dataalignment

Data alignment refers to the practice of organizing data in memory or on disk so that elements start at addresses that are multiples of a given boundary. Alignment boundaries are determined by the architecture, data type size, and programming language, commonly 1, 2, 4, 8, 16 or 32 bytes.

In memory, aligned access can be faster and, on some architectures, required. Misaligned access can incur penalties or trigger hardware traps, while x86 platforms generally tolerate misalignment with slower performance; other architectures, such as certain ARM variants, may trap.

In programming languages like C and C++, compilers insert padding between struct members to satisfy alignment requirements. The overall size of a struct can grow due to padding. Developers can influence this with packing pragmas or attributes such as packed, alignas, or alignof.

For high-performance computing and SIMD, data often must be aligned to 16-, 32-, or 64-byte boundaries to enable vectorized loads.

Aligned memory allocation functions exist, such as aligned_alloc in C11 and posix_memalign on POSIX systems.

When exchanging data between systems or components, explicit alignment guarantees are important for serialization, inter-process communication, and network protocols. Endianness is separate from alignment and can affect portability.

In databases and storage systems, alignment refers to aligning records with page or block boundaries to improve I/O efficiency.

Portability considerations include differing alignment rules across architectures; portable code often avoids relying on default padding and uses explicit alignment attributes where needed.

Data alignment is a fundamental aspect of low-level data representation with performance and portability implications.