Secondary Storage | Computer for GCSE/IGCSE - Year 11 PDF Download

Understanding Secondary Storage

• Secondary storage is essential for storing data permanently, as opposed to volatile primary storage like RAM.
• Unlike primary storage, secondary storage is non-volatile, ensuring data retention even when the device loses power.
• Secondary storage, including HDDs, SSDs, and USB drives, allows both reading from and writing to, unlike ROM which is read-only.
• Examples of secondary storage media are varied, ranging from hard drives to optical discs, facilitating data transfer between systems.
• Data access speeds for secondary storage devices are typically slower compared to primary storage like RAM.
• Secondary storage devices are known for their large storage capacities, enabling the storage of significant amounts of data.
• Operating system software is permanently stored on secondary storage, transferring to RAM when in use.
• Secondary storage devices can be either internal or external to the computer system.

Comparison of primary and secondary storage

Types of Secondary Storage

• There are three main types of secondary storage: magnetic, solid state, and optical.

Magnetic

• Magnetic hard disk drives have historically been the primary form of internal secondary storage in personal computers. However, solid-state drives are gaining popularity due to their durability, low power consumption, and high read/write speeds.
• A magnetic hard disk comprises multiple metal discs coated with a magnetic material known as platters. Each platter's iron particles are magnetized to represent binary data (0s and 1s).

Structure of a magnetic hard disk

• Every disk is segmented by circular bands, forming numerous paths and pie-shaped sections. Their meeting points are called track sectors.

A diagram showing how each platter is divided by tracks and sectors

• The hard drive rotates the metallic disk(s) swiftly, usually at speeds ranging from 5400 to 7200 RPM, propelled by a motor.
• Guided by an actuator, a read/write arm shifts across the disk's surface to access the desired data location.
• Electromagnets are employed to read from or write data onto the disk.

Solid State

• Made of transistors arranged in a grid layout for storing data.
• Utilizes NAND and NOR gates in electrical circuits to control electron flow persistently.
• Represents binary values with 1 for current flow and 0 for no current.
• NAND gate: Requires both inputs to not be 1 to produce an output (1/electrical current).

The truth table for a NAND gate illustrates its functioning.

• A NAND gate produces an output of 0 only when both inputs are 1.

Truth Table for a NAND Gate:

Optical Devices

• Optical media types encompass CDs, DVDs, and Blu-rays, with Blu-rays offering the highest storage capacity, while CDs have the lowest. CD-Rs are exclusively for reading, while CD-RWs allow both writing and reading. Similarly, DVD-RWs permit writing and reading.
• Optical devices function by directing a laser onto the disc's surface and analyzing the reflected light.
• A mechanism moves the laser across the disc's surface.
• In CD-Rs, data is permanently burned onto the disc by a laser, creating pits and lands.
• The laser also serves to read data from these pits and lands.
• When the laser encounters the transition between a pit and a land (or vice versa), the change in reflection is detected by a sensor, indicating a binary value alteration.

• In CD-RWs, the composition of the disk is altered to denote 0s and 1s, and this alteration is reversible, allowing for overwriting.