Memory and Storage
Hardware · 4 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 5% of your exam marks.
RAM vs ROM and primary vs secondary storage comparisons appear regularly.
Solid-state storage has no moving parts. It stores binary data as electrical charge trapped in tiny transistor cells on a flash-memory chip.
How a solid-state drive (SSD) works
- The drive is a chip (or several chips) containing millions of tiny memory cells.
- Each cell contains a special transistor with a floating gate: a small conductor sandwiched between insulating layers that can hold an electrical charge. The charge stays in place even after the power is removed, which is what makes flash memory non-volatile.
- An erased cell holds no trapped charge on its floating gate, and the cell reads as a 1.
- To store a 0, a high voltage pushes electrons through the insulator and traps them on the floating gate; a cell with trapped charge reads as a 0.
- To read, the cell is checked for whether the floating gate is charged: no charge gives a 1, trapped charge gives a 0.
Because there are no moving parts, the drive can be small, silent, and resistant to shock. Reading and writing also happens entirely electronically, which is much faster than mechanically moving a head over a spinning disc.
Common solid-state devices:
- (solid-state drives) inside laptops and desktops, replacing magnetic HDDs as the primary internal drive
- USB flash drives
- SD cards in cameras and phones
- Internal storage of smartphones and tablets
Advantages and disadvantages
| Advantages | Disadvantages |
|---|---|
| Very fast read/write | Expensive per gigabyte compared to HDDs |
| No moving parts: durable, shock-resistant, silent | Limited number of write cycles (cells eventually wear out after billions of writes) |
| Small, light, portable | Smaller maximum capacities than the biggest HDDs |
| Low power use (good for laptops) |
Give features of solid-state storage
What comes up: "Give three features of solid-state storage" or a "which storage type is best for this device?" question asking you to justify solid-state for a smartphone or laptop.
Write (three marks): (1) Solid-state storage has no moving parts, making it durable and shock-resistant. (2) It stores data by controlling the flow of electrons through transistor cells using NAND flash technology. (3) It has fast read/write speeds, so files and applications load quickly.
Watch out: the mark scheme awards a separate mark for "no moving parts" and a further mark for the consequence (durable/robust). When justifying solid-state for a portable device, always pair the feature with its benefit — "no moving parts, so it is durable" scores two marks, but "no moving parts" alone scores only one. Do not describe solid-state as using a laser (that is optical) or a spinning platter (that is magnetic).