Computer Science – 4.2 Assembly Language | e-Consult

The choice of addressing mode significantly impacts program efficiency. Speed: Register addressing is generally the fastest because it avoids memory access. Direct and indirect addressing involve memory accesses, which take more time. Memory Usage: Immediate addressing can lead to larger code sizes if large constants are used. Direct and indirect addressing require more bits to specify the memory address. Code Size: Immediate addressing can result in larger instructions. Indirect addressing can also increase code size due to the need for an extra register to store the address.

Scenarios:

• Immediate addressing is preferred when dealing with frequently used constants, such as mathematical constants (pi, e) or loop counters. This avoids repeated memory accesses. Example: Calculating the area of a circle where pi is a constant.
• Direct addressing is preferred when accessing data stored at fixed memory locations, such as variables in a small data structure. Example: Accessing elements in an array where the base address is known.
• Indirect addressing is preferred when accessing data stored in dynamic data structures like linked lists or tables where the memory address is not known at compile time. Example: Traversing a linked list where each node contains a pointer to the next node. Also useful for implementing function pointers.
• Register addressing is preferred when frequently accessing data that is already stored in a register. This avoids the overhead of memory access. Example: Performing calculations using variables that are stored in registers.

In summary, the optimal addressing mode depends on the specific task and the trade-offs between speed, memory usage, and code size. A good compiler will choose the most efficient addressing mode for each instruction.