Pack — 3 Hardware (AS Level)

Pack — 3 Hardware

Question-and-answer mirror of Jigsaw. Every concept in Jigsaw appears here as a !question with a collapsible !success answer.

How marks are set

• 9618 | — the highest mark tariff that concept has ever carried in a 9618 paper. Answer points = that tariff + 2 spare, newest mark scheme first, older ones filling the gaps.
• 9608 | — same rule, using 9608 tariffs. Still inside the 9618 syllabus wording, but untested in the current series.
• Inferred | — not tested in either series. Tariff estimated from how 9618 marks comparable questions.
• SME | — from the Save My Exams notes. Tariff estimated the same way.

One bullet = one mark, unless the bullet begins … (an expansion of the point above it).

Two sub-topics have no 9608 safety net

Embedded systems (3.1.2) and PROM / EPROM / EEPROM (3.1.7) do not appear in the 9608 Legend at all. Every entry for them below is 9618 or inference — and embedded systems has been examined in almost every series since 2021.

3.2 is a skills sub-topic

The tariffs there are fixed and predictable: draw a circuit from an expression = 2, complete a truth table = 2 (marked in blocks of four rows), write an expression from a circuit = 2–3. Practise the format, not the recall.

---

3.1 Computers and their components

3.1.1 The need for input, output, primary memory and secondary storage

Question

Explain how the amount of RAM installed in a computer affects its performance.

Answer — 5 points for 3 marks

• More RAM means more of the currently running data and instructions can be held in memory
• … so there is no need to use virtual memory
• … and data does not have to be fetched from secondary storage first
• Secondary storage has a much slower access time than RAM
• So there is less latency / delay waiting for instructions or data, and performance improves

Latest: 9618_s25_qp_11_sc_6.a.ii

Question

Identify two items of data or instructions that a device stores in its primary memory.

Answer — 4 points for 2 marks

• The current reading / data from the sensor
• The current or recent video footage
• The instructions currently being executed
• The start-up / BIOS / boot-up instructions (in ROM)

Latest: 9618_s24_qp_11_sc_2.c.i

Question

Describe two ways in which the hardware of a computer could be upgraded to improve its performance. Explain how each upgrade improves performance.

Answer — 2 marks per upgrade (change + effect), 4 marks

• Increase the number of cores
• … each core can independently carry out a process at the same time, so more instructions are performed in parallel
• Increase RAM capacity
• … so more applications can reside in memory at once, saving slow disk access
• Increase cache memory
• … more data is held in fast-access memory, so less time is spent accessing RAM
• Increase the clock speed
• … so more Fetch–Decode–Execute cycles are carried out per unit of time

Latest: 9618_s23_qp_12_sc_5.b

Question

A server stores a large number of video files, which are read and written continuously. Justify the use of magnetic storage rather than solid-state storage.

Answer — 2 points + expansions, 4 marks

• Lower cost per unit of storage
• … so the high capacity required for a large number of video files is less costly
• A large number of read/write operations are performed continuously
• … and magnetic storage is likely to have a longer life span than solid state, which has a limited number of write cycles
• Very large capacities are available in a single drive

Latest: 9618_w25_qp_13_sc_7.d (also 9618_s23_qp_11_sc_4.b)

Question

Complete the table by identifying the most appropriate input or output device for each described use.

Answer — 1 mark per row, 5 marks

• Entering a credit card number into an online form → keyboard / keypad
• Selecting an option at an airport check-in kiosk → touch screen
• Printing a single high-quality photograph → inkjet printer
• Printing several hundred high-quality leaflets → laser printer
• Inputting a hard-copy image into a computer → scanner

Latest: 9608_s15_qp_12_sc_6.a. The device-selection table is a 9608 staple with no 9618 equivalent — note that the printer answer flips on volume, not quality.

Question

A laptop is used by a field engineer who travels constantly. Justify the use of solid-state storage rather than magnetic storage.

Answer — 2 points + expansions, 4 marks

• Solid state has no moving parts
• … so it is far more resistant to being dropped or knocked while travelling
• It has a faster access time
• … so files open and the laptop boots more quickly
• It uses less power, so the battery lasts longer
• It is smaller, lighter and silent, suiting a portable device

Inference: both 9618 questions run the argument one way — why magnetic beats solid state for a server. Every point above already exists in those mark schemes as the rejected side, so the reverse question is set-ready at the same 4-mark tariff.

Question

Explain why a computer system needs secondary storage.

Answer — 5 points for 3 marks

• Secondary storage is non-volatile
• … so data and programs are retained when the power is turned off, unlike RAM
• It has a much larger capacity than primary memory
• … so it holds all the files and software not currently in use
• It costs far less per unit of storage than RAM

Inference: every 9618 question here is a comparison between storage types. The bullet’s actual wording — the need for secondary storage — is untested.

Question

Describe the factors a user should consider when choosing a storage device.

Answer — 6 points for 4 marks

• Capacity — how much data must be stored, now and in future
• Performance — whether fast access is needed (SSD for video editing or gaming)
• Portability — whether the data must be moved between machines (USB flash or external drive)
• Cost — higher capacity and faster devices cost more per unit
• Durability — moving parts make magnetic drives vulnerable to shock
• The same structure fits input/output devices: user needs, user skills, environment, cost

A skeleton for any “recommend a device and justify” question; 9618 marks such justifications at up to 4.

Question

State a typical capacity for each of four storage media and give one trade-off for each.

Answer — 6 points for 4 marks

• HDD 500 GB – 2 TB — low cost per GB, but moving parts make it fragile
• SSD 120 GB – 4 TB — very durable and fast, but a high cost per GB
• USB flash drive 8 – 256 GB — very portable, but small capacity and easily lost
• CD 700 MB, DVD 4.7 – 9 GB, Blu-ray 25 – 50 GB — cheap per disc, but easily scratched
• Optical media are read-only or write-once in many formats
• Figures are not themselves credited, but they make “high capacity” and “cost per unit” concrete

SME supplies the numbers; the trade-off half is what 9618 actually marks.

