Recent Updates  | Mac Upgrades/Repairs  | CPU Upgrades  | Storage  | Video  | Audio/HT  | Apps/OS/Network
News, Tips, Reviews or Questions to News at Xlr8YourMac.com
G5 vs MDD G4 Features and Specs Comparison:Return to News Page


Comparison of G4 Dual 1.25 MDD vs G5 1.6 and Dual G5 2.0GHz
By Dave Linder
Posted: 1/23/2004 (part 1)
Updated: 5/14/2004 (Part 2: Performance tests)

The objective of this review is to highlight some of the issues and differences to consider when looking at purchasing some of the last G4/1.25 Duals or moving to the future with the newest G5 1.6 base model or the G5 Dual 2.0. Both G5 systems were kindly loaned to me from my local authorized Mac dealer Discount Mac Club in Richmond, BC.

While performance is always an important consideration, expandability, compatibility and features also play an important role. Now that all the new G5 models are available and there is also a new G5 Dual 1.8GHz model, you need to know what is the best value for your particular needs.

The Case
The basic concept of the G4 case started with the January 1999 introduction of the B&W G3 towers, and evolved over the years to the current MDD G4's The G4 MDD (Mirror Drive Door) towers supplied a number of features that people have wanted on their tower Macs for years, such as 2 externally accessible (optical) drive bays, a total of 4 internal hard drive bays and a front mounted headphone jack.

With the G5, Apple started from scratch with thermal and noise issues apparently a top priority. Even PC diehards were drooling when I showed off the G5 systems around the office, the look and feel of the hardware is no-nonsense, no cheap plastic or cheesy chrome looking parts here. The all aluminum enclosure is both beautifully clean and strong at the same time. The textured aluminum surfaces and thick rigid panels have a very impressive feel and look of quality, while the shape and clutter-free interior are elegant.

Pictures of the G5 really do not do it justice, I highly recommend that you visit your local reseller and take a look. The best photographic representation I have seen so far was by Bill Noll, even Apple had a link to Bill's site in their Hot News section. (Bill's G5 photo gallery was linked here last fall in the news page and added to the catch-all PowerMac G5 page.)

CPU and System Bus
The Dual G4 1.25 is equipped with 256KB of (onchip) L2 and 2MB of L3 cache per CPU. The system bus or frontside bus as it is also called, runs at 167MHz (non-DDR) for a theoretical maximum throughput of 1.3 GBps (shared by both CPUs), same as the G4 based Xserve.

The G5 1.6 has 512KB of internal L2 cache with no L3 cache. It does have however much faster and less congested bi-directional 800MHz system bus with a 6.4 GBps throughput, a major improvement over the 167MHz MaxBus G4 systems architecture with only 1.3 GBps throughput. The G5 1.8 and Dual 2.0 have the same cache size as the G5 1.6, but run their system buses at 900MHz and 1000MHz respectively. That gives the G5 Dual 2.0 a theoretical maximum throughput of 16 GBps. This high throughput is achieved in dual G5 systems through the use of a dedicated frontside bus for each CPU, unlike the shared frontside bus in all dual G4 systems. Even without all the improvements inside the G5 system IBM PPC970 CPU, the faster system bus allows the processor to communicate more effectively with the other systems on the motherboard such as AGP and PCI cards, hard drives, external ports and most importantly main memory.

A quick rundown on the CPU details of the G4 and G5 chips used in currently shipping systems:

    G4 or Motorola MPC 7455
  • 33 Million transistors, 0.18 micron process on a 106mm die.
  • 64K L1 cache, 256K of L2 cache on-chip, and externally up to 2MB L3 cache.

    G5 or IBM PPC970
  • 58 Million transistors, 0.13 micron process on a 118mm die.
  • 96K L1 cache, 512K of L2 cache on-chip, no L3 cache used.

You can see the G5 has many more transistors, some of them are used to boost the on-chip L2 cache to 512K. It is also apparent that even with the smaller 0.13 micron process, the G5 chips are physically larger and is one of many factors affecting the cost. The new G5 Xserve will use the first 0.09 micron chips from IBM, allowing the G5 Xserve to maintain the low 1RU profile and maintain adequate cooling.

