Obsoleting SBC-2 functions

Pat LaVarre p.lavarre at IEEE.org
Mon Nov 17 10:59:09 PST 2003

* From the T10 Reflector (t10 at t10.org), posted by:
* Pat LaVarre <p.lavarre at ieee.org>
[ BC gop at us.ibm.com, mike at yfl.fujitsu.com ]

 > > following will be obsoleted from the SBC-2
 > > standard unless someone comes forward with a
 > > justification as to why they should not be
 > > obsoleted:
 > >
 > > ... Flexible Disk mode page ...
 > ... ATAPI,USB devices are using "Flexible Disk
 > mode page”. The BIOS are requesting to support
 > of these devices and not obsolete.


I imagine when we say we propose obsoleting SBC FDMP we mean the PDT 
x00 mode page x05 i.e. the page that gives a fictional C:H:S geometry 
for a disk in H:S:C order.
Slander or truth I do not know, but I hear wrong-headed PC Boot BIOS 
still shipping today fetch that page to help guess an interpretation of 
boot code read from lba 0, when that boot code fetches the code to run 
next via the original form of int x13, because that original form of 
int x13 substitutes fictional C:H:S addressing in place of sane lba 
I'm told without that page, the BIOS designer has to align the BIOS 
with one of the major competing traditions for converting between (C, 
H, S, disk capacity) and (lba), and that some BIOS instead flatly 
refuse to try to boot from the device that lacks the H:S:C page.  Also 
I'm told you may observe that all your boot volumes have to begin 
within the first small fraction of your disk, in particular the first 8 
GB or so, because of BIOS brain-damage near here.

The one C:H:S address we can translate without knowing geometry is the 
address C:H:S=0:0:1 which always means lba 0.  I haven't yet heard of a 
BIOS willing to translate that address while unwilling to translate 
less unambiguous addresses.

Pat LaVarre

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