From QB64.org wiki
CALL ABSOLUTE is used to access interrupts on the computer or execute assembly type procedures.
- CALL ABSOLUTE([argumentList,] integerOffset)
- CALL ABSOLUTE is implemented to support older code and is not recommended practice. To handle mouse input, the use _MOUSEINPUT and related functions.
- CALL and parameter brackets are required in the statement.
- argumentList contains the list of arguments passed to the procedure.
- integerOffset contains the offset from the current code segment, set by DEF SEG and SADD, to the starting location of the called procedure.
- QBasic and QB64 have the ABSOLUTE statement built in and require no library, like QuickBASIC did.
- NOTE: QB64 does not support INT 33h mouse functions above 3 or BYVAL in an ABSOLUTE statement. Registers are emulated.