Primary & Secondary Storage (OCR GCSE Computer Science): Revision Notes

Secondary Storage

The Need for Secondary Storage

• Secondary storage is needed to store our files and programmes when they are not in use. These commonly fall into three categories: Optical, Magnetic and Solid State.
• Secondary storage is a long-term, non-volatile storage

Common Types of Storage

Optical

• Lasers write data to the surface of a disc.
• Optical media includes: CD, DVD, Blu-Ray
• Excellent for distributing software
• Good capacity
• Low cost
• Light and portable
• Can get damaged over time
• Slow access speed

Magnetic

• The magnetic tape is moved along a read-write head inside a disc drive.
• Examples: hard disc and tapes
• Used for backups
• High Capacity
• Cheap
• Reliable
• Slow to read due to moving parts

Solid State/Flash

• No moving parts make solid-state memory have very fast access speeds. Most are a type of flash memory.
• Examples: USB drives, memory cards, solid-state hard drives
• Large capacity but less than magnetic tape
• More expensive
• Portable
• Reliable and not affected by being moved around

Suitable Storage Devices

When choosing an appropriate device for a given scenario you need to consider the following characteristics:

• Capacity: How much space there is to store files.
• Access Speed: How quickly the computer can read and write data to or from a storage device or write data to it.
• Portability: Can you easily unplug it and carry it away?
• Durability: How easily is it damaged? Will it survive being dropped?
• Reliability: Can the data always be accessed and be correct?
• Cost: How expensive is the storage device?

Hard Disc Drive (HDD)

• Capacity: Large capacity (up to several terabytes), is ideal for storing large files like games or videos.
• Speed: Slower than SSDs due to mechanical parts, so suitable for applications that don't require extremely fast data access.
• Portability: Reasonably portable but bulky compared to SSDs and external HDDs are available for portable use.
• Durability: Low durability because of moving parts, easily damaged if dropped.
• Reliability: Moving parts are prone to wear and tear, which can lead to failure over time.
• Cost: Low cost per GB and cheaper than SSDs for large amounts of storage.
• Best for: Storing large files, general-purpose use, and desktops where speed is less critical.

Solid State Drive (SSD)

• Capacity: Typically smaller capacity than HDDs (commonly up to 2 TB) but still large enough for most common applications, though more expensive.
• Speed: Much faster than HDDs, thus Ideal for booting up operating systems and running software quickly.
• Portability: Highly portable due to small size and lightweight design and external SSDs are available for portable storage.
• Durability: Very durable since there are no moving parts and more resistant to physical shocks than HDDs.
• Reliability: More reliable than HDDs due to the lack of mechanical components.
• Cost: More expensive per GB compared to HDDs but prices have been decreasing, making them more accessible.
• Best for: Fast access to data, laptops, or high-performance applications like gaming or video editing.

Optical Discs (CD/DVD/Blu-ray)

• Capacity: CD: Up to 700 MB, DVD: Up to 4.7 GB, Blu-ray: Up to 50 GB. Low capacity compared to modern storage solutions.
• Speed: Slow read and write speeds so not suitable for high-speed applications.
• Portability: Very portable and lightweight, however, can be easily scratched or broken.
• Durability: Sensitive to scratches and sunlight and can deteriorate over time, affecting data quality.
• Reliability: Data can degrade over time, but they can be reliable for short-term storage.
• Cost: Very cheap to produce and a low-cost option for storing smaller amounts of data.
• Best for: Distributing media (movies, games), and long-term archiving of small to medium amounts of data.

USB Flash Drives

• Capacity: Varies, typically up to 1 TB. Convenient for transferring moderate amounts of data.
• Speed: Faster than optical discs but slower than SSDs. Sufficient for file transfers, but not ideal for running programmes directly.
• Portability: Extremely portable and easy to carry. Small enough to fit in a pocket.
• Durability: Durable, but their small size makes them easy to lose. Can break or wear out over time, especially if repeatedly inserted and removed.
• Reliability: Reliable for short-term data transfer. Data retention can degrade over many years.
• Cost: Relatively cheap for small to medium capacities. More expensive for higher capacities.
• Best for: Transferring files between devices, and backing up small amounts of data.

Cloud Storage

• Capacity: Potentially unlimited, depending on the service. Can be scaled up as needed.
• Speed: Depends on internet connection speed. Fast for high-speed internet, but slower for large uploads/downloads.
• Portability: Extremely portable as data is accessible from any internet-connected device. No physical device to carry.
• Durability: No risk of physical damage. Data is stored in multiple locations (redundancy), making it very durable.
• Reliability: Highly reliable as cloud providers usually have secure backups. Relies on internet availability.
• Cost: Often subscription-based, with free tiers for limited storage. Costs can increase with higher storage needs.
• Best for: Backups, accessing files from multiple locations, and collaboration.

Magnetic Tape

• Capacity: Very high capacity, often used for backups (up to several terabytes). Suitable for long-term archival storage.
• Speed: Very slow access speed. Suitable for archiving but not for frequent data access.
• Portability: Portable but bulky compared to other modern storage devices.
• Durability: Durable for long-term storage but sensitive to magnetic fields and environmental conditions.
• Reliability: Reliable for long-term storage, but access times can be slow.
• Cost: Very cost-effective for large-scale backup and archival storage.
• Best for: Long-term data storage for archives, and backups for businesses.

Summary of Advantages and Disadvantages by Storage Type

Storage	Capacity	Speed	Portability	Durability	Reliability	Cost
HDD	High	Moderate	Moderate	Low	Moderate	Low
SSD	Moderate	High	High	High	High	High
Optical Discs	Low	Low	High	Low	Low	Very Low
USB Flash Drive	Moderate	Moderate	Very High	Moderate	Moderate	Low
Cloud Storage	Unlimited	Varies	Very High	Very High	Very High	Subscription
Magnetic Tape	Very High	Low	Low	High	High	Very Low

Choosing the best storage device depends on the specific requirements of the application, such as how much storage is needed, the importance of access speed, and the budget.