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ATPM 11.08
August 2005


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by Sylvester Roque,

Is Your Memory Failing?

As most of you know last August or September I purchased a new G5 to replace the Blue-and-White G3 that had come to be known as FrankenMac. For the first time in my Mac computing life I would own a Mac while it was still one of the current machines. This was going to be sweet.

For the first few weeks everything was fine. The machine was everything I had hoped it would be. The only danger was that while sitting slack-jawed in front of this new speed demon I might drool on the keyboard and short something out. Then the trouble started.

Trouble in Paradise

The first sign of trouble came while trying to create a DVD using iDVD 4. I could create very short DVDs, but longer ones would cause iDVD to crash during the encoding process. Sometimes the crash would occur immediately after starting to create the menus. Usually iDVD was the only application affected, but sometimes I would see the dreaded kernel panic screen. You know, the black-and-white text screen that tells you, in several different languages, to restart the computer. Other applications that I use every day, such as Safari and Microsoft Word, were performing quite well. Photoshop was also working well, although I hadn’t tried anything that would really push it.

At this point I was starting to doubt my Mac knowledge. Maybe a dual 2 GHz Mac with 1.5 GB of memory just wasn’t enough machine to work well with about 70 minutes of video? That’s when the second symptom started to occur. Booting the system from scratch took four or five attempts, with each of the failures greeted by a kernel panic. Once the system finally started, everything went wonderfully as long as I didn’t try to run iDVD or Final Cut Express. Something was wrong and the boot-up problems were starting to convince me it might be hardware-related, since the kernel panics were occurring before any software had time to load.

Identifying the Culprit

I knew from reading posts in numerous forums that kernel panics are often the result of some hardware problem. Time to do a little troubleshooting. Without going into a lot of detail here, since that’s not the point of this article, the boot problems were apparently due to a loose card inside the computer. Once that was resolved I could get back to editing video right? Wrong. Problems with iDVD and Final Cut Express persisted.

After putting my project aside for a while, I stumbled on a potential answer one day. In one of the Mac forums I ran into someone who was doing a similar project on a Mac with less memory. Several messages later, he and I concluded that perhaps I had some bad memory chips. Time for more testing.

Trial and Error

If you suspect that your problems are due to bad memory, there are several methods available for testing. One common method is to remove a chip or two, boot the system, and attempt to duplicate the problem. Presumably if the problem persists then the bad RAM is still in the system. If the problem is gone, then the bad RAM is among the chips that have been removed. You are essentially using repeated trials and the process of elimination to help solve the mystery.

You would think that this method would appeal to someone like me. Not so. I have a few problems with this method. First, it is very time consuming and requires a great deal of your attention since it may be necessary to take the system apart several times. Second, you must know how to safely remove components from your Mac. Finally, it requires more knowledge about your Mac than some users want to know. Some Macs have RAM slots that are difficult for users to access while others, like my G5, require that RAM be installed in pairs. Finally, you might actually damage a good chip if it is not carefully removed and replaced.

Users who have only a little more than the minimum amount of RAM required for OS X may face an additional problem using this method. Removing RAM, even if your Mac permits removing one chip at a time, may leave you without enough memory to boot the machine.

Software-Based Testing

If you are uncomfortable taking your machine apart several times, there is another option: software-based memory tests. Testing memory using software is not infallible; it’s almost impossible to test every state of memory. Although it’s not perfect, software-based memory testing is a useful tool.

If your computer shipped with an Apple Hardware Test CD, that’s a good place to start. If a bad chip is identified, it can also pinpoint the slot that chip currently occupies. I didn’t have access to that disc during testing, but it can be a useful tool.

One of the first software tests that I tried was Tech Tool Pro 4. I decided to let it run all of the tests simply to check the overall health of my system. I expected it to find memory errors, but none were found. Normally that would be great news but the application crashes and occasional kernel panics were still occurring while working with large files.

Rember to the Rescue

Searching the Net I came across a tool called Rember. The program essentially provides a graphic user interface to a command-line memory testing tool called memtest. Upon launching Rember, the user is faced with the main Rember tab. From here you can control whether Rember tests all or part of the memory you have installed. You can also control the number of times the test is repeated. Although it is a good idea to run these tests several times, keep in mind that this can be a time-consuming process.

