怎样用一个循环来计算整个个硬盘的大小，内详？该如何解决

怎样用一个循环来计算整个个硬盘的大小，内详？
GetDiskFreeSpaceEx(PChar(driver+ ':\ '),userFreeBytes,totalBytes,@freeBytes);


我只能用这个来得到单个分区的大小，我想得到的是整个硬盘的大小，在哪看过一个　for循环来着，但当时没记下来，现在用到了也找不到了，高手给个帮助，，，，

------解决方案--------------------
function GetDrives: string;
var
DiskType: Word;
D: Char;
Str: string;
i: Integer;
begin
for i := 0 to 25 do
begin
D := Chr(i + 65);
Str := D + ': ';
DiskType := GetDriveType(PChar(Str));
//得到本地磁盘和网络盘
if (DiskType = DRIVE_FIXED) or (DiskType = DRIVE_REMOTE) then
begin
GetDiskFreeSpaceEx(PChar(D+ '\ '),userFreeBytes,totalBytes,@freeBytes);
//sum(userFreeBytes),sum(totalBytes),sum(freeBytes)
end;
end;
end;
------解决方案--------------------
Sum1 跟 Sum2要初始化为 0

procedure TForm1.Button1Click(Sender: TObject);
var
d,dr:Char;
DiskType:Word;
Str:String;
i:Integer;
sum1,sum2,userFreeBytes,totalBytes,freeBytes:Int64;
begin
sum1:=0;
sum2:=0;

for i:= 0 to 25 do
begin
d:=Chr(i+65);
Str:= 'd ';
DiskType:=GetDriveType(pChar(d+ ':\ '));
if(DiskType = DRIVE_FIXED) or (DiskType = DRIVE_REMOTE) then
begin
GetDiskFreeSpaceEx(pChar(d+ ':\ '),userFreeBytes,totalBytes,@freeBytes);

sum1:= sum1+totalBytes;
sum2:= sum2+freeBytes;
end;
end;
Edit1.Text:=Formatfloat( '###,##0 ',(((sum1)div 1000)div 1000)div 1000)+ 'G ';
Edit2.Text:=Formatfloat( '###,##0 ',(((sum2)div 1000)div 1000)div 1000)+ 'G ';
end;