Cambridge IGCSE0478

Computer architecture

Computer Science 0478 Chapter Notes

What this chapter covers

Computer architectureInput and output devicesData storageNetwork hardware

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Computer architecture notes

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1. The CPU and the microprocessor

The central processing unit (CPU) processes the instructions and data that are input into the computer, so that the result can be output.

A microprocessor is a type of integrated circuit on a single chip.

Examiner insight

“Some responses lacked technical understanding, for example explaining that it does the processing, or that it is the brain of the computer.” “Some candidates were able to give a general description of the role of a microprocessor, but they did not apply it to the context given.”

Worked example 13 marks

A building has a security keypad that requires the input of a 3-digit denary number. A microprocessor is used to find out whether a user has input the correct 3-digit denary number.

Explain the role of the microprocessor in this process.

1
The microprocessor compares the denary number received to the stored value / preset code [1]
2
If the denary numbers match, a correct code has been entered [1]
3
If the denary numbers do not match, the code is not correct [1]

2. Components of a Von Neumann CPU

In a Von Neumann architecture, the instructions and the data are stored in the same memory, and the instructions are fetched and executed in order. The arithmetic logic unit (ALU) carries out calculations. The control unit (CU) is responsible for decoding an instruction. A register stores data temporarily.

Five registers matter. The program counter (PC) stores the address of the next instruction. The memory address register (MAR) stores the address of the value to be fetched from RAM. The memory data register (MDR) stores the value fetched. The current instruction register (CIR) holds the instruction. The accumulator (ACC) stores the result of a calculation.

Three buses transmit data, addresses and signals. The address bus carries addresses, the data bus carries data and the control bus carries control signals.

Examiner insight

“Some candidates incorrectly stated that the accumulator stores calculations. Candidates need to understand that the accumulator stores the result of a calculation and not the actual calculation itself.” “Many candidates provided three correct busses. The most common incorrect answer was candidates providing fetch, decode and execute, which demonstrated a misunderstanding of the question.”

Worked example 13 marks

A computer has a central processing unit (CPU).

Identify three components that are built into a CPU from the given list.

accumulator (ACC), binary counter (BC), binary register (BR), binary unit (BU), current instruction register (CIR), instruction unit (IU), program counter (PC), read only memory (ROM)

1
accumulator // ACC [1]
2
current instruction register // CIR [1]
3
program counter // PC [1]

