With jumpers instead of the jumper block, here's the original 400 MHz config.
the JoshMeister™'s
Mac Overclocking Page
** IMPORTANT DISCLAIMER: I don't recommend attempting anything mentioned on this page; the content of this page and the links provided are for informational purposes only. By attempting anything outlined on this page or a linked overclocking site, you agree to take full responsibility for your actions. Please note that doing some of the things outlined on this and linked pages may void warranties. Do not attempt to clock your computer, change cache or bus speed, or anything similar unless you are willing to take the risk of destroying your hardware. **
Last updated 21 December 2005.
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Overclocking a Blue & White Power Macintosh G3/400
B&W G3/400 | Performa 640CD | Tips & Tricks | Links
When my friend Ben got a 450 MHz G4 Cube, I got jealous. I have a B&W "Yosemite" G3 with a 400 MHz processor, which is a pretty good machine. However, when one of my best friends became the owner of a better Mac than mine, I began to want a G4 to be able to take advantage of AltiVec (aka Velocity Engine), and an extra 50 MHz or more would also be cool.
Well, a G4 ZIF upgrade was way out of my price range at the time, and a G3 ZIF upgrade costs almost as much but doesn't have AltiVec. (Frankly, ZIF upgrades aren't all that cheap even as of late 2005, when you consider the price/performance ratio compared to buying a new computer.) A while back I'd read a bit about overclocking, and I remembered a site called "Accelerate Your Mac" (www.xlr8yourmac.com). I checked it out again and went to the pages on G3 overclocking. Following the instructions outlined there, I decided that it was worth voiding my warranty (if it hadn't expired already) in order to get some extra speed. All it would take was changing a few jumpers, and I should be able to overclock it at least 50 MHz, no problem. Well, that's what I thought, anyway.
With jumpers instead of the jumper block, here's the original 400 MHz config.
I pulled off the OEM jumper block and added my own jumpers (under $1.50*, Radio Shack #276-1512A or 276-1512, AKA "DIP Programming Shunts"), and decided to try my luck and clock my G3 at 450 MHz instead of the original 400 MHz (jumpers 4, 5, 6, 8, and 9 instead of 1, 3, 5, 6, 8, and 9; a table of jumper settings can be found at xlr8yourmac.com, partially mirrored at lowendmac.com). It worked!! Well, for short periods of time, anyway. After leaving it on for a while, or bringing my distributed.net client to the front, or especially when playing the demo of Unreal Tournament, my poor G3 would drop into MacsBug with a Bus Error or freeze up altogether.
*Any prices herein are approximate U.S. dollar prices at the time of purchase and may not accurately reflect current prices.
One time when I happened to have the Powerlogix G3/G4 Cache Profiler open, I saw that the processor temperature was reported as 40 degrees Celsius at the time of the crash, higher than I'd ever seen it before. Normally it stayed between 35 and 39 degrees Celsius when clocked at 400 MHz.
I went again to Radio Shack within about an hour of trying to overclock my G3, and picked up a Pentium CPU Cooling Fan with heat sink (about $15, RS #273-248, no longer being sold as far as I can tell). I took it home and disassembled it, screwing the fan onto my G3's heat sink and plugging it in where the hard drive was getting its power, and then piggybacking the hard drive onto it.
Then I had to decide what to do with the heat sink. It didn't seem like it would cool my processor any better than the standard one, so I removed the mounting clip and placed the sink next to my G3's heat sink, touching what was exposed of two chips on the processor board. (According to Mike from Accelerate Your Mac, these are the "cache chips"—L2 cache I believe—and he warns, "make sure no metal contact [sic] with the leads.") I then bent the mounting clip and held the new sink in place by bridging the clip somewhat tightly between the G3's sink and the Pentium sink.
(1) Warranty seal, (2) Pentium sink on 2 chips by CPU, (3) Pentium fan on G3's heat sink.
