1.1 Processors
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What does the Arithmetic and Logic Unit do?
• Handles data processing, performs standard arithmetic operations as well as logic operations and comparisons. • Completes all the arithmetical and logical operations.
What is the Control Unit?
• Controls the way the data moves around the CPU - controls buses and flow of data between CPU and other components. • It executes the instructions given by a program. • A part of the processor which directs operations inside the CPU.
What are registers?
• Quick, small stores of data within the CPU. - Small memory cells that operate at high speeds.
What does the Program Counter do?
• Holds the memory address of the next instruction. - Increments by 1 after each fetch stage.
Which register does all the calculations?
The accumulator
What does the MAR do?
• Holds the memory address of the data needing to be accessed • Holds address of a location that is to be read from or written to
What does the MDR do?
• Holds the data being transferred to or from the memory location by the CPU. • Temporarily stores the data that has just been read from or the data needs to be written.
What does the CIR do?
• Contains the current instruction during processing. - Holds the current instruction divided up into opcode and operand.
What is a Bus?
• Parallel wires which connect 2 or more components together. (The width of the bus is the number of parallel wires a bus has. Directly proportional to the number of bits transferred)
What is the system bus?
The collection of the data bus, address bus, and control bus is called the system bus.
What is the data bus?
• Bidirectional - Transports data and instructions between components (to and from memory)
What is the control bus?
• Bidirectional - Carries commands from the CPU & status messages from other hardware devices.
What does the address bus do?
• Unidirectional (only goes from memory to the CPU) - Transmits the memory address specifying where data is to be sent from or retrieved from.
What does adding a wire to the address bus do to the number of addressable locations?
• It doubles the amount of addressable locations
What does the Bus request indicate?
• indicates a device is requesting access to the data bus
What does Bus Grant indicate?
• Shows that the CPU has granted access to the data bus.
What does memory write do?
• Data is written into addressed location from the data bus.
What does memory read do?
• Data from the addressed location to be placed onto the data bus.
What does the interrupt request control signal indicate?
• Shows that a device is requesting access to the CPU.
What is the clock control signal used for?
• Used to synchronise all the operations/instructions.
What is Assembly Language?
Assembly language is a programming language where mnemonics are used to represent instructions.
What is opcode?
• Part of the instruction code that tells the processor what to do.
What is the operand?
• Contains the data to be acted on, or the memory location of the data in a register.
Describe the Fetch stage.
• The address from the PC is copied to the MAR • Instruction held at that address is copied to the MDR by the data bus, simultaneously the contents of the PC is increased by 1 • The value of the MDR is copied to the CIR