The G5 was developed by IBM as a lower power single core version of the IBM POWER 4 processor, with the addition of an AltiVec core for SIMD instructions like the G4. With its 64-bit data bus, 48-bit address bus, the PPC970 CPU could access up to 4TB of memory, current Apple dual G5 systems are spec'd at a maximum of 8 GB of RAM. (Note: Max ram specs based on 1GB DIMMs. However the Apple G5 developer docs noted support for 2GB DIMMs, which are not generally available yet.)

The G5 has a 1 GHz bi-directional 64-bit wide DDR frontside bus reaching up to 8 GBps bandwidth per CPU, thus the G5 Dual 2.0 has a theoretical maximum of 16 GBps combined bandwidth. The G4 bus maxed at only 167 MHz, and this bus was shared in dual CPU systems reaching 1.3 GBps. This was one of the major limiting factors in the G4 system implementation, not the CPU itself but the data bus connection to the rest of the computer subsystems. With the G5, Apple has removed this limitation, and in doing so surpassed Intel's 800MHz P4 system bus.

The pipelines in the G5 CPU are wide so more instructions can be processed simultaneously in the 12 execution units, but also deep as up to 215 instructions can be in-flight at any one time. Compared to the 16 max in-flight in the G4, code not optimized for the G5 will cause delays by requiring the flushing of up to 215 instructions out of the CPU when the data cannot be handled in order. Branch mispredictions in the G4 only need to re-fill 7 stages, whereas the G5 needs to fill up to 23. (Note: See also the Apple Power Mac G5: Performance White Paper and G5 Performance Primer for more details)

Access to memory with the G5 incurs longer latency, but it accesses the memory bus at a higher data rate than any G4 system. G4 systems maxed out at 333 MHz with a 64-bit data bus reaching up to 2.7 GBps of memory bandwidth. The G5 1.8 and Dual 2.0 systems have 400 MHz PC3200 DDR SDRAM with a 128-bit wide data bus for a maximum of 6.4 GBps memory bandwidth. Memory in all G5 systems must be added in pairs, that is how the data path is widened vs. the G4 systems. Now the two 64-bit wide memory slots are accessed as one block of memory twice as wide at 128-bits. (See also the memory compat. notes previously posted here in the G5 tech info/compat. page, as some CL2/2.5 PC3200 dimms do not work in G5s.)

The 1.6 GHz G5 differs from the 1.8, Dual 1.8 and Dual 2.0 G5's in 2 ways other than CPU clock speed:

  1. The G5 1.6 supports a maximum of 4 GB of 333 MHz PC2700 DDR SDRAM, vs the higher models maximum 8 GB of 400 MHz PC3200 DDR SDRAM. It will be unlikely for most people to need more than 4 GB of RAM in the near future, but there is another factor to consider. The G5 1.6 has 4 RAM slots, 2 of which are populated from Apple, and 2 empty, so when you need to add RAM you should choose the size wisely as you will be filling all available RAM slots during the first upgrade. The G5 1.8, Dual 1.8 and Dual 2.0 on the other hand, come from Apple with 2 of the 8 slots filled, meaning that you will have 3 pairs of RAM slots to fill without removing any RAM to upgrade again later.

  2. PCI slot types differ and there has been a lot of confusion about this, so I have dedicated the PCI section below to explaining it in hopefully easy to understand terms. (See also the PCI compat. section in the previously posted G5 tech info/compat. page.)

The G5 systems are the first from Apple to make use of the HyperTransport protocol. The HyperTransport Consortium is a non-profit organization that promotes open, freely available industry specification for high bandwidth chip-to-chip communications. In the G5 systems, this means the interconnection of I/O systems to the system controller, such as analog and digital audio, Serial ATA, Ethernet, USB and FireWire. The bi-directional 800MHz bus has a maximum throughput of 1.6 GBps.

The G5 systems are the first Apple desktop systems to incorporate "Processor and Bus Slewing". The user can control this slewing mode in the Energy Saver system preference, where the choices are Automatic, Highest and Reduced. In the default Automatic mode, the bus speed, processor speed and voltages continually adjust according to demand, with processor speed varying from 1.3 GHz up to the rated clock speed. The result is lower power consumption, less heat and fan noise. (See the Apple tech docs section of the G5 tech info page here for more details.)