---

3.1.2 Embedded systems

Question

Describe what is meant by an embedded system. Use an example in your answer.

Answer — 5 points for 3 marks

• A microprocessor / microcontroller within a larger system
• … that performs one specific task
• Example: the embedded system in a washing machine only controls the programs for the washing cycle
• … it is part of the washing machine but performs no other function within it
• It is a combination of dedicated hardware and software

Latest: 9618_s21_qp_11_sc_5.a

Question

Identify three characteristics of an embedded system.

Answer — 7 points for 3 marks

• Dedicated to a single task // has a limited number of functions
• Built into / integrated into a larger system
• Contains a processor, memory and I/O capability // uses dedicated hardware
• Hardware and software are designed together for a specific function
• Not easily changed or updated by the owner
• Does not require much processing power
• Usually has no operating system of its own

Latest: 9618_w23_qp_12_sc_1.c.i (also 9618_w22_qp_13_sc_10.b.ii)

Question

A device contains sensors, a camera and software dedicated to one task. Identify the characteristics that suggest it is an embedded system.

Answer — 5 points for 3 marks

• The device only performs the specific tasks described
• The sensors and camera are built into it
• The CPU, memory, storage and software are dedicated to this task only
• Only a dedicated microprocessor is needed, because the processing requirements are limited
• The user cannot install other software on it

Latest: 9618_s24_qp_11_sc_2.a. Each point must be applied to the device given — generic characteristics score nothing.

Question

Give one example of an embedded system and explain why it is an embedded system.

Answer — 5 points for 3 marks, each applied to the example

• Example: a central heating thermostat / satnav / traffic light controller
• It is dedicated to one task — for example, maintaining the set room temperature
• It does not require much processing power
• It is built into a larger system (the heating system), not used on its own
• It contains firmware that cannot easily be updated by the user

Latest: 9618_w23_qp_11_sc_9.b. Have an example ready that is not the one in the question — examined scenarios so far are a video doorbell, a car alarm, a television, a washing machine and factory machinery.

Question

Describe the drawbacks of using embedded systems.

Answer — 5 points for 3 marks

• The firmware is difficult to change or update by the user // hard to upgrade to newer technology
• Errors cannot be fixed easily // troubleshooting and repair are specialist and expensive
• Functionality cannot be extended // it cannot be adapted for another task
• Faulty or outdated devices are often thrown away rather than repaired
• … contributing to e-waste

Latest: 9618_w24_qp_12_sc_2.a

Question

Explain the reasons why ROM is used in an embedded system.

Answer — 5 points for 3 marks

• To store data that does not change
• The data must be retained when the device has no power // it is non-volatile
• It stores the boot-up instructions / system software / firmware / BIOS
• The contents cannot be accidentally overwritten by the user
• Only a small capacity is needed, so it is cheap

Latest: 9618_w22_qp_12_sc_3.c

Question

Describe the benefits of using an embedded system in a device.

Answer — 5 points for 3 marks

• Small and compact, so it fits easily inside the host device
• Low power consumption, so it is efficient and cheap to run
• Cheaper to produce, because minimal dedicated hardware is needed
• Fast and reliable at the repetitive task it is designed for
• Operates in real time, which suits time-critical jobs such as alarms and braking

Inference: 9618 has asked for the drawbacks at 3 marks and the characteristics repeatedly, but never for the benefits. The inverse of an existing question, at the same tariff, is overdue.

Question

Discuss the benefits and drawbacks of using embedded systems.

Answer — 6 points for 4 marks

• Benefit: small, compact and easily fitted into a dedicated device
• Benefit: low power consumption and cheap to produce, using minimal hardware
• Benefit: fast, reliable and real-time for repetitive, time-sensitive tasks
• Drawback: limited functionality, memory and processing power
• Drawback: hard to upgrade or repair, being built into the device
• Drawback: may be less secure, with limited protection if connected to other systems

The security point is in no mark scheme but is a defensible modern drawback. 9618 marks two-sided “discuss” questions at 4.

---

3.1.3 Principal operations of hardware devices

Question

Complete the description of the principal operation of a magnetic hard disk drive.

Answer — 6 points for 4 marks

• The disk has one or more platters that can be magnetised
• These are mounted on a spindle and rotate at high speed
• A read/write head is moved across the surface on an arm
• When data is read, changes in the magnetic field produce a change in the electric current
• When data is written, the head magnetises areas of the platter
• The platters are divided into tracks and sectors, so data can be addressed

Latest: 9618_s25_qp_11_sc_6.a.i

Question

Describe the principal operation of an optical disc reader/writer.

Answer — 7 points for 5 marks

• The disc is spun at high speed
• A laser is shone onto the surface of the disc to read or write
• An optical head moves the laser into position
• It follows the spiral track, from the centre outwards
• When writing, the laser burns pits to represent the data
• When reading, the laser reflects from the pits and lands
• The reflection from a pit differs from that of a land, and the difference is interpreted as 1 or 0

Latest: 9618_w24_qp_11_sc_3.d.i

Question

Describe the principal operation of a touchscreen.

Answer — 6 points for 4 marks

• Resistive: the screen has two conductive layers separated by a gap
• … pressure makes the layers touch, completing a circuit at that point
• Capacitive: the screen holds an electrical charge
• … a finger changes the charge / electric field where it touches
• The point of contact is identified from that change
• The microprocessor / software calculates the coordinates of the touch

Latest: 9618_s24_qp_13_sc_7.d

Question

Explain how a touchscreen detects a user’s touch and converts it into a menu selection.

