A computer is useless without ways to get data in, results out and work saved. This lesson explains why each kind of hardware is needed, how nine named devices actually operate, and why a buffer sits between a fast processor and a slow printer.
A computer needs input devices to capture data, output devices to present results, primary memory (RAM and ROM) that the CPU can access directly to hold the instructions and data in use, and secondary storage that is non-volatile to keep programs and files when the power is off; removable storage lets data be moved between computers or kept off-site as a backup. At AS you must be able to describe the principal operation of each named device as a sequence of steps. A buffer is a temporary area of memory that holds data being transferred between two devices or processes that work at different speeds.
Exam questions often ask you to justify a type of hardware rather than just name it. Tie each one to what would go wrong without it.
| Hardware | Why it is needed |
|---|---|
| Input devices | Data from the user or the environment must be converted into a digital form the computer can process (keyboard, microphone, touchscreen, sensors). |
| Output devices | Results must be converted into a form people or other devices can use: printed, displayed, heard or acted on. |
| Primary memory | The CPU can only fetch instructions and data from memory it addresses directly; programs and data currently in use are loaded into RAM, and ROM holds the start-up (bootstrap) instructions. |
| Secondary storage | RAM is volatile and small; programs, the operating system and files must be kept permanently on non-volatile storage with a much larger capacity. |
| Removable storage | Lets files be transferred between computers that are not networked, and lets backups be stored away from the computer (for example on an external drive or a USB flash drive). |
Do not say secondary storage is needed "to store data": RAM stores data too. The mark is for non-volatile (kept when the power is off) or for a much larger capacity.
For each named device, learn the operation as a short chain of steps. Mark schemes give one mark per correct step in a sensible order, so a vague overall description earns little.
| Device | Principal operation |
|---|---|
| Laser printer | A rotating drum is given an electrostatic charge. A laser beam scans across the drum, changing the charge where the page has text or images, so an electrostatic image of the whole page forms. Charged toner sticks to the image on the drum. Paper is given a charge that attracts the toner off the drum. A fuser (heated rollers) melts the toner onto the paper; the drum is then discharged and cleaned for the next page. |
| 3D printer | A 3D design (from CAD software or a 3D scan) is sliced into thin horizontal layers by software. The object is built layer by layer (additive manufacturing): for example a heated nozzle melts plastic filament and extrudes it along each layer, and the build platform moves down after each layer. Resin printers instead use a UV laser to harden liquid resin. |
| Microphone | Sound waves make a diaphragm vibrate. The diaphragm moves a coil inside the field of a magnet, which induces a varying electrical current: an analogue signal. An ADC samples it to produce digital data. |
| Speaker | Digital sound data is converted to an analogue signal by a DAC and amplified. The varying current flows through a coil (an electromagnet) next to a permanent magnet, so the coil is pushed back and forth. The coil is attached to a cone, which vibrates and produces sound waves. |
| Magnetic hard disk | Platters coated with magnetic material spin at high speed. Read/write heads on an actuator arm move across the surface to the correct track and wait for the sector to rotate beneath them. To write, the head magnetises tiny areas in one of two directions (0 or 1); to read, it detects the direction of magnetisation. |
| Solid-state (flash) memory | No moving parts. Each cell is a transistor with a floating gate and a control gate, separated by insulating oxide. Applying a voltage forces electrons into (or out of) the floating gate, where they stay trapped without power; the presence or absence of charge represents a bit. NAND flash is written in pages and erased in whole blocks. |
| Optical disc reader/writer | The disc spins and a laser is focused on a single spiral track of pits and lands. Reading: the reflected light is detected by a light sensor; the changes in reflection are interpreted as 1s and 0s. Writing (recordable discs): a higher-power laser changes the dye or phase-change layer so that some areas no longer reflect. |
| Touchscreen | Capacitive: a transparent conductive layer holds an electrostatic field; a finger draws a small charge, changing the capacitance at that point, and the controller calculates the coordinates. Resistive: pressing pushes two conductive layers together, completing a circuit, and the voltage is used to calculate the position. |
| Virtual reality headset | Two screens (one per eye) show slightly different images, and lenses focus them so the brain sees a 3D scene. Sensors (accelerometer, gyroscope, magnetometer) track head movement and the images are updated in real time to match. Headphones give 3D sound; some headsets also track the eyes or hand controllers. |
A touchscreen is both an input and an output device, and so is a VR headset (screens out, motion sensors in). Say which part does which job.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Why does a computer need secondary storage as well as RAM?
In a laser printer, what is the job of the fuser?
How does a solid-state drive store a single bit?
When the printer buffer becomes empty, what does the printer do?
The CPU can send data far faster than a printer can print it. Without help, the processor would sit idle waiting for every character. A buffer solves this.
A buffer does not make the printer itself faster. It frees the processor so its time is not wasted.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Which sequence correctly describes how a microphone captures sound?
Which statement about a capacitive touchscreen is correct?
How is data written to a recordable optical disc?
What is the purpose of a buffer?
This skill is now recorded on your profile. Keep the chain going.