CPU Architecture, Performance & Embedded Systems (OCR GCSE Computer Science)
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1/47What is the purpose of the CPU?
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What is the purpose of the CPU?
The purpose of the CPU is to fetch, decode and execute instructions.
True or False?
The CPU is the brain of the computer and its job is to take an input, process data and produce an output.
True.
The CPU is the brain of the computer and its job is to take an input, process data and produce an output.
Define the fetch-execute cycle.
The fetch-execute cycle is the cycle that the central processing unit (CPU) runs through billions of times per second to make a computer work.
During which stage of the fetch-execute cycle is the next instruction fetched from memory?
During the fetch stage of the cycle, the next instruction or data must be fetched from the computer's memory (RAM).
What happens during the decode stage of the fetch-execute cycle?
During the decode stage of the cycle, the CPU needs to work out what is required from the instruction.
What are two events that take place during the execute stage?
During the execute stage, the CPU will carry out the instruction that was fetched, such as performing a calculation or storing a result in memory.
State the three key stages of the fetch-execute cycle.
The three key stages are: fetch, decode, execute.
An input is...
An input is clicking a button on the gamepad (or any user input to the computer).
A process is...
A process is the CPU inside the system following a set of instructions to carry out a task based on the input.
An output is...
An output is the result produced by the computer, such as the player moving on screen.
What are the four key components of the CPU?
The four key components of the CPU are:
Arithmetic Logic Unit (ALU)
Control Unit (CU)
Cache
Registers
Define Arithmetic Logic Unit (ALU).
The Arithmetic Logic Unit (ALU) performs arithmetic operations and logical decisions.
What is the function of the Control Unit (CU)?
The Control Unit (CU) coordinates how data moves around the CPU by sending signals to control the flow of data, and it decodes the instructions fetched from memory.
Define cache.
Cache is very small, very fast memory located in the CPU which is used to provide quick access to frequently used instructions and data.
What is the purpose of Cache?
The purpose of Cache is to prevent the CPU from having to repeatedly fetch frequently used instructions from RAM, speeding up performance.
Define registers.
Registers are extremely small, extremely fast memory located in the CPU, where each register has its own specific purpose.
True or False?
The more cache there is, the fewer instructions need to be fetched from RAM.
True.
The more cache there is, the more frequently used instructions or data can be stored, resulting in fewer fetch cycles from RAM.
What component performs logical decisions like "IF X > 5 THEN ..."?
The Arithmetic Logic Unit (ALU) performs logical decisions like "IF X > 5 THEN ...".
What does the Control Unit (CU) decode?
The Control Unit (CU) decodes the instructions fetched from memory.
Which has a faster read/write speed, cache or RAM?
Cache has a significantly faster read/write speed than RAM.
What is the Von Neumann architecture?
The Von Neumann architecture is a design of the CPU proposed by John Von Neumann in the 1940s, which outlines how the computer memory, input/output devices and processor all work together.
Name the four main registers in the Von Neumann architecture.
The four main registers are:
Program Counter (PC)
Memory Address Register (MAR)
Memory Data Register (MDR)
Accumulator (ACC)
What is the purpose of the Program Counter (PC) register?
The Program Counter (PC) holds the memory address of the next instructions to be executed.
What happens to the Program Counter during the fetch-execute cycle?
The Program Counter increments by 1 as the fetch-decode-execute cycle runs.
Define Memory Address Register (MAR).
The Memory Address Register (MAR) holds the memory address of where data or instructions are to be fetched from.
What does the Memory Data Register (MDR) store?
The Memory Data Register (MDR) stores the data or instruction which has been fetched from memory.
Define Accumulator (ACC).
The Accumulator (ACC) stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU).
True or False?
The Von Neumann Architecture consists of 5 main registers.
False.
The Von Neumann Architecture consists of 4 main registers: Program Counter, Memory Address Register, Memory Data Register, and Accumulator.
What register holds the address of the next instruction to fetch?
The Program Counter (PC) holds the memory address of the next instructions to be executed.
What register temporarily stores fetched data or instructions?
The Memory Data Register (MDR) stores the data or instruction which has been fetched from memory.
What are the three common characteristics of the CPU that impact its performance?
The three common characteristics are:
Clock Speed
Cache Size
Number of Cores
Define clock speed.
Clock speed is measured in Hertz (Hz) and measures the number of fetch-decode-execute cycles that can take place in 1 second.
True or False?
Modern computers have a clock speed measured in Gigahertz (GHz), meaning billions of cycles per second.
True.
Modern computers have a clock speed in Gigahertz (GHz), meaning billions of cycles per second.
What is the impact of a faster clock speed?
The faster the Clock Speed, the more instructions can be fetched and executed per second.
What does a Clock Speed of 3.5GHz mean?
A Clock Speed of 3.5GHz means it can perform up to 3.5 billion instructions per second.
What is cache used for?
Cache is used as temporary storage to provide quick access to frequently used instructions and data.
What is the benefit of a larger cache size?
The larger the Cache Size, the more frequently used instructions or data can be stored, resulting in fewer fetch cycles from RAM and improved performance.
Define number of cores.
Each core works like its own CPU, so multiple cores allow multiple processing units to fetch, decode and execute instructions simultaneously.
True or False?
A dual-core CPU with a Clock Speed of 3.6GHz can fetch, decode & execute more instructions in 1 second that a quad-core CPU with a Clock Speed of 2.5GHz?
False.
A dual-core CPU (2 cores) running at 3.6GHz can perform 2 x 3.6 billion instructions = 7.2 billion instructions per second.
A quad-core CPU (4 cores) running at 2.5GHz can perform 4 x 2.5 billion instructions = 10 billion instructions per second.
For a dual-core 2.5GHz processor, what does "dual-core" mean?
For a dual-core processor, "dual-core" means there are two cores (processing units) that can fetch, decode and execute instructions.
Define embedded system.
An embedded system is a computer system with a single function, inside a larger mechanical unit.
What are three examples of embedded systems?
Examples of embedded systems include:
Heating thermostats
Hospital equipment
Washing machines
What are the three key properties of an embedded system?
The three key properties of an embedded system are:
small size
use less power than general-purpose computers
lower cost
True or False?
A laptop is an example of an embedded system.
False.
A laptop is not an example of an embedded system. A laptop is an example of a general-purpose computer.
Why do embedded systems use less power?
They have a single dedicated function rather than being general-purpose computers.
True or False?
A fridge is an embedded system.
False.
While a fridge has a single main function, it does not contain a CPU, so it is not considered an embedded system.
Are mobile phones considered embedded systems?
No.
Mobile phones are general-purpose computing devices, not single-function embedded systems.