Addressing Modes An addressing mode is a specific way the processor uses memory to locate data and instructions during instruction execution. It dictates...
An addressing mode is a specific way the processor uses memory to locate data and instructions during instruction execution. It dictates the type of addressing used in a particular instruction.
There are 4 main addressing modes:
Direct addressing: The processor uses memory addresses directly, like a human pointing to specific locations on a book.
Register addressing: A register is a temporary storage location that can hold data for use in an instruction. The processor uses the address of the register instead of directly accessing memory.
Indirect addressing: The processor accesses data through memory locations represented by another memory location. This requires additional processing to calculate the final address.
Relative addressing: The address of the data is specified as a relative value within the memory segment. This allows instructions to be executed in different memory locations without absolute memory addresses.
Understanding these modes is crucial for:
Deciphering assembly code (machine language)
Writing and debugging computer programs
Choosing appropriate data structures and algorithms
Examples:
Direct addressing: In a program reading a value from memory location 100, the instruction would use direct addressing.
Register addressing: A variable declared in a register, like count, would be used for register addressing in an instruction that increments its value.
Indirect addressing: If a function is called with a relative address, the processor would add 100 to the current memory address to find the final address of the function parameters.
Relative addressing: If an array of 10 integers is stored at memory location 100, the instruction accessing the 5th element would use relative addressing, starting at the address of the 5th element in the array