⤷ Get free/total disk space

Use DiskSize and DiskFree functions for this problem.
ComboBox1 contains a list of drives letters.

var
  Disk: Integer;
...
procedure TForm1.Button1Click(Sender: TObject);
var
  Total, Free: LongInt;
begin
  Total:=DiskSize(Disk) div 1024;
  Free:=DiskFree(Disk) div 1024;
  Gauge1.MaxValue:=Total;
  Gauge1.Progress:=Free;
  Label1.Caption:='Total size - '+IntToStr(Total);
  Label2.Caption:='Free - '+IntToStr(Free);
end;

procedure TForm1.ComboBox1Change(Sender: TObject);
begin
  Disk:=ComboBox1.ItemIndex+1;
end;
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