Low End Mac Reviews

Boosting a 'Digital Audio' Power Mac with a 1.6 GHz Dual G4 Upgrade

Dan Knight - 2009.03.11 (updated 2009.07.06) - Tip Jar

We're putting together an in-house development server at Low End Mac headquarters. The original plan was to use our dual 500 MHz 'Mystic' Power Mac G4, max out memory to 2 GB, get a copy of OS X Server, and maybe find a low cost CPU upgrade. We mentioned this on the LEM Swap List, and received several donations - including a "bare bones" Power Mac.

The 'Digital Audio' Power Mac G4 was the first Power Mac with a 133 MHz system bus, a step up from the 100 MHz bus in earlier AGP Power Macs. This machine started out with a single 533 MHz G4 CPU, which we've already benchmarked. We're comparing that to a second-hand Giga Designs Dual 7447 G-celerator with two 1.8 GHz Freescale 7447 G4 CPUs. These CPUs each have an onboard 512 KB level 2 cache that runs at full CPU speed. This is the same CPU used in the 1.67 GHz G4 PowerBooks.

The upgrade is theoretically capable of over 3x the performance of this Mac's original 533 MHz CPU under the Classic Mac OS (which can only use one CPU) and over 6x under Mac OS X, which utilizes both processors. We ran an extensive suite of benchmark tests under Mac OS X 10.3, 10.4, and 10.5 to measure performance. (This upgrade requires a version of Mac OS 9 or Mac OS X 10.3.5 or later, although we were unable to boot into OS 9.)

As I began putting everything together, I began to wonder if I might not end up with a more powerful computer than the dual 1 GHz 'Mirror Drive Door' (MDD) Power Mac G4 that's been my workhorse machine for several years. More on that below.


The first step is preparing your Power Mac G4 for the upgrade. This discontinued upgrade is compatible with Sawtooth (AGP Graphics), Mystic (Gigabit Ethernet), Digital Audio, Quicksilver, and Quicksilver 2002 models. You first have to make sure that your Power Mac has Boot ROM 4.1.9 or later installed - choose "About This Mac" under the Apple menu, click on the "More Info..." button, and find the Boot ROM Version.

If you don't have version 4.1.9 or later (version 4.2.8 is strongly recommended), you can get it from Apple. Note that you must boot into Mac OS 9.x to update the Boot ROM. This is just another good reason to keep a copy of OS 9 handy - preferably on your Mac's hard drive.

The next step should be installing the 7447 Firmware Update, which is on the CD that comes with the upgrade. This is necessary because the 7447 CPU was designed after these Power Macs, so they can't take advantage of all it offers without a firmware update. However, the program never finished installing itself under any version of OS X, so we switched to the PowerLogix software, which can be freely downloaded from OWC. It worked!


The first thing I noticed about this upgrade is its weight. It's not large, but it is heavy. I weighed it on the postage scale, and it came in as just under 22 oz. with it's massive copper heatsink. The CPU can be set to several different speeds up 1.8 GHz using DIP switches, although I have not been able to achieve that speed.

Installation of the processor upgrade isn't difficult - all you need is a #2 Phillips screwdriver, needle-nose pliers, and a compatible Mac with OS X 10.3.5 or later installed. Before installing the upgrade, you attach a 2-fan cooling unit. Then unclip the heat sink from the Mac's CPU and remove 3 screws to take out the original CPU card. This upgrade is integrated; the heat sink isn't separate from the CPU card. The upgrade snaps into place, and putting the retaining 3 screws in is a breeze, unlike the last CPU upgrade I reviewed.

Once the upgrade is installed, there are two more steps: You need to set the DIP switches for your desired CPU speed and connect additional power to the CPU with the supplied cable.

