1.1.1 Structure and function of the processor Flashcards
Arithmetic Logic Unit ALU
Performs:
- Arithmetic Operations (subtract/multiply/divide) on fixed/floating point numbers.
- Logical Operations (AND/OR/NOT)
-Shift bits left or right within a register
Control Unit (CU)
Controls & coordinates activities of the CPU => directs flow of data.
Accepts the next instruction, decodes it into sequential steps, manages its execution, and stores data back into memory/registers.
Program Counter (PC)
Holds the address of the next instruction to be executed.
Current Instruction Register (CIR)
Holds the current instruction being executed (divided into operand/opcode).
Memory Address Register (MAR)
Holds the ADDRESS of the memory location from whom data is to be fetched/written.
Memory Data Register (MDR)
Used to temporarily store the data read from/written to memory.
Control Bus
- Bi-directional, so signals can be carried in both directions.
- Transmit command, timing, and specific status information between system components.
Examples of control lines: Bus Request, Bus Grant, Memory read/Write, Interrupt request, Clock
Data Bus
- Consists of 8, 16, 32, or 64 separate lines.
- Provides a bi-directional path from moving data and instructions between system components
Address Bus
- Each word (fixed-size groups of digits) in memory has its own address.
- The address bus transmits the memory addresses of words that are used as operands in program instructions so that data can be retrieved/sent back to the processor.
Fetch Phase
- Address of the next instruction copied from the PC to the MAR.
- Instruction held at that address is copied to MDR. Simultaneously, the PC is incremented.
- Contents of the MDR copied to the CIR.
Decode Phase
The instruction held in the CIR is decoded & split into either:
- Operand, which holds the address (copied to MAR), data (copied to MDR)
- Opcode, which is the type of instruction/hardware.
Execute Phase
The appropriate opcode is carried out on the operand.
Clock Speed on processor performance
- The system Clock generates a series of signals to synchronise CPU operations.
- The greater the clock speed => the faster instructions will be executed.
Number of Cores on processor performance
- Each core can process a different instruction at the same time with its own fetch-execute cycle.
- It does not always perform twice as fast, because the software may not always be able to take full advantage of both processors.
Amount/Type of Cache Memory on processor performance
- Cache is a small amount of expensive, fast memory in the CPU.
- When an instruction is fetched from main memory, it is copied into cache so that when it is needed again, it can be fetched from cache, which is quicker.
- Different levels of cache: Level 1 (very fast/small), Level 2 (fairly fast. medium)