Answer — max 2 for detection, max 2 for selection, 4 marks

• Detection — resistive: two layers make contact and complete a circuit
• Detection — capacitive: the contact creates a change in charge
• Detection — infra-red: the beams across the screen are broken
• Detection — optical imaging / acoustic pulse: a shadow is created // the wave is absorbed
• Selection: the point of touch determines the x and y coordinates
• The menu item corresponding to those coordinates is recognised and added to the order

Latest: 9618_w25_qp_12_sc_8.b.i. Two halves — an answer that only describes the technology caps at 2.

Question

Complete the description of resistive and capacitive touchscreens.

Answer — 5 points for 4 marks

• A resistive touchscreen has two layers
• … when touched, the layers make contact and a circuit is completed
• A capacitive touchscreen has several layers
• … when the top layer is touched there is a change in the electric current / charge
• A microprocessor identifies the coordinates of the touch

Latest: 9618_s23_qp_13_sc_3.a

Question

Explain how a model is produced using a 3D printer.

Answer — max 3 generic + max 1 specific, 4 marks

• It uses additive manufacturing
• The design comes from a digital file created with 3D modelling or CAD software
• The printer builds the model one layer at a time, from the bottom up, using x, y and z coordinates
• The process is repeated for each layer, fusing or curing it to the one below
• Some materials need time to cool and set, or UV curing using LEDs
• Specific (max 1): FDM — material is heated and pushed through a nozzle / extruder
• Specific: SLA — photosensitive liquid resin is exposed to a UV laser; DLP — resin exposed to a projected UV image; SLS — a laser fuses powdered material

Latest: 9618_w25_qp_11_sc_10.a (also 9618_w23_qp_11_sc_7.a). Only one mark is available for the named technology — the generic process carries the answer.

Question

Describe the principal operation of a microphone.

Answer — 5 points for 3 marks

• The microphone contains a diaphragm / ribbon
• Incoming sound waves cause it to vibrate
• The vibration causes a coil to move past a magnet (dynamic)
• … or changes the capacitance (condenser), or deforms a crystal (crystal microphone)
• This produces an electrical signal, which varies with the sound

Latest: 9618_w21_qp_12_sc_3.a

Question

Complete the description of how a virtual reality headset works.

Answer — 6 points for 4 marks

• A headset has one or two LCD displays / screens / lenses that output the image
• Head movements are detected using a sensor
• … a gyroscope and/or accelerometer
• The data is analysed by a microprocessor
• … to identify the direction and speed of movement
• Some headsets use digital cameras that record the user’s eye movements

Latest: 9618_s24_qp_12_sc_2.a

Question

Complete the table about the construction of solid-state memory.

Answer — 1 mark per row, 4 marks

• The two types of logic gate used to create solid-state devices → NAND and NOR
• The number of transistors in each cell → 2
• The type of gate that retains electrons without power → floating gate
• The type of gate that allows or stops current passing through → control gate

Latest: 9618_s24_qp_11_sc_2.c.ii

Question

Describe the principal operation of a laser printer.

Answer — 6 points for 4 marks

• The page image is drawn by a laser onto a photosensitive drum
• … the laser changes the electric charge wherever it strikes the drum
• Toner powder is attracted to the charged areas of the drum
• … forming the shape of the text or image
• The drum rolls the toner onto the paper as it passes
• The paper passes through hot fusing rollers, melting the toner permanently onto it

Inference: the laser printer appears repeatedly in 9618, but only ever as the setting for a buffer question (w23_qp_13_sc_7.c). Its own operation is named in the syllabus notes and has never been asked — an obvious gap at the same 4-mark tariff as the other device questions.

Question

Describe the principal operation of a loudspeaker.

Answer — 5 points for 3 marks

• An electrical signal is sent to the speaker
• … and passed through a coil that acts as an electromagnet
• The changing current changes the magnetic field, making the coil move back and forth against a permanent magnet
• The coil is attached to a cone / diaphragm, which vibrates with it
• The vibrating cone moves the air, producing sound waves

Inference: named in the syllabus notes alongside the microphone, and the microphone has been examined. The speaker is its mirror image and is untested in 9618.

Question

Describe how one cell of solid-state memory stores a bit of data.

Answer — 6 points for 4 marks

• Each cell contains a transistor acting as a switch, holding one bit
• The control gate is the top layer — it connects to the circuit and controls whether current flows
• The floating gate sits between two insulating oxide layers and holds the charge
• To store data, a high voltage on the control gate pushes electrons through the oxide onto the floating gate
• To erase, a high voltage in the opposite direction pulls the electrons off
• The charge stays on the floating gate without power, which is why the memory is non-volatile

SME supplies the mechanism behind the four one-word answers credited in s24_qp_11_sc_2.c.ii.

Question

Describe how the surface of a magnetic hard disk is organised and accessed.

Answer — 5 points for 3 marks

• Each platter is divided by concentric circles into tracks
• … and by wedge shapes into sectors
• The intersection of a track and a sector is a track sector, the smallest addressable unit
• The disk spins at typically 5400–7200 RPM
• A read/write arm controlled by an actuator positions the head, which reads and writes using electromagnets

Tracks and sectors are not in the 9618 cloze but are standard credited detail elsewhere.

Question

For each scenario, identify the most suitable type of microphone or touchscreen and justify your choice.

Answer — 2 marks per scenario (choice + justification), 4 marks

• Loud live environment → dynamic microphone … it is robust and handles high sound levels without distorting
• Recording studio → condenser microphone … it is far more sensitive and captures fine detail
• Smartphone or tablet → capacitive touchscreen … it reacts to the charge in a finger, supports multi-touch and gives a brighter image
• ATM or till → resistive touchscreen … it responds to pressure, so it works with gloves or a stylus and is cheaper and more durable

Knowing which type suits which scenario is what turns a generic description into an applied answer.

---

3.1.4 The use of buffers

Question

Explain how a memory buffer is used when data is transferred from a computer to a hard disk drive.

