CPU
- Created by: CJMoseley
- Created on: 28-06-16 13:17
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- CPU
- The Control Unit (CU)
- In control of the CPU.
- Main Job = execute program instructions by following the fetch-decode-execute cycle.
- Controls the flow of data inside the CPU and outside the CPU
- registers, ALU, cache
- main memory, input/output devices
- The Arithmetic Logic Unit (ALU)
- Does the calculations
- Completes simple addition, subtraction and can do multiplication and division by repeating addition and subtraction
- Compares the size of numbers
- Performs logic operations such as AND, OR and NOT and binary shifts
- The Cache
- Very fast memory. Slower than registers but faster than RAM
- Stores regularly used data so that the CPU can access it quickly
- When CPU requests data, it checks the cache first, if its not in there, it will fetch it from the RAM
- Very low capacity and are expensive compared to RAM and secondary storage
- Different levels of cache memory - L1, L2, L3.
- L2 is slower than L1 but can hold more
- L1 is the quickest but has the lowest capacity
- L3 is slower than L2 but can hold more
- Fetch-Decode-Execute
- 1. Copy memory address from the program counter to the MAR
- Copy the instruction stored in the MAR address to the MDR
- Increment (increase) the program counter to point to the address of the next instruction
- The instruction in the MDR is decoded by the CU.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR
- The instruction is then performed.
- Fetch-Decode-Execute
- 1. Copy memory address from the program counter to the MAR
- Copy the instruction stored in the MAR address to the MDR
- Increment (increase) the program counter to point to the address of the next instruction
- The instruction in the MDR is decoded by the CU.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR
- The instruction is then performed.
- The instruction is then performed.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR
- The instruction in the MDR is decoded by the CU.
- Increment (increase) the program counter to point to the address of the next instruction
- Copy the instruction stored in the MAR address to the MDR
- 1. Copy memory address from the program counter to the MAR
- Fetch-Decode-Execute
- The instruction is then performed.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR
- The instruction in the MDR is decoded by the CU.
- Increment (increase) the program counter to point to the address of the next instruction
- Copy the instruction stored in the MAR address to the MDR
- 1. Copy memory address from the program counter to the MAR
- The Control Unit (CU)
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