[NumLock]

исходник компонента TDriveComboBox:

Код:

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;