I have done a lot of fiddling with the DIP switches - the first time I set them to 1.8 GHz, but the CPUs ended up running at 933 MHz. Other settings that should have resulted in higher speeds ended up at 1.33 GHz. The only setting that gave me the expected speed was 1.53 GHz with all 5 DIP switches set to the off position. I don't know if could be due to using the PowerLogix software instead of the Giga Designs software, which I was unable to install.

Anyhow, the system runs very reliably at 1.53 GHz and boots quickly into Mac OS 9.2, 10.2, 10.3, 10.4, and 10.5. It's also very fast.


My primary computer is a 'Mirror Drive Door' Power Mac G4 with dual 1 GHz 7455 CPUs, 2 GB of RAM, a 400 GB 7200 rpm Deskstar hard drive, and its stock ATI Radeon 9000 Pro video card. Subjectively, the dual 1.8 GHz upgrade in the Digital Audio (DA) feels every bit as fast for everyday tasks, and our Xbench test results (below) verify that.

Our testbed computer has an 80 GB 7200 rpm Deskstar hard drive, 768 MB of RAM, and it's stock ATI Rage 128 Pro AGP 2x video card. The drive has separate partitions for Mac OS X 10.3 "Jaguar", 10.4 "Tiger", and 10.5 "Leopard". Each has been updated to the latest version of that OS, and the only additional software we installed prior to benchmarking are System 9.2.2 for Classic Mode and the benchmark programs we ran.

The computer is booted, and the benchmark apps are then run in order.

User Experience

With its stock 533 MHz CPU, the DA isn't a fast computer under OS X, but it's usable. Drop in a fast dual processor upgrade, though, and that changes. Safari and Camino load fairly quickly, YouTube videos run smoothly, windows fly open, and it feels about as fast as our 1 GHz dual G4. With more RAM, it might feel even faster.

If you have an older AGP Power Mac that you're pretty happy with but lacks horsepower, a "brain transplant" is worth considering. I only wish this upgrade was compatible with my Mirror Drive Door Power Mac, as I would appreciate the extra speed on a daily basis.

The big question is the value of the upgrade: Is it worth $250 or $600 - or somewhere in between - to upgrade your older G4 Power Mac? After all, a CPU upgrade could cost more than the whole computer is work. It comes down a question of how much it's going to improve your productivity.

Other World Computing has a wide-ranging line of G4 upgrades using single and dual 7447A (512 MB onboard cache) and 7448 (1 MB cache) CPUs:

  • 1.6 GHz 7447A, $250
  • 1.7 GHz 7448, $329
  • 1.8 GHz 7448, $360
  • 2.0 GHz 7448, $400
  • 1.6 GHz dual 7447A, $450 (Xbench 1.1.3 = 175.0)

As fast as this upgrade is on a 133 MHz system bus, I have to wonder how much it might benefit from the 167 MHz bus in a Mirror Drive Door G4. Too bad there's only one CPU upgrade option for my Mirror Drive Door, a dual 1.8 GHz 7447A from Sonnet that sells for $600 - the same price as a brand new Mac mini with its 2.0 GHz dual-core CPU.

Mac OS 9.2.2

You can't boot into the Classic Mac OS with a dual-processor upgrade unless you remove the Multiprocessing folder from the Extensions folder. On startup, the computer will warn of a cache memory error - just click OK and move forward.

Speedometer 4

The Classic Mac OS only runs the slightest bit faster than Classic Mode on this dual-processor Power Mac.

        10.3.9  10.4.11  native
CPU      93.40    93.47    93.67
disk      4.85     4.92     4.83
math   3954.3   3960.0   4009.5

MacBench 5

The system was tested under Mac OS 9.2.2. Display run at 1024 x 768 and millions of colors. The disk cache was set to its default of 8 MB. Results are relative to a Power Mac G3/300, which rates 1000.

CPU   math  disk graphics
3714  3773  3508   n/a 

These figures show that our 1.53 GHz CPU is just 3.7x as fast as a 300 MHz G3. It is also 3x the performance of my old 400 MHz PowerBook G4 and twice the power of the stock 533 MHz CPU. All of these are less than predicted, but it's one wicked fast OS 9 machine.

