SWI-Prolog 10.1.6 Reference Manual: Section 2.20

## 2.20 SWI-Prolog and 32-bit machines

Most today's platforms are native 64 bit and 64 bit applications are to be preferred. The current version of SWI-Prolog primarily targets 64 bit platforms. 32-bit platforms are still supported as they are used on embedded devices and the WASM (Web Assembly, see section 13) still has poor support for 64 bits.

While the (currently) stable 9.2 series still has a real 32 bit version were Prolog data structures are based on 32 bit word units, the 9.3 development series represents all Prolog data as 64 bit units, regardless of the hardware's pointer size. This provides better uniformity and avoids the 128Mb stack limit of the 32-bit 9.2 series.

Choices in the data representation such as the placement and number of tag bits are still based on 32-bit units. This is expected to change in due time, simplifying the code and improving performance.