fat size : 3c8
rsvd sec cnt : 0x1870
tot : 0x3e780
FirstDataSector = BPB_ResvdSecCnt + (BPB_NumFATs * FATSz) + RootDirSectors;
FirstDataSector = 0x1870 + 2 * 0x3c8 + 0x80 == 0x2080

FirstSectorofCluster = ((N – 2) * BPB_SecPerClus) + FirstDataSector;
(0x17a-2)*2 + 0x2080 = 0x2370

DataSec = TotSec - (BPB_ResvdSecCnt + (BPB_NumFATs * FATSz) + RootDirSectors);
datasec = 0x3e780 - (0x1870 + 2 * 0x3c8 + 0) = 0x3c780
3c780
CountofClusters = DataSec / BPB_SecPerClus = 0x3c780 / 2

0x0000017a
0x017a3d16
(0x017a-2)*2 + 0x2080 = 0x2370

first fat?: 0x1870 + 0x80 = 0x18f0 = 6384
31E000

totsec32:0x3e780

(0xf9e - 2)*2 + 0x2080 = 003FB8 = 0016312

0x00- : mbr
0x3f - ??: pat0 fat32
0x3f : boot sect
  0x00 - 0x3f : reserved sect
  0x40 - 0x13f : fat 1
  0x140 - 0x23f : fat 2
  0x240 - : root dir (clus 2-2 (1クラスタのみ使用))
	0x242: bootmgr(clus3- 断片化しないように入れておく)
  