Art of Assembly Language, 1st Edition

3.5. 3.5 HLA Support for Data Alignment

In order to write fast programs, you need to ensure that you properly align data objects in memory. Proper alignment means that the starting address for an object is a multiple of some size, usually the size of object if the object's size is a power of two for values up to 16 bytes in length. For objects greater than 16 bytes, aligning the object on an 8-byte or 16-byte address boundary is probably sufficient. For objects less than 16 bytes, aligning the object at an address that is the next power of two greater than the object's size is usually fine.^[47] Accessing data that is not aligned on at an appropriate address may require extra time; so if you want to ensure that your program runs as rapidly as possible, ...