crossbitness

Crossbitness refers to the ability of software systems to interoperate across different bitness levels, typically 32-bit and 64-bit architectures, and across the corresponding application binary interfaces (ABIs). It covers compatibility between processes, libraries, data formats, and runtimes when components assume different sizes for pointers and integers.

Context and scope: Crossbitness arises in environments that support mixed architectures, such as 32-bit applications running on a 64-bit operating system, or communication between components compiled for different bit widths. It also affects data serialization, network protocols, and plug-in architectures where modules may be built for different bitness.

Technical considerations: Differences in pointer size, integer width, structure layout, and alignment can create incompatibilities. System call interfaces and calling conventions may differ between 32-bit and 64-bit ABIs. Endianness can compound complexity when combined with crossbitness. Large-file support, file formats, and memory-mapped I/O may require special handling to avoid truncation or misinterpretation. Libraries may require separate 32-bit and 64-bit runtimes, and dynamic linking can be constrained by the operating system’s compatibility infrastructure.

Approaches: Compatibility layers and emulation can enable 32-bit code to run on 64-bit systems, or allow crossbitness communication through wrappers and data marshaling. Data formats and RPC protocols can be designed with explicit, fixed-width types to improve portability. Virtualization or containerization can isolate components by bitness, while careful API design and modularization reduce crossbitness dependencies.

Examples: Windows supports 32-bit applications on 64-bit Windows via compatibility layers such as WoW64; many 64-bit Linux distributions provide 32-bit compatibility libraries. Some language runtimes offer distinct 32-bit and 64-bit builds, and binary formats with explicit size fields (such as 64-bit offsets) facilitate crossbitness interoperability.

See also: 32-bit vs 64-bit, ABI, binary compatibility, cross-platform, emulation.