FAT boot sector info


what		offset		length		Note
bytes/sector	11 (&b)		2               (little endian)
secs/cluster	13		1		1,2,4,8,16,32,64,128 only
reserved secs	14		2		Secs to start of 1st FAT min 1
FATS		16		1
Root entries	17		2
Small Sectors	19		2		secs/disc or 0 if > 64k
Media descr	21		1		F8 = fixed disc ?? F0
Secs/FAT	22		2
Secs/Track	24		2
Heads		26		2
HiddenSecs	28		4		secs on disc before boot sector
LargeSecs	32		4		Secs in volume if Smallsecs 0
???             36              4

convert LBA to CHS:
    cylinder = LBA / (heads_per_cylinder * sectors_per_track)
        temp = LBA % (heads_per_cylinder * sectors_per_track)
        head = temp / sectors_per_track
      sector = temp % sectors_per_track + 1

convert CHS to LBA:
         LBA = ( (cylinder * heads_per_cylinder + heads ) *
                    sectors_per_track ) + sector - 1

last 2 bytes of bootsec are 0x55 0xaa

before that come 4 off 16 byte partitions.

first then at offset 0x1be (0x200 sector size)

byte 0:		0x80		bootable disc
byte 1:		starting CHS in INT13 format
byte 2:
byte 3:
byte 4:		type byte.. suggest 0x41 for riscos
byte 5:		ending CHS in INT13 format
byte 6:
byte 7:
word 8:		Starting LBA (little endian)
word c:		Size in Sectors

BIOS boot uses CHS only.  ignores LBA

CHS format. first byte is H                          max H = 255
            2nd byte bottom 6 bits are S.            max S = 63
            2nd byte top 2 bits are top 2 bits of C  max C = 1023
            3rd byte is low byte of C