operating-systems hardware computer-architecture
Definition
Processor
A processor is the primary electronic circuitry within a computer system that executes instructions specified by a computer program. It serves as the core execution engine, responsible for performing arithmetic, logic, control, and input/output operations.
The behaviour of a processor is dictated by its Instruction Set Architecture (ISA), which defines the set of operations it can perform and its interface with software.
Core Components
A modern processor typically includes the following sub-systems:
- Arithmetic Logic Unit (ALU): Performs mathematical operations (addition, subtraction) and logical comparisons (AND, OR, NOT).
- Control Unit (CU): Decodes instructions from memory and coordinates the movement of data between the ALU, registers, and other components.
- Registers: High-speed internal storage locations used to hold data currently being processed, such as the Program Counter (PC) and the Program Status Word (PSW).
- Cache: Fast, local memory used to reduce the average time to access data from the main memory.
Instruction Cycle
The processor operates in a repetitive cycle known as the Fetch-Decode-Execute cycle:
- Fetch: Retrieve the next instruction from memory at the address stored in the program counter.
- Decode: The control unit interprets the instruction to determine the required operation.
- Execute: The ALU or other component performs the operation.
- Store: Results are written back to registers or memory.
OS Interaction
The processor works closely with the operating system to manage system resources:
- Execution Modes: Hardware support for User and Kernel modes allows the OS to protect sensitive instructions.
- Interrupts: The processor provides hardware mechanisms to handle asynchronous events, allowing the OS to react to I/O completion or timer timeouts.