I just software overclocked my G4 400 to 533MHz!

Discussion in 'PowerPC Macs' started by grabberslasher, Apr 23, 2003.

  1. macrumors 6502

    I just software overclocked my Rev A. G4 400 to 533MHz!

    Well, sort of. Following instructions on XLR8yourmac.com I went into the Open Firmware prompt and typed in a few commands to increase my system bus from 100MHz to 133Mhz.

    Suddenly on restarting my G4 it happily proclaims to be a G4 533MHz in About this Mac and Apple System Profiler (10.2.5).

    I was in a state of shock at first - over 25%. The XLR8yourmac article stated that it probably wont work over 50MHz but I have been running it at that speed for a few weeks now with less than 1º increase in heat.

    Has anyone got any comments/suggestions (apart from EVACUATE!).

    For those interested - these are the commands I typed (from xlr8):

    "How to edit and store the NVRAMRC for 133MHz bus

    (1) Boot by holding down "Cmd" + "Opt" + "O" + "F" keys to enter the OpenFirmware terminal.

    (2) Enter the NVRAMRC editor. (<return> shows you should type "return" key)
    nvedit <return>

    (3) Type following script exactly (including spaces).

    " /" select-dev <return>
    7efdc44 " clock-frequency" get-my-property 2drop ! <return>
    " /cpus/PowerPC,G4@0" select-dev <return>
    1fca0554 " clock-frequency" get-my-property 2drop ! <return>
    7efdc44 " bus-frequency" get-my-property 2drop ! <return>
    1fbf711 " timebase-frequency" get-my-property 2drop !

    (4) Type "Cntl" + "C" to exit NVRAMRC editor.

    (5) Save the script
    nvstore <return>

    (6) To enable the NVRAMRC, type this command.
    setenv use-nvramrc? true <return>

    (7) Reboot with new timebase constant.
    reset-all <return>

  2. macrumors 6502

    Can you provide a link to the article? I'd like to know of a way back when things go wrong. It's a cool hack!
  3. macrumors 6502

    To undo

    See the last step of the post:

    "setenv use-nvramrc? true"

    To undo any changes just type:
    "setenv nvramrc? false"

    All it does is tells the Open Firmware to run a setting script at startup.

    To completely reset it just zap your PRAM -
    Hold command-alt-p-r at startup.

    Wait a minute while I get the URL.
  4. macrumors 6502

  5. macrumors 6502a


    They say it does not work for OSX though.:( That sucks.
  6. macrumors 6502


    Of course it runs in OS X - as I said, I am using 10.2.5. It doesn't run on OS X prior to 10.1.1 (I think) - but who in their right mind would use such an early version of X at this stage?

    Don't flame me for saying that!
    It works perfectly - especially with it's new Geforce3Ti 64Mb graphics card and extra RAM - 384Mb.

    The article also states that it will only read from two RAM slots and you must have 133MHz Ram to use it.

    I have only the original RAM with my machine and all 4 slots are fully used after the hack.
  7. macrumors 6502


    If you want screenshots/photos to prove it I can show you. The serial number on the back of the machine will prove that it was a 400MHz machine.
  8. macrumors 6502a


    Re: What?

    Sorry, I misread that part.
  9. macrumors 6502


    Of the 120+ people who have viewed this thread do any others have any comments?

    Say something...
  10. macrumors 65816


    Re: ?

    Yeah, I do.

    I have a Sawtooth G4 500, processor upgraded to 1.3Ghz, with the processor jumpers set for a 100Htz bus, anyone know how applying this hack would affect that?
  11. macrumors 6502

    I could tell you if I knew your multiplier (for your upgrade card).

    Your original multiplier is 5 (5x100Mhz) so your upgrade card must be 13(?!). I'm not sure, but multiply 133MHz by 13 for your end result.

    1.729 GHz!

    But I doubt that the hack will apply to your upgrade card. More likely it will only overclock your 500MHz (to 665). There's no harm in trying - I don't think a simple hack such as this can damage your computer. All it is is basically a startup setting.

