PC-100 or PC-133?

Discussion in 'Mac Pro' started by jwt, Sep 15, 2007.

  1. jwt macrumors 6502

    Mar 28, 2007
    I have a powermac g4. I put a stick of PC-133 memory in an available slot. System profiler says it's PC-100. So, at what speed is it really running?
  2. Yoursh macrumors 6502

    May 28, 2006
    It is would be running at PC-100. Most likely you have a G4 with a 100mhz bus and Pc-133 steps down and runs at 100.
  3. jwt thread starter macrumors 6502

    Mar 28, 2007
    Actually, I have a 133 MHz bus. The memory from Apple in slot 1 says 133, but the one in slot 2 says 100. I just now installed a 3rd stick and it also says 100. What gives?
  4. yippy macrumors 68020


    Mar 14, 2004
    Chicago, IL
    What model of G4 do you have? Either the ram is bad, your ram bus is 100Mhz or the ram doesn't meet Apple specs.
  5. leekohler macrumors G5


    Dec 22, 2004
    Chicago, Illinois
    Yep- we need to know what model you have before we can advise you.
  6. jwt thread starter macrumors 6502

    Mar 28, 2007
    OK. The new one is a Crucial 512MB 3.3 volt 168-pin DIMM, PC133CL2 SDRAM, unbuffered. The other is Kingston, and I have to shut the computer down to take a look. According to system profiler, it has the same specs as the Crucial unit. Under the speed column in System Profiler, both the 3rd party sticks are listed as PC100-322S, whereas the Apple module is PC133-333. What does the S mean?

    Oh, and it's a 2002 Quicksilver G4 upgraded with a Fastmac 1.5 GHz 7455 upgrade.
  7. statikcat macrumors 6502


    Mar 20, 2007
    If one of the sticks is 100 it could bottleneck all the others. Usually all ram runs at the speed of the slowest stick.
  8. weg macrumors 6502a


    Mar 29, 2004
    It might also be that you bought relabelled RAM...
  9. jwt thread starter macrumors 6502

    Mar 28, 2007
    weg, your avatar really freaks me out. I thought Safari crashed.

    Anyway, I started pulling modules to see how the computer would respond. I tried every module independently, booting the computer from each module one at a time. Only the Apple module shows up as PC133. I tried placing the offending modules in different slots. I paired the two aftermarket sticks, leaving out the Apple module. I also tried resetting the PRAM. Nothing works. Only the Apple module shows up as PC133. What do I do now? There's no BIOS-like method of forcing the memory to run at 133, is there?
  10. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    What the System profiler reports is the SPD setting as reported by the module, it does NOT test how fast the modules is ACTUALLY running.

    So it's possible that the module has its Serial Presence Detect setting written to PC100, and it may be running at 133 MHz or at 100 MHz, there is no easy way to tell what the speed actually is running at.

    Likely, someone can chime in with something out of the Developers tools that can actually report on system performance. Any consumer-level utility is simply going to parrot what System Profiler says.
  11. Sun Baked macrumors G5

    Sun Baked

    May 19, 2002
    As said...

    Likely it is PC133 with improperly coded SPD settings.

    This is not the speed the RAM is running at, just what is written into the RAMs SPD EEPROM.

    System profiler/hardware/memory section is just reading what is written into the DIMMs ROM.

    It isn't reporting info on the bus speed. For that you need to look at the System Profiler's Hardware Overview (i think).

    Likely it will say "Bus Speed: 133MHz"
  12. HW-Hack macrumors newbie

    Aug 25, 2007
    PC100 or PC2700 ---- these are industry specifications followed by memory vendors and motherboard designers along with BIOS writers --- so the whole thing should work pretty much flawlessly if everything is correct.

    The the BIOS code on a PC or a Mac reads the SPD settings set by the DRAM manufacturer and embedded on each stick of DRAM. Bottom line is if the BIOS reads 2 sticks rated for 133MHz and 1 stick rated at 100MHz .... then your memory bus will be throttled down to 100MHz. The slowest chip
    always determines the overall bus speed.

    Either way you've bad parts - or parts that are not being read correctly by a Mac (but that goes against the spec ) ----- take them back to the shop and have them put in a PC and see what that comes up with.

    Don't settle for having a slow memory bus;)
  13. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Correct, but only as far as it goes. Which is not far enough to be useful.

    The PC100 (or PC2700) 'standard' is only one of a dozen or more parameters that are required to make a given RAM module work in a particular machine.
    Ignoring for the moment that you can have PC100 modules that are ECC, non-ECC, Buffered or unbuffered, DIMM, SODIMM and MicroDIMM format, with CAS latencies of 2 or 3, stacked or non-stacked...

    You can still build a PC100 CL2 non-ECC 168 pin SDRAM DIMM in four or five different ways, with different densities and numbers of chips, and different arrangements of logical rows and columns, and different physical sizes, and all will be PC100 'standard'. But most of them won't work in a given Mac. The classic examples are the standard PC100 modules that read 1/2 capacity on G3s and early G4s, because they are high density.

    On top of that, the SPD settings have to be written correctly for the machine to recognize it. A SPD can also be programmed to respond at multiple speeds -- for example a PC133 module can be programmed to work at both PC133 and PC100, and at CAS Latencies of 2 and 3. This is also the case with the PC2700 SODIMMs that can be used in iBooks and Powerbooks that require PC2100.

    So please, don't talk about PC100 (or PC2700) as "the" standard and all you have to know for things will work flawlessly. That's like saying that this wheel is a standard 15" wheel and therefore it will fit all cars that take 15" wheels -- and ignoring the width, bolt patterns, etc.
  14. jwt thread starter macrumors 6502

    Mar 28, 2007
    So if I have one bad stick causing my memory bus to be throttled back, how would I know? Under Hardware Overview on System Profiler, it says Memory 1.25 GB, Bus 133 MHz; yet under the Memory tab it breaks down the individual modules as 133, 100, and 100.
  15. Sun Baked macrumors G5

    Sun Baked

    May 19, 2002
    It isn't running the FSB and the memory bus at two different speeds, it is running it all at 133MHz.

    No throttling up or down depending on the RAM you stick in.

    If there was a problem, the machine either wouldn't recognize the DIMMs -- or you'd get kernal panics.

    With the PPCs, there is no real BIOS setting for overclocking RAM -- you need to hack the machine or change a jumper with a soldering iron.
  16. jwt thread starter macrumors 6502

    Mar 28, 2007
    So basically it either runs at 133 or doesn't at all, i.e. the module doesn't register as even being installed?
  17. Anonymous Freak macrumors 603

    Anonymous Freak

    Dec 12, 2002
    Another possibility is that in the PC100/PC133 era, SPDs were not 'required', and many modules didn't have SPDs at all. It's possible that your aftermarket sticks do not have SPDs, so the G4 just reports them at the 'lowest common denominator' speed of PC100.

    I'm not sure about the 133 MHz bus G4 Macs, but most computers in the PC133 days could run their memory bus at 100 MHz or 133 MHz, regardless of the bus speed of the processor. This was because PC133 was defined as a JEDEC standard very late in life. (Basically, PC100 was a standard for quite a while, and memory manufacturers were creating 133 MHz RAM and calling it "PC133" well before the JEDEC actually approved a standard.) So chipsets had to expect that they might run into 'nonstandard' PC133 that would need to run at 100 MHz.

    Also note that all 166 MHz bus "SDRAM" (non-DDR) Macs use 133 MHz RAM, since there was no "PC166" standard. (In the 166 MHz bus, DDR RAM models, some used PC2100 (133 MHz DDR,) some used PC2700 (166 MHz DDR.))

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