SWI-Prolog has a number of memory areas which are not enlarged at run time, unless you have a version with dynamic stack allocation. The default sizes for these areas should suffice for small applications, but most serious application require larger ones. They all can be modified by command line options. The table below shows these areas. The first column gives the option name to modify the size of the area. This option character should be followed immediately by a number and expresses the number of kilo bytes to use for the area. There are no other limits than the available memory of the machine to the sizes of the areas. The areas are described in table 3.
The heap is a memory area to store atoms, clauses, records, flags, etc. This area is dynamically enlarged at runtime on all versions of SWI-Prolog.
| Option | Default | Area name | Description |
| -L | 2M | local stack | The local stack is used to store the execution environments of procedure invocations. The space for an environment is reclaimed when it fails, exits without leaving choice points, the alternatives are cut of with the !/0 predicate or no choice points have been created since the invocation and the last subclause is started (tail recursion optimisation). |
| -G | 4M | global stack | The global stack is used to store terms created during Prolog's execution. Terms on this stack will be reclaimed by backtracking to a point before the term was created or by garbage collection (provided the term is no longer referenced). |
| -T | 4M | trail stack | The trail stack is used to store assignments during execution. Entries on this stack remain alive until backtracking before the point of creation or the garbage collector determines they are nor needed any longer. |
| -A | 1M | argument stack | The argument stack is used to store one of the intermediate code interpreter's registers. The amount of space needed on this stack is determined entirely by the depth in which terms are nested in the clauses that constitute the program. Overflow is most likely when using long strings in a clause. |