The shape of the lesson
By the end of the lesson, learners can
- Why each part is needed: Exam questions often ask you to justify a type of hardware rather than just name it.
- Principal operations of devices: For each named device, learn the operation as a short chain of steps.
- Buffers: smoothing out speed: The CPU can send data far faster than a printer can print it.
- Operations: write each device's operation as separate steps in the order they happen.
- Use the key words: drum, charge, toner, fuser; platter, track, sector, head; floating gate; pits and lands.
- Justify, do not just name: secondary storage is needed because it is non-volatile and larger.
- Buffers: different speeds, temporary memory, CPU freed for other tasks, interrupt when empty.
One picture every idea returns to
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.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, How the hardware works.. A computer is useless without ways to get data in, results out and work saved. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Why each part is needed | Exam questions often ask you to justify a type of hardware rather than just name it. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Principal operations of devices | For each named device, learn the operation as a short chain of steps. Model the worked example A four-mark description on the board, one line at a time. Your turn: Give two differences between how data is stored on a solid-state drive and on a magnetic hard disk. | Pairs |
| 21 to 30 min | Teach and check: Buffers: smoothing out speed | The CPU can send data far faster than a printer can print it. Your turn: Explain why a buffer improves the efficiency of the processor when a long document is printed. | Cooperative Concept Mapping |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 21 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Buffers: smoothing out speed, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| 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. |
| 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. |
| A buffer does not make the printer itself faster. | It frees the processor so its time is not wasted. |
Input, output and storage devices: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
Explain why a computer needs both primary memory and secondary storage.
Describe how a laser printer prints a page.
Describe how a speaker produces sound from digital data stored in a computer.
A company is choosing between a solid-state drive and a magnetic hard disk drive for a laptop that sales staff carry between customers. Recommend one, giving two reasons.
Describe how a virtual reality headset gives the user the impression of being inside a 3D scene.
A student says: "A printer buffer makes the printer print faster." Explain why this is wrong and state the real benefit.
Answer key and marking notes
- Primary memory (RAM) is accessed directly by the CPU, so the programs and data currently in use must be loaded into it.
- RAM is volatile (and smaller), so secondary storage is needed to keep programs and files permanently when the power is off.
- The rotating drum is given an electrostatic charge.
- A laser beam scans the drum, changing the charge to form an electrostatic image of the page.
- Charged toner is attracted to the image on the drum.
- Charged paper passes over the drum and attracts the toner off it.
- A fuser (heated rollers) melts the toner onto the paper; the drum is discharged ready for the next page.
- The digital data is converted to an analogue signal by a DAC (and amplified).
- The varying current passes through a coil, making it an electromagnet.
- The coil is attracted and repelled by a permanent magnet, so it moves back and forth.
- The coil moves a cone, which vibrates the air to produce sound waves.
- Solid-state drive.
- It has no moving parts, so it is more robust if the laptop is dropped or moved while in use.
- Any one of: faster access, because there is no head movement or rotational delay; lighter; uses less power, so the battery lasts longer.
- There is a separate screen (or half a screen) for each eye.
- Each eye is shown a slightly different image, so the brain sees depth (stereoscopic 3D); lenses focus the images.
- Sensors such as a gyroscope and accelerometer detect the movement of the head.
- The images are updated in real time to match the head movement.
- The printer still prints at its own (slow) speed.
- The buffer stores data sent quickly by the CPU, so the CPU does not have to wait for the printer.
- The CPU is free to do other tasks and is only interrupted when the buffer needs refilling.
6 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Why does a computer need secondary storage as well as primary memory?
- ASecondary storage is non-volatile, so programs and files are kept when the power is switched off
- BSecondary storage can be accessed directly by the CPU, faster than RAM
- CSecondary storage holds the instructions the CPU is executing at this moment
- DSecondary storage is volatile, so it can be cleared quickly between users
In a laser printer, a laser beam has just scanned across the charged drum. What happens next?
- ACharged toner sticks to the electrostatic image of the page on the drum
- BHeated rollers in the fuser melt the toner onto the paper
- CThe drum is discharged and cleaned ready for the next page
- DInk is sprayed through tiny nozzles onto the paper
Why is a buffer used when a computer sends a long document to a printer?
- AThe CPU can fill the buffer quickly and go back to other tasks while the slower printer empties it
- BThe buffer converts the digital data into an analogue signal that the printer understands
- CThe buffer stores the document permanently in case the printer runs out of paper
- DThe buffer makes the printer print faster than it otherwise could
How does a solid-state (flash) drive store a single bit?
- AAs the presence or absence of electrons trapped in a transistor's floating gate
- BAs a tiny area of a spinning platter magnetised in one of two directions
- CAs a pit or a land on a spiral track, read by a laser
- DAs charge on a capacitor that must be refreshed many times a second
A warehouse worker wears thick protective gloves all day and needs to use a touchscreen. Which type of screen should be chosen, and why?
- AResistive, because pressure from any object pushes two conductive layers together to complete a circuit
- BCapacitive, because the glove draws charge from the screen's electrostatic field
- CCapacitive, because it detects the pressure of the touch rather than the material
- DResistive, because a finger changes the capacitance of the screen at that point
Why does it usually take longer to start reading a file from a magnetic hard disk than from a solid-state drive?
- AThe actuator arm must move the head to the correct track, then wait for the sector to rotate under it
- BThe hard disk must refresh every magnetised area before it can be read
- CThe hard disk must erase a whole block before any data in it can be read
- DThe hard disk must shine a laser on the platter and wait for the reflection
Quiz key
RAM is volatile, so anything that must survive power-off (the operating system, applications, users' files) has to be kept on non-volatile secondary storage. The CPU cannot access secondary storage directly: data is first loaded into primary memory, which is faster. The instructions being executed now are held in primary memory. Secondary storage is non-volatile, not volatile.
The laser changes the charge where the page has text or images, forming an electrostatic image; charged toner is then attracted to that image. The paper is charged to pull the toner off the drum, and only after that does the fuser melt it on, so fusing comes later. Discharging and cleaning the drum is the final step. Spraying ink through nozzles is how an inkjet printer works.
A buffer is temporary memory between devices that work at different speeds: the CPU fills it quickly, then carries on with other work while the printer prints at its own pace, sending an interrupt when it needs more data. It does not convert digital to analogue. It is temporary, not permanent, storage. The printer still prints at its own speed; the buffer frees the CPU rather than speeding up the printer.
In flash memory a voltage forces electrons into or out of a floating gate, where they stay trapped without power; their presence or absence represents the bit. Magnetised areas on a spinning platter are a hard disk. Pits and lands read by a laser are an optical disc. A capacitor needing refresh is a DRAM cell, which is volatile.
A resistive screen works by pressure: pressing pushes two conductive layers together, so a gloved finger or stylus works. A capacitive screen needs something conductive, such as a bare finger, to draw charge and change the capacitance, and an insulating glove does not. Capacitive screens do not detect pressure. The last option gives the right type with the capacitive screen's principle, so the reason is wrong.
A hard disk has mechanical delays: the arm moves the head to the right track (seek time) and the drive waits for the sector to spin round (rotational delay); an SSD has no moving parts. Magnetised areas keep their state without refreshing, which applies to DRAM. Erasing in blocks happens when flash memory is written, not when a hard disk is read. Lasers are used by optical drives, not magnetic ones.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.