Answer — 5 points for 3 marks

• The computer and the hard disk transmit and receive at different speeds
• … the computer transfers data faster than the drive can receive it
• The buffer provides temporary storage for the data
• … so the computer can transfer data into the buffer at the higher speed, and is not held up waiting
• Data is then transferred from the buffer to the hard disk at its own slower rate

Latest: 9618_w24_qp_13_sc_2.b

Question

Explain how a buffer is used when data is written to an optical disc.

Answer — 6 points for 3 marks

• The computer and the optical disc reader/writer send and receive at different speeds
• The buffer allows temporary storage of the data
• … so the computer transfers data at the higher speed and is not held up
• … and can carry on with other tasks meanwhile
• The optical drive is not overloaded with data it cannot yet write
• Data is transferred from the buffer to the drive at the slower rate

Latest: 9618_w24_qp_11_sc_3.d.ii

Question

Describe how a laser printer makes use of a buffer when printing a document from a laptop.

Answer — 6 points for 4 marks

• The print instructions and data are sent by the laptop to the buffer, at laptop speed
• The data is transferred from the buffer to the printer at printer speed
• This allows the user to continue using the laptop
• … and the processor to continue processing other tasks
• … instead of waiting for the relatively slower printer
• When the buffer is empty, an interrupt is sent to the laptop requesting more data

Latest: 9618_w23_qp_13_sc_7.c

Question

Explain how a buffer is used when a computer transmits data to a peripheral device.

Answer — 6 points for 4 marks

• The buffer is a temporary store for data on its way to the device
• Data is transferred into the buffer by the computer
• Data is retrieved from the buffer by the device
• … each working at its own speed, independently of the other
• When the buffer is empty, an interrupt is sent to the computer requesting more data
• When the buffer is full, an interrupt stops further data being sent

Latest: 9618_s24_qp_12_sc_2.b

Question

Explain the purpose of a buffer and give one example of where a buffer is used.

Answer — max 2 purpose + max 1 example, 3 marks

• Purpose: to act as temporary storage for data // to store downloaded data
• … before it is used by the receiving device
• … so that processes or devices can operate at different speeds, independently of each other
• Example: a printer buffer holding a document while the processor moves on
• Example: a video buffer while streaming; a keyboard buffer during data entry

Latest: 9618_w22_qp_13_sc_1.c. Three purpose points will still only score 2 — the example mark must be taken.

Question

State one reason why a 3D printer needs a buffer.

Answer — 3 points for 1 mark

• To free up the processor to carry out other tasks
• … because the rate at which the printer receives data differs from the rate at which it can process it
• To manage the mismatch in speed between the processor and the peripheral

Latest: 9618_w25_qp_11_sc_10.b

Question

Describe the role of the address bus, the data bus and buffers when data is written to a device.

Answer — 1 mark per component, 3 marks

• Buffers — temporarily hold the data until it is ready to be transmitted to the device
• Address bus — carries the address (in RAM) of the data to be written to the device
• Data bus — carries all the data to be written to the device / buffer
• Each mark must name what is carried to the device, not generically

Latest: 9618_w23_qp_12_sc_8.c.ii

Question

Describe the sequence of events that takes place when an application program reads a file from the hard disk, including the use of the disk buffer.

Answer — 10 points for 8 marks

• The application program executes a read statement
• … which passes the request to the operating system
• The OS spins the disk up to speed
• It looks up the track and sector in the directory file
• The read/write head moves to the correct track
• It waits for the correct sector to rotate beneath it
• The first cluster is read into the disk buffer
• Successive clusters continue to be read into the buffer
• An interrupt is generated when the transfer is complete
• The OS transfers the buffer contents into the program’s data area in memory

Latest: 9608_w16_qp_12_sc_3. An 8-mark sequencing question with no 9618 equivalent — the same question also anchors the Chapter 5 Pack.

Question

Explain how buffering allows a streamed video to play without pausing.

Answer — 6 points for 4 marks

• The user needs a high-speed broadband connection
• Data is streamed into a buffer in the computer before it is played
• Playback begins only once the buffer holds enough data
• Buffering stops the video pausing as further bits are streamed
• As the buffer empties it is refilled, so viewing is continuous
• Actual playback is a few seconds behind the time the data is received

Latest: 9608_w16_qp_13_sc_6. Filed under buffers in 9608 and under bit streaming in Chapter 2 — cross-check with the Communications Pack.

Question

Explain how buffers and interrupts work together when a computer sends data to a peripheral.

Answer — 5 points for 3 marks

• Data is placed in the buffer by the computer and drawn from it by the device
• When the buffer becomes empty, the device raises an interrupt
• … which is a signal to the processor requesting more data
• The processor finishes its current instruction, saves its state, and runs the interrupt service routine to refill the buffer
• When the buffer is full, an interrupt tells the computer to stop sending, so no data is lost

Inference: “when the buffer is empty an interrupt is sent” is a mark point in three separate 9618 questions but has never been the subject of one. It is the natural synoptic bridge to Chapter 4.

---

3.1.5 Differences between RAM and ROM

Question

Describe what is stored in the ROM of a computer.

Answer — 4 points for 2 marks

• The bootstrap program // the start-up instructions for that computer
• The BIOS
• The start-up instructions for the attached system // the firmware
• The kernel // parts of the operating system

Latest: 9618_s23_qp_11_sc_4.a.i

Question

State the purpose of the RAM and of the ROM in an embedded system.

Answer — 1 mark each, 2 marks

• RAM — stores the choices / program the user has entered
• … stores the data read from the sensors, and the time left in the current program
• ROM — stores the start-up instructions / firmware
• Any answer given by example from the scenario is credited

Latest: 9618_s21_qp_11_sc_5.b

Question

Describe three differences between RAM and ROM.

