From: "Angus Johnson" <ajohnson(@)rpi.net.au>
Subject: Re: FAT and cluster size
Date: 12 Jun 1999 00:00:00 GMT
Message-ID: <7js8ma$bm116@forums.borland.com>
References: <7jor8m$8kq38@forums.borland.com>
Organization: Another Netscape Collabra Server User
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Newsgroups: borland.public.delphi.winapi


Deborah Pate wrote in message <7jor8m$8kq38@forums.borland.com>...
>I'm trying to display drive usage, and in particular the amount of a
>drive wasted by the FAT16 filing system. How can I determine the size
>of the FAT and disc clusters under Windows 95? It doesn't seem to be
>possible to use DeviceIOControl for this, except under NT.


the GetDiskFreeSpace() function *is* reliable in deriving cluster size
*if* it is a FAT16 drive. if it is a FAT32 drive, ie Win95b & Win98, then
GetDiskFreeSpace() is not reliable. most FAT32 drives will be formatted
to a 4k cluster size but *not all*.

DeviceIOControl can be used to derive the cluster size, there are a couple
of function codes which can be used...
Get_ExtDPB and Get_ExtFreeSpace.

see
http://msdn.microsoft.com/library/sdkdoc/winbase/fat32_3fow.htm
http://msdn.microsoft.com/library/sdkdoc/winbase/fat32_6y40.htm

and
http://www.undu.com/Articles/980525d.html

to make a long story shorter...
using Get_ExtFreeSpace is a little simpler (see my UNDU article)
however there seems to be a bug with it when more
than one hard drive resides on the local machine.
i now use Get_ExtDPB.

i've cut out a bit of my own code which should do what you want
on FAT32 drives... (as you will see i'm only interested in the
cluster size returned by this function call -
Cluster Size := BytesPerSector * SectorsPerCluster)


type
  //DeviceIoControl registers structure...
  TDevIoCtl_Registers = Record
    Reg_EBX   : DWord;
    Reg_EDX   : DWord;
    Reg_ECX   : DWord;
    Reg_EAX   : DWord;
    Reg_EDI   : DWord;
    Reg_ESI   : DWord;
    Reg_Flags : DWord;
  end;

  {the following structure def. thanks to : Geir Wikran -
kran@online.no    }
  TExtDPB = packed record { Extended Drive Parameter Block for FAT32: }
    DriveNumber        : Byte;  { Drive number (0=A, 1=B, and so
     }
    UnitNumber         : Byte;  { Drive unit number on device
        }
    SectorSize         : Word;  { Size of each sector in
       }
    ClusterMask        : Byte;  { Number of sectors per cluster minus
   }
    ClusterShift       : Byte;  { Number of sectors per cluster as power of
2. }
    FirstFAT           : Word;  { First sector for the File Allocation
Table.  }
    FATCount           : Byte;  { Number of FATs on the
       }
    RootEntries        : Word;  { Number of entries in root
y.         }
    FirstSector        : Word;  { First sector of the first
         }
    MaxCluster         : Word;  { Number of clusters on drive plus
   }
                                { Field is undefined for FAT32
        }
    FATSize            : Word;  { Number of sectors occupied by each
     }
                                { Zero indicates a FAT32
       }
                                { Use ExtFATSize for FAT32
       }
    DirSector          : Word;  { First sector for the root
y.         }
                                { Field is undefined for FAT32
        }
    Reserved2          : DWord;
    MediaID            : Byte;  { Media descriptor for the
       }
    Reserved           : Byte;
    Reserved3          : DWord;
    NextFree           : Word;  { Most recently allocated cluster. Cluster
at  }
                                { which to start search for free
ters.     }
    ExtFreeCount       : DWord; { Number of free clusters on the
       }
                                { FFFFFFFF if the number is
         }
    ExtFlags           : Word;  { Flags describing the
       }
                                { bits 0-3: 0-based number of active
    }
                                { bits 4-6:
         }
                                { bit 7: FAT mirroring enabled if bit
cleared  }
                                { bits 8-15:
         }
    ExtFSInfoSec       : Word;  { Sector containing information about the
file }
                                { system in TBifFATBootFSInfo
ure.       }
                                { This field is set to 0FFFFh if there is
   }
                                { FileSysInfo sector. Otherwise, this
ue    }
                                { must be non-zero and less than the
reserved  }
                                { sector
       }
    ExtBkUpBootSec     : Word;  { Sector containing the backup boot
tor.    }
                                { This field is set to 0FFFFh if there is
   }
                                { backup boot sector. Otherwise, this
ue    }
                                { must be non-zero and less than the
reserved  }
                                { sector
       }
    ExtFirstSector     : DWord; { First sector of the first
         }
    ExtMaxCluster      : DWord; { Number of clusters on drive plus
   }
    ExtFATSize         : DWord; { Number of sectors occupied by each
     }
    ExtRootCluster     : DWord; { First cluster in the root
y.         }
    ExtNextFree        : DWord; { Most recently allocated cluster. Cluster
at  }
                                { which to start search for free
ters.     }
  end;

  TDPBWithSize = packed record
    dpbSize: word;
    dpb    : TExtDPB;
  end;

{-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-}
//My Delphi implimentation of - Int 21h Function 7302h Get_ExtDPB (FAT32)
//to get cluster size...
{-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-}
function GetClusterSizeFAT32(Drive: PChar; var SperC, BperS: integer):
boolean;
const
  VWIN32_DIOC_DOS_DRIVEINFO = 6;
var
  DevIoHandle         : THandle;
  BytesReturned       : DWord;
  Reg                 : TDevIoCtl_Registers;
  DPBWithSize: TDPBWithSize;
  DriveNum: DWord;
begin
  DriveNum := byte(Drive^) - ord('@');
  result := false;
  FillChar(DPBWithSize, sizeof(TDPBWithSize),0);
  FillChar(Reg, sizeof(TDevIoCtl_Registers),0);
  with Reg do begin
    reg_EAX :=  $7302;
    reg_EDX := DriveNum; //DS:DX
    Reg_EDI := DWord(@DPBWithSize); //ES:DI
    reg_ECX := sizeof(TDPBWithSize);
    reg_Flags := $00000001; //set carry flag to assume error.
  end;

  DevIoHandle :=
CreateFile('\\.\vwin32',0,0,nil,0,FILE_FLAG_DELETE_ON_CLOSE,0);

  if DevIoHandle <> Invalid_Handle_Value then begin
    result := DeviceIoControl(DevIoHandle, VWIN32_DIOC_DOS_DRIVEINFO,
        @Reg, SizeOf(Reg), @Reg, SizeOf(Reg), BytesReturned, nil);
    CloseHandle(DevIoHandle);
    if result and (Reg.reg_Flags and $1 = $0) then
      with DPBWithSize.dpb do begin
        BperS := SectorSize;
        SperC := ClusterMask+1;
        result := true;
      end;
  end;
end; {GetClusterSizeFAT32}
{=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=}

Note: check in the initialization section (or formcreate method)
if it is Win95b or later version of window as this function will
*not* work on Win95a.

var
  VI: TOsVersionInfo;
begin
  // First check if Win95 OSR2 is running ...
  VI.dwOSVersionInfoSize := SizeOf(VI);
  GetVersionEx(VI);
  with VI do
    IsOSR2 := (LoWord(dwBuildNumber) > 1000) and
                 (dwPlatformID = VER_PLATFORM_WIN32_WINDOWS);


hope this helps

aj