I powered on and tried it out for quite a while (still at 450 MHz, in hopes that cooling was the only issue and that the new additions would be sufficient). I don't think the distributed.net client crashed after that, but Unreal Tournament demo and Excel still crashed after using them for a while. I set the jumpers back to 400 MHz and left the new fan and sink installed.
Total cost so far: over $16.50 after tax. Benefits so far: basically none.
Next, I took another trip to Radio Shack and bought a small tube of silicon-based thermal grease (about $2, RS #276-1372). I applied a semi-thin layer of grease to the bottom of the G3's heat sink, so that when it touched the processor it would have every part touched by the grease. (Note: Many OCing sites tend to vaguely specify applying "a thin layer" of grease. It seemed logical to me to make the layer not as thin as possible, but just thin enough that the sink touched the entire face of the processor, as evidenced by where the sink left a grease mark behind after pressing it down.) After initially applying the grease and turning the computer on, the processor temperature was reported as 31 degrees Celsius (perhaps because the grease was cold when fresh out of the tube), which quickly increased to 35, and eventually went to 39 after more use.
One night I mounted a standard Holmes Air brand desk fan, about 8.5 inches (22.6 cm) in diameter, approximately 6 inches (15.2 cm) away from the right side panel of the case. I tilted it slightly downward so more air could blow underneath the case. (I got this idea after reading about the G-Riser by Contour Design, which raises a G3/G4 tower case a few inches and is supposed to "result in cooler operation and greater system reliability and longevity.") After heavy processor usage that night, the processor stayed at 35 degrees instead of going up to 39 like usual!
The next day, however, the processor temperature went to 39 degrees Celsius again after some heavy usage. Apparently, the desk fan helped a little bit, but was more efficient when the air outside the case was cooler to begin with. Disadvantages: It's certainly not as glamorous as an in-case solution, and on the High setting it's a bit louder than I would prefer.
Later I obtained two Cyber Cooler ATX ball bearing case fans (80 mm, 36 CFM for each fan). The cost including shipping was $14.95 (bringing the total monetary cost of the project to about $33.50; I didn't buy anything after these fans). I had to "ghetto-rig" (in the words of my PC overclocking friend) the fans in the case. I used twist-ties and clear tape in order to mount the fans sturdily. I set up one of the fans so it rested on the little ledge next to the standard internal fan, and I attached the other to the bottom of the Zip drive, facing the back of the case. Both fans blew air onto the heat sink and processor. Since installing the fans, the processor temperature was consistently reported as 35 degrees C when clocked at 400 MHz.
Glamor shot of the 80 mm case fans I installed.
For the first time after installing the Cyber Cooler fans, I tried 450MHz. This time I changed the L2 cache ratio to 5:2 (180 MHz) rather than the standard 2:1 (200 MHz). I changed this setting using G3/G4 Cache Profiler from Powerlogix. Temp was 39 degrees C immediately after booting. Able to run Unreal Tournament Demo for a while without crashing or temperature increase. [Weird side effect (possibly related to G3/G4 Profiler INIT): Extensions Manager would crash with Error Type 2 upon first open. Next open would crash Finder, and give a strange error message -- the typical "There are extensions installed that are not in this set" dialog, except the letters in the sentence w e r e s p a c e d o u t like so! To try to remedy this, I restarted holding space bar, got the message (sans weird spacing), and had it Update the extension set. After bootup, I opened the Extensions Manager and was disappointed to get another crash, this time Type 1. Normally Type 1 (in my experience) rarely has to do with amount of allocated memory, but I upped EM's preferred memory to 512K from 484K and it didn't crash again.]
Finally, a little while after trying UT Demo, the frontmost application crashed (ironically as I was typing results for this page) with same error message that I used to get after a while when trying to run at 450 MHz: "Unimplemented Instruction at 00000000." The only way to recover from such a crash is to force-restart the computer. Discouraged, I set the cache ratio back to 2:1, disabled G3/G4 Profiler INIT, and set the jumpers back to the standard 400 MHz setting. The temp was back to the normal 35 degrees C.