Classic Mode in OS X

With the upgrade installed, the Mac won't boot into the Classic Mac OS - it reports a cache error and stops loading the OS. However, we can benchmark Classic Mode in Panther and Tiger. (Update: Gene Osburn wrote that the Multiprocessing folder must be removed from the Extensions folder. We did that, and now it boots into Mac OS 9.2.2.)

Apple does something unexpected with Classic Mode: In many ways, Mac OS 9.2.2 runs better inside Mac OS X than it does natively. Why? Because OS X handles all of the disk access, networking, and graphics, leaving OS 9 to handle the rest. Best of all, in a dual processor system, Classic is free to take over one CPU while leaving the other one to handle I/O in OS X.

Speedometer 4

With Classic Mode in Panther and Tiger, here are Speedometer 4 results:

        10.3.9  10.4.11
CPU      93.40    93.47
disk      4.85     4.92
math   3954.3   3960.0

Speedometer scores in Classic mode are virtually identical whether we're running Mac OS 10.3.9 or 10.4.11.

Mac OS X Benchmarks

Let 1000 Windows Bloom

The system was tested on 10 March 2009 at 533 MHz and also after installing the dual processor upgrade.

               533 MHz    1.53 GHz
OS X 10.2.8   49.7 sec. 
OS X 10.3.9   40.1 sec.   39.4 sec.
OS X 10.4.11  22.4 sec.   16.1 sec.
OS X 10.5.6   44.4 sec.   32.0 sec.

As we've seen before, Mac OS X 10.4 seems to be the best platform in terms of performance - approximately twice as fast as 10.3.9 and 10.5.6 with either CPU.

The system was retested on 6 July 2009 with the CPU upgrade running at 1.6 GHz, 1.25 GB of RAM, a Radeon 9000 graphics card, and an booting from an external FireWire hard drive. This benchmark ran in 14.0 sec. under OS X 10.4.11 (a 13% improvement) and 24.3 under 10.5.7 (a 24% improvement). The change in CPU speed can only account for 4.5% of that difference; the rest comes from the better graphics card.

Power Fractal

Power Fractal doesn't run under Jaguar. Under Panther, this test takes 7.0 sec. on the base computer and just 1.8 sec. with the CPU upgrade. Under Tiger, it reports 7.9 sec. with dual 450 MHz CPUs and 2.1 sec. with the 1.8 GHz upgrade. I suspect Power Fractal is only using one CPU.

                533 MHz       1.53 GHz
OS X 10.3.9   2096 Mflops   13176 Mflops
OS X 10.4.11  2079 Mflops   13065 Mflops
OS X 10.5.6   2043 Mflops   12534 Mflops

Power Fractal seriously takes advantage of dual processors, providing in excess of 6x the performance of the stock 533 MHz CPU. We also see increasing system overhead as we move from Panther to Tiger to Leopard - and corresponding small decreases in performance.

The system was tested on 6 July 2009 with a 1.6 GHz CPU, 1.25 GB of RAM, Radeon 9000 graphics, and an external FireWire hard drive. Power Fractal reported 13,290 MFlops under OS X 10.4.11 (1.7% better) and under 10.5.7 (6% better). The change in CPU speed should result in a difference of 4.5%, yet the score fall short of that under 10.4.11 while exceeding it with 10.5.7.

Xbench 1.3

Xbench 1.3 doesn't run under Jaguar, so we ran it under Panther, Tiger, and Leopard. Xbench is calibrated to a 2.0 GHz dual Power Mac G5, which would score 100.

