bytealignment

Byte alignment refers to the practice of arranging data so that each data element begins at an address that is a multiple of a specified number of bytes. The constraint is typically the natural alignment of the type, often a power of two, and is determined by the architecture and compiler. Proper byte alignment helps hardware access data efficiently, especially for multi-byte types such as 2-, 4-, or 8-byte integers and floating-point values.

The rationale for alignment lies in how memory subsystems fetch data. Aligned accesses can be completed in fewer cycles and are less likely to trigger special handling or faults on architectures that enforce alignment. Unaligned or misaligned accesses may incur extra memory operations, be slower, or even be disallowed on certain processors. Alignment also affects cache behavior, as correctly aligned data tends to map more predictably to cache lines.

In programming languages, compilers enforce alignment when laying out structures and objects. The layout typically places fields at offsets that satisfy their alignment requirements, often introducing padding between fields. Developers can influence this with compiler-specific directives or attributes (for example, to change packing) and with allocation strategies that provide higher alignment guarantees. However, increasing alignment can raise memory usage due to padding.

Byte alignment is distinct from bit-level packing. Some data formats or communication protocols may pack fields tightly within bytes, while others ensure that multi-byte fields start on aligned addresses. Cross-platform data exchange often relies on explicit alignment and careful serialization to avoid portability issues.