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What is the primary function of the CPU?
The CPU is responsible for processing all data within the computer.
What are Registers?
Registers are temporary storage/memory locations in the CPU
used for a specific purpose e.g. Program Counter (PC) , Memory Data Register (MDR) , Memory Address Register (MAR) , Current Instruction Register (CIR) , Accumulator (ACC)
What are the main components of the CPU?
The main components include the Arithmetic and Logic Unit (ALU), Control Unit (CU), and various registers.
What does the Arithmetic Logic Unit do?
Performs any arithmetic calculations and logical operations or any logical comparistons (AND, OR , NOT, XOR)
The Arithmetic Logic Unit (ALU) is made up of several components, what are they and what do they do?
Arithmetic Circuit - Carries out arithmetic calculations (add, sub, div, multiply)
Logic Circuit - Carries out logical operations (AND, OR, XOR, NOT)
Registers - Additional registers to store data
Status Flags - Includes overflow flags (if value is too large for register) or could include a zero flag (to tell if the answer is zero easily)
Buses - Used to transport data around the ALU to other parts of the CPU
What is the fetch-decode-execute cycle?
It is the process that the CPU goes through repeatedly to process instructions, consisting of fetching, decoding, and executing instructions.
Explain the FDE cycle
Fetch
Program Counter (PC) is loaded with 0
Value of PC(0) is copied to Memory Address Register(MAR)
The data from that location in memory(0) is sent across the control bus to the Memory Data Register
PC is incremented to 1
Decode
The data is sent from the MDR to the Current Instruction Register(CIR) where it is split into opcode and operand
This is sent to the Control Unit(CU) to be decoded
Execute
Which registers are used here will depend on the instruction being executed
If a value is being inputted (INP) the ACC will store the value
If a value is being outputted (OUT) this will be the value currently in the ACC
If a value is loaded from RAM (LDA) this will be sent across the data bus from RAM (in the address location in the MAR) to the MDR
If a value is to be stored (STA) it will take the value from the ACC, send it to the MDR and then send it across the data bus to RAM (to the address location in the MAR)
If a value is being added to or subtracted from another value (ADD/SUB)
If the LMC code is to branch (BRA/BRZ/BRP) the comparison will take place in the ALU
What role does the Control Unit (CU) play in the CPU?
The CU decodes instructions and controls data movement within the CPU.
What is the purpose of the Accumulator?
The Accumulator is where the values are stored temporarily, either after they’ve been inputted or loaded, or after being calculated in the ALU
What is the purpose of the Program Counter (PC)?
The Program Counter stores the address in memory of the next instruction to be fetched.
What role does the Memory Address Register (MAR) play in the CPU?
The MAR is where addresses are stored, either for where the data is being sent in memory, or where it is being fetched from
What role does the Memory Data Register (MDR) play in the CPU?
The MDR is where addresses are stored, either before it is sent to memory, or after being fetched
What role does the Current Instruction Register (CIR) play in the CPU?
When an instruction is being fetched from memory it is located here before being split into opcode and operand, after this, it will be decoded
What is Pipelining?
Pipelining is the process of carrying out multiple instructions concurrently
Each instruction will be at a different stage of the fetch-decode-execute cycle
One instruction can be fetched while the previous one is being decoded and the one before is being executed
In the case of a branch, the pipeline is flushed
How does pipelining improve processor performance?
Pipelining allows multiple instructions to be processed concurrently, reducing latency and increasing execution speed.
What is Von Newmann Architecture?
This architecture includes the basic components of the computer and processor (single control unit, ALU, registers and memory units) in which a shared memory and shared data bus is used for both data and instructions
Von Neumann architecture is built on the stored program concept
What is Harvard Architecture?
The CPU processes all data in the computer.
Advantages of Von Newmann Architecture
Cheaper to develop as the Control Unit is easier to design
Programs can be optimised in size
Advantages of Harvard Architecture
Quicker execution as data and instructions can be fetched in parallel
Memories can be different sizes, which can make more efficient use of space
What is Contemporary Processing?
Uses a combination of Harvard and Von Newmann
Von Newmann is used when working with data and instructions in the main memory
Harvard is used to divide the cache into instruction cache and data cache
What is the difference between Von Neumann and Harvard architecture?
Von Neumann architecture has unified memory for both instructions and data, whereas Harvard architecture has separate memory for instructions and data.
What are the three types of buses in a CPU?
The three types of buses are the Data bus, Address bus, and Control bus.
What does the Data Bus do?
Holds data being sent to or from the CPU (Read/Write operations)
What does the Address bus do?
Holds addresses being sent to or from the CPU and RAM (Read or Write Operations)
What does the Control Bus do?
Sends signals to determine whether the other buses are in read or write mode (sends signals operations)
Assembly Language
Assembly Language used in Little Man Computer
Assembly Language uses mnemonics to represent instructions e.g. ADD for addition
The instruction is split between operand and opcode in the Current Instruction Register
How is CPU performance measured?
CPU performance is measured by clock speed, number of cores, and cache.
What does cache do in a CPU?
Cache stores frequently used data and instructions for faster retrieval compared to RAM.
Clock Speed
Clock Speed is determined by the system clock
The clock speed is the time taken for one clock cycle to complete
System Clock = This is an electronic device which generates signals, switching between 0 and 1
How does the Number of Cores affect CPU performance
A core is an independent processor that’s able to run it’s own fetch-decode-execute cycle
A computer with multiple cores can complete more than one fetch-decode-execute cycle at any given time
Dual-core processor can theoretically complete tasks twice as fast as a single core processor - not all programs are able to use multiple cores efficiently as they didn’t design it to do so
Note 
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