Computer Architecture (Cambridge (CIE) O Level Computer Science)
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What 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.
Define the term microprocessor.
A microprocessor is a type of integrated circuit on a single chip.
What does CPU stand for?
CPU stands for Central Processing Unit.
True or False?
The CPU is only used in desktop computers.
False.
The CPU is used in various devices including laptops, desktops, games consoles, and mobile devices.
Input
Data and commands inputted by the user using an input device.
Process
The execution of instructions by the CPU to manipulate data.
Output
The results of processing displayed to the user via an output device.
What are the three main steps in computer data processing?
The three main steps in computer data processing are input, process, and output.
True or False?
The terms CPU and microprocessor can be used interchangeably.
True.
The terms CPU and microprocessor can be used interchangeably.
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 most general-purpose computers are built upon.
Program Counter (PC)
Holds the memory address of the next instructions to be executed.
Memory Address Register (MAR)
Holds the memory address of where data or instructions are to be fetched from in memory.
Memory Data Register (MDR)
Stores the data or instruction which has been fetched from memory.
Current Instruction Register (CIR)
Stores the instruction the CPU is currently decoding or executing.
Accumulator (ACC)
Stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU).
What is a bus in computer architecture?
A bus is a set of parallel wires through which data/signals are transmitted from one component to another.
Name the three types of buses in computer architecture.
The three types of buses are address bus, data bus, and control bus.
What is the function of the address bus?
The address bus carries location data (addresses), data is written to/read from.
True or False?
The data bus is unidirectional.
False.
The data bus is bidirectional, carrying data or instructions in both directions.
What is the Fetch-Decode-Execute Cycle?
The Fetch-Decode-Execute Cycle is the cycle that the central processing unit (CPU) runs through billions of times per second to make a computer work.
What are the three main stages of the FDE Cycle?
The three main stages are Fetch, Decode, and Execute.
In the fetch stage, what register holds the address of the next instruction?
In the fetch stage, the Program Counter (PC) holds the address of the next instruction to be fetched from memory.
What happens to the Program Counter after an instruction is fetched?
The Program Counter increments by 1 so it is pointing to the next instruction to be executed.
Opcode
The part of an instruction that specifies what operation to perform.
Operand
The part of an instruction that specifies what to perform the operation on.
What happens during the decode stage?
During the decode stage, the CPU works out what is required from the instruction by splitting it into opcode and operand.
True or False?
The execute stage always involves performing a calculation.
False.
The execute stage can involve performing a calculation, storing a result, or fetching data from memory, depending on the instruction.
What is the purpose of the Control Unit (CU) in the fetch stage?
The Control Unit sends a signal along the control bus to initiate the read operation from main memory.
How many times per second does a modern CPU typically perform the Fetch-Decode-Execute cycle?
A modern CPU typically performs the Fetch-Decode-Execute cycle billions of times per second.
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.
What is an instruction set?
An instruction set is a list of all the commands that can be processed by a CPU.
Machine code
The binary code representation of a CPU instruction.
What are the two parts of a machine code instruction?
The two parts of a machine code instruction are the operation code (opcode) and the operand.
What is a mnemonic in the context of CPU instructions?
A mnemonic is a short, human-readable code that represents a machine code instruction.
True or False?
CPU instruction sets are universal across all processors.
False.
Instruction sets are machine-specific and can vary between different processor manufacturers.
What does the ADD instruction typically do?
The ADD instruction typically adds a value to the value currently stored in the accumulator (ACC).
What does the LDA instruction typically do?
The LDA instruction typically loads the value stored in a memory location into the accumulator.
What does the HLT instruction typically do?
The HLT instruction (halt) typically stops the program.
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.