DVD drive won't recognise 10.4 upgrade disc.

Question

Our lovely old G4 comes with a DVD drive - no burner, but the reader is in there. I can play DVDs just fine; but it's (finally) time to update from 10.1. I have an upgrade disc for a previously overwritten update on a different mac and figured I'd use that.
The DVD drive gets quite confused by the system DVD, either trying to reformat it for burning, trying to play it like a movie, or just refusing to acknowledge that there's a disc present.
I've tried everything I can think of to make this work, and no results so far.

Answer 1

There should be some build information, even System Profiler
often will have some hardware information handy in finding out
what the stuff in the box really is. Some of the computer models
have some model configuration information on the outside of
the computer, written on the bottom or back. Others may have
such info & it isn't easy to find, or it says little more than basics.
A full retail installer disc and not some upgrade disc is a path;
the other disc may be for a specific model and won't put a
full system if anything, into the computer at hand. The optical
drive in the computer may support DVD installer (read only)
discs if they are universal full retail type. MacTracker will say
some info about what configuration within a series may have
had what kind of optical drive. Yours may also have a simple
defect and that may prevent a full installer from booting.
{Startup from a DVD media install disc is the same as from CD,
the C -key is held on startup to see if or when it will load and
then the Installer screens will appear; if it is a correct disc.}
In a series, and in older computers it is more noticeable, the
lower-end configuration may have offered a CD-ROM drive
and it can boot the computer from a CD system install disc;
further up the food-chain, the next-up one could record to CD
media and play CDs, boot from CD. Later on, the Combo
drive could boot from some DVD media, play DVDs, may
have included system software on CDs in a packet. And later
ones with a Combo, had OS media on DVD and booted from
it to perform installs, disk maintenance, and other tasks. The
last configuration is a DVD write/read drive, a superdrive, &
can also handle CD write/read; boots Mac with DVD installer.
The specifications can sometimes also be found for older
Macs in Apple Support's specification page. Some specs
and other related information may be found in the download
from MacTracker which runs free as an app, from their web
page, at http://mactracker.ca and this may help generally.
There is some information on OS X system discs and also
computer specifications, supported systems, etc from there.
Some "upgrade discs" require a certain version of OS X
to be installed prior to being able to use that disc. It may
not be a full installer at all, and is simply an upgrade over
some earlier system; in some cases these may also be
for a specific computer series and not a universal retail
type of full installer disc; so they should be avoided.
{An "upgrade" disc may have been meant for a computer
already running some version of a previous OS and may
have been put in the box as an easy path for that owner
to get into the next OSX version without a full retail buy.
In some instances, those may be only good as coasters.}
Good luck & happy computing!
edited.