The right side of the main tab also presents you with an option to “Quit all applications.” Checking that option also lets you choose an option to quit the Finder. During testing I usually choose both of these options. Doing so frees up more memory for testing. The second tab, called Logs lets you see the results of testing. In my case, Rember began identifying errors almost as soon as the test started.

I also used memtest directly. memtest is the same core code that Rember uses. The principal difference is that memtest is a command-line utility that can be run in single-user mode. This allows it to test areas of memory that would normally be occupied by OS X. Even if you are unfamiliar with the command line, this might be a good choice. The directions included with this program are fairly easy to follow.

Installation is of memtest is easy, since it is installed using a standard OS X installer package. Once the program is installed, it can be run by completing the following steps:

  1. Boot the system in single-user mode by holding down Command-S as the system boots. Once you see text scrolling by, it’s safe to let go.

  2. Now you can run memtest by typing:

    /Applications/memtest/memtest all 3 -l

In this command, the text before the word all is the path to memtest. If you have not installed it in the default location, you will need to enter a different path. The word all tells the program to test all available memory. The number indicates how many times the test is to be run, and the -l tells memtest to place the results of testing in a log file. That file will be located in the same folder as memtest.

If you try to test all available memory and test results do not start appearing on the screen almost immediately, there may be a problem. Under some circumstances, Darwin does not appear to like the all part of the command. In that case, repeat the startup procedure replacing all with a specific amount of memory to test. In essence you are replacing all the the number of megabytes of memory to test. Although I can’t give you a definitive number for the upper limit the documentation suggests entering a value that is two or three percent less than your total memory.

The output from Rember and memtest will report the results of testing, as well as the memory address of any errors. The addresses are reported in hexadecimal notation. I’m not very good at converting these number to specific chips, but at least I know there is likely to be a problem. I’m going to start by pulling the pair of chips that were installed as an upgrade.

Now What

I expected Rember and memtest to yield the same results and have the same problems testing all memory because they are essentially the same test engine. Having said that, I am left with a puzzle. These two programs are reporting memory errors and Tech Tool 4 is not reporting errors. Which one is right?

I like Tech Tool Pro 4, but in this case I think there may be some memory errors creeping into my system. If my system were performing memory-intensive tasks better, I would think maybe Tech Tool was right. I guess it’s time to start shopping for memory.

Also in This Series

Reader Comments (21)

Lynnr · August 1, 2005 - 23:55 EST #1
Tech Tool Pro 3 never helped me detect memory problems. I quit using it.
David · August 2, 2005 - 11:28 EST #2
Apple Hardware Test, in extended mode, is an excellent resource. Unfortunately, RAM errors may not appear in a single pass. All but the most current systems ship with a version of AHT which has a 'looping' mode - expect to let this run for several hours or days (depending on the amount of install RAM, and the nature of the issue). If AHT presents you with an error code, write it down and call AppleCare - they can help you decipher it.

If AHT and other third-party tools are not giving a definitive RAM failure but you suspect bad RAM anyways, take your system to an Apple-Authorized Service Provider; they have more advanced diagnostic software and some also have the capability of testing the RAM modules directly.
George Lien · August 2, 2005 - 13:18 EST #3
Everytime whenever I decided to buy a new computer--nowadays often an used one--I would factor in the cost of quality RAM.

Without good memory, your Mac would be like car without gas.
Terry · August 2, 2005 - 16:59 EST #4
DON'T MISS THIS ABSOLUTELY VITAL STEP in the process of replacing or upgrading ram. DO NOT LEAVE THIS OUT!

Good article - in fact it may have led to my just recently found solution to the memory problem I've been having with a 700 mhz G4 iMac seemingly forever.

Kernel panics have been the operative phrase with this particular machine since I installed additional ram.

In fact, it was really the principal reason I had to get a new G5 iMac. (Given what I read in this article I'm hoping this wasn't a bad decision)

Nowhere in this article did I see the recommendation to reset the NVRAM after ram replacement. With my Mac's ongoing kernal panics, I had reset the PRAM countless times, but nowhere did I read of the recommendation to reset the NVRAM.

Given my encounter with this ongoing problem I was quite interested in memory problems such as those described in this article. Having already used the programs described in this article and finding no problem with the memory - I was more than frustrated!