Since then, I rearranged the Cyber Cooler fans in the case. The one attached to the bottom of the Zip drive is still blowing onto the processor/heat sink (facing toward the back of the case). However, I decided to move the other fan so it could blow hot air out of the case. To do this, I removed two metal PCI slot covers (the bottom two, leaving one still covered, and the top one occupied by the SCSI card). I then carefully fastened the second fan to the slot openings, making sure to leave clearance so that the case could be closed all the way. It took some tweaking to get the case to close as it should, but I accomplished the task.
Knowing that hot air rises, I thought that I might gain some benefit from siphoning hot air from the top of the case down and out through the bottom fan. I cut an old flexible tube to the right length and tried to position it so that it could suck air from the top of the case out through the fan. However, this was much more trouble than it was worth: having the tube installed didn't decrease the processor temperature, and likely didn't do any good for the overall case temperature because of the blockage of airflow it caused. Plus it was very difficult to open the case with the tube attached to the fan. I decided to remove the tube.
I've considered peltier cooling. However, the maximum output of the G3's power supply is 200 watts, and peltiers generally recommend 300 watts. Thus, the only way to properly add a peltier would be to either swap in a better power supply (not practical), add a second power supply in the case (impossible, wouldn't fit), or get a cheap PC case with a 300+ watt power supply and power the peltier from that (possible, but not very practial). A PC tower case would allow me to house my external SCSI CD-RW drive in addition to powering the peltier, but a second tower would take up precious desk space (and with wires and cables going between the cases, it would look very "ghetto").
Considering the potential dangers of peltier cooling, this potential solution seems a bit extreme -- especially considering the possibility that 400 MHz may be the max that my particular chip can handle. (As mentioned several times on www.xlr8yourmac.com, even chips in the same batch can have different maximum clockable speeds.)
Interesting note: 8 May 2001 was a very hot day in my area, and the extreme external temperature brought my processor temp up to 42 degrees C (107 degrees F) according to Gauge Pro -- even with the desk fan on High. (Typically it has stayed around 38 degrees C recently. This is at the default 400 MHz clock speed.) The system seemed to run fine despite the heat, so this leads me to believe that heat alone is not why my machine is unstable at 450 MHz. Another interesting thing I noticed was that if I quit my distributed.net client, the temperature dropped to 38 degrees C fairly quickly. Upon relaunching the program, the temp would reach 42 degrees again within a couple minutes. I wonder if my system would be more stable at 450 MHz if I wasn't running the distributed.net client.
Norton System Info 6.0 ratings (processor MHz/L2 ratio/bus MHz):
I'm curious why the slower L2 cache seems to have resulted in faster CPU performance for 400/5:2/100 than for 400/2:1/100. (Note: All tests had 4096K disk cache and VM on, against System Info recommendations.) *Note that this configuration seems to be unstable on my test system. **FPU for 400/2:1/100 scored 905 in later tests, which I consider to be more accurate.
Note: I've discovered that Newer Technology Gauge PRO 1.1 seems to give a more accurate temperature reading than PowerLogix G3/G4 Cache Profiler 1.3 and Sonnet Metronome 1.4.5. Unfortunately, Newer Technology has ceased operation as of December 2000. I have mirrored Gauge PRO 1.1 here (80K). [Note: This program does not run natively in Mac OS X or in the Classic environment. I have yet to see a free app for Mac OS X that accurately reads my G3's processor temperature.]
On 30 October 2001, I read a couple articles on AMDMB.com (now pcper.com) referenced by Slashdot, and I decided that they're well worth mentioning here:
After reading these articles, I decided to again rearrange my Cyber Cooler 80 mm fans. I turned around the one attached to the PCI slots so that it would blow air into the case instead of out of the case. I thought this might help improve internal air flow since the power supply (at the top of the case) blows air out. Next I moved the fan attached to the bottom of the Zip drive so that instead of blowing air sideways onto the G3's heat sink, it would blow air from the side of the case opposite the door onto the heat sink/fans -- this is close to where I originally put the other Cyber Cooler fan. (Before this latest rearrangement, I had suspected that the fan might have been counterproductive where it was because it had been opposing the heat sink fan in airflow direction.)The same day, I decided to look up some info on certain chips on the motherboard, to see what might be worth getting a miniature heat sink for. Here's what I found out:
(4) Motorola Grackle XPC106, (5) Sharp ROM.
