ICT 0417 - Topic 3: Storage Devices and Media - Magnetic Drives

This section focuses on understanding magnetic storage devices, specifically magnetic hard disks and magnetic tape. It covers their principles of operation, advantages, disadvantages, and typical applications.

Magnetic Hard Disks (HDDs)

Principles of Operation

A magnetic hard disk is a non-volatile storage device that uses magnetic polarization to store data. It consists of one or more rotating platters coated with a magnetic material. A read/write head, mounted on an actuator arm, moves across the surface of the platters to read and write data.

Data is stored on the platters in the form of magnetic domains, which are tiny areas with a specific magnetic orientation representing a bit (0 or 1). The read/write head detects the magnetic orientation to read data or changes the magnetic orientation to write data.

Types of Hard Disks

Hard disks are typically classified by their interface and connection method:

• IDE (Integrated Drive Electronics): An older interface, now largely obsolete.
• SATA (Serial Advanced Technology Attachment): The most common interface for modern internal hard disks.
• SAS (Serial Attached SCSI): Used in servers and enterprise storage systems for higher performance and reliability.

Advantages of Hard Disks

• High Storage Capacity: HDDs offer large storage capacities, typically ranging from hundreds of gigabytes to several terabytes.
• Relatively Low Cost: Compared to other storage technologies like SSDs, HDDs are generally more cost-effective per gigabyte.
• Mature Technology: HDDs are a well-established technology with a long history of reliability.

Disadvantages of Hard Disks

• Mechanical Components: HDDs contain moving parts (platters and read/write heads), making them susceptible to damage from physical shock or vibration.
• Slower Access Times: Accessing data on an HDD is slower than on an SSD due to the time it takes for the read/write head to move to the correct location.
• Higher Power Consumption: HDDs generally consume more power than SSDs.

Typical Applications

Hard disks are commonly used for:

• Operating System Storage: Storing the operating system and applications.
• Data Storage: Storing documents, multimedia files, and other data.
• Backup Storage: Creating backups of important data.

Feature	Description
Storage Capacity	Ranges from hundreds of GB to several TB
Access Time	Relatively slow due to mechanical movement
Cost	Relatively low cost per GB
Reliability	Susceptible to damage from physical shock

Diagram

Magnetic Tape

Principles of Operation

Magnetic tape is an older form of magnetic storage that uses a narrow strip of plastic coated with a magnetic material. Data is written onto the tape in a sequential manner using a read/write head that moves along the tape. Data is stored as magnetic patterns on the tape.

Advantages of Magnetic Tape

• High Storage Capacity: Tape offers very high storage capacities, often exceeding HDDs.
• Low Cost per GB: Tape is one of the most cost-effective storage media per gigabyte.
• Archival Storage: Tape is ideal for long-term archival storage due to its durability and ability to withstand harsh conditions.

Disadvantages of Magnetic Tape

• Sequential Access: Data can only be accessed sequentially, making it slow for random access.
• Slow Access Times: Accessing specific data on tape can be time-consuming.
• Fragile: Tape is susceptible to damage from dust, moisture, and magnetic fields.

Typical Applications

Magnetic tape is primarily used for:

• Data Archiving: Storing backups of large datasets for long-term retention.
• Data Backups: Creating full or incremental backups of systems and data.
• Data Migration: Moving large amounts of data from one storage system to another.

Feature	Description
Storage Capacity	Very high, often exceeding HDDs
Access Time	Sequential access, slow for random access
Cost	Lowest cost per GB
Durability	Susceptible to damage from environmental factors

Diagram