I looked at Apple's website once again to see whether there was any other solution. Just prior to doing this I'd pulled out the added (certified for OS X) 512 MB chip that seemed to be causing the issue. After it's removal, there was no kernal panic problems - but 128 MB of original Apple installed just won't cut it with any version of OS X.

I thought what else might the problem be? It boiled down to resetting the NVRAM, because the memory tested as passing in all instances.


After replacing ram, one can reset the NVRAM by booting with the CMD-OPTION, O and F keys depressed. Not an easy key combination.

Then type reset-nvram, hit return, then reset-all, return, the machine will reboot.

The problem was solved with this simple, but apparently absolutely vital step in memory replacement process!

Had I known this tech tip, I'd have not experienced months of frustration with and about this particular Mac.

Hope this stomps out another possible issue many may have or will encounter!
kevin spahr · August 2, 2005 - 23:14 EST #5
I had this problem with iDVD4 on an iMac (on a stick) if i removed the extra ram (installed by the dealer) iDVD stopped crashing. When I got iDVD5 it no longer crashed even with the extra ram re-installed and I have never had any other problems since then.
Sylvester Roque (ATPM Staff) · August 3, 2005 - 00:53 EST #6
Thanks for the feedback. I hope the information has proven helpful.

Terry, thanks for that reminder about resetting the NVRAM. I have so seldom had this type of issue arise that I forgot about including that step.

Kevin, although not mentioned in the article, I tried upgrading the iLife suite. In my case it dod not resolve the issue. The upgrade was worth it for me though because of other improvements in the software.
Terry · August 3, 2005 - 01:08 EST #7
Decided to review this article one more time. It occured to me that resetting the NVRAM is vital when adding (and perhaps) changing ram sizes or components. I'd guess when the machine is first set up, it loads the configuration, ram amount, slots filled, etc., into a non-volital place. When the machine isn't re-instructed that the hardware is different - then it perhaps isn't permitted to carry out modified instructions for the different allocation of RAM.

I'd really appreciate it if an Apple tech or someone familiar with repairs and replacement could address this. Perhaps its one of those issues that techs who work on Macs would prefer to "fix" at the regular shop fees.
Michael Tsai (ATPM Staff) · August 3, 2005 - 09:38 EST #8
I am *not* an Apple tech, but Terry's first comment was the first time I'd heard someone recommend resetting the VRAM during normal use (rather than to troubleshoot a problem). I searched Apple's support site and did not find anywhere where they recommend this. I've never reset the NVRAM on my Macs when adding or removing memory.
Terry · August 6, 2005 - 00:23 EST #9
Here's the applecare link; you'll have to read down the page a bit.

I think I read the recommendation somewhere else with regard to reseting the nvram. I'll retrace my browsing and perhaps I'll find the source.

In retrospect, I probably would say that in my case and perhaps others it would be advisable to reset the nvram when encountering issues such as the one I encountered. Oh yes, my machine had reached the point where it was exhibiting kernel failure at reboot.

I did reset my nvram on my 300 mhz B&W. It was much more difficult to reset up that machine, so I'll withdraw my earlier remarks about resetting the NVRAM every time, and say perhaps only when encountering kernel failures and all else has failed.

Rememeber, the advice you receive is worth what you paid for it.
Rafael Sainz · August 27, 2005 - 11:41 EST #10
Hi terry I being having this kernel panic problem and looking all over internet untill I find your opinion heare my machine is a g5 dual 1,8 ghz with 1,2gb of memmory (gota love it) and had the problem when encoding the 3rd step on idvd and will have to restart even heare the fans run at full speed now i reseted nvram with the funcy key convination and VUALA the program encoded and recorded with no complains I bougted my machine on internet with a two month used i dont know if it was brand new with all of the memmory by now it is working better ( at least idvd is not giving any problems) so I will shut it outload RESET NVRAM COULD BE THE SOLUTION because i have tried out other solutions like repair permitions etc... so thanks again for sharing any way it was the only problem i had on paradise cause i being using final cut express with no problems....wait it was a problem with it but actualy it was a quick time problem so watch out for the newest release of quick time have a bug so i have to go back to 6.2 which did the trick and now i painting a happy face again for ma mac.
Hank Roberts · October 5, 2005 - 13:44 EST #11
RE: 'looping' mode

Please -- HOW do you make this work? I have a G3 "Pismo" and have never been able to find the way to make the Hardware Test loop, although I've been told often that it's there.