Answer — 5 points for 3 marks

• RAM is volatile — it loses its contents when the power is off; ROM is non-volatile
• RAM can be written to and altered; ROM is read only and cannot be changed in normal use
• RAM stores the files, data and operating system currently in use; ROM stores the BIOS / bootstrap / pre-set instructions
• RAM is usually much larger in capacity than ROM
• RAM is faster to access than ROM

Latest: 9608_s15_qp_13_sc_4.b (3 marks; also 9608_w16_qp_12_sc_6.a at 2). 9618 has only ever asked what each one stores — never the differences — despite the bullet being titled “explain the differences”. This is the most likely gap in the whole chapter to be filled.

Question

Describe the purpose of the RAM and the ROM inside a laser printer.

Answer — max 2 for each, 4 marks

• RAM — stores the currently running parts of the printer software
• … stores the data being printed / the contents of the buffer
• … stores the current progress of the print job and data such as toner levels
• ROM — stores the printer’s operating software and boot-up instructions
• … stores the printer’s built-in fonts

Latest: 9608_s20_qp_13_sc_2.b

Question

State two differences between RAM and ROM.

Answer — 4 points for 2 marks

• RAM is volatile — its contents are lost when power is removed
• ROM is non-volatile — its contents are retained without power
• RAM can be read from and written to; ROM is normally read only
• RAM holds what is currently in use; ROM holds permanent start-up instructions

Inference: volatile vs non-volatile — the single most important RAM/ROM fact — appears in 9618 only implicitly, as “data must be stored even when the device is without power”. A direct “state two differences” would catch anyone who has learned only the 9618 storage-contents answers.

Question

Compare RAM and ROM in terms of speed, capacity, contents, access and volatility.

Answer — 6 points for 4 marks

• Speed — RAM very fast; ROM fast but slower than RAM
• Capacity — RAM gigabytes; ROM megabytes
• Contents — RAM the programs and data in use; ROM the bootstrap / start-up instructions
• Access — RAM read and write; ROM read only
• Volatility — RAM volatile; ROM non-volatile
• Both are primary memory, directly accessible by the CPU; ROM is a small chip on the motherboard holding the BIOS

SME’s table form; 9608 marks the equivalent comparison at up to 3, and the extra rows make 4 defensible.

---

3.1.6 Differences between SRAM and DRAM

Question

State three differences between DRAM and SRAM.

Answer — 6 points for 3 marks

• DRAM requires refreshing / recharging; SRAM does not
• DRAM stores each bit as a charge; SRAM uses a flip-flop
• DRAM is less expensive to manufacture; SRAM is more expensive
• DRAM has slower access speeds; SRAM is faster
• DRAM has a higher storage density; SRAM lower
• DRAM is used in main memory; SRAM in cache

Latest: 9618_w25_qp_11_sc_6.c

Question

Identify two advantages of using DRAM rather than SRAM in a device.

Answer — 4 points for 2 marks

• It costs less per unit of storage
• It has a higher storage density // more data can be stored per chip
• It has a simpler design, using fewer transistors per cell
• A fast access speed is not needed for this device, so the cheaper option is suitable

Latest: 9618_w24_qp_12_sc_2.b (also 9618_s23_qp_11_sc_4.a.ii, 9618_w23_qp_11_sc_7.c)

Question

Identify two disadvantages of using DRAM rather than SRAM.

Answer — 4 points for 2 marks

• DRAM requires constant refresh cycles, unlike SRAM
• … which uses processor time and power
• DRAM has a lower access speed than SRAM
• Its contents are lost more quickly without refreshing, so it is unsuitable for cache

Latest: 9618_w24_qp_11_sc_3.c

Question

Explain why SRAM is used rather than DRAM in a particular part of a computer.

Answer — 5 points for 3 marks

• SRAM has a faster access time
• … because it does not need to be refreshed
• It is used on the CPU to improve cache speed
• … where speed matters far more than capacity or cost
• The small capacity needed for cache makes the higher price acceptable

Latest: 9618_w23_qp_13_sc_7.a

Question

Tick to show whether each statement describes SRAM or DRAM.

Answer — 1 mark per row, 5 marks

• More expensive to make → SRAM
• Requires refreshing → DRAM
• Made from flip-flops → SRAM
• Has less complex circuitry → DRAM
• Mainly used in cache memory, where speed is important → SRAM
• Requires higher power consumption under low levels of access → DRAM

Latest: 9608_w18_qp_13_sc_6.c (5 marks; also 9608_w21_qp_11_sc_4.c). 9618 asks for the differences in prose; the tick/match format is 9608’s.

Question

Explain the difference in power consumption between SRAM and DRAM, and why it matters.

Answer — 4 points for 2 marks

• DRAM requires higher power consumption under low levels of access
• … because it needs extra circuitry to carry out the constant refreshing
• SRAM uses less power when idle, as it has no need to refresh
• This is significant in battery-powered devices, where idle time is common

Latest: 9608_s19_qp_12_sc_4.c. Credited repeatedly in 9608 and absent from every 9618 mark scheme — a genuine content difference, not just a format one.

Question

Describe how one memory cell of SRAM differs from one memory cell of DRAM.

Answer — 5 points for 3 marks

• A DRAM cell uses a single transistor and a capacitor
• … the capacitor leaks charge, which is why the cell must be refreshed thousands of times a second
• An SRAM cell uses several transistors forming a flip-flop
• … which holds its state as long as power is applied, so no refresh is needed
• The extra transistors make SRAM larger, costlier and lower density

Inference: 9608 credits the transistor counts directly, and 9618 accepts “simple design — uses fewer transistors” once in s23_qp_11_sc_4.a.ii, but never asks for the cell structure. It is the physical reason behind cost, density and refresh.

Question

Explain why SRAM is used for cache memory and DRAM for main memory.