Apple states that the adjustment is carried out gradually and should not impact the performance of the system, but there are some types of work that do benefit from changing the mode to Highest performance as we will see in Part 2 of my review. When running Apple's high end software Shake 3 on G5 systems, Apple specifically recommends the Highest setting in Info Doc 93448. Another Kbase Doc 135001 states a benefit for the Highest setting for "applications that require sudden bursts of processor power (such as music and video-editing applications)". Digidesign also specifies "For optimal Pro Tools performance, you must set Processor Performance to Highest". It is advantageous to change the Processor Performance to Highest if you run high end applications on a G5, but of little benefit for more mundane tasks.

It is important to note if the system detects excessively high temperatures, it will override the chosen processor mode to lower the temperature, regardless of the user setting.

In the G4 systems you can add RAM one stick at a time, some older (pre-SDRAM) Macs used interleaving to get better performance if you add RAM in (like) pairs. In the G5 RAM must be added in pairs as the 2 modules are connected as one large 128-bit wide data connection, vs. individual 64-bit connections as in the MDD G4 systems. The MDD G4 memory is PC2700 DDR SDRAM giving a maximum theoretical memory throughput of 2.7 GBps. (But you will never see this in that system as the FSB isn't DDR) In the G5 1.6 you still get PC2700 DDR SDRAM but with the paired 128-bit wide RAM bus, throughput doubles to 5.3 GBps, and the G5 1.8 and Dual 2.0 with their faster PC3200 DDR SDRAM reach 6.4 GBps.



G5 1.6

G5 1.8 and G5 2.0

Memory Bus Width




Memory Speed

PC2700 DDR (333MHz)

PC2700 DDR (333MHz)

PC3200 DDR (400MHz)

Max. Throughput

2.7 GBps

5.3 GBps

6.4 GBps

Max. Total RAM

2 GB

4 GB*

8 GB*

Number of RAM Slots




* - Max G5 ram specs with 1GB dimms. (2GB dimms supported per Apple Dev. Docs.)

The maximum amount of RAM a system can use has also changed, in the MDD G4 you get 4 DIMM slots that hold a maximum of 2GB. The G5 1.6 allows for up to 4GB in 4 DIMM slots, while the G5 1.8 and 2.0 systems are rated up to 8GB total (using currently available 1GB Dimms) and have 8 DIMM slots. This means that on G5 1.6 systems there will be 2 slots used and only 2 slots free for future upgrades.

Now with the G5 models, we give up the ability to have both a SuperDrive and a fast CD burner internally. Gone are the 4 hard drive bays, we are now down to 2, but it uses the new S-ATA 150 spec (Serial ATA) vs. the 2 x ATA-100 connections and 2 x ATA-66 for hard drives. Apple states that you cannot use S-ATA to IDE adapters, perhaps as there is little physical space to fit most adapters on the market. Other readers have had success, and others have had compatibility issues, check xlr8yourmac.com for the latest news. (as mentioned previously here, all SATA/PATA adapter reports have noted problems after waking from sleep with the attached drives. Two readers w/G5s also have used 2 drive cables attached to the G5's ATA/100 Optical drive bus to use a std (Parallel) IDE drive, but it's not the best option.) Of course you could always use an external FireWire case and place your existing IDE drive there.

Drive Bays



Internal HD Bays



Front Panel Optical Drive Bays



The actual hard drive shipping in the G5 1.6GHz was the Seagate Barracuda 7200.7 series S-ATA drive, the ST380013AS to be exact. This is Seagate's first generation S-ATA drive series. The G5 Dual 2.0 system I tested used the 160GB version, the ST3160023AS. (As with the Superdrive, Apple uses more than one OEM drive mfr, so the drive brand/model can vary from one production run to the other.) The G4/1.25 MP machine I last ordered included the same drive series but in an ATA version, the ST380011A.

Both drives feature Seagate's 6th generation fluid dynamic bearing motor, for lower noise and less heat. There is another difference between the drives than just the interface, the S-ATA version has an 8 MB buffer, the ATA version has 2MB. Both drives seem very quiet, though in the G4 the fans are louder than the drive. Only in the G5 1.6 can you truly appreciate how quiet the Seagate drive is when idle, and you can hear the usual clicking sounds when the disk is busy.

