Storage Devices

Storage Devices

Backing storage keeps data long term

In the last lesson, RAM was described as temporary memory for programs and data currently in use. Backing storage has a different job. It keeps files, programs and data when the computer is switched off. This makes backing storage non-volatile. Examples include the internal drive in a laptop, a USB flash drive, an external hard drive, a Blu-ray disc and a memory card.

Storage is usually slower than RAM, but it has a much larger capacity and costs less per gigabyte. A computer loads a program from storage into RAM when it needs to run it. When a file is saved, data is written from RAM back to storage so it can be kept for the future.

Device and medium

A storage device is the hardware that reads and writes data. A storage medium is what the data is stored on. Sometimes these are separate. For example, a DVD drive is the device and the DVD disc is the medium. Sometimes they are built together, such as a USB flash drive, where the device and flash memory are in one small object.

Magnetic storage

Magnetic storage uses magnetised areas to represent binary data. A hard disk drive (HDD) contains spinning magnetic platters and moving read/write heads. HDDs often have large capacity and a lower cost per gigabyte than solid-state drives. They are widely used for desktop computers, servers, backups and external drives.

The main weakness of HDDs is that they have moving parts. This can make them slower than SSDs and more vulnerable to damage if dropped while operating. Magnetic tape is another magnetic storage medium. It is very slow for finding one specific file, but it can have extremely high capacity and low cost, so it is still used for large backups and archives.

Optical storage

Optical storage uses a laser to read marks on a disc. Common examples are CD, DVD and Blu-ray. Optical discs are portable, low-cost and useful for distributing media or keeping a copy that is not easily changed. Some optical discs are read-only, while others can be written once or rewritten depending on the format.

Optical storage usually has lower capacity and slower access speed than HDDs or SSDs. Discs can also be scratched, and many modern laptops no longer include optical drives. This makes optical storage less common for everyday file transfer than it used to be, but it is still useful in some archive and media situations.

Solid-state storage

Solid-state storage stores data electronically in flash memory. It has no moving parts. Examples include solid-state drives (SSDs), USB flash drives and memory cards. SSDs are usually much faster than HDDs, so they are commonly used for operating systems and applications where speed matters. They are also quieter and more durable because they do not rely on spinning platters or moving heads.

USB flash drives and memory cards are very portable, which makes them convenient for moving files between devices. Their small size is also a risk: they can be lost easily. Solid-state storage can cost more per gigabyte than magnetic storage, especially at higher capacities, but the speed and durability often make it the best choice for modern computers.

Choosing a storage device

Exam questions often describe a person or organisation and ask for a suitable storage device. A good answer should use the details in the scenario. For example, a photographer carrying files between locations may need portability and reasonable capacity, so a solid-state external drive or memory card may be suitable. A school server backup may need very high capacity and low cost, so magnetic tape or large external magnetic drives may be suitable.

Useful comparison criteria include capacity, speed, portability, durability, reliability and cost. Avoid vague statements such as "it is better". Instead, say why it is better for that situation: "An SSD is suitable for a laptop because it has no moving parts, so it is more durable when the device is carried around, and it has fast access speeds for loading programs."