APL_FAST_FCHK

This parameter specifies whether Dyalog APL should optimise ⎕FCHK by allowing it to reliably determine whether a component file had been properly untied and therefore does not need to be checked (this is overridable using the ⎕FCHK option force).

Optimising ⎕FCHK in this way has a performance impact on ⎕FUNTIE and it is recommended this optimisation is switched off if your application frequently ties and unties files. 

Note: this only affects component files with journaling enabled. 

The values of the parameter are:

0	Do not optimise ⎕FCHK (optimise ⎕FUNTIE instead)
1	Optimise ⎕FCHK

The default value of the parameter is 0 on all platforms. On Windows, setting the value 1 has no effect.