History -- this Pismo took five AppleCare vacations, and Apple was never able to nail down the problem causing its intermittent failures.

Once AppleCare expired, I was able to replace the original 64Meg RAM chip that came in the lower processor memory slot -- the factory default.

(I'd tried 128, 256 and 512-Meg chips in the upper slot, over the three years, which of course Apple always blamed for the problems even though removing the aftermarket RAM never fixed the problems)

As soon as I removed the original Apple factory RAM, the intermittent problems disappeared and have not come back.

Now I have two Techworks 512-Meg chips, the high density ones that are half the size of the older ones (more room for air circulation).

In all this time, I was never able to find a failure by running any memory test, even with the Apple chip in place; I have the original Hardware Test, and TechTool 4, and Drive10.

Oh, and, yes, I always did reset the NVRAM. Had to, in fact, when I was having those intermittent problems, quite often.

Not that it gave me or the AppleCare people a clue, unfortunately.

Oh, well. It's better than the experience I had with my Powerbook 540c -- back when AppleCare was in New York and was sending computers back with the SevenDust trojan/virus for a while, during the year before Virex was able to detect it. Ah, history. I'm glad it's over.
Jimmy · October 10, 2005 - 01:14 EST #12
Terry, thanks so much for the tip of resetting NVRAM. After a week of headaches, kernel panics and even an upgrade in computers (an older than into a new mac mini) you have solved the problem.
Now, I just wish the apple store guys who upgraded the memory for me had given me such solid advice instead of just shrugging their shoulders.

take care
James · November 8, 2005 - 06:16 EST #13
I am sorry you guys had to trawl around for these fixes! Apple staff should know these fixes and I have no idea why they are not being more helpful.

I am a manager at the Taylor Square Sydney store and I monitor the onsite upgrading to MAKE SURE that the memory and machines run properly before we release them; sending out a crippled machine to annoy a customer is not worth the five minutes saved by not resetting the NVRAM.

Another good and cool-looking test you can do to check the RAM is go into open-system mode; MD-OPTION, O and S key.

Then type "hostinfo", the machine should read your specs, telling you your processor type, number and memory config. If it doesnt match what you think you have then it is bad news.

Additionally, you can then do lots of other entertaining things, like repair permissions by typing "fsck -f". [just "fsck" if your HD is not being Journaled - this you can change in the Disk Utility; -f forces it] Then type "halt" to make the processor "halt", or "reboot" as you see fit.

If you accidently get 'lost' in this mode [it happens if curiousity gets the better of you], simply hold down the power button to force the machine to shutdown, this does come in useful sometimes.
Max · November 30, 2005 - 23:14 EST #14
"Apple staff should know these fixes and I have no idea why they are not being more helpful."

I notice you're using the technical term 'should'....

I am looking forward to trying your suggestion of resetting the NVRAM as a possible solution to a studio machine we recently upgraded (with Kingston RAM), and which started exhibiting instability soon afterwards.

As an aside, I have long found it rather suspicious that OS X is so sensitive to minor RAM defects, in ways that neither OS 1-9 nor Microsoft Windows are. It seems a rather serious design flaw in an other wise reasonably attractive operating system.

One can only hope that the recompile of OS X for Intel does not replicate the error. My test install of OSx86 on a plain old 3 GHz PIV Dell box with the cheapest RAM imaginable has yet to show any problems in this respect, but maybe I just got fantastically lucky with the generic RAM I bought. It also runs considerably.....faster than our dual-processor studio G5s.
Lisa Wheeler · January 19, 2006 - 18:41 EST #15
I have not tried resetting the NVRAM yet but have been having kernel panics with my G4 powerbook since I had an additional gig installed. It has now been removed and I don't have the problem. It seemed to only happen with final cut express and the additional RAM. I bought a new G5 two days ago and had two gigs of Ram installed by the retailer. it also Kernel paniced with Final cut express and I have been beside myself with grief. Two new movie making. I hope your solution brings some light.
Grant Power Mac G5 1.8 · February 18, 2006 - 02:04 EST #16
Installed 2 x 512 cards bought from Mac store - first set sold to me didn't even work so took them back and got them replaced (always a good idea to get the chips tested in a similar machine so you know they work before leaving the store...will save you hours of swearing lol)

Ok so got 2 new 512 cards, installed them with my existing pair of 256 cards and got kernal panics after 5 minutes...(more swearing) - scoured the internet and found this thread - reset the NVRAM and so far everything running smoothly... will let you know if I ever get another kernal panic...

