Storage and peripheral devices
Storing and moving data
- Secondary storage keeps your files safe when the power is off.
- Different technologies trade speed, cost and durability.
- We also meet some key peripherals and the handy buffer.
Magnetic, solid-state and optical storage
- Magnetic hard disk (HDD) — data on spinning platters with tracks and sectors; a read/write head magnetises tiny regions. Cheap per GB, but slower with moving parts.
- Solid-state drive (SSD) — data as charge in transistors (flash), no moving parts. Faster, tougher, lower power, but dearer per GB and each cell wears out after many writes.
- Optical disc (CD/DVD/Blu-ray) — a laser reads tiny pits; writing changes the surface's reflectivity.
How does an SSD differ from a magnetic hard disk?
SSDs store charge in flash transistors — no moving parts, faster and tougher, but dearer per GB and cells wear out.
How does an optical disc (CD/DVD) store and read data?
A laser reads the pattern of pits; writing uses a stronger laser to change reflectivity.
Other peripherals
- Laser printer — toner sticks to a charged drum, transfers to paper, melted on by a fuser. Fast and sharp.
- 3D printer — builds an object layer by layer (melted filament, or UV-cured resin).
- Touchscreen — resistive (two layers pressed; works with anything, less accurate) or capacitive (a finger disturbs a charge field; accurate, multi-touch).
- Microphone turns sound into a signal, digitised by an ADC; a speaker does the reverse.
A capacitive touchscreen (as in phones):
Capacitive screens detect the change a conductive finger makes to a charge field — accurate and multi-touch. Resistive screens press two layers together.
A microphone's analogue signal must pass through which component to be stored digitally?
An ADC converts the continuous analogue signal into digital samples the computer can store.
Buffers
- A buffer is memory that holds data temporarily while it moves between devices of different speeds.
- Example: the CPU writes a document to the printer buffer quickly, then is free to do other work while the printer prints from the buffer at its own pace.
- Buffers stop the fast device having to wait for the slow one (also used in streaming and disk access).
The purpose of a buffer is to:
A buffer lets a fast device (CPU) hand off data and carry on, while a slow device (printer) consumes it at its own pace.
You've got it
- HDD = magnetic platters (cheap, moving parts); SSD = flash (fast, no moving parts); optical = laser + pits
- a touchscreen is resistive (any object) or capacitive (finger, multi-touch)
- a microphone needs an ADC to digitise its analogue signal
- a buffer temporarily stores data between devices of different speeds