const
  VWIN32_DIOC_DOS_INT13=4;
type
_DEVIOCTL_REGISTERS=packed record
  reg_EBX:DWORD;
  reg_EDX:DWORD;
  reg_ECX:DWORD;
  reg_EAX:DWORD;
  reg_EDI:DWORD;
  reg_ESI:DWORD;
  reg_Flags:DWORD;
end;
DEVIOCTL_REGISTERS=_DEVIOCTL_REGISTERS;
PDEVIOCTL_REGISTERS=^DEVIOCTL_REGISTERS;

function DoIOCTL(preg:PDEVIOCTL_REGISTERS):Boolean;
var hDevice:THandle;
    cb:DWORD;
begin
  preg.reg_Flags := $08000; // assume error (carry flag set)
  Result:=FALSE;
  hDevice := CreateFile('\\\\.\\vwin32', GENERIC_READ,
            FILE_SHARE_READ or FILE_SHARE_WRITE,nil,OPEN_EXISTING,
            FILE_ATTRIBUTE_NORMAL, 0);
  if (hDevice = INVALID_HANDLE_VALUE) then exit
  else
    Result := DeviceIoControl(hDevice, VWIN32_DIOC_DOS_INT13,
              preg, sizeof(preg^), preg, sizeof(preg^), cb, nil);
  CloseHandle(hDevice);
end;

function GetDiskType(nDrive:Cardinal, SizeKb: DWORD):Boolean;
var
  reg:DEVIOCTL_REGISTERS;
begin
  reg.reg_EAX := $01500;      // IOCTL for block devices
  reg.reg_EDX := nDrive;  // receives media ID info
  Result:=DoIOCTL(@reg);
  Result:=Result and ((reg.reg_Flags and $08000)=0) and ((reg.reg_EAX and $FF00)=$0000);
  if ((reg.reg_EAX and $FF00)=$0300) then
    SizeKb:=((reg.reg_ECX and $ffff)*$10000+reg.reg_EDX)/2
  else
    SizeKb:=0;
end;

{
INT 13 - DISK - GET DISK TYPE (XT 1/10/86 or later,XT286,AT,PS)
        AH = 15h
        DL = drive number (bit 7 set for hard disk)
Return: CF clear if successful
            AH = type code
                00h no such drive
                01h floppy without change-line support
                02h floppy with change-line support
                03h hard disk
                    CX:DX = number of 512-byte sectors
        CF set on error
            AH = status (see AH=01h)
SeeAlso: AH=08h,AH=16h,AH=17h,AH=19h"SCSI"
}

procedure TDriveComboBox.BuildList;
var
  DriveNum: Integer;
  DriveChar: Char;
  DriveType: TDriveType;
  DriveBits: set of 0..25;

  procedure AddDrive(const VolName: string; Obj: TObject);
  begin
    Items.AddObject(Format('%s: %s',[DriveChar, VolName]), Obj);
  end;

begin
  { fill list }
  Clear;
  Integer(DriveBits) := GetLogicalDrives;
  for DriveNum := 0 to 25 do
  begin
    if not (DriveNum in DriveBits) then Continue;
    DriveChar := Char(DriveNum + Ord('a'));
    DriveType := TDriveType(GetDriveType(PChar(DriveChar + ':\')));
    if TextCase = tcUpperCase then
      DriveChar := Upcase(DriveChar);

    case DriveType of
      dtFloppy:  Items.AddObject(DriveChar + ':', FloppyBMP);
      dtFixed:    AddDrive(VolumeID(DriveChar), FixedBMP);
      dtNetwork:  AddDrive(NetworkVolume(DriveChar), NetworkBMP);
      dtCDROM:    AddDrive(VolumeID(DriveChar), CDROMBMP);
      dtRAM:      AddDrive(VolumeID(DriveChar), RAMBMP);
    end;
  end;
end;