Blue RAM

Posted:
in Current Mac Hardware edited January 2014
You know, I've been looking closely at the G5 innards, in all its glory, and it would be great to have some RAM with a blue PCB to match the motherboard. Does anyone know where I can get some? Someone could make a killing selling it for Macs...

Comments

  • Reply 1 of 5
    Quote:

    Originally posted by chrismusaf

    You know, I've been looking closely at the G5 innards, in all its glory, and it would be great to have some RAM with a blue PCB to match the motherboard. Does anyone know where I can get some? Someone could make a killing selling it for Macs...



    Mushkin's midrange PC3200 DDR RAM has a blue PCB, but I wouldn't pick it just for the color of the board. Their higher-end (black Level 2) RAM is much better.



    -- Mark
  • Reply 2 of 5
    What is the CAS latency of the OEM g5 RAM? Is it 2.5? 3? Would someone with a G5 check.... hopefully it is marked on the chips.



    Is it worth it to use (more expensive) CAS-2 RAM like this?
  • Reply 3 of 5
    Quote:

    Originally posted by flyhigher

    What is the CAS latency of the OEM g5 RAM? Is it 2.5? 3? Would someone with a G5 check.... hopefully it is marked on the chips.



    Is it worth it to use (more expensive) CAS-2 RAM like this?




    You can determine the CAS latency with the Apple Hardware Test CD that comes with the machine.



    However, CAS 2 RAM will only buy you a tiny performance improvement (maybe 5% at most) and can be MUCH more expensive.



    -- Mark
  • Reply 4 of 5
    A more interesting question to me is, would this DDR4000 500Mhz memory allow the 1Ghz G5 bus to reach full speed?



    I assume the interleaved 400Mhz RAM (800Mhz effective speed) that comes with the machine is causing a lot of "wait" cycles.









    it was the world's fastest computer when I ordered it!
  • Reply 5 of 5
    Quote:

    Originally posted by hawkman

    [B]A more interesting question to me is, would this DDR4000 500Mhz memory allow the 1Ghz G5 bus to reach full speed?



    I assume the interleaved 400Mhz RAM (800Mhz effective speed) that comes with the machine is causing a lot of "wait" cycles.



    The 1 GHz HyperTransport bus connects the G5 to the peripheral controllers, including the U3 IC which is the RAM controller. RAM on the G5 systems is either DDR 333 (for the 1.6) or DDR 400 (for the 1.8 and dual 2).



    RAM with a higher speed spec CAN be clocked faster, but the system wouldn't do so. On a PC, you may or may not have a control for the RAM clock in the BIOS, but on a Mac you have no control over it.



    In any case, overclocking the memory wouldn't help: 20% of the bandwidth on the Hypertransport bus is used for signalling, so the remaining 80% (at least on the dual 2 GHz) matches the RAM's peak bandwidth. Speeding up the RAM would just saturate the HT bus.



    In fact, on the 1.6 and 1.8 machines the RAM is able to pump out data faster than the HT bus can carry it.



    Also, it's not necessarily good to buy RAM faster than PC3200 for a G5. You have no manual control over the CAS latency, and the SPD system, which tells the computer what timings your RAM will support, uses fractions of the RAM's rated speed to indicate timings.



    Because of this, timings in the SPD system for faster RAM will generally be more cycles than are optimal, because PC4000 (500 MHz DDR) RAM cycles are shorter than PC3200 cycles and the SPD values on PC4000 RAM use PC4000 cycles to measure timing. On a PC, this is no problem because you use the SPD values as a guide and set the timing yourself, by hand, in the BIOS. On a Mac, where you can't override the SPD timings, these timings measured in the faster PC4000 cycles will be misinterpreted as slower PC3200 cycles, and this will just slow things down more than if you bought PC3200 RAM made with the same chips.



    -- Mark
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