Drive Offset and Sector Conversions
and
"What's the Sector-Size of Your HDD?"

The default sector-size for almost every single HDD is:
512 bytes per Sector. So that's what was used for each calculation below. Although most of this page is a Table of HexOffsets and Sector Numbers, you'll also find some important notes here about disk structures!

Formulas for converting a given Hexadecimal Offset to a Sector Number.

The Table: Hexadecimal OFFSETs and Absolute SECTOR Numbers.

How Many Sectors are there on Your  Hard Drive? -- The total number of sectors for some ideal-sized HDDs. Almost every drive produced will be a little more or less than these sizes.

FORMULAS for Converting OFFSETs to SECTOR Numbers and Vice Versa

Using the Calculator that comes with any Windows OS, you can easily convert between Hexadecimal and Decimal (when in 'Scientific View'). To find the sector that a given Hexadecimal (or Decimal) Offset byte resides in use these formulas:

Sector Number = Round Down to the Nearest Integer Number:
[ Hexidecimal Offset / 200 hex ] and convert to Decimal, or:
[ The Decimal Offset / 512 ].
If you're lucky enough to pick the very first byte of a Sector, it will divide exactly!
For example, converting the byte at Hex Offset 7C00  to  31,744 (in Decimal) and dividing it by 512 equals 62 exactly, so 7c00 is the first byte of Absolute Sector 62.

Decimal Offset = (Sector Number x 512) + offset within the sector.
[the "+ offset within the sector " simply means adding 0 through 511 depending upon where the byte is in a given 512 byte sector.]
To find the Hexadecimal Offset, either convert the Decimal answer above to Hex, or use the following:
Hexadecimal Offset = [ Hex conversion of: (Sector Number x 512) ] + Hex offset within the sector.
For example, (69 x 512 = 35,328)giving us an Offset of:  8A00 Hex  for the first byte of Absolute Sector 69.

If an HDD has an NTFS File System in its First Partition, then this is normally where its $MFT Records begin. The $MFT file record area can be very long.
( NOTE: the exact length in sectors for the $MFT basically depends upon how large the volume is, but there are other factors as well. )

If an HDD has a FAT32 File System in its First Partition, then this is normally the first sector of its FAT. The first eight bytes of a FAT32 - FAT will begin with either:
F8 FF FF 0F FF FF FF FF   or:  F8 FF FF FF FF FF FF FF
or even:  F8 FF FF 0F FF FF FF 0F
(unless viewed with a disk editor after booting into a Windows 9x OS; in which case, it will usually begin with the bytes:
F8 FF FF 0F FF FF FF F7   or:  F8 FF FF FF FF FF FF F7
or even:  F8 FF FF 0F FF FF FF 07 instead. See my page about the "Dirty Shutdown Flag" for more on why these FAT bytes are changed by the Windows OS!)
( NOTE: the exact length in sectors for each copy of the FAT depends upon how large the partition is and what tool was used to format the drive!  However, I've observed that the same formatting tool may create slightly different FAT lengths for exactly the same partition! This would require much further study to understand why; any volunteers? )

HDDs of exactly    10 GB  have:    19,531,250  sectors.
HDDs of exactly    20 GB  have:    39,062,500  sectors.
HDDs of exactly    30 GB  have:    58,593,750  sectors.
HDDs of exactly    40 GB  have:    78,125,000  sectors.
HDDs of exactly    60 GB  have:  117,187,500  sectors.
HDDs of exactly    80 GB  have:  156,250,000  sectors.
HDDs of exactly  100 GB  have:  195,312,500  sectors.
HDDs of exactly  120 GB  have:  234,375,000  sectors.
HDDs of exactly  140 GB  have:  273,437,500  sectors.
HDDs of exactly  160 GB  have:  312,500,000  sectors.
HDDs of exactly  180 GB  have:  351,562,500  sectors.
HDDs of exactly  200 GB  have:  390,625,000  sectors.
HDDs of exactly  250 GB  have:  488,281,250  sectors.
HDDs of exactly  300 GB  have:  585,937,500  sectors.
HDDs of exactly  320 GB  have:  625,000,000  sectors.
HDDs of exactly  500 GB  have:  976,562,500  sectors.