The SuperDrive installed in my test G5 1.6 machine is the Sony DWU10A, which is the OEM version of their DRU-500A drive. This drive not only supports DVD-R/RW but also DVD+R/RW. Apparently the DRU-500A is already obsolete, and now Sony only lists a DRU-510A on their website. (Sony also just released a DRU-530 model w/8x DVD+R speeds and faster CDR/CDRW speeds. They also noted a future firmware update to the DRU-530 for 8x DVD-R speeds is expected in Feb. 04.) At least we get a drive that has DVD+R/RW support even if Apple does not officially support that yet. From sample machines I have seen, all new G5 systems seem to come with the Pioneer DVR-106D now, but this may not be true of all shipping systems. (As noted in late Sept. 2003 here, my early shipped Dual G5 2GHz had the Pioneer DVR-106D drive, but again that can vary by production run.)

Here is a quick comparison of the Sony DWU10A SuperDrive with the Pioneer DVR-106 that is apparently in other shipping G5 systems, including the G5 Dual 2.0 I tested:


Sony DWU10A

Pioneer DVR-106

Write Speeds:




4 X

4 X


2 X

2 X


2.4 X

4 X


2.4 X

2.4 X


24 X

16 X


10 X

10 X

Read Speeds:




8 X

8 X


32 X

32 X

Access Time: DVD/CD



RAM Buffer

8 MB

2 MB

The Sony drive has a much larger buffer and faster CD-R write speeds. The Pioneer on the other hand, has faster access times and faster write speeds to DVD+R media. (I've seen some DWU10A drives reportedly rated for 4x DVD+R speeds like the DVR-106D.) Some have complained about the inclusion of the older Sony drive, but if you write to CD more often than DVD it will be faster for you in the long run.

PCI and AGP Slots
There are 3 PCI slots in the G5 1.6, and they are not the newer PCI-X type, however there has been a lot of confusion as to what that means for users. Even in the G5 1.6, PCI cards need to be able to run on only a 3.3 Volt supply. The slot is physically keyed to allow only the use of PCI cards that run on 3.3 Volts. (starting with the 66MHz PCI slot equipped B&W G3, many PCI cards are keyed/slotted for both 3.3v and 5V PCI. However not all cards can run on only 3.3v power and signaling.) Many PCI cards in use today still need 5 Volts, are keyed differently and are incompatible with all the G5 models including the 1.6 GHz. This was the case with my ProTools 24 TDM, ProTools 001 and Adaptec 2930U SCSI PCI cards. So before I started, I knew none of these cards would work in any of the current G5 models, as they are electrically and physically incompatible with the G5 systems. This is to say nothing of hardware or software compatibility in a G5 system.

As a point of reference, the G4 systems PCI slots would accommodate cards requiring 3.3 Volts, 5 Volts and 12 Volts. Most users never thought about the voltages feeding their PCI cards but it matters with the G5. In the quest for faster speeds and lower power consumption, the trend is to move to lower voltage components. This also means many older PCI cards are unlikely to work in systems beyond the current G4 MDD systems. To preserve their current investment in PCI cards, some are purchasing new G4 systems to replace older Apple systems. Personally I have changed out a PowerMac 9600 with a G4 MDD, and was able to keep the ProTools 24 TDM hardware, cards that will not work in a G5. Others will sell their PCI cards and upgrade to G5 ready systems.

The G5 1.8 and 2.0 systems feature the new PCI-X specification, and cards that can take advantage of the improved performance will increase with time. Two of these PCI-X slots run at 100 MHz and one runs at 133 MHz, vs the three 33 MHz slots in the G5 1.6 system. (they can also run 33MHz PCI cards if they are 3.3v compatible) Maximum combined throughput on the PCI bus in the last G4 towers was 266 MB/s, in the G5 1.8 and 2.0 systems we now have up to 2000 MB/s, more than 8 times faster. It is important to note that not only is PCI-X faster; it is also more efficient than PCI in its use of available bandwidth.

If you plan to purchase or move existing cards to a G5, be sure to check with the manufacturer or xlr8yourmac.com for compatibility info. (For G5 PCI card compatibility reports and tips, see the PCI section of the G5 Tech Info/Compat. page here.) Most manufactures have now posted such info on their websites, so do some research if you want to preserve your current PCI card investment. If you know of a specific card that works in a G5 system be sure to let us all know by sending a report to xlr8yourmac.com.