Answer — 6 points for 4 marks

• SRAM keeps data as long as power is on, using flip-flops, with no refreshing
• … so it is very fast and uses little idle power
• … but it is expensive and low density, so only a small amount is affordable
• … which suits cache, where speed matters more than size
• DRAM stores each bit in a tiny capacitor and needs constant refreshing
• … so it is cheaper and far denser, but slower — which suits main memory, where large cheap capacity is wanted

Framing the answer as “which property matters in this device” is what turns a list of differences into an applied answer; 9618 marks applied justifications at up to 4.

---

3.1.7 Differences between PROM, EPROM and EEPROM

Question

Complete the table by writing PROM, EPROM or EEPROM against each description.

Answer — 1 mark per row, 3 marks

• Contents erased using a voltage pulse, and changed many times without removing the chip → EEPROM
• Contents erased using ultraviolet light, and the chip must be physically removed to be reprogrammed → EPROM
• Contents can be written only once after manufacture → PROM

Latest: 9618_w25_qp_13_sc_4.c

Question

Give two differences between EPROM and EEPROM.

Answer — 4 points for 2 marks

• EPROM is erased using ultraviolet light; EEPROM uses an electrical signal
• EPROM must be removed from the circuit board to be changed; EEPROM stays in the circuit
• EPROM erases all the data; EEPROM can erase selected parts (a byte at a time)
• EEPROM can therefore be reprogrammed by the user, without special equipment

Latest: 9618_w24_qp_12_sc_2.c

Question

Explain the benefits of using EEPROM in a device.

Answer — 7 points for 4 marks

• EEPROM allows frequent read, write and erase operations
• … so the device can be updated to take advantage of new features
• The firmware need not be fully erased first — a particular byte or the whole chip can be erased
• The chip does not have to be removed from the device
• … so the firmware can be changed by the user, without technical expertise
• No additional equipment (such as a UV eraser) is needed
• It is cheaper to manufacture, so the device is cheaper to buy

Latest: 9618_s24_qp_12_sc_2.c (also 9618_w23_qp_13_sc_7.b, 9618_w22_qp_11_sc_9.b)

Question

Describe what is meant by PROM and give one situation in which it would be the appropriate choice.

Answer — 5 points for 3 marks

• PROM is supplied blank and is programmed once after manufacture
• … after which the contents cannot be changed or erased
• It is non-volatile, retaining its contents without power
• Appropriate when the program will never need to change — a remote control, a basic calculator
• … and when producing high volumes cheaply, since it is cheaper than EPROM or EEPROM

Inference: PROM appears only as one row of the w25_qp_13_sc_4.c matching table. Neither “describe PROM” nor an applied “where would you use it” has been asked.

Question

Explain why a manufacturer would use a programmable ROM rather than a ROM fixed at manufacture.

Answer — 5 points for 3 marks

• A mask ROM is written during manufacture and can never be altered
• … so any error in the firmware makes the whole chip scrap
• A programmable ROM can be written after manufacture
• … so the same blank chips can be used for different products or versions, and in small volumes
• EPROM and EEPROM additionally allow the firmware to be corrected or updated later

Inference: every 9618 question compares the three variants with each other. The prior question — why programmable ROMs exist at all — is untested.

Question

Compare PROM, EPROM and EEPROM.

Answer — 6 points for 4 marks

• Reprogrammable? PROM no (once only) · EPROM yes · EEPROM yes
• Erased using — PROM cannot be erased · EPROM UV light · EEPROM electric voltage
• Removed from the device? EPROM yes · EEPROM no, erased in place
• Erased all at once? EPROM yes, the whole chip · EEPROM no, selected parts
• Typical use — PROM permanent firmware (remote controls, basic calculators)
• Typical use — EPROM reprogrammable development work (older arcade machines, early consoles); EEPROM flash memory and BIOS (smart cards, key fobs, USB sticks, SSDs)

The “typical use” row is the part no mark scheme supplies, and it is exactly what an applied question would want.

---

3.1.8 Monitoring and control systems

Question

Describe the differences between a monitoring system and a control system.

Answer — 6 points for 4 marks

• A monitoring system takes no action; a control system acts autonomously to change the environment when values fall outside a prescribed range
• A control system uses actuators; a monitoring system does not
• A control system makes use of feedback; a monitoring system does not
• The output of a monitoring system does not affect the subsequent input
• … whereas the output of a control system changes the next input from the sensor
• A monitoring system only records, displays or warns

Latest: 9618_w25_qp_11_sc_9

Question

For the system described, identify whether it is a monitoring system or a control system. Justify your answer.

Answer — no mark for the identification — all 3 marks are in the justification

• Control: the system uses an actuator to perform an action
• … the output changes the input to the sensor
• … the system acts autonomously on the feedback from the sensor
• … input data causes the action, the action changes the measured quantity, and that new value determines the next action
• Monitoring: there is no feedback — the output is only an indicator or warning
• … the output does not affect the input from the sensors, and there are no actuators

Latest: 9618_w25_qp_12_sc_11 (also w24_qp_12_sc_9.b, w24_qp_11_sc_5.c, s24_qp_11_sc_2.b, s21_qp_11_sc_5.c). The most repeated question in the chapter, and the one candidates most often answer with the choice alone.

Question

Explain the importance of feedback in a control system.

Answer — 5 points for 3 marks

• Feedback ensures the system operates within set criteria / constraints
• … by enabling the system output to affect the subsequent input
• … so conditions are adjusted automatically, without human intervention
• The system can check whether the action it took had the intended effect
• … and respond to further changes in the environment as they occur

Latest: 9618_s24_qp_13_sc_7.c (also 9618_w22_qp_13_sc_10.a, 3 marks)

Question

Identify a suitable sensor for the system described and state how it is used.

