1.1.1) Structure and function of the processor Flashcards
(a) The Arithmetic and Logic Unit; ALU, Control Unit and Registers (Program Counter; PC, Accumulator; ACC, Memory Address Register; MAR, Memory Data Register; MDR, Current Instruction Register; CIR). Buses: data, address and control: how this relates to assembly language programs. (b) The Fetch-Decode-Execute Cycle; including its effects on registers. (c) The factors affecting the performance of the CPU: clock speed, number of cores, cache. (d) The use of pipelining in a processor to improve (43 cards)
What is the ALU and what is it’s role?
Arithmetic Logic Unit, it performs all calculations and logical operations
What are some functions of the ALU? (4)
Addition, subtraction, multiplication and division
Logical bitwise operations- AND, OR, NOT and XOR
Comparisons between values, such as greater than, less than, equal to.
Shifting binary patterns to the left or right.
What is the CU?
the Control Unit
What are the functions of the CU? (5)
Controls the inputs and outputs of the CPU
Directs the flow of data
Sends and receives control signals to and from other components
Decodes instructions
Manages the timing of data flow around the system
What are the different registers? (7)
GPRs (General Purpose registers)
PC (Program Counters)
CIR (Current Instruction registers)
SR (Status register)
MAR (Memory Address register)
MDR (Memory Data register)
Accumulator
Describe the role of GPRs…
- Used as temporary storage registers to speed up processing instead of having to access RAM every time.
- used by the ALU to store results of intermediate calculations produced as part of a larger computation.
Describe the role of the Program Counter…
Holds the address of the next instruction to be executed
Describe the role of the Current Instruction Register….
Holds the current instruction being executed.
Describe the role of the Status register…
- stores any indicators such as errors or exceptions.
- allows or disables interrupts
- brings attention to incomplete calculations or hardware malfunctions
Describe the role of the MAR….
temporarily holds the address of the data in RAM needing to be read/written to.
Describe the role of the MDR…
temporarily holds the data value retrieved from the address held in the MAR.
Describe the role of the accumulator…
Stores the result of ALU’s calculations. The processor accesses other GPRs where temporary values are stored while calculations are completed. Any result resides in the accumulator.
What are the 3 types of buses? (3)
Data bus, Address bus, Control bus
What does the data bus do? (4)
(where does it transfer between?, which directions?, what do the parallel lines mean?, why can it affect CPU performance?)
The data bus transfers between I/O, the CPU, main memory and secondary storage devices.
Each line is bidirectional meaning data can be read/written from.
The amount of parallel lines correlates with the number of bits able to be transferred in one operation.
The quantity able to be transferred can affect the CPU performance
What does the Address Bus do? (3)
(what does it hold?, what is the width?, what does this determine? what is this called?)
Holds the location of where data instructions are held.
The number of parallel lines determines the number of bits that can be used to form an address.
The width determines the maximum number of addressable memory locations i.e the maximum memory capacity of a computer system.
This is called the address space and can effect processor performance.
What does the Control bus do?
Sends control signals that manage and orchestrate operations.
It manages instructions outside of the CPU.
It is bi directional as it needs access to all components in order to coordinate them.
What is the FDE cycle?
The FDE cycle iterates through 3 main stages (Fetch, Decode, Execute) every time an instruction is carried out.
What happens in the Fetch part of the FDE Cycle? (4)
- Address in PC copied to MAR
- PC incremented to “point” to next instruction
- Instruction found at address held in MAR copied to MDR
- Instruction in MDR copied to CIR
What happens in the Decode part of the FDE Cycle? (1)
- The CIR splits the instruction into opcode and operand
- The CU then directs the instruction to the appropriate unit.
What happens in the Execute part of the FDE Cycle? (1)
- CU sends signals to relevant components
- The components execute the instructions
What are the factors that affect the CPU? (3)
Clock speed, number of cores, cache
What is the system clock? (3)
The clock generates a series of signals (0->1 when starting an instruction and 1-> 0 when ending)
This happens several million times per second.
The CPU cannot perform any faster than this.
How does clock speed effect CPU performance?
The greater the clock speed the faster instructions can be executed.
1GHz= ?
One billion clock cycles per second
