Mac Forum / General / Hardware / August 2004

In article
<eckleinspammenot-C93A74.07360529082004@news2.west.earthlink.net>,

Opps -- sorry, I didn't read correctly.  I saw OS X, but missed the
_cant run on_.  Too early - haven't had my coffee yet.

In article <290820041404489288%NoSpamDammit@invalid.com>, Mark Conrad
<NoSpamDammit@invalid.com> wrote: ...lots, of interest to very few.

Thanks everyone for the help, I would be lost if it were not for these
NGs.

The following routine worked for me.  I am in no way advocating the use
of memtest for others, because like lots of Terminal programs, it could
be very dangerous in the hands of a novice.

That said, I am very impressed with this free utility, so it will have
a regular place in my periodic maintenance of my OSX Macs.

To do fairly extensive RAM testing on an OSX-only computer:

1) Download memtest from versiontracker.com
2) Draged unstuffed memtest folder from
     the desktop into my hard disk icon.
3) Restarted computer while holding down shift key
     to enter "SafeMode".
4) Logged in as root.
5) Double-clicked my hard drive icon to open it,
      dragged the memtest folder onto the desktop.

      The name of that folder in my case is
       "memtest-4.03M"

      (very important to know exactly what that
        name is, because that name
        will be used shortly)

6) Opened Terminal, then I typed the commands
     listed a little further down.

     The first command relies on Terminal being
     opened in my home directory.  If for any reason
     that first command threw up an error message,
     I would then have typed instead:

            cd /Users/mark/Desktop

     The second command uses the exact name of
     the memtest folder, no spaces in that name.

     The last command actually starts the
     memtest program running.  The first item in
     the command is a period, the last item in the
     command is the number one.

I typed the commands, each command followed
by pressing the return key:

cd Desktop

cd memtest-4.03M

./memtest all 1

In my case, the program took 3 hours to completely check "all" the RAM.

(actually, a portion of RAM is not checked, because that portion is
needed to actually run the memtest program)

If the number one of the last command was replaced by the number four,
the program will run the entire test four times, and take 12 hours to
finish in my case.

It is easy to monitor the progress of the program, because the Terminal
readout provides me with a blow-by-blow report of what is being checked
at any moment.

Below is a portion of the Terminal readout at the end of the 3 hour run.

It is very important that the lines below about the success of
"locking" memory be there, otherwise I might as well force-quit
Terminal, because the results will be invalid.

Last part of Terminal readout at end of testing.
*********************************************
Attempting to lock allocated physical
memory....memory locked successfully!

Test Pass 1/1:
 Stuck Address       : ok        
 Random Value        : ok
 Compare XOR         : ok
 Compare SUB         : ok
 Compare MUL         : ok
 Compare DIV         : ok
 Compare OR          : ok
 Compare AND         : ok
 Sequential Increment: ok
 Solid Bits          : ok        
 Block Sequential    : ok        
 Checkerboard        : ok        
 Bit Spread          : ok        
 Bit Flip            : ok        
 Walking Ones        : ok        
 Walking Zeroes      : ok        

All tests passed.
********************************************

The first batch of tests through "Compare AND" only take about ten
minutes to run, and correspond to the testing that might be done by
utilities like TechTool Pro.

At the end of testing, I cleaned up everything, threw out the memtest
folder, restarted computer to get back into "regular" OSX.

Mark-

As I mentioned in a previous post, I made a terrible mistake in my
initial post in this thread.  I was very tired, having stayed up all
night battling another program.

My wrong statement:
"Is there any utility capable of doing a thorough testing of RAM on
modern Mac models that can't run OS X?"

I can't believe I wrote that.   In the first place, there are probably
no "modern" Mac models that cannot run OSX, so that statement of mine
does not make sense at all.

I "intended" the statement to read correctly this way:

"Is there any utility capable of doing a thorough testing of RAM on
modern Mac models that can ONLY run OS X?"

Anyhow, TechTool Pro does some RAM testing, an it will indeed reveal
defective RAM that is real bad, however it is not all that great at
detecting borderline RAM problems.

The reason is, individual RAM cells are influenced by "nearby" adjacent
RAM cells, because they are packed together so tightly in the RAM chip.

Kinda like the old telephone lines of many years ago, where one could
hear the conversations of other people because of poor shielding of the
individual lines in a packed cable of many lines.

A really good RAM testing utility will therefore toggle every possible
combination of nearby RAM cells, in an effort to "corrupt" the
particular cell being tested at the time.

As you can imagine, this extensive testing of RAM takes a horrendous
amount of time, however it is capable of detecting RAM faults that are
missed by more simplified testing.

The specific test that toggles all possible combinations of nearby RAM
cells is called the "Major March" test, however that test can only be
ran on extremely fast computers, otherwise it would take forever to
run.

Other lesser testing patterns are called by various names like
"Minor-March" and "Apegio".

Years ago I had a problem of random freezes of my Pismo powerbook,
which was under warranty at that time.   The usual RAM tests all passed
with flying colors, every time.

I had a program called "Hard Disk Toolkit", which did more extensive
RAM testing, among which the so-called "Arpegio" test pattern was used.
(HDT will still not work on an OSX-only type of computer)

Arpegio revealed a defect about 30% of the time.   The text readout of
the results mentioned that the memory-manager chip might possibly be
bad, instead of the RAM itself.

I sent the computer to the Apple repair depot in Texas, and they sent
it back saying they could find nothing wrong with it.

That kept going on for three seperate turn-arounds over a three month
period, me insisting that freezes still occured, Apple doing things
like replacing the entire motherboard.<g>

Eventually, in desperation and to get me off their back, they finally
listened to the testing results I was trying to get across to them.

They replaced the CPU board, which also had the "memory manager" chip
on it.  The CPU board is a seperate board, not part of the motherboard
in that particular Mac powerbook.

That fixed the freeze problem, and the Apegio test passed 100% of the
time.

I was not out one cent, Apple paid for everything, even shipping costs.

Mark-