In spanish newsgroups someone remember us an unsolved (and introduced) BUG since VFP7.

My HDD is 40 GB, 500 MBs free.

?VAL(SYS(2020))/(1024*1024*1024)

***************************************
*   VFP6-SP5  |  VFP7-SP1  |  VFP8    *
***************************************
*  37.2678 GB | 0.5415  GB |0.5415 GB *
*-------------------------------------* 

From the Help: "Returns the total size in bytes of the default disk."
So, we have unexpected values, between versions not documented in help.