Secondary storage: Common types of storage Optical Magnetic Solid state

The idea

Secondary storage falls into three common categories: optical, magnetic and solid state. Optical storage uses a laser to read pits and lands on a reflective disc, for example CD, DVD and Blu-ray; it is portable and cheap but has lower capacity and slower access than magnetic or solid-state media. Magnetic storage uses magnetised areas on a spinning platter read by a moving head, for example a hard disk drive (HDD); it offers high capacity at low cost per gigabyte but contains moving parts, making it less robust and slower than solid state. Solid-state storage uses flash memory with no moving parts, for example an SSD, USB flash drive or SD card; it is fast, durable and silent but often more expensive per gigabyte and has a finite number of write cycles. Choosing a type depends on capacity, speed, durability, portability and cost.

What earns the marks

• Optical storage uses a laser to read data from pits and lands on a reflective disc, such as CD, DVD or Blu-ray.
• Magnetic storage uses magnetised regions on a spinning platter read by a read/write head, such as a hard disk drive (HDD).
• Solid-state storage uses flash memory with no moving parts, such as an SSD, USB flash drive or SD card.
• Optical storage is portable and inexpensive but generally has lower capacity and slower access than magnetic or solid-state storage.
• Magnetic storage offers high capacity at a low cost per gigabyte but has moving parts, so it is less robust and slower than solid state.
• Solid-state storage is fast, durable and silent but often more expensive per gigabyte and has a limited number of write cycles.

Common mistakes and how to put them right

• Describing an SSD as having spinning platters.

  Put it right: SSDs use flash memory with no moving parts; HDDs use spinning magnetic platters.

• Saying optical storage uses magnetism.

  Put it right: Optical storage uses a laser to read pits and lands on a reflective surface.

• Claiming solid-state storage has unlimited write cycles.

  Put it right: Solid-state storage has a finite number of write cycles, which can limit its lifespan.

• Treating all three types as equally fast.

  Put it right: Solid-state storage is generally faster than magnetic and optical storage for random access.

Exam tips

• Name a specific example for each type, such as DVD for optical, HDD for magnetic and SSD for solid state.
• When comparing types, refer to at least two characteristics such as speed, capacity, durability, portability or cost.
• Use correct terminology: pits and lands for optical, platters and read/write heads for magnetic, flash memory for solid state.
• Avoid saying a type is simply better; state the context, such as portability for a USB flash drive or capacity for a server HDD.