PCI Slots



External Ports

Front Panel Ports:
Finally Apple has added front mounted USB 2.0 and FireWire 400 ports to the G5, so we can easily plug in our "Digital Hub" components like portable CD burners, FireWire hard drives, iPods, digital cameras and DV video cameras without digging behind our computers through a nest of wires. The G5 towers are the first Mac tower systems to have 3 USB ports, and they are now all USB 2.0, however even the current iMac has 3 USB 2.0 ports. In the past I have had some USB devices unstable or unusable when attached to the keyboard USB hub, so an extra USB port is a welcome change, even with USB 1.1 devices. (For G5 owner reports on Firewire and USB devices including Hubs, see the G5 FW/USB feedback page.)

Like the MDD G4 systems, the G5 has retained the convenient front panel headphone jack, with improvements as discussed in the Analog Audio section below.

Wireless Ports:
On the rear panel of the G5 systems, there are now external Bluetooth and Airport Extreme antennae connectors as the all aluminum G5 enclosure makes internal antennae impractical due to the shielding of the case. Already 3rd party manufactures have more powerful external Airport antennae compatible with the G5. When you purchase a Bluetooth or Airport Extreme card for a G5 system, you get the appropriate external antenna included in the box that will fit the G5's connections.

Digital Audio:
Below the wireless ports are 2 standard S/PDIF format TOSLink connector optical audio connections, one each for input and output. If you have a newer home theater receiver it will have the same type of ports. Many other products with optical ports give you a plastic insert that you are supposed to remove first and then put away somewhere without misplacing it. Apple went further than most manufactures by using optical ports with "doors" that keep dust and dirt out of the connector as shown below:

Optical out port held open

When you play a DVD with the special v3.3 build of Apple DVD Player on the G5's, you can set the prefs to output the Dolby Digital AC3 stream to your external Dolby Digital receiver. This works great but as you see in the "Audio output formats" screenshot below, Jaguar and Apple DVD Player 3.3 will only send 2 channels of AC-3 audio output to your receiver, not the full 5.1 channels on a commercial DVD. To get full 5.1 surround AC-3 audio output, you will need Panther to get Apple DVD Player 4.0. All G5 systems also can input optical digital audio from CD players, DAT machines, MiniDisc and other devices all in the digital domain without external hardware. There are also inexpensive optical to coaxial converts should your equipment only input or output coaxial digital formats.

Choosing output type in DVD player v3.3

The digital input includes a sample rate converter, allowing the G5 to have one data rate going in while recording the data at another rate of your choice. This conversion process does not incur any CPU utilization as it is done in a hardware audio IC on the motherboard. Sampling rates of 32.0 kHz, 44.1 kHz, and 48.0 kHz at bit depths of 16 bits and 24 bits are supported in "External Clock" mode by the G5 hardware. In "Internal Clock" mode, the sample rate converter (SRC) accepts a range of 16 kHz - 96 kHz sampling rates. This setting is accessed in the Audio MIDI Setup utility as shown below.

Selecting if the SRC hardware is used or bypassed

For the best fidelity, Apple recommends the audio clocking preference be set to "External Clock" in the Sound prefs. This bypasses the SRC and ensures bit accurate audio data when you intend to handle the audio data at the rate it is fed into the computer. This was the default setting on my test systems.

Digital audio formats for input and output are shown below:



Audio input formats

Audio input sources





Audio output formats

Audio output sources

As you can see there are many supported formats with the internal hardware, far more than built-in to any Mac before the G5. I look forward to someone thoroughly testing the audio specs at the new 24-bit analog settings. I would think the harsh electrical environment inside a computer would significantly degrade the performance, but Apple did at least shield the audio line in and out connectors.

Analog Audio:
A new IC is behind the audio capabilities of the G5 systems, we now have a stock Mac that support up to 24 bit 48 kHz audio, in both analog and digital domains up from the 16 bit 44.1 kHz audio of past Macs.

The G5 developer documentation notes that the G5's audio subsystem employs DSP functions such as EQ and dynamic range compression. This is only used for the internal speaker output (hmm... well at least they tried to get decent sound out of a 2" speaker). Audio to the external headphone and line outputs is not processed this way, only level control is adjustable in the digital domain for these ports.

In the G5 architecture, analog audio for the mono speaker, stereo headphone port and stereo line output port are all treated separately. This means each port is separately amplified and there should be no interaction with loading on the various ports. However the audio output to all analog outputs and the optical digital output will be the same. You cannot send one audio feed to the headphones and another to the optical output, both will always play the same audio. For audio input, you can have either the analog line in port or the optical digital input active, but not both at the same time.