3. The fetch–decode–execute cycle

The CPU repeats the fetch–decode–execute (FDE) cycle. To fetch an instruction, the address of the next instruction goes from the PC to the MAR. The instruction at that address in RAM is copied into the MDR.

``` MAR ← address held in PC MDR ← value held in RAM at that address CIR ← instruction held in MDR ```

The instruction is then copied to the CIR from the MDR, and the control unit decodes it. A mark scheme credits the copy to the CIR as an action in the decode stage. In the execute stage the instruction is carried out, using components such as the ALU and the accumulator.

Examiner insight

“Some candidates had some understanding that the MAR and the MDR are used in this process, but lacked accuracy about how they are used.”

Worked example 13 marks

A value is fetched from random access memory (RAM) to the CPU.

Explain how the MAR and MDR are used in this process.

1
The MAR stores the address / location [1]
2
… for the value / data that is to be fetched from RAM [1]
3
The MDR stores the value / data [1]

4. Cores, cache and clock

A CPU can have more than one core. With more cores, a CPU can execute more instructions simultaneously: four cores can execute four instructions at once, where two cores can execute two.

The clock controls the number of FDE cycles. Clock speed is a measure of how many clock cycles are completed each second. A 3 GHz clock is 3 billion clock cycles processed per second.

The number of cores, the size of the cache and the speed of the clock can each affect the performance of a CPU. A faster clock speed may process more instructions per second. Fewer cores cannot process as many instructions simultaneously.

Examiner insight

“A common error was identifying that computer B could run 2.5 billion instructions each second without taking into consideration the dual cores.” “Some candidates incorrectly stated that it would mean that more fetch- decode-execute cycles could be carried out simultaneously.”

Worked example 14 marks

The tablet computer has a 1.8 GHz quad-core processor.

The student wants a new tablet computer that has a 2.4 GHz dual-core processor.

Explain whether the processor of the new tablet computer would have a better performance than the processor of her current tablet computer.

1
It has a faster clock speed … [1]
2
… so it may process more instructions per second, which may mean its performance is better [1]
3
It has fewer cores, so it cannot process as many instructions simultaneously … [1]
4
… which may mean its performance is worse [1]

5. The instruction set

An instruction set is a list of all the commands that can be processed by a CPU. The commands are machine code.

In the decode stage the control unit uses the instruction set to decode the instruction, converting it into an opcode and an operand.

Examiner insight

“Many responses found it difficult to define the term without using the term instruction or the term set.” “Some candidates gave the answer mnemonics. These are used in an instruction list but are not accurate for the name of the list.”

Worked example 13 marks

The processor performs the fetch-decode-execute (FDE) cycle.

Describe the actions that take place in the decode stage of the FDE cycle.

1
The instruction is copied to the current instruction register from the MDR [1]
2
The control unit decodes the instruction, using an instruction set [1]
3
The instruction is decoded / converted into the opcode and operand [1]

6. Embedded systems

An embedded system is used to perform a dedicated function. Examples are domestic appliances, cars, security systems, lighting systems and vending machines.

A general purpose computer, such as a personal computer (PC) or a laptop, is used to perform many different functions.

Examiner insight

“Candidates need to have a greater understanding of the features of an embedded system beyond it being designed to perform a dedicated function.” “Candidates were often able to identify that the ATM performed a limited number of functions. Some candidates were able to expand on this to identify that the functionality could not be changed or that the hardware was dedicated to its functions.”

Worked example 13 marks

A washing machine is controlled by an embedded system. A laptop is a general purpose computer.

Explain why the washing machine's controller is an embedded system and the laptop is not.

1
An embedded system performs a dedicated function [1]
2
The washing machine's controller does only one job: it controls the wash [1]
3
The laptop is used to perform many different functions [1]

Recap

The CPU processes instructions and data that are input so that the result can be output.
A microprocessor is an integrated circuit on a single chip.
ALU carries out calculations. CU decodes. Registers store data temporarily.
PC stores the address of the next instruction. MAR stores the address to fetch from. MDR stores the value fetched.
CIR holds the instruction. ACC stores the result of a calculation.
Buses: address bus, data bus, control bus.
More cores means more instructions executed simultaneously. A faster clock means more cycles per second.
An instruction set is a list of all the commands a CPU can process. The commands are machine code.
An embedded system performs a dedicated function. A general purpose computer performs many.

7. Input devices

An input device is a device that enters data into a computer so that it can be processed. A computer needs input devices because without them it has no data to work on.

The input devices on the syllabus are the barcode scanner, digital camera, keyboard, microphone, optical mouse, QR code scanner, touch screen (resistive, capacitive and infra-red), and 2D and 3D scanners.

