Unit 1 Components of a Computer
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What are the components of a CPU? (4)
• Control Unit • Buses • ALU • Dedicated Registers
What is the Control Unit?
Part of the processor that coordinates the activity of all other components
How many lines does a Bus normally consist of?
8, 16, 32, 64
What is a Bus?
A series of connectors that transfer signals between components
What are the Control Signals? (5)
• Memory Read • Memory Write • Bus Request • Bus Grant • Clock
What does Control Signal: Memory Read do?
Causes data from the addressed location in RAM to be placed on the data bus
What does Control Signal: Memory Write do?
Causes data on the data bus to be written into the addressed location in RAM
What does Control Signal: Bus Request do?
Indicates that a device is requesting use of the data bus
What does Control Signal: Bus Grant do?
Indicates that the CPU has granted access to the data bus
What does Control Signal: Clock do?
Synchronizes operations
What are the Logical Operations of the ALU? (4)
• AND • OR • NOT • XOR
What are the Arithmetic Operations of the ALU? (4)
• Add • Subtract • Divide • Multiply
What is the job of the ALU?
Performs arithmetic, logical and shift operations on data
What is the job of the Accumulator?
Stores the results of the ALU
What are the Dedicated Registers? (5)
• Program Counter (PC)- • Current Instructions Register (CIR) • Memory Address Register (MAR) • Memory Data Register (MDR) • Accumulator
What does the Program Counter do?
Holds the memory address of the next instruction to be executed
What does the Current Instruction Register do?
Holds the current instruction (which is split into opcode and operand)
What does the Memory Address Register do?
Holds the address in memory where the processor is required to fetch or store data from or to
What does the Memory Data Register do?
Temporarily holds data moving between the processor and main memory
What does the Processor do?
Carries out instructions from programs stored in memory
What is the Fetch section of the FDE Cycle? (4)
• The address of the next instruction is copied from the PC to the Memory Address Register • The instruction held at that address is copied to the Memory Data Register • Simultaneously, the contents of the Program Counter (PC) are incremented • The contents of the MDR are copied to the current Instruction Register
What is the Decode section of the FDE Cycle? (3)
• The instruction held in the CIR is decoded • It is split into operand and opcode to determine the type of instruction it is • Additional data, if required, is fetched from memory and passed to the accumulator
What is the Execute section of the FDE Cycle?
The instruction is executed and the result held in accumulator or stored in memory
What is a usual Word Length?
8, 16, 32, 64