What if you are playing audio that is at 32 kHz/16 bits and your output preference is set to 48 kHz/24 bits? The G5 will up-sample the audio to the audio output section with OS X's Core Audio functions, using 32-bit floating point math for increased precision during the conversion.

More and more Macs are getting fast USB 2.0 connections, with two rear mounted fast USB 2.0 in addition to the one on the front panel on all G5 systems. This is good, as many new consumer devices use the fast version of USB 2.0 such as newer digital cameras and scanners. Some manufacturers have in fact updated older products that had FireWire last year to USB 2.0 this year, due to the lack of FireWire connections on most PC systems.

On the MDD G4 (FW400/OS 9 bootable model) there are two FW400 ports and on some models (FW800/No OS 9 booting) also 1 FW800 port, all on the rear of the system. On the G5 we get one front panel FW400 port and on the rear panel, one FW400 and one FW800 port. The G5 is an improvement here as now we can plug in our FireWire camcorders, iPod's etc without digging behind the computer.

The G5 is similar to the G4 in that they both support 10/100/1000 Ethernet onboard. The G5 still supports auto-negotiated speeds, auto-sensing and self-configuring so you'll never need to use a crossover cable. Here the G4 and G5 seem to both have the same capabilities.

Wind Tunnel - anyone unlucky enough to have used one of the loud G4 MDD models before the CPU fan and power supply replacement program, knows what I am talking about. It was not only the loudness of these machines, but the varying pitch seemed to be particularly annoying. After performing the exchange on a G4 MDD Dual 867 at work things improved, but the G5 goes much further in the noise department than any G4 tower.

The fans in the G5 systems, 9 in a single processor system, 8 in the dual CPU systems are optimized to cool one zone of the G5 system. There are 7 thermal sensors in the G5 systems that I am aware of, which provide data to control the speed of the variable speed fans. One is visible above the HD bays where you can see it, but I could not locate the others. Using the ThermographX temperature utility, a total of 7 sensors are shown in a single CPU G5 system, 8 in the duals. They are identified as:

  • 1 sensor per CPU
  • 1 for the U3 memory controller/PCI bus bridge IC
  • 1 for the drive bay
  • 1 labeled as MLB (Main Logic Board) MAX6690 AMB (Ambient?)
  • 1 labeled as MLB (Main Logic Board) INLET AMB (Ambient?)
  • 1 labeled as BACKSIDE (back of MLB/case?)
  • 1 labeled as GPU, although this value never varied at all, cold or hot so I doubt it's accuracy.

According to Jeremy Kezer, author of ThermographX, the GPU data has varied based on OS version and video card on G5 systems, although it is accurate on PowerBook systems. Apple has removed the GPU sensor data under Panther, as it was apparently inaccurate on G5 systems.

OS 10.2.7 or later is required on the G5 systems to keep the fans running at the lowest possible speeds by monitoring sensor data and controlling fan speed. Looking at what data I could find for the fans in the G5 systems, you will understand how they can be either so loud or so quiet.

Starting with the front CPU fans, one per CPU, these are specially designed for low air resistance, and able to run at extra high RPM's. So when spinning slowly they let air pass easily, but can spin at up to 4000 RPM and move 79 CFM of air if needed. The operating voltage for these fans is 4 to 13.2 V, which is a much wider range than most 12V fans accept, and is what allows for the wide range of operating speeds in the G5 systems. The rear CPU fans are a little less sophisticated, designed for a voltage range of 7 to 13.8 V, but are capable of moving up to 67 CFM of air when running at a high 3800 RPM.

At room temperature under normal use, the systems are meant to be both cool and quiet, with the fans running nowhere near their maximum speeds. However all G5 models are not the same in that regard. On a hot day running intensive 3D rendering and benchmarking tests, Energy Saver set to "Highest" Processor Performance, there was no audible increase in noise level with the G5 1.6 system in a quiet home environment. Even after hours of intensive use the CPU heatsink was barely warm to the touch, a far cry from the CPU heatsinks in a dual G4 that mandate a warning sticker.