A microphone is an input device. A smartphone or tablet has several built in: a touch screen, a microphone, a camera and buttons.

Examiner insight

“It would be beneficial for candidates to understand that an input device should not be described as an analogue to digital converter.” “Some candidates stated that an input device was used to input something. An increased level of detail is required.”

Worked example 12 marks

A student is playing her piano. She uses her tablet computer to record the sound produced by the piano.

(i) Give the name of the input device built into the tablet computer that is used to record the sound produced by the piano.

(ii) Identify one other input device that can be built into the tablet computer.

1
(i) microphone [1]
2
(ii) any one from: button, touchscreen, sensor, touch pad, camera [1]

8. Output devices

An output device is a device that presents the result of processing to the user, or acts on it. A computer needs output devices because without them the user cannot see, hear or use the results.

The output devices on the syllabus are the actuator, DLP projector, inkjet printer, laser printer, LED screen, LCD projector, LCD screen, speaker and 3D printer.

An actuator is an output device that produces physical movement. Every output device gives an output, so that is not what makes an actuator special.

Examiner insight

“Fewer candidates could describe an actuator, the most commonly correct responses referred to it as producing physical movement. Answers that were not specific enough often described it giving an output, which all output devices do.” “The most common incorrect answer given was microphone. The most common correct answer missed was actuator.”

Worked example 12 marks

A smartphone has a quad-core 2.4 GHz processor. The smartphone has built-in input and output devices.

(ii) Identify two output devices that could be built into the smartphone.

1
any one from: screen // touchscreen, speaker, LED // light, actuator [1]
2
a second, different device from the same list [1]

9. What a sensor is

A sensor is an input device. It measures its environment and sends the data to the computer. A sensor is not only "a device": the mark is for saying it is an input device.

A sensor does not decide anything. It measures the environment. The decision is made later, when a microprocessor processes the data.

Examiner insight

“Many stated that a sensor is a device, but not that it is an input device.”

Worked example 11 mark

A smartwatch has a built-in microphone that allows a person to use voice commands to control the smartwatch.

(d) Identify one example of a sensor that would be built into the smartwatch.

1
any one from: accelerometer, light, temperature, proximity, infra-red, acoustic, magnetic field, moisture, humidity, pressure [1]

10. Choosing the right sensor

The syllabus names fourteen sensors: acoustic (sound), accelerometer, flow, gas, humidity, infra-red, level, light, magnetic field, moisture, pH, pressure, proximity and temperature.

Give the type of sensor, not an example of one: gas sensor, not "O2 sensor"; pH sensor, not "acidity sensor". Pick the sensor for the quantity in the question. Soil acidity needs a pH sensor, not a moisture sensor. Being near an object needs a proximity or infra-red sensor.

A flow sensor measures the amount of flow of a material. Say both: the amount, and what is flowing.

Examiner insight

“Some candidates gave motion or movement sensor. These terms require more precision as to that actual type of sensor within it, for example infra-red.” “The most common error made was candidates not using the correct name for a type of sensor and rather listing and example of the type of sensor, such as O2 sensor or CO2 sensor for gas sensor, and acidity sensor for pH sensor.”

Worked example 11 mark

A drone is used to search for lost animals. The drone has a built-in system to stop it from crashing into objects, for example a tree. The system uses sensors and a microprocessor.

(i) Identify one sensor that could be built into the drone to detect if it is near an object.

1
proximity // infra-red [1]

11. Sensor and microprocessor together

A sensor sends a continuous stream of data. The data is digitised before the microprocessor receives it.

The microprocessor compares the data with a stored value. If the comparison shows action is needed, it sends a signal and an actuator makes the movement. Otherwise no action is taken. The process repeats until the system is turned off.

Use the numbers and the situation in the question. Repeating the question back earns nothing.

Examiner insight

“Few candidates were able to demonstrate an understanding of a sensor continually sending data to the microprocessor for analysis, instead suggesting that the sensor only sends data when an object is detected.” “An actuator converts a digital signal into physical movement for example to move a motor to open a door, it does not display a message on a digital screen.”

Worked example 14 marks

A drone is used to search for lost animals. The drone has a built-in system to stop it from crashing into objects, for example a tree. The system uses sensors and a microprocessor.

(iii) Explain how the sensor and microprocessor work together to stop the drone crashing into an object.

1
the sensor continually transmits digitised data to the microprocessor [1]
2
the microprocessor compares the received data to the stored data of an object // distance [1]
3
if the data is less than, greater than or matches the stored distance, the microprocessor transmits a signal to stop the drone in that direction [1]
4
an actuator is used to stop, change or control the drone [1]

