Panther freezes on Power Mac G4 (MDD): problem solved

Posted by Pierre Igot in: Macintosh
September 7th, 2004 • 5:12 am

Regular Betalogue readers know that, for the past few months, I have been experiencing unexplained system-wide freezes in Panther. I went through all kinds of trouble-shooting procedures, and was unable to isolate the source of the problem.

Multiple reports on such freezes on various other forums, including and, also led me to think that the problem was not with my own system configuration, but with the Panther system itself. Some reports seemed to indicate that the problem had been acknowledged (albeit unofficially) by Apple as a complex Virtual Memory-related bug.

One of the benefits of having a blog (with a comments feature) is that you get feedback from readers, and sometimes that feedback can be very useful indeed.

A couple of weeks ago, Andrew Aitken, a reader from Manchester, England, who happens to be a technical support analyst for GBM AppleCentre Manchester, offered some words of advice by e-mail. He mentioned that he had seen a couple of customers with similar problems and made a number of suggestions.

Some of the trouble-shooting procedures he recommended represented a lot of work, and I didn’t really have time to go through them right away. However, one particular suggestion that he made was that I try and move my internal hard drives from one ATA bus to another. My Power Mac G4 (MDD) has three ATA buses: one ATA-33 bus for the optical drives (I have the built-in SuperDrive that came with the machine and another Pioneer DVR-107D SuperDrive that I added more recently); one ATA-100 bus for two hard drives that can be mounted vertically against the wall of the G4; and one ATA-66 bus for two more hard drives that can be mounted horizontally underneath the optical drives.

My two internal hard drives (both recent Seagate models replacing the IBM drive that came with the G4) were connected to the ATA-100 bus.

Following Andrew’s instructions, I moved both hard drives to the ATA-66 bus. The move was actually very easy, because the metallic mounting piece that is used to attach the two hard drives to the wall next to the ATA-100 bus is the exact same as the piece that is used to attach the two hard drives underneath the optical bay. So I only had to remove one screen, detach the mounting piece with the two hard drives, and swap it with the empty mounting piece underneath the optical bay. It just took a few minutes.

Well, this was 12 days ago. I restarted the machine and resumed normal operations. And I haven’t had a single freeze since then. Right now, I am looking at the CPU indicator menu in MenuMeters and it tells me that I have had nearly 12 days of continuous uptime.

In other words, changing ATA buses appears to have fixed the problem. I have not refrained from doing anything with my G4 since the change, including activities that are hard disk-intensive or CPU-intensive. The weather conditions here have been fluctuating, with temperature increases that, at some point, I suspected of having something to do with the freezes. It now appears that temperature had nothing to do with them.

Unless something happens in the next few weeks that contradicts what has happened since I changed buses, the conclusion here is that I have a defective ATA bus. What kind of defect is it? I am afraid I don’t know enough about such hardware issues. Andrew mentioned that he had seen similar faults before (hence his suggestion), but that’s all I know. It could be a defective cable. It could be a defect on the logic board itself. Who knows?

The bottom-line is that I am one happy camper :). Regular Betalogue readers know that I was getting a few days of continuous uptime at best (sometimes not even 24 hours between freezes). This is obviously much, much better. All of a sudden, Mac OS X feels strong and reliable again. What a relief!

As far as I can tell, moving from an ATA-100 bus to an ATA-66 bus has not had any significant impact on hard disk performance. I remember reading a while back that such bus speeds didn’t mean all that much because, in typical use, today’s hard drives cannot make use of all the available bandwidth anyway. My current experience would seem to confirm this.

The only (slight) drawback that I have noticed is that the new location for the hard drives seems to have caused some changes to the air flow inside the machine, which seem to causing the G4’s cooling fans to change speeds a bit more often than before. It’s only a minor issue, because the G4 is already a noisy machine even with its fans at the lowest speed, so it doesn’t make such a big difference, and with the average outside temperature dropping now that we are in September, I expect that I will notice the problem even less.

What do all this mean for other people who have been experiencing freezes in Panther? Well, I am not sure. If you are getting the freezes and have a G4 with several ATA buses, I would definitely suggest that you try to change buses as I did. Otherwise… it could be that my freezes were only due to a defect in the ATA-100 bus or that there is indeed a bug in Panther itself, but that the bug only manifests itself when using the faster bus.

I am afraid that I have now shared as much information as I could — and that I am going to move on to other issues now that this one is solved for me. To those who are still experiencing freezes, I can only offer my sympathy and my best wishes of luck. And once again, I would like to publicly thank Andrew Aitken for his priceless help. If you need help with your Mac and live in the Manchester (UK) area, I can only recommend that you give him a call at AppleCentre Manchester!

4 Responses to “Panther freezes on Power Mac G4 (MDD): problem solved”

  1. Pierre Igot says:

    Henry: I wouldn’t say the evidence is that clear. The freezes started happening when I was still using the original HD by itself in the default location on the G4. After using the G4 for months without any problems, I started getting the freezes, even though I hadn’t change anything to the config. Thinking that the HD was defective, I replaced it with a newer (hence faster) one, in the same location. It didn’t help. I added a second drive later on. It didn’t result in an increase in the frequency of the freezes. (As far as I could tell, the freezes were unpredictable. Sometimes I’d get three in a day. Sometimes I’d go several days without one.)

    It could still be that there is a defect on the ATA-100 bus that is aggravated by the presence of two drives and heavy HD use. But the evidence suggests that the defect is there even in the normal config.

  2. Henry Neugass says:

    The evidence seems clear: your drives were not capable of running reliably at the higher bus speed. (Sorry, I don’t recall, did you double check the drive specifications for 100 MHz operations?) Or, (very unlikely, but possible) your ATA-100 bus was running a little fast, and your drives –or one of them– was barely meeting the 100 MHz specification. Did you check operation with one drive at a time on the ATA-100? You could leave the other one on the ATA-66 for the duration. Just one drive being a little slow could easily muck up the bus.

    I suppose it is even possible that one drive was specified for 100 MHz but had a manufacturing defect not caught by testing — it’s simply running at a slower speed.

    I don’t know about this particular case, the ATA bus, but it is common in hardware that operation simply gets flakey if one item on a bus simply isn’t fast enough. It’s a consequence of trying to make things faster, actually — it takes precious time to synchronize every single transaction.

    It’s also reasonable that you suffer crashes in such a situation. The disk driver may be able to cope with event “B” not occurring with a certain interval after event “A”, but it could easily be assumed that “C” would follow “B” within a specified interval. Why? Because “A” and “B” occurred, there’s no reason to doubt “C” will meet the specification. Or it is simple as this: your data got scrambled.

    Glad to hear you are fixed up.

  3. LoonyPandora says:

    Glad to hear it is running smoothly again – Enjoy Panther as nature intended, with no freezes!

  4. Daft Cow? » Blog Archive » MDD G4 Kernal Panic on Startup. says:

    […] I have history with these G4’s… Some of it is well documented in my friend Pierre’s betalogue. […]

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