            - - - 533 MHz - - -    - - dual 1.53 GHz - -
           10.3.9 10.4.11 10.5.6  10.3.9 10.4.11  10.5.6 
Overall    24.7    29.8    16.1    46.4    58.1    29.0
CPU        34.2    33.4    30.3    81.9    82.0    82.4
Threads    25.3    25.2    22.5    84.8   107.7    86.0
Memory     25.4    27.1    26.6    28.9    28.9    27.0
Quartz     29.7    29.9    20.0    27.8    57.6    32.6
OpenGL     53.0    58.4    13.7   103.7   108.1    31.3
User Int.   9.7    17.3     5.8    21.7    55.2    10.5
Drive      52.6    49.7    44.3    52.6    50.9    43.3

Under OS X 10.4.11, the overall score for the 1.53 GHz dual G4 upgrade is roughly double that of the single 533 MHz processor that came in the computer (and over half the power of a dual 2.0 GHz G5), but that's far from the whole story. The CPU score is 2.5 times as high, the Threads rating roughly quadruple, Quartz and OpenGL are almost twice as fast, and User Interface is over 3x as fast. Drive scores are barely changed at all.

It's interesting that the Threads, Quartz, and User Interface scores are highest under Tiger, yet Panther has a small edge in hard drive performance. Threads and Memory are higher with dual processors under Tiger vs. Panther but lower with the single CPU. Leopard doesn't do so well with half the overall score of Tiger.

By way of comparison, my dual 1 GHz "Mirror Drive Door" Power Mac G4 benchmarks 42.4 overall under Panther and 50.4 under Tiger (54.3 for the CPU). The CPU test score for the 1.53 GHz dual G4 upgrade is 51% higher than the 1 GHz dual G4 - exactly what you'd expect. However, Memory is over 30% faster on the Mirror Drive Door model (38.2) with its 167 MHz system bus (vs. 133 MHz in the DA).

The system was tested on 6 July 2009 with a 1.6 GHz CPU, 1.25 GB of RAM, Radeon 9000 graphics, and an external FireWire hard drive. While the overall 10.4 score is a bit lower than before, the Leopard score has improved significantly. Let's look more closely.

         10.4.11 10.5.7
Overall    56.3   45.7
CPU        86.3   86.3
Threads   114.2   75.0
Memory     28.4   30.7
Quartz     62.8   65.7
OpenGL     74.1   64.5
User Int.  48.4   21.6
Drive      53.5   53.7

We would expect CPU and Threads results to be about 4.5% better, and they're a bit better than that under 10.4. Memory results are almost the same. Quartz scores 9% higher, OpenGL is 31% lower, and the User Interface score is 12% lower. Drive scores with the FireWire 400 drive are 5% better than with the internal Ultra ATA66 drive used in earlier benchmarks. A real mixed bag of results under "Tiger".

Mac OS X 10.5.7 "Leopard", on the other hand, scores 57% better overall. That's huge! The CPU score is exactly what we'd expect based on the G4 upgrade running at 1.6 GHz this time vs. 1.53 GHz in earlier tests. Threads takes a 13% hit, but Memory benchmarks 14% higher. Quartz measures just over twice as fast, as do OpenGL and User Interface - the Radeon 9000 graphics really shines here. And the Drive score improves by an impressive 24%.

In contrast to Xbench scores using our 500 MHz dual G4 "Mystic" Power Mac, where the internal Ultra ATA66 drive outperformed the external FireWire 400 drive, this time around the FireWire drives are superior. Between a slightly faster CPU, a much more powerful video card, 512 MB of additional memory, and using a FireWire drive, we're seeing significant improvements.


Geekbench only runs on Tiger and Leopard. Here are our results:

                 533 MHz      1.53 GHz dual   1 GHz dual
             10.4.11 10.5.6 10.4.11 10.5.6  10.4.11 10.5.6 
Overall         362    321    1140   1116     894    939
Integer         406    354    1627   1598    1159   1131 
Floating Point  400    361    1288   1277    1015   1179 
Memory          314    265     495    443     495    470
Streams         177    187     214    214     351    342

Overall results show the dual 1.53 GHz upgrade provides over 3x the power of the original 533 MHz CPU, while the Integer score in Tiger shows the upgrade has 4x the power.

