Chapter 1 - Processor components Flashcards
What is the purpose of the CPU?
1 Mark
» Processes instructions using the FDE cycle
What is the purpose of the control unit?
4 Marks
» Controls the flow of bits inside the CPU between the registers
» Decodes instructions
» Controls the execution of instructions
» Maintains synchronisaton
What is a bus?
1 Mark
» Set of parallel wires/lines connecting 2 or more components of a computer in which data can be sent around the computer
What is an address bus?
1 Mark
» A bus used to access a particular main memory location
What is a data bus?
1 Mark
» Returns the data of the location to the CPU
What is a control bus?
1 Mark
» A bus which carries control signals, and also the clock’s pulses
What is a system bus?
1 Mark
» The three buses: control, signal and address
What is a shared transmission medium?
» Each bus has one of these, and it means only the device can transmit along a bus at any one time
What is bi-directional ?
1 Mark
» Can travel both forwards and backwards
What buses travel in both directions?
2 Mark
» Data bus
» Control bus
What is unidirectional?
1 Mark
» Data flows in one direction only
Which bus travels in one direction only?
1 Mark
» Address bus
Where does the address bus travel to?
» To memory or an I/O controller
What is an I/O controller?
1 Mark
» A series of micro ships which helps in the communication of data between the CPU and motherboard
What does I/O stand for?
» Input and output devices
What is the purposes of control lines in a control bus?
» To ensure that access to and use of that data and address buses by the different components of system does not lead to conflict
How can the components of the system buses lead to conflict?
» As data and address buses are shared by all components, control lines are needed to regulate the timing signals
What are some examples of control signals?
» Bus request
» Bus grant
» Memory Write/Read
How many lines usually does a data bus have?
» Usually 8,16,32,64 separate lines.
What is a word?
1 Mark
» Fixed size group of digits that are divided up internally in memory, which has its own specific address
What is the purpose of the ALU?
2 Marks
» Performs arithmetic and logical operations on the data
» Acts as a gateway to the processor for easy calculations
What are registers?
2 Mark
» A discrete small piece of memory used for storing data
» Within the processor
What is the purpose of the accumulator?
1 Mark
» To store the results of the calculations from ALU
What is the purpose of program counter?
1 Mark
» Stores the address of the next instruction to be processed
What is the purpose of the CIR?
1 Mark
» Stores the most recently fetched instruction
» Which will be decoded and executed
What is the purpose of the MAR?
1 Mark
» Contains the address of the data to be accessed from memory
What is the purpose of the MDR?
3 Marks
» Contains the instruction of the memory location address specified in the MAR
» Acts as a buffer to store instructions and data
» Copies the data into the CIR
What is the 1st part of the fetch phase in the FDE cycle?
2 Marks
» Address of next instruction is copied from the PC to the MAR
» After being sent to MAR , a read signal is sent across the control bus and the contents of the MAR are sent across the address bus
What is the 2nd part of fetch phase in the FDE cycle?
2 Marks
» Instruction held at that address is copied to MDR by the data bus and is stored in MDR
» Simulatenously the PC is incremented by 1
What is the last phase in the fetch phase of the FDE cycle?
1 Mark
» Contents of MDR are copied to CIR
What is the 1st phase of the decode phase in the FDE cycle?
1 Mark
» Instruction is split into opcode and operand in the CIR
What is the operand?
1 Mark
» This is the value the instruction uses - it is a value which is manipulated by the CPU
What is the Opcode?
1 Mark
» Is the part of the instruction that specifies which operation the processor should perform
What happens if the Operand is an address?
2 Marks
» Passed to MAR, gets to the memory location of the address in RAM
» Reads the value and is sent to the MDR via the data bus, which is copied to the accumulator
What is the final phase in the Execute phase in the FDE cycle?
1 Mark
» Appropriate instruction/opcode is carried out on the operand
What does read command do?
1 Mark
» Load data
What does write do?
1 Mark
» Store data
How does the control unit coordinate the activates of the CPU?
2 Marks
» Controls the execution of instructions - By sending timing signals
» Send control signals to enable data to be read from and written to main memory
Describe what the process of the control bus is
1 Mark
» Transmits control signals from the control unit, which contains the timing signals
Explain why special registers are needed in addition to primary memory?
2 Marks - To do with cache
» Allows fast access to data which is needed frequently
» Faster than acessing RAM
Explain 2 reasons why the value held in the register which holds the address of the next instruction be processed may change?
4 Marks
» Program counter increments - during FDE cycle
» A jump instruction from the CIR/Operand changes to address given
Where does the jump instruction send the address?
3 Marks
» Sends to the PC from the CIR
» PC increments by 1
» MDR copies data to CIR
Explain the need for the Current Instruction Register (CIR) and describe how the data which it holds is used
» Purpose to hold recently fetched instructions ready to be decoded and executed
» Decode phase - CIR splits data into 2 bits
» Opcode and Operand
» Operand is the actual data - the value that will be manipulated by the CPU
» Opcode - It is the instruction which tells the CPU what to do with the instruction
» CIR sends jump instructions also
