Re: Minimum hardware requirements and a few odds and ends.

From: Bob Ramstad <rramstad_at_alum_dot_mit_dot_edu>
Date: Thu Apr 22 2004 - 13:00:15 CDT

David Mertz wrote:

> Question though: Is it simple to boot a live-CD from a multi-session
> CD-R? How does that work? Boot from the first session always?
> Something else? I think I've read about problems with older CD-R's and
> multi-session capability. Am I imagining this, or is there a real issue?

The BIOS and CD-R firmware determine the result of booting from a
multisession CD-R.

In my limited experience i.e. on the hardware around here, systems boot
only from the first session on a CD-R. This makes sense as the boot
sector for the CD is the first sector on the CD-R i.e. it always gets
written when the disc is first written, and the firmware in the CD-R
drive would have to have some pretty interesting programming to do
otherwise i.e. it would have to scan the disc from the last session to
the most recent, looking for bootable sessions, and picking the most
recent one.

It is true that some ancient CD-R are not multisession compatible, and
there have also been OS related issues with lack of support for
multisession. That said, multisession support has been stable and
common for a couple of years now.

It would be a good idea to do some additional experimentation and
research on the topic of multisession CD-R. I suspect the various
specifications for ISO9660 and similar filesystems would make it clear
what behavior is standard.

It may also be that in some common supported filesystems -- perhaps even
ISO9660 -- that it is clearly defined that bootable areas must fall in
specific sector addresses, or that there can only be one bootable area
per piece of physical media.

In any case, as long as the CD-R is created properly with a single
bootable copy of the OVC software which runs on the given hardware and
the appropriate configuration files for that election, any alteration of
the CD-R with unauthorized additional sessions or whatnot can easily be
detected after the fact.

-- Bob

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Received on Fri Apr 30 23:17:16 2004

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