The dual 1 GHz G4 has an overall score of 894 (Tiger) and 939 (Leopard) - the upgraded DA Power Mac is 27.5% faster overall in Tiger, 18.9% in Leopard. It's interesting that the Memory results under Tiger are identical for the dual 1 GHz on its 167 MHz system bus and the dual 1.53 GHz upgrade on a 133 MHz system bus. This indicates the DA with the 1.53 GHz upgrade may be a suitable replacement for the dual 1 GHz MDD.

The system was tested on 6 July 2009 with a 1.6 GHz CPU, 1.25 GB of RAM, Radeon 9000 graphics, and an external FireWire hard drive. While the overall 10.4 score is a bit lower than before, the Leopard score has improved significantly. Here are the results:

               10.4.11 10.5.7
Overall          1218   1311
Integer          1673   1638
Floating Point   1471   1784
Memory            486    454
Streams           210    235

The improved graphics card and use of a FireWire boot drive should have negligible impact, and the 4.5% faster CPU should result in better Integer and Floating Point scores.

Under 10.4, the Integer score is just 2.8% better, but Floating Point results are 14% better. Memory and Streams are just a bit slower, and overall the system benchmarks about 6.8% better than before.

Under 10.5, the overall score is 17.5% higher. The Integer score is only 2.5% better, but Floating Point is nearly 40% higher, which points to some optimization in 10.5.7 vs. 10.5.6. This could be due to the operating system moving more graphics work to the graphics processor. Memory scores 2.5% higher, while Streams takes a 31% performance hit.

Where Next?

At present, the DA Power Mac suffers from too little memory (768 MB) to unleash the power of OS X and an antiquated video card. We hope to boost this to 1.5 GB of RAM using donated memory, and I suspect this will make it feel quite a bit snappier.

UPDATE: We have since upgraded to 1.25 GB of RAM.

There are two drawbacks to the older Power Macs:

  1. They don't support hard drives over 128 GB on the internal bus without third-party drivers, and I have two 400 GB drives in the MDD Power Mac. [UPDATE: Since moved to external NewerTech miniStack hard drive enclosures.]
  2. The ATI Rage 128 Pro video card is hopelessly outdated. (UPDATE: The 2002 Radeon 9000 makes a significant difference, doubling several graphics benchmarks. More modern graphics cards would do even better.)

We'll solve the first problem by moving both drives to external NewerTech miniStack v2 enclosures, which use FireWire 400 and will make it possible to move to a different computer easily. FireWire doesn't have the "big drive" problem, and being less resource intensive than IDE, FireWire drives could result in better performance than using the drives inside the computer.

We'll solve the second problem by swapping the ATI Radeon 9000 Pro from the MDD into the DA Power Mac. Since our server won't be doing any graphic-intensive work, it shouldn't matter that it will have an older, slower video card.

The end result may well be moving to the "Digital Audio" Power Mac for production and setting up the MDD as our in-house server. It's fast system bus, 2 GB of RAM, and twin 1 GHz CPUs should make it a great server.

Time will tell.


The Power Mac G4 line was the last family of PowerPC Macs that can readily take a CPU upgrade, and while the 350 MHz and faster G4 processors that shipped with them offered a lot of power in their day (the era of the Classic Mac OS), Apple never offered G4 Power Macs with 1.6 GHz to 2.0 GHz CPUs.

If you have a Power Mac G4 (Sawtooth through Quicksilver 2002) that you're happy with but need more horsepower, CPU upgrades are certainly worth consideration.

Only you can put a dollar value on increased performance and productivity. One huge plus to upgrading your current setup is that you don't have to worry about memory, drives, add-in cards, etc. not being compatible, because you're not migrating to a newer Mac. LEM

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