Load and Store

The operands for all arithmetic and logic operations are contained in registers. To operate on data in main memory, the data is first copied into registers. A load operation copies data from main memory into a register. A store operation copies data from a register into main memory .

When a word (4-bytes) is loaded or stored the memory address must be a multiple of four. This is called an alignment restriction. Addresses that are a multiple of four are called word aligned. This restriction makes the hardware simpler and faster.

The lw instruction loads a word into a register from memory. The sw instruction stores a word from a register into memory. Each instruction specifies a register and a memory address (details in a few pages).