storage device and contains all crucial data and instructions required for initiating the booting process.

  • On the other hand, bad block is a region or sector of a data storage device which is damaged or malfunctioned and is not reliable to store data.

Now, let’s discuss boot block and bad block in operating system in more detail.

What are Boot Blocks?

The process of starting or restarting a computer system or any other computing device is called booting. For booting a computer system, a set of data and instructions is required which is managed by the operating system of the computer.

In a computing device, the part of the operating system which resides in a region of a data storage devices like hard disk, optical disk, floppy disk, etc. and contains all the data and instructions required for starting the booting process of the system is referred to as boot block. It is also known as boot sector, as it is a sector in the memory device which contains all the instructions required to boot the system.

Boot block generally resides in the first sector of the data storage device like hard disk and is designed in a standard format so that the BIOS (Basic Input Output System) can understand and execute it.

Components of a Boot Block

The following are the important components of the boot block −

  • Master Boot Record (MBR) − The master boot record (MBR) is a first part of a storage device that contains the boot block, boot code, partition table, and other required data and instructions. In a computer system, the master boot record is an essential part that helps to understand how the storage device is organized and which partition is required to boot.

  • Bootloader − Bootloader is a computer program which is responsible for starting the system and loading the operating system into the main memory. It executes all the essential steps required to initiate the booting process.

  • Boot Code − Boot code, also called bootstrap code, is another important component of boot block. Bootstrap code consists of all the essential instructions written in low-level language like machine language or assembly language. Bootstrap code performs some important functions, including configuration of system components, initialization of hardware parts, loading of operating system into the main memory, etc.

  • Partition Table − Partition table is another important component of the boot block. It is basically a data table that contains information about the different partition of the data storage device. It helps in identifying the active partition on the disk from which the operating system is to be loaded into the main memory.

Therefore, the boot block is a small region of a storage device that contains essential components like MBR, bootloader, boot code, partition table, etc. It is an important part that required for system initialization and loading the operating system.

What are Bad Blocks?

A storage region or sector of a data storage device like hard disk drive, flash drive, optical disk, etc. that cannot be used for storage and retrieval of data due to permanent damage is referred to as a bad block. Sometimes, a bad block is also known as a bad sector.

In other words, the damaged sector or portion of a storage device is called bad block. In a data storage device, the bad blocks can occur due to various reasons, such as physical damage, software error, wear and tear due to aging, manufacturing defects, etc. In a computer system, the effect of bad blocks could be the loss of data and system instability.

When a bad block occurs in a system and is encountered by the operating system, the operating system takes corrective actions to prevent data loss, system instability and other issues. For this, the operating system is generally empowered with tools to identify and manage the bad blocks.

For instance, in Windows operating system, a disk utility named, "Check Disk (chkdsk)" is integrated to scan the file system to detect the bad blocks. Once a bad block on a storage device is detected, the operating system marks it as not for use. Thus, this portion of the disk is not used to store any data.

Types of Bad Blocks

There can be several different types of bad blocks in a storage device. Some common types are explained her −

  • Physical Bad Block − The type of bad block that occurred due to any kind of physical damage like wear and tear, magnetic interference, scratches, etc. to the data storage device is known as physical bad block. This type of bad block is also referred to as hard bad block because it is permanent and cannot be repaired. Therefore, it can result in loss of data permanently.

  • Logical Bad Block − Logical bad block is a type of bad block that caused due to software errors like virus infection, file system errors, etc. It is also known as soft bad block because it can be repaired using software tools.

  • Unreadable Bad Block − The type of bad block whose data is not available to read due to data corruption or any other issues is called unreadable bad block. Unreadable blocks result in data loss.

Aspects to Handle Bad Blocks

The following are some major aspects to handle the bad blocks occurring in the storage device −

  • Bad Block Identification − The modern operating systems and storage devices are equipped with built-in error correction tools that can identify and mark bad blocks automatically. For this, storage devices or device drivers utilize built-in error reporting mechanisms.

  • Bad Block Mapping − Modern operating systems are able to maintain a mapping or table to track the locations of the bad sectors. Hence, the operating system utilizes these bad block mappings to avoid the use of bad blocks during a read or write request.


From the above discussion, it is clear that a bad block is a damaged block on a storage device that is unusable for data storage, while a boot block is a first block on a storage device that contains all the instructions and data required to initiate the boot process of the system.

Updated on: 07-Aug-2023

1K+ Views

Kickstart Your Career

Get certified by completing the course

Get Started