Recap

An input device enters data into a computer. An output device presents or acts on the result.
A microphone is an input device. A speaker is an output device.
An actuator is an output device that produces physical movement.
A sensor is an input device that measures its environment.
Name the type of sensor: gas, pH, proximity, infra-red, not motion, O2 or acidity.
The sensor measures. The microprocessor compares the data with a stored value and sends a signal.
The sensor sends data continually, not only when something happens.

12. Primary storage: RAM and ROM

Primary storage is directly accessed by the CPU. The two kinds on the syllabus are random access memory (RAM) and read only memory (ROM).

RAM is volatile and ROM is non-volatile, so primary storage is both volatile and non-volatile. RAM holds the data and the parts of software that are currently in use. A comparison of RAM and ROM must give both sides.

Examiner insight

“Primary storage is directly accessible by the CPU.” “‘Software’ is inaccurate, because the data for software is stored in secondary storage, the currently running parts of the software will be stored in RAM.”

Worked example 11 mark

A computer has primary and secondary storage.

Tick one box to show which is an example of primary storage.

A cloud storage · B firmware · C read only memory (ROM) · D solid-state drive (SSD)

1
C: read only memory (ROM) [1]

13. Secondary storage

Secondary storage is not directly accessed by the CPU. It is necessary for more permanent storage of data. It is non-volatile.

Hard disk drives (HDD) and solid-state drives (SSD) are secondary storage. Neither is primary storage.

Examiner insight

“The most common incorrect response was candidates categorising an Solid state drive (SSD) as primary storage.” “Some candidates identified a larger storage capacity than primary, which is not always accurate depending on the devices.”

Worked example 12 marks

A student stores their schoolwork on secondary storage devices.

Give two characteristics of secondary storage.

1
non-volatile [1]
2
not directly accessible by the CPU [1]

14. Magnetic storage

Magnetic storage uses platters which are divided into tracks and sectors. Data is read and written using electromagnets. The example on the syllabus is the hard disk drive (HDD).

Pits and lands belong to optical storage, not to magnetic storage.

Examiner insight

“Many candidates ticked that pits and lands are used to store data for magnetic storage.” “Some candidates identified pits and lands instead of electromagnetic field.”

Worked example 12 marks

Complete the description of how magnetic hard disk drives and solid-state drives (SSD) read data. Use terms from the list. Not all terms need to be used. You should only use a term once.

control · electromagnetic field · flow · loss · NOR gates · opened · pits and lands · platters · ports · remove · sectors · XOR gates

A hard disk has several platters. Each platter is split into tracks and ............ . To read data, the read/write head moves over the platters to the position where data starts. The ............ indicates if the data is a 1 or a 0.

1
tracks and sectors [1]
2
the electromagnetic field indicates a 1 or a 0 [1]

15. Optical storage

Optical storage uses lasers to create and read pits and lands. The examples on the syllabus are CD, DVD and Blu-ray.

To read the disc, a laser is shone at it.

Examiner insight

“Most candidates were able to gain a mark for understanding a laser it shone at the disk.”

Worked example 13 marks

A film is stored on a Blu-ray disc.

(a) State what an optical storage device uses to create and read data.

(b) Name the two features that it creates on the disc.

1
(a) a laser [1]
2
(b) pits [1]
3
and lands [1]

16. Solid-state (flash memory) storage

Solid-state (flash memory) storage uses NAND or NOR technology. It is made of transistors, which are used as floating gates and control gates. The gates control the flow of electrons to memory cells.

Examples are the solid-state drive (SSD), the SD card and the USB drive. A solid-state drive is non-volatile.

Examiner insight

“Most candidates were able to identify solid-state as being non-volatile.” “It would be beneficial for candidates to understand that USB flash memory drive and solid state drive (SSD) both operate using the solid-state memory method.”

Worked example 13 marks

Complete the description of how magnetic hard disk drives and solid-state drives (SSD) read data. Use terms from the list. Not all terms need to be used. You should only use a term once.

control · electromagnetic field · flow · loss · NOR gates · opened · pits and lands · platters · ports · remove · sectors · XOR gates

A solid-state drive uses NAND gates or ............ . It is made of transistors that work as floating gates and ............ gates. The gates control the ............ of electrons to memory cells.

1
NAND gates or NOR gates [1]
2
floating gates and control gates [1]
3
the gates control the flow of electrons [1]

17. Virtual memory

Virtual memory is created from part of the secondary storage. When RAM has no space for a page that is needed, another page is moved from RAM to virtual memory to make space in RAM. Pages of data are transferred between RAM and virtual memory when needed.

Examiner insight

“The most common mark awarded was for stating that secondary storage is partitioned to create the virtual memory.” “The most commonly awarded mark points were page B can be moved to virtual memory to make space for page D in RAM.”

Worked example 13 marks

A computer has pages A, B and C of a program in RAM. Page D is needed. There is no space in RAM for it.

