Array of structures

In computing, AoS and SoA refer to contrasting ways to arrange a sequence of records in memory, with regard to interleaving, and are of interest in SIMD programming.

Structure of arrays (or SoA) is a layout separating elements of a record (or 'struct' in the C programming language) into one parallel array per field. The motivation is easier manipulation with packed SIMD instructions in most instruction set architectures, since a single SIMD register can load homogeneous data, possibly transferred by a wide internal datapath (e.g. 128-bit). The downside is requiring more cache ways when traversing data, and inefficient indexed addressing. (see also: planar image format)

Array of structures (or AoS) is the opposite (and more conventional) layout, in which data for different fields is interleaved. This is often more intuitive, and supported directly by most programming languages.

A hybrid approach is possible, e.g. de-interleaving a number of objects that correspond to the number of SIMD lanes.

It is also possible to split some subset of a structure (rather than each individual field) into a parallel array – this can actually improve locality of reference if different pieces of fields are used at different times in the program (see data oriented design).

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