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An Instruction Set Architecture (ISA) defines the software-hardware interface for a processor, specifying the set of instructions, data types, registers, memory, and addressing modes that a CPU can understand and execute. It serves as the fundamental "language" of the processor, allowing software developers to write programs independently of the specific hardware implementation, ensuring software portability and enabling modular hardware/software design. Examples of ISA's include x86 and ARM, and they define what the processor can do and how it does it.

Key Components and Functions of an ISA

Instructions: The fundamental operations a processor can perform, such as arithmetic (addition, subtraction) and logical operations (AND, OR).

Instruction Formats: How instructions are structured and encoded in binary.

Data Types: The different kinds of data the processor can work with.

Registers: Small, high-speed storage locations within the CPU used to hold data and instructions temporarily.

Memory Model: How the processor interacts with and accesses memory.

Addressing Modes: The various ways instructions can specify the location of data in memory or registers.

Behavior: The precise way each instruction is executed.