Master Boot Record and Disk Formatting Essentials

Master Boot Record (MBR) Structure

The Master Boot Record (MBR) is a small program that runs on each operating system and is located in the first sector on the disk. It seeks to transfer control to the Partition Boot Sector (Boot).

MBR Contents

• Partition Table: Contains information regarding the start and end of up to 4 partitions.
• Partition Types:
  • Primary: Partition information is directly on the partition table.
  • Extended: Created to overcome the limit of 4 partitions; it saves the partition table information.
  • Logical: Partitions whose start and end information resides outside the main partition table.
• A small program that reads the contents of the partition table, specifically the active partition and the Partition Boot Sector.
• Free space reserved to place a small program, often a boot manager.

Disk Formatting Processes

Low-Level Formatting

Low-level formatting is the logical organization of the disk surface. It involves the creation and numbering of tracks and sectors. Modern hard disks recognize this formatting automatically.

High-Level Formatting

High-level formatting creates the necessary structures to save and locate files. Each operating system performs this to establish a file system.

Disk Allocation Units

Sector and Cluster Definitions

• Sector: The smallest division of a hard drive. Its standard measure is 512 bytes.
• Cluster: A multiple of the sector extent. It is the minimum block of data transferred to or from the disk.
• File Size: The amount of data contained within the file.
• Measure of File to Disk: When a file is saved to disk, it occupies a minimum of one cluster, depending on the amount of data it contains.

Common File Systems

• Ext and Ext2: Widely used in Linux, offering excellent performance.
• Ext3: Lists transactions related to file operations.
• ISO 9660: The file system used in CD, DVD, and Blu-ray media.
• NCPFS: Originally from Novell, it provides access to NetWare resources.

Disk Errors

Types of Disk Failures

• Physical Failure: Occurs when a hard disk sector is damaged.
• Logical Error: Involves a failure or loss of information regarding the structure needed to find data files. There are two types of logical errors:
  • Lost Clusters: Clusters containing data whose location address has been lost, making the data inaccessible.
  • Crossed Clusters: A situation where a single cluster is pointed to by two different files.