Registersized

Register-sized is an adjective used in computing to describe data, types, or operations that are sized to the native width of a processor’s general-purpose registers—the processor’s word size. The word size is architecture-dependent: on a 32-bit system it is 32 bits, and on a 64-bit system it is 64 bits. Data that is register-sized is typically aligned to the processor’s word boundary to enable efficient memory access and arithmetic.

In programming, register-sized types map to this native width. In C and C++, types such as size_t and uintptr_t are defined to hold sizes or pointer values and have widths equal to the implementation’s word size. In Rust, usize and isize provide register-sized unsigned and signed integers, respectively, matching the pointer width of the target platform. Other languages offer analogous concepts where certain integers or handles automatically adapt to the host’s word size.

The concept is important for performance, as register-sized operations can often be executed in a single CPU instruction and benefit from optimal alignment. It also influences memory layout and compiler backend decisions, particularly in low-level code, systems programming, and performance-critical paths.

Portability considerations arise when code relies on register-sized types across architectures with different word sizes. For cross-platform data exchange or persistent storage, developers may prefer fixed-width types (such as 32-bit or 64-bit) to avoid surprises when moving between architectures. Register-sized types therefore sit at the intersection of performance and portability in software design.