Speicheralignment

Speicheralignment refers to the arrangement of data in memory so that each object begins at an address that satisfies specified alignment requirements. Alignment is typically a power-of-two boundary and is often tied to the size of the type or to the constraints of the hardware and application binary interface (ABI). Proper alignment enables efficient memory access and can prevent faults on architectures that require aligned accesses. In practice, a 1-byte type may have 1-byte alignment, a 4-byte type commonly uses 4-byte alignment, and an 8-byte type uses 8-byte alignment; larger composite types may have an alignment equal to the maximum alignment of any member.

For composite types, the compiler may insert padding between members to keep each member correctly aligned, and it may also add trailing padding to ensure the overall size is a multiple of the alignment requirement. Some languages or compilers provide explicit control over alignment through attributes, keywords, or pragmas. This control is useful for performance optimization, interoperability with binary interfaces, or memory usage considerations, but it can reduce portability if a program runs on systems with different ABIs.

Performance and portability considerations: aligned memory accesses are generally faster, especially when using cache lines and vector instructions. Misaligned accesses can incur penalties or, on some hardware, trigger faults. Allocators and memory pools may be designed to return pointers with specific alignment guarantees, and structures intended for binary interfaces should adhere to the target platform’s alignment rules.

See also: memory alignment, padding, ABI, cache line.