Terry · April 9, 2006 - 21:09 EST #17
I'm glad all have had success with my suggestion. Unfortunately, my success was short-lived - so the iMac sits in the corner and a new Intel iMac sits in its place!

Although the memory, I placed in the user installable slot was high quality (Crucial, I think), whenever I placed it in the extra slot it eventually caused failure - notwithstanding the NVRAM reset.

The G4 , original iMac, is still a good machine, I'm just unwilling to purchase replacement ram any longer. Besides, a new machine is so much more fun!

I've been instructed to dispose of the machine (a government purchase), so I may just attempt to buy it back from surplus and mess with it at home if I can.

For the record, I'm extremely happy with the new MacIntel. What a sweet machine!
David Britten · May 2, 2006 - 04:07 EST #18
I cry for help! I've had a Mac for the past 15 years and have always been able to fix problems that have arisen, but now I'm stumped. There seems such a font of knowledge on this site, I'm sure someone out there can advise me on a problem I've been having, at least I hope so.

I had a power outage one day when the Mac was running. After power was restored, I got the dreaded restart message in several languages when I tried to boot. I rebooted several times with the same result before I achieved success. Since then, the system boots OK and, for the most part seems OK, but I now have problems that seem to be related to USB connectivity.

1. I can't print. A message tells me that the printer isn't connected, although it is.

2. I can't connect to the web via my broadband provider (I'm using a USB ADSL modem), and Netword Prefs and ADSL monitor tell me the the modem isn't connected, although it is.

I've run several checks using Disk Utility and Norton tools, and there seems to be a corrupted file in my OS (10.3.9) that neither DU nor Norton can fix.

When I run DU, I get a message that there is a problem that cannot be repaired. I've also had a message that DU has lost its connection to Disk Management.

I've completely restored the OS on another drive and find that, booting into that system, I can print, but I still can't get connected. This, however, may be a problem with the local telephone network, so I'm leaving that one out for the moment.

I'm now losing files, in particular, tracks I've imported into iTunes disappear from the library and I can't find the files in the source 'Music' directory.

I've reinstalled the OS twice, reinstalled all my applications and drivers, and applied the latest security upgrades etc., and run DU and Norton Disk Doctor ad-nauseum, but the problems persist.

I intend to try the memory tests recommended as soon as I can, just for the sake of it but, in the meantime, has anyone out there got a clue for me?


Dave Britten.
Brian Reynolds · August 15, 2006 - 17:14 EST #19
I have a windows keyboard, so I've held down the Ctrl Alt P and R keys and I'm positive I have not reset my NVRam.
I'm on a Mdd G4. Did I miss another step?
ATPM Staff · August 15, 2006 - 17:31 EST #20
Brian - the key combination to zap nvram is Command-Option-P-R. Not CTRL. You'll find, on the Mac OS, almost anything that would have used the Control key on Windows uses the Command key on the Mac.

The Command key on an Apple keyboard has an Apple logo outline and a cloverleaf-looking symbol. Since a non-Apple keyboard won't have this symbol, the Mac OS usually defines the Windows key as the Command key. And the key that is labeled "Alt" (Alternate) is known in Mac circles as the Option key.

Confusing things even more is that Apple keyboards have these two in reverse order. The Command key normally lives right next to the space bar. Therefore, users often use software to swap these two keys. If you have an actual Microsoft-branded keyboard, you can use their keyboard utility for Mac OS X which is a free download. This utility permits the swapping of these keys, as well as the ability to program the extended function keys for use on the Mac. Without this utility, those keys are inactive. If your keyboard is made by another company, you can check with them as to the availability of a Macintosh utility.
Scott Davis · September 6, 2006 - 05:02 EST #21
I went round and round with my used imac g4 from ebay, idvd crashing. And I'm 99% sure it was ram. It's running fine now. Also, a friend has a new intel imac and her machine acts a little wierd with new ram.
Ram is a four letter word sometimes, if you know what I mean. Here's my advice when in doubt check the ram. I don't care where it came from or who put it in.

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