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SPD App for Mac OS X version Tiger or Leopard?

mac57mac57

mac57mac57

macrumors 6502a
Original poster
Aug 2, 2024
681
429
Myrtle Beach, SC
I just recently ordered PC2-4200U RAM DIMMs for my G5 Quad. Despite being clearly labeled as PC2-4200U, my G5 Quad detects them as PC2-3200U. I thought the vendor had pulled a"bait and switch" on me, and I have contacted them to ship the CORRECT speed this time.

Then I started reading about Serial Presence Detect (SPD), essentially a configuration EEPROM on all RAM DIMMs. Apparently, it has a table describing size, timing, etc. for the module. It can often be edited to change the RAM timings if the DIMM supports it.

It is *possible* that the DIMMs I have received *are* PC2-4200U, but the SPD lacks the right entries, and so the Quad's memory controller falls back to PC2-3200U. There is a roughly 33% RAM access performance penalty as a result of this "downgrade".

The infamous CPU-Z utility for Windows can read and change SPD values.

Does anyone know of a Mac OS X Tiger or Leopard utility that will do the same? My Google efforts on this have come up dry.
 
mac57mac57 said:
I just recently ordered PC2-4200U RAM DIMMs for my G5 Quad. Despite being clearly labeled as PC2-4200U, my G5 Quad detects them as PC2-3200U. I thought the vendor had pulled a"bait and switch" on me, and I have contacted them to ship the CORRECT speed this time.

Then I started reading about Serial Presence Detect (SPD), essentially a configuration EEPROM on all RAM DIMMs. Apparently, it has a table describing size, timing, etc. for the module. It can often be edited to change the RAM timings if the DIMM supports it.

It is *possible* that the DIMMs I have received *are* PC2-4200U, but the SPD lacks the right entries, and so the Quad's memory controller falls back to PC2-3200U. There is a roughly 33% RAM access performance penalty as a result of this "downgrade".

The infamous CPU-Z utility for Windows can read and change SPD values.

Does anyone know of a Mac OS X Tiger or Leopard utility that will do the same? My Google efforts on this have come up dry.
Click to expand...

As far as I recall, it does not matter what is nominally reported there, RAM will work at max supported (by the Quad) speed. Whether it is physically 3200 or higher, should be seen on the sticker (honestly I do not see someone faking that).
 
Likewise @barracuda156, I agree that it seems unlikey that someone would put fake higher speed stickers on lower speed RAM; that is why I went looking for some other explanation, and hit upon SPD.

My Quad detects the new RAM as PC2-3200U, but it also correctly detects the original two sticks of PC2-4200U as PC2-4200U. So, sticker or not, that is what it is seeing. I have read that RAM controllers read the SPD to determine how to access the RAM modules. It does at least make some degree of sense that if the SPD did not reflect RAM timings parameters that the Quad's memory controller can use, it falls back to the lowest common denominator.

There is a subjectively visible performance difference. I have two Quads. The first is filled with RAM that is recognized as PC2-4200U and the second is the one I just added the new RAM to.

The first one is noticeably faster, and it is not a disk speed difference. The first one is running an older, slower HDD. The second one (the one I just added the new RAM to) is running a new 4 TB spinner equipped with a whopping 256 MB of cache. It is a FAST drive, and yet the machine is visibly slower than the other. My guess is that it is the RAM speed that is slowing it down.

BTW, just to close the loop with other threads I am posting to here at MacRumors, both of these Quads have LCS cooling issues and are outrageously loud in operation, with fans pegged at the max. I am *still* working on that issue. It may take months... each iteration takes a day or two. I just don't have enough free time to work on this full time, so it is "a bit here, a bit there". Slowly but slowly, it WILL get done!
 
Last edited:
mac57mac57 said:
Likewise @barracuda156, I agree that it seems unlikey that someone would put fake higher speed stickers on lower speed RAM; that is why I went looking for some other explanation, and hit upon SPD.

My Quad detects it as PC2-3200U. It also correctly detects the original two sticks of PC2-4200U as PC2-4200U. So, sticker or not, that is what it is seeing. I have read that RAM controllers read the SPD to determine how to access the RAM modules. It does at least make some degree of sense that if the SPD did not reflect RAM timings parameters that the Quad's memory controller can use, it falls back to the lowest common denominator.

There is a subjectively visible performance difference. I have two Quads. The first is filled with RAM that is recognized as PC2-4200U and the second is the one I just added the new RAM to.

The first one is noticeably faster, and it is not a disk speed difference. The first one is running an older, slower HDD. The second one (the one I just added the new RAM to) is running a new 4 TB spinner equipped with a whopping 256 MB of cache. It is a FAST drive, and yet the machine is visibly slower than the other. My guess is that it is the RAM speed that is slowing it down.
Click to expand...

I would be surprised if this difference in RAM speed (if there is any real difference at all) results in a consistently visible difference in performance.
BTW, I recall a faster RAM is not accurately detected, but cannot check at the moment, which values I have.
 
If/when I can thermally correct this Quad, I will run GeekBench on it before and after PC2-3200U and PC2-4200U. That will provide objective results on this topic. I can't do that now though. Right now, if I tried to GeekBench the machine, I am certain that it would overheat and halt.
 
I just read about an older Mac OS X utility called SPDTool. Does anyone recognize it? Does anyone know where it could be downloaded from? I am coming up dry on the web.
 
mac57mac57 said:
OS X utility called SPDTool
Click to expand...
Pretty sure the Mac Version of SPDTool was Intel only.

Code: 
(Requires Java 7 or later) Macintosh : OS X 10.9 or later : OS X 10.9 or later

So even of you do find a copy of it, won't do you any good on PPC.
 

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I have discovered that Apple Service Diagnostics 2.6.3 displays MORE of the SPD info than System Profiler does, but still not the full thing. However, it may be the best I can get, short of running a live Linux CD and using a Linux tool... hmmm, not such a bad idea ..
 
Thanks @PowerPC74, that helps to know. I have not managed to find it at all, and have pretty much given up the search. I even tried Macintosh Garden to no good end. Wherever this tool is hiding out, it is a dark, quiet corner of the internet, that is for sure!
 
Get the hex of the SPD in Open Firmware using the `iic-read` commands, then convert that to a binary that can be parsed by one of those SPD tools for Linux or Windows or make your own parser.

What version of Open Firmware do you have?
 
Good tips @joevt, I will try the iic-read command and see what I get.

This brings up a good general question. I have not been able to find an Open Firmware reference manual; something that lists ALL the available commands. Does anyone know where such a thing could be found?
 
 
Thank you @joevt, your first link:


is a GREAT start. I learned all kinds of new commands I didn't know OF supported. Thanks!

p.s.> My apologies for the long "ugly" link. I just did a copy/paste of what you put in your post and that is what I got. It works - it takes you to the Wiki - but it is unsightly, to say the least!
 
mac57mac57 said:
p.s.> My apologies for the long "ugly" link. I just did a copy/paste of what you put in your post and that is what I got. It works - it takes you to the Wiki - but it is unsightly, to say the least!
Click to expand...
What I put in my post is https://forums.macrumors.com/threads/the-open-firmware-wiki.2225024/
Not that.

Did you somehow reply using e-mail instead of the forum in a browser?
 
Lucky you are it dose not shows up randomly as RAM/Thumb disk or suddenly it behaves like RAMBUS 2!x16 memory. lol ;)
 
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