Answer — 1 mark for the sensor, 1 for its applied use

• Pressure — detects when an item is removed from or replaced on a shelf; detects an intruder sitting in a seat; detects a hit obstacle
• Infra-red — detects when a beam is broken; detects the heat of a person; measures the height of a vehicle
• Light — detects when the external daylight level falls below a set amount
• Sound — detects a sound inside a car; detects someone speaking
• Proximity / infra-red — counts items passing on a conveyor belt
• The use must be tied to the scenario — “measures pressure” alone scores nothing

Latest: 9618_s25_qp_11_sc_4.b (also w24_qp_12_sc_9.a, w24_qp_11_sc_5.a, s24_qp_13_sc_7.a, w22_qp_13_sc_10.b.i)

Question

Describe the role of an actuator in a control system.

Answer — 4 points for 2 marks

• The actuator generates a signal / causes an action when instructed by the microprocessor
• … by converting electrical energy into a mechanical force / movement
• For example, to push an arm, open a trap door or pick up an item
• It is what makes a system a control system rather than a monitoring one

Latest: 9618_w23_qp_12_sc_1.b

Question

Describe the purpose of the temperature sensor in the device described.

Answer — 4 points for 2 marks

• To prevent the device overheating
• … or to ensure the material is hot enough to work correctly
• By identifying the temperature of the object being printed / processed
• By identifying the temperature of the material being used

Latest: 9618_w23_qp_11_sc_7.b

Question

A greenhouse must be kept between 18 °C and 24 °C. Identify a suitable sensor, state what it measures and explain how the system uses its readings.

Answer — 5 points for 3 marks

• A temperature sensor is used
• It measures the current air temperature inside the greenhouse, continuously
• The reading is converted to digital by an ADC and compared with the stored range by the microprocessor
• If the temperature is too high, an actuator opens the vents (or too low, turns on the heater)
• The change alters the next reading — feedback — so the system adjusts automatically

Inference: the syllabus notes name temperature, pressure, infra-red and sound. 9618 has examined pressure, infra-red, sound and light; temperature appears only inside the 3D-printer and refrigerator scenarios, never as “identify a suitable sensor” — despite being listed first.

Question

Describe a system that both monitors an environment and controls it, explaining which parts do which.

Answer — 5 points for 3 marks

• Sensors take readings continuously, and the readings are displayed or logged — this is the monitoring part
• The microprocessor compares each reading with a stored range
• While readings stay in range, the system only records them and takes no action
• When a threshold is crossed, an actuator is operated — this is the control part
• The resulting change alters the next reading, so feedback closes the loop

Inference: every question asks which of the two a system is. s24_qp_11_sc_2.b (the video doorbell) accepts either answer if justified, which is the closest Cambridge has come to setting this.

Question

Define a monitoring system and a control system, giving an example of each.

Answer — 6 points for 4 marks

• Monitoring — collects data continuously through observation, passively
• … it does not interact with or change the environment, and takes no action on the data
• … example: a weather station; hospital patient monitoring, which records, displays and alerts staff
• Control — automatically manages or adjusts a process based on sensor data
• … it monitors input, then acts when conditions are met, keeping the system stable without human input
• … example: central heating (thermostat → boiler on → target reached → heating off); automatic irrigation

The useful nuance: a patient monitor that alerts staff is still a monitoring system, because the alert does not change the patient’s readings.

Question

Name four sensors other than temperature and state what each measures.

Answer — 1 mark per sensor with its measurement, 4 marks

• Accelerometer — acceleration, tilt and vibration (airbags, phone orientation)
• Gas — presence of a specific gas, such as carbon monoxide
• Humidity — water vapour in the air (greenhouses)
• Flow — rate of movement of a gas, liquid or powder
• Level, moisture, pH, magnetic field, proximity, acoustic are also credited
• Lead with the four the syllabus names — temperature, pressure, infra-red, sound — and use these when a scenario demands something specific

Only four sensors are named in the 9618 syllabus, so the rest are insurance rather than core.

---

3.2 Logic Gates and Logic Circuits

3.2.1–3.2.2 Symbols and functions of the six gates

Question

Identify one logic gate that is not used in the circuit shown, draw its symbol, and complete its truth table.

Answer — 1 mark each, 3 marks

• 1 mark for naming a gate genuinely absent from the circuit
• 1 mark for a symbol that matches the gate named
• 1 mark for a truth table that matches the gate named
• The symbol and table are marked against your own answer — a wrong gate can still earn 2

Latest: 9618_w21_qp_11_sc_3.c

Question

Describe the operation of the NAND, NOR, XOR and OR gates.

Answer — 1 mark each, 4 marks

• NAND — the output is 0 when both inputs are 1, otherwise the output is 1
• NOR — the output is 1 when both inputs are 0, otherwise the output is 0
• XOR — the output is 1 when one input is 1 and the other is 0, otherwise 0
• OR — the output is 0 when both inputs are 0, otherwise the output is 1
• AND — the output is 1 only when both inputs are 1
• NOT — the output is the opposite of the input

Latest: 9618_s24_qp_12_sc_1.a (also 9618_s23_qp_11_sc_5.b for NAND and NOR). Any four of the six can be chosen — NOT and AND have never yet been the ones asked.

Question

Describe the operation of a two-input XOR gate.

Answer — 3 phrasings for 1 mark

• The output is 1 only if one input is 1 and the other is 0
• The output is 1 only if the two inputs are different
• The output is 0 only if the two inputs are the same

Latest: 9618_w24_qp_13_sc_1.a

Question

Tick to show which logic gate each statement describes.

Answer — 1 mark per row, 3 marks

• The output is 1 only when both inputs are 1 → AND
• The output is 1 only when both inputs are different → XOR
• The output is 1 only when both inputs are 0 → NOR
• The output is 0 only when both inputs are 1 → NAND

Latest: 9618_s21_qp_11_sc_8

Question

The truth table shown for the given logic expression contains errors. Identify the rows that are incorrect.

