[syslinux] isohybrid and ISO images whose size is not a multiple of 2048 bytes vs. VirtualBox
Ady
ady-sf at hotmail.com
Tue Feb 17 14:52:46 PST 2015
> An alternative would be to request a cylinder size which
> is divisible by 2048. E.g.
>
> isohybrid -h 252 -s 63
>
> The cylinder sizes 64x32 and 255x63 emerged as best
> candidates when we compared our collections of questionable
> experience and rumors. More substance is not to see behind
> them.
> (Actually Cylinder/Head/Sector addressing is so brain
> damaged that only ill firmware can insist in it having
> a particular form. All sane firmwares will simply use
> LBA numbers for addressing.)
>
Let's not forget that the goal usually is to select CHS values so that
the resulting (optical and/or other) media would boot correctly in as
many systems as possible while maintaining a "sane" file system. This
is the reason for the recommended '-h' and '-s' values.
I'd rather not comment (at least, not at this opportunity) on the
(minimal and preferred) conditions to be (hard-code) included in the
source code.
Now, if the proposed (temporal?) workaround is to use a different pair
of '-h' and '-s' values, I would suggest choosing them according to
commonly-used conventions or standards for CHS translations (e.g.
h={15,16,32,64,128,240,255}; s={16,32,63}) instead of completely
arbitrary values. That is, in addition to making the total size a
multiple of 2048 bytes, avoiding partial cylinders and maintaining the
resulting amount of cylinders to equal or less than 1024.
Regards,
Ady.
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