I personally don't plan to try to get a mini heat sink for the PCI/memory controller because the only safe way I know how to attach it would be to epoxy it, and I don't want to put any kind of epoxy inside my case, thankyouverymuch.
7 February 2004 - It's been a couple of years since I last tried to overclock my G3. Now I'm running Mac OS X 10.3, which is a much more advanced and robust OS than 9 ever was. Since I was junking my Performa (the same one I had cooled previously -- see below), I took out the old heat sinks and fan (one sink being the thin one on the 80486 processor on the OEM PC compatibility card). I thought about the possibility of putting the 486 heat sink on the Grackle PCI/memory controller, as mentioned above. It was the perfect fit! My previous concern about adding a sink to the controller was that I wouldn't be able to safely get the sink to stay in place. Well, this particular sink fit snugly and stayed in place with some heat sink compound and a tiny drop of superglue attaching a corner of the sink to the white plastic ZIF base. Beautiful! Now it was worth a try to overclock again.
...And so far so good this time! I've run SETI@home (which takes 100% of the unused CPU cycles and uses them to analyze data to aid the Search for Extraterrestrial Intelligence) for hours straight without experiencing a crash. I've also been using the computer for various everyday tasks without problems so far.
So what's the speed increase? Unreal Tournament framerate is about 5 frames per second higher (about a 7 percent increase). The benchmarking tool AltiVec Fractal Carbon indicates that the processor runs about 27 MegaFlops faster (an 8.6 percent increase). I haven't yet booted in OS 9 to see if it would eventually crash like it used to when running at 450 MHz, so I don't yet know if OS X or the heat sink on the Grackle or a combination of the two (or some other factor) may be responsible for allowing me to overclock to 450 MHz without abnormal crashes.
I cannot test the processor temperature since there are no utilities that are compatible with my machine under OS X. Your mileage may vary -- VersionTracker has a list of temperature testing apps for OS X.
Here's the current configuration (presently working without crashing at 450 MHz, up from 400 MHz):
I added the fan and the two black heat sinks. The smaller black heat sink is on the Grackle PCI/memory controller.
I added both of the big Cyber Cooler fans. The fan attached to the empty PCI slots blows air into the case. The other fan blows air onto the heat sinks. Both are nicely ghetto-rigged with twist ties.
13 February 2004 - Here's my summary writeup for xlr8yourmac.com:
After many, MANY failed attempts to overclock my G3/400 to 450 MHz, I've finally had success. It's been running flawlessly at 450 MHz for several days now, even under heavy processor loads (hours on end at 100% load). All the details (plus pictures!) of what my final working configuration is (and what didn't work) are available at my overclocking page: http://users.aol.com/furballguy/oc/ To give a very brief summary (although I recommend you read my page if you're interested in overclocking a similar machine, or overclocking in general): *I added a cooling fan to the stock G3 heat sink *I put silicon-based thermal paste under the G3 heat sink *I added a Radio Shack Pentium heat sink with thermal grease to the CPU card chips by the processor *I added two big 80 mm fans to improve air movement in the case *I added a low-profile 80486 heat sink with thermal compound to the Motorola Grackle PCI/memory controller *I upgraded to Mac OS X 10.3.2 Upgrading to Mac OS X from OS 9 may perhaps be significant; my failed attempts had been with Mac OS 9, and I notice in the System Profiler under Software> Extensions that AppleGracklePCI, AppleGossamerPE (which Apple calls "a Platform Expert for the Blue and White G3 computer"), and other extensions related to my hardware have been updated within the past year or two. Also notable was that this was the first time I had tried to overclock after adding a heat sink to the Grackle PCI/memory controller, which I had suspected could possibly help -- the fact that I found the perfect sink for it was what got me to try overclocking my G3 again. Tons more info with photos on this overclock (and a little writeup on how I got my old Performa 640CD to run cooler and keep it from lagging after being on all day -- using a modified 486 heat sink and fan!) are available at my page above. Good luck, overclockers! -tJMMike from Accelerate Your Mac commented that the heat sink on the PCI/memory controller should not have been necessary since I only overclocked the CPU and not the system bus. This is true, but since that chip seemed to be one of the hottest on the board I felt that it wouldn't hurt to keep it a bit cooler to potentially keep the system a bit more stable. I can't verify whether this has helped stabilize the system significantly, if at all, but I've kept the heat sink in place anyway.
