PE>> No, I meant that it is 64, not 63.  I say it is 63.

RS> It allows you to specify sector 64.

Is this one program or lots?

RS> You could prove that more convincingly by say using DiskEdit
RS> to manually write a sector number in the first byte of the
RS> series of sectors, and then go back an reread those and check
RS> that you do have full access to sectors numbered 1-64 etc.

Or maybe just reading a sector at a time and seeing if any of them give errors.

PE>> I am doing address translation from
PE>> absolute number (as used in the fat)

RS> Fats dont even HAVE sectors, they have CLUSTERS. A cluster
RS> is usually more than a single sector except on a floppy.

Yeah, I meant the whole fat filing system, everything resolves down to a
logical sector number.  I then need to convert that to a pseudo-physical
number in order to do the BIOS call (int 013h)

PE>> to physical number (as used by the BIOS),
PE>> in order to boot PDOS. It is all working.

RS> Doesnt prove a damned thing if sector 64 isnt
RS> actually used in the boot process, and it isnt.

The question is does the booting sequence read more than the first track.
The answer is YES, IO.SYS comes AFTER the FAT, and that can be quite large.
 Like the 407th sector.  To translate 407 into a cylinder, head + track, I
need to divide by 63, if that is the number of sectors/track. I do so (by
63 not 64), and it works.

RS>> Its also complicated by what level you are doing the direct access at.
RS>> There is lots of translation and faking with a modern IDE drive. You
RS>> dont actually have a fixed number of sectors per track anymore, that
RS>> varys in bands across the platter and that is faked up into something
RS>> completely different at the level of the commands down the cable to the
RS>> drive. Even more dramatically if the drive is being used in LBA mode.

PE>> Yeah, I'm not talking about that,

RS> You are actually all these processes are going on all the time.

When I'm making the BIOS call, I don't need to care about that.

PE>> It is shown as 63, and I just want to know if that means 63 or 64.

RS> Christ you're cryptic Paul. Where the fuck 'is it shown as 63'

In the boot sector (sector 0) of the floppy or HD partition.

PE>> BTW, the floppy shows as 18. Do you think that means 19?

RS> Nope, a 1.44MB floppy has 18 sectors per track. Numbered 1-18.

They only have 6 bits for the sector number, agreed?  That allows you to
specify a number from 0 to 63.  In logical sector 0 of my HD, it reads 63
(which you say means 64).  In logical sector 0 of my FD, it reads 18 (which
you say means 18).  Quite sure you don't want to change your story yet? 
BFN.  Paul.
@EOT:

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