Describe how virtual memory is used.

1
page B (or A or C) is moved from RAM to virtual memory [1]
2
to make space in RAM [1]
3
page D is loaded into RAM [1]

18. Cloud storage

Cloud storage is storage of files and data on remote, third-party, off-site servers. It can be accessed remotely, in comparison to storing data locally.

Physical servers and storage are needed to hold the data. A local server on the same network is not cloud storage.

Examiner insight

“Some candidates identified it as being data storage on servers without identifying the location of these servers to differentiate them from a local server on the same network.”

Worked example 11 mark

State what is meant by cloud storage.

1
storage of files/data on remote / third-party / off-site servers [1]

19. Cloud or local?

Cloud storage lets the data be reached from any device, and the data is still on the cloud if the computer fails. Local storage can be used without internet access and gives control over maintenance, backup and security.

An advantage must be one the other option does not have.

Examiner insight

“Some candidates gave advantages that were not unique to cloud storage, for example that the data could be accessed at any time.” “Candidates should understand the photos could also be hacked when stored locally, so this is not a disadvantage of storing in the cloud over storing locally.”

Worked example 14 marks

A student stores their schoolwork on secondary storage devices. They store their schoolwork on their home computer and on cloud storage.

(a) Explain the advantages to the student of storing their data on cloud storage instead of storing the data locally on their home computer.

(b) Explain the advantages to the student of storing their data locally on their home computer instead of using cloud storage.

1
(a) any one from: data can be accessed from any device; they can store the data at school and access at home [1]
2
any other from: if anything happens to their computer the data is still on the cloud; can free some storage space on their computer [1]
3
(b) any one from: can access without internet access; if the Internet goes down they still have access [1]
4
any other from: no dependence on a third party; control over maintenance, backup or security [1]

Recap

Primary storage is directly accessed by the CPU: RAM and ROM.
RAM is volatile and holds what is in use. ROM is non-volatile.
Secondary storage is not directly accessed by the CPU and is non-volatile. HDD and SSD are secondary.
Magnetic: platters, tracks and sectors, electromagnets. Optical: lasers, pits and lands. Solid-state: NAND or NOR, floating gates and control gates.
Virtual memory: pages move between RAM and virtual memory when needed.
Cloud storage is on remote servers and is accessed remotely. Local storage works without the internet.

20. The network interface card

A computer needs a network interface card (NIC) to access a network. The NIC allows the device to connect to the network.

A NIC is given a MAC address at the point of manufacture.

Examiner insight

“Very few candidates were able to provide accurate definitions of a router and a NIC.” “The most common incorrect answer was router.”

Worked example 12 marks

A desktop computer is being set up in an office. It must join the office network. Identify the component the computer needs to access the network. State the type of address this component is given at the point of manufacture.

1
network interface card (NIC), not a router [1]
2
media access control (MAC) address [1]

21. MAC addresses

A media access control (MAC) address identifies a device on a network. It identifies the device, not the location of the device. A NIC is given its MAC address at the point of manufacture.

A MAC address is usually written as hexadecimal, in pairs of values separated by colons. It is made from the manufacturer code and the serial code.

The first half is the manufacturer code and the second half is the serial code.

Examiner insight

“Many candidates gave incorrect reference, most commonly Media Access Code, Media Address Control and Memory Access Code.” “It would be beneficial if candidates understood that a MAC address is used to identify a device on a network and not the location of the device.”

Worked example 13 marks

A network interface card has the MAC address 00:1B:44:11:3A:B7. Describe the structure of this MAC address.

1
it is written in hexadecimal [1]
2
the first half, 00:1B:44, is the manufacturer code [1]
3
the second half, 11:3A:B7, is the serial code [1]

22. IP addresses: purpose and types

An internet protocol (IP) address identifies a device on a network. It is allocated by the network. An IP address can be static or dynamic. An IP address can be changed even after it has been set.

Say where the identification is needed: on a network. A bare "it gives the device an address" repeats the question.

Examiner insight

“These responses required more about the purpose of the IP address, the reason why a device needed an address.” “The most common incorrect answer was candidates identifying the statement ‘Once an IP address has been set it cannot be changed’ as true.”

Worked example 13 marks

A laptop joins a network and is given an internet protocol (IP) address. State how the laptop gets this address. Describe the purpose of the address.

1
the address is allocated by the network [1]
2
it identifies the device ... [1]
3
... on a network [1]

23. IPv4, IPv6 and comparing addresses

IPv4 and IPv6 are the two types of IP address. Both are unique addresses and both can be used to identify a device. A MAC address and an IP address are similar in the same two ways.

