Structure and Function of the Processor (1.1.1) Flashcards
What is a computer processor?
A hardware device which runs the FDE cycle in order to execute instructions for programs to run.
What is the function of the ALU?
The ALU carries out all arithmetical and logical operations.
What is the control unit?
The control unit directs the operations of the CPU.
What are the control unit’s jobs?
- Controlling and coordinating the activities of the CPU
- Managing the flow of data between the CPU and other devices
- Accepting the next instruction
- Decoding instructions
- Storing the resulting data back in memory
What are registers?
Small, high speed memory cells that temporarily store data in the processor.
What are the five main registers in the CPU?
- Program counter
- Accumulator
- Memory Address Register
- Memory Data Register
- Current Instruction Register
What does the program counter do?
Holds the address of the next instruction to be executed.
What does the accumulator do?
Stores the results of calculations made by the ALU.
What does the memory address register do?
Stores the memory address of a location that will be read from or written to.
What does the memory data register do?
Temporarily stores data that has been fetched from or will be written to the memory.
What does the current instruction register do?
Holds the instruction currently being executed, divided into opcode and operand.
What are buses?
A set of parallel wires which connect components within the CPU.
Which three buses make the system bus?
- Data bus
- Control bus
- Address bus
What is the width of the bus?
The number of parallel wires in the bus, it is directly proportional to the number of bits which can be transferred simultaneously.
What is the data bus?
A bi-directional bus used for transporting data and instructions.
What is the address bus used for?
Carries memory addresses which specify where data will be sent to or retrieved from. Width=number of addressable memory locations
What is the control bus?
A bi-directional bus used to transmit control signals between internal and external components.
What are some examples of control symbols?
- Bus request: shows a device wants to use the data bus
- Bus grant: shows a device has been allowed access to the data bus
- Memory write: data is written into the addressed location
- Memory read: data is read from a specific location and put on the data bus
- Interrupt request
- Clock: used for synchronisation
What is assembly language?
A simplified way of expressing machine code using mnemonics- consisting of operand and opcode.
What is the operand?
The data or address of data that will be manipulated
What is the opcode?
The type of instruction to be executed.
What is pipelining?
The process of completing the FDE cycles of three separate instructions simultaneously by having one instruction at each stage of the cycle at all times. It aims to reduce the amount of the CPU which is kept idle.
What is the FDE cycle?
A sequence of operations that are completed to execute an instruction.
What happens in the fetch phase?
- Address from PC is copied to MAR
- The address is sent to the memory along the address bus
- Instruction at address is copied to MDR along the data bus
- At the same time the PC increments by 1
- The value in the MDR is copied to the CIR
What happens in the decode phase?
The contents of the CIR are split into operand and opcode
What happens in the execute phase?
The decoded instruction is executed by the ALU and results are stored in the ACC->MDR->MEMORY
What are the three factors that affect CPU performance?
- Clock speed
- Number of cores
- Amount and type of Cache memory
What is clock speed?
The frequency at which the CPU executes instructions/ no. FDE cycles per second.
What is the processor clock?
A timing device connected to the processor which synchronizes the FDE cycles.
What is a core?
An independent processor in a CPU which can run its own FDE cycle.
What are the benefits of having multiple cores?
Multiple FDE cycles can be completed at any time, however some programs are not designed to do this.
What is cache memory?
The CPU’s on board memory which can be accessed much faster than main memory. The most frequently used instructions are stored here.
What are the three main computer architectures?
- Von Neumann
- Harvard
- Contemporary
What does the Von Neumann architecture consist of ?
- Single control unit
- ALU
- Registers
- Memory units
- Shared memory and data bus for both data and instructions.
What is the stored program concept?
Used by the Von Neumann architecture, it states that machine code instructions are executed serially. They must be stored in the memory to be executed.
What is the Harvard Architecture?
- There are separate memories and buses for instructions and data.
- Instructions and carried out serially
- Used by embedded processors and RISC processors
Von Neumann ADVS
- Cheaper as control unit is easier to design
- Programs can be optimized in size
Von Neumann DISADVS
-Having a shared bus for data and instructions can cause the “Von Neumann bottleneck”
Harvard ADVS
- Quicker execution as data and instructions can be fetched in parallel.
- Memories can be different size allowing for efficient use of space
What are contemporary processors?
A modified Harvard architecture whereby there is no strict separation of data and instructions but there are multiple memory buses.
Von Neumann architecture is used to communicate with main memory, Harvard is used with the cache.
