13.1.1 Virtual Machine

• The internal representation of Prolog terms and code has been redesigned, resulting in code that runs up to twice as fast as in release 3.
• Certain memory limitations that existed in release 3 have been dropped. All available virtual memory can be used without any limitations imposed by SICStus Prolog.
• The limitations on “temporary” and “permanent” variables for compiled clauses have been dropped. There is no size limit on compiled clauses.
• The number of available atoms is four times larger than in release 3 (1M atoms are available on 32-bit platforms).
• The range of small integers is eight times larger than in release 3. Although the size of integers is practically unbounded, small integers are handled more efficiently than other numbers.
• Multifile predicates are compiled by default; in release 3, they could not be compiled.
• Native code compilation has been dropped. Update: JIT, a different variant of native code compilation, was added in release 4.3.0.
• Execution profiling is available for compiled as well as interpreted code. The profiling data accessible by profile_data/1 and library(gauge) is more precise. Some of the choices of release 3 have been dropped.
• Execution profiling has been generalized to support coverage analysis for compiled as well as interpreted code.