To give a difference between a MAC address and an IP address, give the feature of both. A MAC address cannot normally be changed, but an IP address can sometimes change.

Examiner insight

“Candidates are reminded that if they are asked to provide a difference between two elements, they need to provide the information about the feature or characteristic of both.” “The most common correct answer given was that a MAC address cannot normally be changed, but an IP address can sometimes change.”

Worked example 12 marks

Give two differences between a MAC address and an IP address.

1
a MAC address is given to the NIC at the point of manufacture, but an IP address is allocated by the network [1]
2
a MAC address cannot normally be changed, but an IP address can sometimes change [1]

24. The router

A router sends data to a specific destination on a network.

A router can assign IP addresses. A router can connect a local network to the internet.

Examiner insight

“It would be beneficial for candidates to have a greater understanding of these components, especially a router.” “The most common mark awarded was for the router sending packets towards their correct destination.”

Worked example 13 marks

A family has a home network. Describe the role of the router in the network.

1
sends data to a specific destination on the network [1]
2
can assign IP addresses to the devices [1]
3
connects the local network to the internet [1]

Recap

A computer needs a network interface card (NIC) to access a network.
A MAC address identifies a device on a network. It is given to the NIC at manufacture.
A MAC address is written in hexadecimal: manufacturer code, then serial code.
An IP address identifies a device on a network. The network allocates it.
An IP address can be static or dynamic, so it can change.
IPv4 and IPv6 are both unique addresses that identify a device.
A router sends data to a specific destination, can assign IP addresses and connects a local network to the internet.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

State what is meant by a microprocessor.1 mark
State the role of the CPU in a computer.1 mark
State what the program counter stores.1 mark
Name the CPU component that carries out calculations. Name the register that stores the result of a calculation.2 marks
Give the names of the three buses in a CPU.3 marks
Describe what is meant by a clock speed of 2 GHz.2 marks
Describe what is meant by an instruction set.2 marks
A vending machine is controlled by an embedded system with a single-core 1 GHz processor. A shop owner's laptop has a quad-core 1 GHz processor. (a) Give one reason why the vending machine's controller is an embedded system and the laptop is not. [1] (b) Explain why the laptop could have a better performance than the vending machine's controller, even though the clock speeds are the same. [3]4 marks
A weather station's data logger has a 1.5 GHz dual-core processor. A student writes: 'The processor can process 1.5 billion instructions each second. Raising the clock speed to 3 GHz would let it execute more instructions simultaneously.' (a) Explain the mistake in the student's first sentence. [2] (b) Explain the mistake in the student's second sentence. [2] (c) State a change to the processor that would let it execute more instructions simultaneously. [1]5 marks
A car park barrier is controlled by a microprocessor. In its RAM, address 40 holds instruction P, address 41 holds instruction Q and address 52 holds the value 17. The program counter holds 40. (a) The next instruction is fetched and copied ready to be decoded. State what is then stored in the MAR, in the MDR and in the CIR. [3] (b) To execute this instruction, the value at address 52 is fetched from RAM. Explain how the MAR and the MDR are used to fetch this value. [2] (c) The instruction carries out a calculation with this value. Name the component that carries out the calculation and the register that stores the result. [2]7 marks
State whether a microphone is an input device or an output device.1 mark
A tablet computer has a touch screen. Give two other input devices that can be built into the tablet.2 marks
A student says that an input device is a device that inputs something. Give an improved description of an input device and state why a computer needs one.2 marks
Give one output device that produces a printed copy and one that produces sound.2 marks
A shop door opens by itself when a customer walks up to it. A student says the actuator shows the word "Welcome" on a screen. Explain why she is wrong.2 marks
State what is meant by a sensor.2 marks
Name the most suitable sensor for each job. (a) Checking the acidity of the soil in a garden. (b) Showing how close a robot is to a wall.2 marks
A weather station records how much water vapour is in the air, how bright it is and how warm it is. Name the sensor for each.3 marks
A fish farm needs three sensors. The first checks how acidic the water in the tanks is. The second monitors the water moving through the inlet pipe. The third measures the carbon dioxide in the air above the tanks. A student suggests an acidity sensor, a movement sensor and a CO2 sensor. (a) Give the correct type of sensor for each of the three jobs. (b) State what the sensor on the inlet pipe measures.5 marks
A greenhouse window opens automatically when the air inside is warmer than 28 °C. It closes again when the air is at 28 °C or cooler. The system uses a temperature sensor, a microprocessor and an actuator. A student writes: "The sensor detects that the greenhouse is too hot and then sends data to the microprocessor." (a) Give two errors in the student's sentence. (b) Describe how the microprocessor uses the data from the sensor to control the window. Use the value in the question. (c) State what the system does after the window has moved.7 marks
