Central Processing Unit (CPU)
Computer Science - CPU - The Fetch-Decode-Execute System (FDE)
Central Processing Unit
The main processing area of the computer. Nearly all instructions are carried out here. It consists of three parts, the ALU, the CU, and the IAS.
Arithmetic Logic Unit (ALU)
Carries out all arithmetic and logical operations in the computer. E.g. Addition, substraction, comparisons etc.
Immediate Access Store (IAS)
An extremely fast area of memory located on, or next to the CPU, which stores the currently needed instructions and data. Usually referred to as Cache.
Control Unit (CU)
Manages the operation all other parts of the CPU. It contains the CURRENT INSTRUCTION REGISTER (CIR) and the PROGRAM COUNTER (PC).
Pathways in the computer which transport electrical signals for specific purposes. The CPU has three main buses; the address bus, the data bus, and the control bus.
Retrieves data or instructions from the cache, and stores in specific internal registers on the CPU.
Interprets the instruction in the register, and readies other parts of the CPU to carry out the instruction.
The instruction is carried out, which may involve fetching data from a register, performing a calculation, or storing a value in memory. The CPU will begin the FDE again after completion of this step.
Memory Address Register (MAR)
Contains the location of the memory location currently being accessed by the CPU.
Memory Data Register (MDR)
Contain the data found in the location currently being accessed by the CPU.
Program Counter (PC)
Contains the address of the next memory location for the next instruction to be fetched.
Current Instruction Register (CIR)
Contains the current instruction being executed by the CPU.
Status Register (SR)
Holds information about the current state of operations. It is used to set flags (e.g. carry or overflow) or to detect error conditions
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