21 December 2005 - It's been over 22 months (close to 2 years) of running at 450 MHz, and I still have not seen any related system stability problems. My G3 is currently running Mac OS X "Tiger" v10.4.3 without any problems (and quite smoothly for such an old machine; I'm glad that Apple has continued to support the Yosemite G3 for the past several OS updates).
Cooling a Performa 640CD DOS Compatible
B&W G3/400 | Performa 640CD | Tips & Tricks | Links
Once upon a time, my Performa 640CD DOS Compatible didn't run well after staying on all day. After being on for several hours, it would always act very sluggish until shut down. At this time, I had no experience computer cooling, so I took a look at the Web. I read about heat sinks, and since I had an old heat sink/fan designed for a PC 80486 processor handy, I decided to modify it and try it out. Here's how I modified it:
Sketch of my modified 80486 heat sink (bottom view).
The gray is where I filed down the protruding corners. After filing the corners like so, I placed thin strips of double-sided sticky tape side-by-side on the bottom of the heat sink (at this time I wasn't aware of heat sink clips or thermal paste). I then put the sink slightly offset onto the Mac's 68LC040 processor, so that the half-corners of the sink touched the edges of the processor:
Sketch of the sink on the processor (ratio of processor to heat sink size is not to scale).
I made sure that the heat sink was secure. I then plugged in the fan where the hard drive gets its power, and piggybacked the hard drive onto it. I can now run my Performa all day without a slowdown! My first attempt to cool a processor to make a machine run more reliably was a success.
Years later, I bought an 040 Chiller from Output Enablers (specifically designed for the Mac's 68040 and 68LC040 processors) for my girlfriend's aging Performa 575. While $20 seems a bit pricey for improving an old system (apparently it's now only $10 as of December 2005), it was nice to have a sink that actually fit on the processor without modification. The 040 Chiller came with some documentation which would be helpful to newbies. If you're not as adventurous as I am, you might prefer to go the 040 Chiller route instead of modifying your own 486 heat sink. However, doing the latter will be fun, and you can brag about it to your slightly less techno-savvy friends and make them think you're some sort of genius comparable to Einstein. =)
Tips and Tricks
B&W G3/400 | Performa 640CD | Tips & Tricks | Links
Links
B&W G3/400 | Performa 640CD | Tips & Tricks | Links
If you have any personal experiences with overclocking that you'd like to have shared on this page, or to give me some advice related to overclocking or computer cooling, or to let me know of other good Mac overclocking sources not listed in the above Links, please e-mail me to let me know!
©2000-2005 the JoshMeister. All rights reserved. Attempting certain things mentioned on this page may void any warranty you may have on your computer or its parts. the JoshMeister™ has provided this information for educational purposes only, and does not support or recommend overclocking. Overclocking is risky business, and can in some circumstances result in hardware failure. Do not attempt to overclock or underclock your computer, change cache settings, change bus speeds, or change other hardware settings unless you are willing to take the risk of destroying your hardware. Always make backups of your important files before attempting anything potentially dangerous.