State what is meant by primary storage.1 mark
A laptop has RAM, an SSD, ROM and a cloud account. Identify the two that are primary storage.2 marks
A student writes: ‘RAM is volatile. RAM stores software.’ (a) Complete the comparison by writing the matching fact about ROM. (b) Correct the student's second sentence.3 marks
A tablet keeps a student's files after it is switched off. Give two reasons why this storage is secondary storage.2 marks
A hard disk drive has platters. State what each platter is divided into, and what is used to read and write data.3 marks
Name the type of storage described, and give one example of each. (a) It uses a laser to read pits and lands. (b) It uses floating gates and control gates.4 marks
A camera stores photographs on an SD card. Describe how the SD card stores data.3 marks
A school keeps files on a server in its own office. A teacher says, ‘We use cloud storage, because our files are stored on a server.’ (a) State what is meant by cloud storage. (b) Explain why the teacher is wrong.3 marks
The RAM in a games console has space for three pages. Pages J, K and L of a game are in RAM. The game needs page M, and the console chooses page K to move out. Later the game needs page K again. A student writes: ‘Page M is stored in virtual memory, which is extra RAM.’ (a) Give two corrections to the student's statement. (b) Describe, in order, every transfer of pages from when page M is needed until page K is in use again.6 marks
A vet's surgery keeps its animal records on a hard disk drive in the office computer. The internet connection in the village often fails. The owner plans to move the records to cloud storage and delete the local copy. A colleague gives three arguments. A: ‘On the cloud, the records can be accessed at any time.’ B: ‘On the cloud, the records could be hacked.’ C: ‘Cloud storage needs no physical storage devices.’ (a) Explain what is wrong with each argument. (b) Explain one advantage and two disadvantages to the surgery of the owner's plan.6 marks
State the component a computer needs to access a network.1 mark
Give the full name of the address abbreviated MAC.1 mark
A MAC address is 7A:2C:90:5E:11:F4. State which pairs of values are the manufacturer code and which are the serial code.2 marks
A student says: "Once an IP address has been set it cannot be changed." State whether the student is correct.1 mark
Describe the purpose of an IP address.2 marks
Describe a dynamic IP address.2 marks
Give two similarities between an IPv4 address and an IPv6 address.2 marks
The router in a school network stops working. State three things the network can no longer do.3 marks
A weather station has a sensor hub on a school network. A technician records the two addresses of the hub on two days, in the table below. (a) Identify which address is the MAC address. Give one reason from the way it is written and one reason from the two days. [3] (b) State the serial code of the hub. [1] (c) A second hub has an Address A that begins 3C:5A:B4. State what this tells you about the two hubs. [1] (d) Explain why Address B is different on Friday. State whether it is static or dynamic. [2] | Day | Address A | Address B | | --- | --- | --- | | Monday | 3C:5A:B4:07:9E:21 | 192.168.1.14 | | Friday | 3C:5A:B4:07:9E:21 | 192.168.1.37 |7 marks
A café moves its till computer from the shop network to a market stall network. The owner writes four notes: 1. "The router inside the till lets it access the network." 2. "The MAC address tells the stall network where the till is." 3. "The stall network will give the till a new MAC address." 4. "The IP address was set in the shop, so it cannot be changed." (a) Each note contains a mistake. Correct each note. [4] (b) State the device on the stall network that can assign the till an IP address. Give one other thing this device does. [2]6 marks

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Number systems Types and methods of data transmission Types of software and interrupts The internet and the world wide web Automated systems Algorithm design and problem-solving

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1. The CPU and the microprocessor#

2. Components of a Von Neumann CPU#

3. The fetch–decode–execute cycle#

4. Cores, cache and clock#

5. The instruction set#

6. Embedded systems#

7. Input devices#

8. Output devices#

9. What a sensor is#

10. Choosing the right sensor#

11. Sensor and microprocessor together#

12. Primary storage: RAM and ROM#

13. Secondary storage#

14. Magnetic storage#

15. Optical storage#

16. Solid-state (flash memory) storage#

17. Virtual memory#

18. Cloud storage#

19. Cloud or local?#

20. The network interface card#

21. MAC addresses#

22. IP addresses: purpose and types#

23. IPv4, IPv6 and comparing addresses#

24. The router#

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Chapter at a Glance

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Related chapters

1. The CPU and the microprocessor

2. Components of a Von Neumann CPU

3. The fetch–decode–execute cycle

4. Cores, cache and clock

5. The instruction set

6. Embedded systems

7. Input devices

8. Output devices

9. What a sensor is

10. Choosing the right sensor

11. Sensor and microprocessor together

12. Primary storage: RAM and ROM

13. Secondary storage

14. Magnetic storage

15. Optical storage

16. Solid-state (flash memory) storage

17. Virtual memory

18. Cloud storage

19. Cloud or local?

20. The network interface card

21. MAC addresses

22. IP addresses: purpose and types

23. IPv4, IPv6 and comparing addresses

24. The router