iMac video timings

[Marcelo A. Ferreira Gomes]

At 13:38 +0100 14/11/2002, Samuel Rydh wrote:
>On Wed, Nov 13, 2002 at 03:30:14PM -0800, Matt Brubeck wrote:
>>  The original iMac (not the new LCD one) requires unusual video timings
>>  to drive the built-in monitor.  These modes are not in fb.modes on some
>>  distributions (e.g. Debian), which prevents MOL from working in 800x600
>>  and 640x480.
>>
>>  Here are the modes I use on my iMac.  Could this file become part of the
>>  standard MOL distribution?  I've seen some people asking about this on
>>  the MOL mailing lists, but I haven't seen any solution posted before.
>
>Thanks, consider them added.
>  > Note: The 640x480 mode has some problems on my system -- it will only
>>  work in 8-bit color.  Does anyone know what the problem might be?
>
>No idea.

I have been doing some research on this, since my own iMac wouldn't 
work with those modes. I have found this table on an old Apple 
Developers Note:

Resolution	Vertical rate	Pixel depth	Pixel depth
		(2 MB SGRAM)	(4 or 6 MB SGRAM)
640 by 480	117.233 Hz	32 bits	32 bits
800 by 600	94.97 Hz	32 bits	32 bits
1024 by 768	75.03 Hz	16 bits	32 bits

You can find this devnote at: 
<http://developer.apple.com/techpubs/hardware/Developer_Notes/Macintosh_CPUs-G3/original_iMac/iMacDevNote.pdf>, 
and the above info is on table 3-2, page 35.

Note that, even though it describes the original iMac (rev. A), it 
seems to apply to revs. B-D as well. And it should, since I couldn't 
find any similar document about these models. The oldest one dated 
after this note documents the iMac DV (the first iMac with Firewire 
ports).

I haven't tried this out yet, since I only have my powerbook to play 
with now -- I'm currently in the process of repartitioning the iMac's 
hard drive and reinstalling everything.

BTW, I'd like to warn people out there with these early iMacs (revs. 
A through D) about the problem I had with my hard disk. I have found 
that you should boot from a partition entirely contained within the 
first 8GB of your disk. Otherwise, you run the risk of having to boot 
from a file above 8GB, which even the newest version of OpenFirmware 
for these macs can't cope with, and you will end up dropping into OF 
with a message that reads something like "Default catch!", and some 
hex numbers whose meanings I didn't have clue.

So, if you try to upgrade your system in a partition not entirely 
within the first 8GB, and it won't boot anymore, dropping into OF, 
this is probably the cause of your headaches. Apple seems to have 
noticed this, and Mac OS X 10.1 (and onward, I guess) won't install 
in a partition that's even partly outside the first 8GB in those 
iMacs.

Notice that the "Mac OS ROM" file (and possibly others) must be 
within the first 8GB, not the partition itself. So, you might be able 
to boot from a partition larger than that. My own Mac OS 9 boot 
partition has been 20GB in size and it had worked flawlessly for over 
an year. I had problems recently when trying to upgrade from 9.0.4 to 
9.1.

-- 
"People who think that they know it all are
very annoying to those of us... who do!"
- Garfield.
:-)