    True speed increase though.
  12. macrumors member

    I tried it and nothing happenened.Igot a G4 Sawtooth,too.Don´t I have to press return after

    1fbf711 " timebase-frequency" get-my-property 2drop !

    And what does type "Cntl"+"C" mean?
    Directly after the line I quoted before?
    So I have to type "Cntl" "C"?
    What is this + for?Do I have to type it too?My god,this is not that easy
  13. macrumors member

    Anyway,#i give it a try again.
  14. macrumors member

    I tried again and nothing changed.Maybe I had some typos,I do not know.It is hard to see sometimes if I have to type space or not.
  15. macrumors 6502

    Re: Re: ?

    Well, this hack basically overclocks the bus to 133, so it might help the upgraded processor indirectly. You will have to change the multipliers on the Gigadesigns card to the 133mhz bus versions to get 1.33ghz. I bet it would help your performance. The only reason it "overclocks" the processor is the bus running faster. Most of the time when u overclock the bus you downclock the multiplier on the processor so you dont fry it.

    I might try it on my sawtooth 500, I can't permanently break anything if it doesn't work right? and if I do, it would just be the processor right? I was planning on gettin a faster one anyway....
  16. macrumors regular


    Will this work on a 667 PB? My baby is starting to show its age.
  17. macrumors 6502

    Cntrl C means press
    the control button and c at the same time. Like command-c for copying.

    Trust me, it does work.

    Yes you must press return after each line. Spaces are also important.
  18. macrumors member


    WOW. I just tried this on my AGP G4 400, and it worked!!! I attached a screen shot to prove it. It shows 133mhz bus and a machine speed of 533mhz. I cant tell if it is any faster so far. Is there a way to test this? Hey, other guy that did this, does yer machine seems faster? Let me know.
  19. macrumors 65816


    I tried the similar hack on my MDD 867, and the computer presented info of a faster bus, but the machine was not running any faster.

    Do a pair of XBench tests to see if there is an actual difference going on.
  20. macrumors member

    Sorry, here is the screen shot. I will do xbench now and compare the results.

    Attached Files:

    • picj.jpg
      File size:
      96.8 KB
  21. macrumors 6502

    me hate windows


    i am still confused about the ram, would my pc100 still work?
  22. macrumors member


    About the RAM, when i did the hack all 4 of my ram modules were recognized! Sadly, when i used xbench on the computer while the hack was applied my xbench score was only 46.24, which is lower than my original xbench test score of 50.03 taken just before applying the firmware hack!! I don;t understand why this would actually SLOW DOWN my machine, even if it just was displaying fake information. Well, it didnt seems to do any harm, and zapping the p-ram returned my system to normal. I guess others could give it a try and see if they get better results, but i doubt this actually does anything beneficial.
  23. macrumors 68030


    Re: I just software overclocked my G4 400 to 533MHz!

    Be careful... technically a "Rev A. G4 400" is the Yikes G4, not the Sawtooth.

    Fortunately I know that this would not work on my Yikes G4 (as the Yikes is overclocked by changing the jumpers on the mobo), but if someone else with a Yikes G4 came along and tried this, it could possibly screw up their computer. (Not sure about that, but messing with OF is never a light matter...)

    Anyways, I would suggest clarifying that by "Rev A." you mean Sawtooth.
  24. macrumors 6502

    I don't see why the 350MHz G4 (Yikes) would be classed as a Rev A. - it came out at the same time as the Sawtooth model.

    Let's just say "early Sawtooth G4s" (originally 400-450MHz after Apple reduced the speeds of the lineup).

    In other words - if you have a Sawtooth G4 with a green glowing power button you can do this.

    It is untested on later G4s (white glowing power button).

    I tried the X bench tests and got a score of about 52.4 on mine (compared to about 49). I don't see why yours might have slowed down. Interesting.
  25. macrumors 6502

    I just checked my G4 - one of my newer RAM sticks is actually 133MHz RAM. Maybe it only speeds up your computer if you have faster RAM. I'll try taking out the stick and checking X Bench.

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