Answer — block marked, 2 marks

• Work the expression through for each row, using the working-space column
• Name the row numbers whose output value is wrong
• 1 mark for one or two rows correctly identified; 2 marks for all three
• Do not change the table — the answer is the list of row numbers

Latest: 9618_w25_qp_12_sc_9.b

Question

Draw the symbol for each of the NOT, AND, OR, NAND, NOR and XOR gates.

Answer — 6 symbols, marked in pairs, 3 marks

• NOT — a triangle with a small circle on the output
• AND — a flat-backed D shape
• OR — a curved-back shape with a pointed output
• NAND — the AND shape with a circle on the output
• NOR — the OR shape with a circle on the output
• XOR — the OR shape with an extra curved line across the input side

Inference: the syllabus lists all six symbols, and every 9618 question expects them inside a drawn circuit. A question asking for them alone has never been set — but a wrong symbol silently costs marks in every circuit question, so they must be automatic.

3.2.3–3.2.5 Constructing circuits, truth tables and expressions

Question

Draw the logic circuit for the logic expression given.

Answer — always 2 marks, split into two named halves

• 1 mark for the first half of the circuit — e.g. NOT B XOR C correctly drawn
• 1 mark for the second half — e.g. NOT A, the final AND, and the closing NOT
• Alternative correct forms are accepted — a NAND gate drawn in place of AND followed by NOT
• Marks are lost for superfluous gates, so draw only what the expression contains
• Work outwards from the brackets, and label each wire with the sub-expression it carries

Latest: 9618_w25_qp_13_sc_3.b (also 9618_s24_qp_11_sc_1.b)

Question

Complete the truth table for the logic expression / circuit given.

Answer — always 2 marks, marked in blocks

• 1 mark for the first four rows correct
• 1 mark for the second four rows correct (or per shaded block)
• A single wrong row loses the whole half, so the working-space column is worth using
• Build the working column one gate at a time, left to right through the expression
• … rather than trying to evaluate the whole expression per row

Latest: 9618_w25_qp_13_sc_3.a (also 9618_s25_qp_11_sc_1.b)

Question

Write the logic expression for the logic circuit shown. Do not simplify the expression.

Answer — marked per named sub-expression, up to 3 marks

• 1 mark per correct sub-expression — e.g. A NAND B
• … e.g. NOT (B XOR C)
• … e.g. the final NAND combining them
• Where the circuit has two outputs, 1 mark for each output expression
• The instruction is usually “do not simplify” — a simplified answer can lose marks

Latest: 9618_w25_qp_12_sc_9.a (also 9618_s25_qp_13_sc_4.a)

Question

Write the logic expression represented by the truth table shown.

Answer — 2 marks

• Identify each row where the output is 1
• Write the AND-term for that row, using NOT for each input that is 0
• OR the terms together
• 1 mark for one correct term; 1 mark for the second term plus the OR in the correct place
• e.g. Q = (R AND S AND NOT T) OR (NOT R AND NOT S AND T)

Latest: 9618_w25_qp_11_sc_3.b

Question

Draw a line to match each truth table to the logic expression it represents.

Answer — 1 mark per correct line, 3 marks

• Work each expression through all eight rows and compare the output column
• Match on the whole column, not on one or two rows
• Eliminate as you go — a wrong match usually costs two marks, not one

Latest: 9618_s24_qp_13_sc_6

Question

Tick the logic statement that matches the truth table shown.

Answer — 1 mark

• Evaluate each offered statement against the output column
• One row where the statement disagrees is enough to rule it out

Latest: 9618_s24_qp_11_sc_1.a

Question

A table defines each parameter and the condition its binary value 1 represents. Write the logic expression for each output described.

Answer — 1 mark per expression, 2 marks

• Read the parameter table first — note what binary 1 means for each letter
• The floodlight turns on if the security system is on and daylight is low and a person is detected → X = E AND A AND C
• The alarm sounds if the security system is on and one or more doors are open or a person is detected → Y = E AND (B OR C OR D)
• The brackets carry the mark in the second expression

Latest: 9618_w24_qp_11_sc_5.b

Question

Using the parameter table given, draw the logic circuit for the system described in the prose.

Answer — 5 points for 3 marks

• Read the parameter table first, noting what 1 means for each letter — it is often the reverse of the intuitive reading (A = 1 means daylight is low)
• Translate the prose directly: “and” → AND, “or” → OR, “unless” → AND NOT, “is closed” when 1 = open → NOT
• Draw the inner conditions first, then the gate that combines them
• Marks go to each named sub-circuit, and superfluous gates lose marks
• Worked example: a fan turns on if temperature and humidity are too high and the door is closed, unless maintenance mode is active → F = (T AND H) AND (NOT D AND NOT M)

Inference: the syllabus says all three — circuit, truth table and expression — can be constructed “from a problem statement”. 9618 has only ever asked for the expression that way (w24_qp_11_sc_5.b). The circuit version is harder, because the parameter table must be read correctly first.

Question

Complete the truth table for the four-input logic circuit shown.

Answer — 2 marks, marked in blocks

• Sixteen rows: count in binary from 0000 to 1111 down the input columns
• Use a working column per gate, filled top to bottom, rather than evaluating row by row
• Marks are expected in blocks of eight rows, mirroring the three-input pattern
• The circuit is drawn the same way — only the number of rows changes

Inference: every 9618 truth table so far has three inputs and eight rows, but four-input circuits are drawn regularly and nothing in the syllabus rules out the table.

Question

Two logic circuits are shown. State whether they produce the same output for all inputs, and justify your answer.

Answer — 4 points for 2 marks

• Build the truth table for each circuit and compare the output columns
• They are equivalent only if the outputs match for every row
• A single differing row is enough to justify “not equivalent” — quote that row
• A gate is redundant if removing it leaves the output column unchanged (e.g. a double NOT)

Inference: Boolean simplification is A Level (15.2), not AS — but the recurring instruction “do not simplify” implies awareness. A question asking whether two circuits are equivalent sits at the edge of the AS wording and has not been asked.