The G5 Dual 2.0 system was far different in this regard, it not only ran a little nosier at all times (fans always spun faster) but also was easily provoked into spinning the fans even faster during certain operations. I still find it odd that the clock speed from 1.6 to 2.0 GHz would make such a difference in cooling needs. (Two G5 CPUs are also a factor of course) For example while using Final Cut Pro 4.0, on the G5 1.6 there was no audible fan changes regardless of what task was being performed, but on the G5 Dual 2.0 it was easy to get the fans spinning faster, even shuttling up and down a timeline in FCP.

Even more interesting, another audible hardware sound was present in the G5 Dual 2.0 system, originating from the power supply area at the bottom of the case. I found specific conditions would cause this high-pitched noise, one that is easily repeatable occurred during the HD tests in the Xbench benchmarking utility. Below I have a table of settings and the presence of the noise. These combinations were repeatable on the G5 dual 2.0 system I tested. The Nap mode setting is available in the CHUD tools from the Apple developer website, for those interested in trying this on their systems. The headings in bold are the defaults as shipped from Apple, Nap ON and Processor Performance set to Auto.

It would be interesting to hear from other G5 systems owners if all shipping systems exhibit this behavior. (For the first reports on this chirping noise and the common fix many used, see the G5 Noise/CHUD Tools Nap Mode Fix page. Later revision Power Supplies (as of late 2003) do not seem to change this behavior.)


Nap ON


Processor Auto

Processor Reduced

Processor Highest

Normal Sound Level






Normal Sound Level






Normal Sound Level but Fans Faster






High Pitch Sound during Uncached Read Test






High Pitch Sound during Uncached Read And Uncached Write Tests






High Pitch Sound during Uncached Read And Uncached Write Tests






I would like to clarify that running Xbench was not the only way to cause the high pitch sound from the power supply on the Dual 2.0 system, I also heard it during other operations. The Xbench test allowed the most repeatable circumstances I am aware of, which anyone would be able to test. (I find that if Nap mode is not disabled, simply opening the Startup Disk Control panel results in the chirping/squealing sound as it scans for drives in this Dual G5 w/2 HDs.)

Operating System
The G4's currently available from Apple will likely be the last Apple hardware able to boot OS 9. Classic mode is still available on the G5's so you can run some OS 9 applications that way, same as a G4 system, but you will not be able to boot up into OS 9. If you need OS 9 booting, better get a G4 tower while they last, as it is time for Apple to move on with OS X.

The first G5's shipped with Jaguar 10.2.7 (G5), a retooled version of Jaguar that works with G5's new hardware and architecture. Current shipping G5 systems should include Panther installed on the hard drive, or on CD in the box.

While I had the early G5 1.6 system, 10.2.7 was the only version available, but the G5 Dual 2.0 had 10.2.8 installed and I purchased Panther on October 24, allowing some tests with both Jaguar and Panther. Any performance differences between Jaguar and Panther on the G5 Dual 2.0 system will be specifically mentioned in Part 2, the Benchmarks and Real World Tests section.

Part 2: Performance Tests: Dave sent Part 2: Performance tests on May 17th.

Other G5 related articles Here (from the Systems page G5 section.)

(Ad/Sale items)

= UPGRADES by Mac =
Upgrades just for

= Refurb Mac Pros =
(Click for List)

SSDs up to 4TB
Fast SSDs for Most Macs/PCs

= ThunderBolt =
Drives, Docks & More

Up to 12TB HDDs
HGST, WD, Seagate, Toshiba

= 2.5in HDs & SSDs =
Notebook Hard Drives and DIY drive/case kit bundles

Lifetime warranty RAM Upgrades!

Internal and External Superdrives/Blu-Ray drives

Graphics cards, Displays, Adapters, Cables & more

Interfaces, Cables, Software, Speakers, Headphones & more

Apps, Utilities, OS, VM, Games and more

WiFi and Bluetooth Devices/Adapters/More

= Repair Service =
for iPhone, iPad, Macs

= iPad/iPhone/iPod =
Accessories, Cases, Repairs & More

NuGuard KX Cases
*Extreme* Drop Tested!

XLR8YourMac T-Shirts

= back to www.XLR8YOURMAC.com =

= Other Site Topic Areas =
Mac Mods/Upgrades | CPU Upgrades | Storage | Video | Audio/HT | OS Updates/Network | Recent

Copyright © 1997-2018. All Rights Reserved.
All brand or product names mentioned are properties of their respective companies.

Legal: Site Privacy and terms/conditions of use.