VMINT sys_drive = -1;
VMUINT sys_drive_size = 0;
if ((sys_drive = vm_fs_get_system_drive()) >= 0)
{
    VMCHAR drive_str[2] = {0};

    sprintf(drive_str, "%c", (VMCHAR)sys_drive);
    sys_drive_size = vm_fs_get_disk_free_space(vm_ucs2_string(drive_str));
}