IGCSE Computer Science C3

Explain the role and purpose of the central processing unit (CPU).

• Processes instructions and data that are input into the computer so that the result can be output 

• Most important part of a device, basically like the brain 

• It is central to all devices including: 

• Laptops 

• Desktops 

• Games-Consoles 

• Mobile Devices 

• Data and commands are inputted by the user using an input device, the central processing unit (CPU) processes data by executing instructions and the results are outputted to an output device 

• Consists of control unit (CU), arithmetic and logic unit (ALU), registers and buses and a system clock 

 Purpose of CPU 

•  - It processes data  

• - It processes/executes instructions  

• - It carries out calculations  

• - It carries out logical operations 

• CPU is part of Von Neumann architecture 

Define a microprocessor.

A microprocessor is a single chip containing the CPU and sometimes additional components like memory controllers and I/O interfaces.

Describe the Von Neumann architecture.

• A system where data and programs are stored in the same memory

• CPU fetches and executes instructions sequentially.

State the purpose of the Arithmetic Logic Unit (ALU).

Performs arithmetic and logical operations (AND, OR, NOT).

State the purpose of the Control Unit (CU).

• Coordinates and controls all activities taking place within the CPU 

• Decodes instructions and executes them 

• Receives signals from the system clock 

• Directs the timing and control of other parts of CPU 

Describe the function of registers in the CPU.

• Very small 

• Holds small amounts of data needed as part of the fetch-execute cycle 

5 different types of registers: 

• PC (Program Counter) →stores address of next instruction to be fetched from memory 

• MAR (Memory Address Register) →stores address of data currently being fetched from/written to memory 

• MDR (Memory Data Register) →stored data that has been fetched from or is being written to memory 

• CIR (Current Instruction Register) →stores current instruction that is being decoded and executed 

• ACC (Accumulator) →stores results of calculation performed by ALU

Describe the fetch-decode-execute cycle.

Fetch: PC → MAR → RAM → MDR → CIR
Decode: CU decodes instruction using instruction set
Execute: CU coordinates ALU to process, result stored in accumulator

Pneumonic: Phil Collins and Mar said Ramos is Mierda like Cheese in Russian

Explain how cores, cache, and clock speed affect CPU performance.

More cores = multitasking
Larger cache = faster access
Higher clock speed = more instructions per second

Define instruction set.

• A list of binary-coded instructions a CPU can execute,

• including opcodes (action) and operands (location/value).

Describe the purpose of an embedded system. (PERMILAUTONO)

• Used to perform a dedicated function 

• Has a microprocessor  

• Normally built into a larger device/system  

• Works automatically // works without human intervention  

• User normally cannot reprogram  

State one benefit of using an embedded system.

It performs a specific function automatically, making the device more efficient and reliable.

Define an input device.

A hardware component that converts physical input into digital data for processing by the computer.

Define an output device.

A hardware component that presents processed data to the user in a readable or understandable form.

Describe the function of a barcode scanner.

Uses a red laser to read parallel black and white lines, converting them into a digital product code.

Explain the difference between resistive, capacitive, and infra-red touchscreens.

Resistive: Pressure connects conductive layers
Capacitive: Detects change in electrical field
Infra-red: Detects breaks in invisible light beams

State one advantage of using a capacitive touchscreen over a resistive one.

Capacitive screens are more responsive and support multi-touch; resistive screens require pressure.

Describe the function of an actuator.

Converts electrical signals into motion to perform a physical action.

Explain the function of a 3D scanner.

Captures the shape of a 3D object by measuring its geometry in x, y, and z dimensions.

State the purpose of a sensor.

Measures physical data (e.g., temperature, light) and sends it to a microprocessor for processing.

Describe how a microprocessor uses sensor data.

• Sensor sends analogue signal

• Signal converted to digital by ADC

• Compared to stored value

• Microprocessor sends output signal to actuator if needed

Distinguish between primary and secondary storage.

Primary: Volatile, accessed directly by CPU (e.g., RAM, ROM)
Secondary: Non-volatile, used for long-term storage (e.g., HDD, SSD)

Compare RAM and ROM.

RAM: Volatile, read/write, temporary
ROM: Non-volatile, read-only, stores BIOS

Describe magnetic storage.

Uses spinning platters and magnetic heads to read/write data (e.g., HDD).

Describe optical storage.

Uses lasers to read pits and lands on disks (e.g., CD, DVD).

Describe solid-state storage.

Uses NAND flash memory and transistors to store data (e.g., SSD, USB).

State one reason why SSDs are preferred over HDDs in portable devices.

SSDs have no moving parts, making them more durable and faster than HDDs.

Define virtual memory.

• Is an extension of primary storage (RAM) located on secondary storage 

• When RAM is close to being full, virtual memory can be used (computer remains operational) 

• Programs and data not currently being executed are transferred to virtual memory 

• Programs and data are transferred back to RAM when they are needed 

• Programs are stored as pages of data 

• Pages of data are transferred between RAM and virtual memory when needed 

State one benefit and one drawback of virtual memory.

Advantages :

• Allows more applications to run at the same time  

• Enables larger programs to run when there isn’t enough physical RAM  

• Prevents system crashes when RAM is full  

• Cheaper than adding more RAM 

Disadvantages 

• Slower than RAM, as it uses the hard drive or SSD  

• Makes the computer slower  

• The computer keeps switching between RAM and storage too much  

• Using it too much can wear out the storage drive 

Explain what is meant by cloud storage.

• Is a form of long-term (secondary) storage that allows users to store files and data on the internet (which is held on physical remote servers), often a collection of servers.  

• Data can be accessed remotely in comparison to storing data locally. 

• 3 types of cloud storage: Public cloud, private cloud and hybrid cloud 

State the function of a Network Interface Card (NIC).

Enables a device to connect to a network and communicate by sending/receiving data packets.

Explain the purpose of a MAC address.

A unique identifier for network hardware used in local network communication, written in hexadecimal.

State the purpose of a MAC address.

Uniquely identifies a device on a local network to ensure correct delivery of data packets.

Explain the purpose of an IP address.

Identifies a device on a network to allow data to be routed correctly; can be static or dynamic.

Compare IPv4 and IPv6.

IPv4: 32-bit, 4.3 billion addresses, decimal format
IPv6: 128-bit, larger range, hexadecimal, more secure

Explain one reason for using IPv6 instead of IPv4.

IPv6 supports a larger number of addresses and includes improved security features.

Describe the role of a router.

• Forwards data between networks,

• assigns IP addresses,

• connects a local network to the internet.

Explain why increasing cache size can improve CPU performance.

Frequently used data is accessed faster from cache than from RAM, reducing the need for slower memory access.

Explain how a 2D scanner is used in a library system.

• Scans the barcode of a book to identify

• retrieve its data from a database for borrowing/returnin