More iMac G5 Details

By on September 10, 2004

While we’re waiting for the first round of iMac G5 reviews to hit the net, MacMinute found Apple’s Developer Note on the new system. I found a few interesting tidbits amidst the technical stuff.

Available as a fully-integrated, build-to-order option, Bluetooth is an open specification that enables short-range wireless connections between desktop and laptop computers and a host of other peripheral devices.

[…] Bluetooth is available as a build-to-order option, which is installed by Apple at the time of purchase as a fully integrated module. Accessing the Bluetooth capabilities without purchasing the integrated module will require a third-party dongle that may not support all present and future features supported by the internal module.

Translation: If you think you might want Bluetooth, and you don’t want to use a dongle, you’ll have to pony up the extra $50 up front, because you won’t be able to add it later.

Here’s a neat feature that might be common on Macs, but it was new to me:

The user has the option at boot time to put the computer into a mode of operation called Target Disk Mode (TDM).

When the iMac G5 is in Target Disk Mode and connected to another Macintosh computer by a FireWire cable, the iMac G5 operates like a FireWire mass storage device with the SBP-2 (Serial Bus Protocol) standard. Target Disk Mode has two primary uses:

  • high-speed data transfer between computers
  • diagnosis and repair of a corrupted internal hard drive

That’s a pretty cool idea. You could debug the HD without removing it. Of course, there have been problems in the past with OSX actually causing corruption on external FireWire drives. I guess they figure that they have that sorted out. There’s also a note on the measures taken for cooling:

The iMac G5 uses an advanced system management unit (SMU) to manage the thermal and power conditions, while keeping the acoustic noise to a minimum.


Temperature and power consumption are monitored by the operating system which communicates with the SMU, which in turn controls and monitors fan operation. If Mac OS X is not booted, thermal management must be provided by the alternate development operating system.
Note: If Mac OS X is not booted and the alternate development operating system does not manage the fans, the fans go into an unmanaged state and run at full speed.

Linux kernel developers, start your emacs sessions.



  1. The Target Disk thing has been with Macs since the G4’s were introduced, and it can be a life saver. Anybody supporting any number of Macs can use this for a good excuse to keep a laptop around ;o)

    The only time that there has been trouble with corruption on external Firewire devices was when upgrading the OS — I think from 10.3 to 10.3.something — and only when the device was connected during the install.

    The variable speed fan system sounds similar to what’s already used on the G5 tower. The fans run on an as-needed basis. Funny thing is, I’ve got a Compaq server here running Win2K that does something similar; when it’s being booted up, the fans scream like an F-16 taxiing. Once the OS is loaded, they slow down considerably. When the machine is being taxed (it’s used as a raster image processor, so it gets a real workout some days) the fans will kick into high gear. But it’s either low speed or high speed; no in-between.

  2. On the cooling, my laptop has a feature like that too, since it uses a desktop Pentium 4 wedged into a laptop case. It’s an entirely hardware-based solution though. It’s interesting that the Mac’s method relies so much on a hardware driver.

    Reading the tech details, it sounds like they didn’t assume the software driver would always do its job. In addition to running the fans full-speed if another OS is installed, it will kick the fans up to full speed if it receives no updates from the OS for a certain period of time, so if the OS gets stuck in an endless loop or something while you’re away from the machine, it won’t have a meltdown.

    With the target disk thing, they mention repeatedly that the host computer needs to be running OSX, but I imagine that’s just due to the filesystem on the disk? Since Linux can mount UFS/HFS volumes, there’s really nothing to stop you from jacking in with a Linux box, is there?

  3. “With the target disk thing, they mention repeatedly that the host computer needs to be running OSX.”

    It should also work with OS 9 in a pinch.

    “Since Linux can mount UFS/HFS volumes, there’s really nothing to stop you from jacking in with a Linux box, is there?”

    That I don’t know, but I think it would work. From Apple’s doc #58583 it sounds like the target computer must have built-in Firewire — won’t work on older machines with FW cards in them — but the host computer only needs a working FW port on it. And from what I understand, when the target machine is in target disk mode it basically becomes a great big external drive enclosure for the primary hard drive, so if you’ve got a Linux machine with FW it should be possible to pull it off. (I think I’d back up my machine before I tried it though, Joe! Just in case.)

  4. Target disk mode works on any Mac with Firewire built onto the motherboard which leaves out all the G3’s, since that firewire is on a daughtercard. Target disk works fine with Mac OS 9. We use it extensively to do new installs. We set up one Mac the way we want it, with all the apps and stuff installed. Then just plug another one in and start it up in TDM. Once it’s drive shows up on the deskop, erase it, drag the files and folders from the source mac to the erased drive. Reboot the new mac, change a couple of settings and it’s done. Very slick.

  5. I ordered an Imac G5. I haven’t received it yet. I currently use a Powermac 7200, running OS 9.1. How can I transfer my files to my new machine? Sounds as if the Target Disk Mode is not an option (no FW) on the 7200. The 7200 has PCI slots. Is there a PCI to Firewire adaptor available? I have spent a small fortune on the new machine, and would like to pull this off without breaking the bank. Any suggestions would be much appreciated.

  6. Your best bet would be to get an ethernet cable (maybe a crossover) to go between the two machines, then enable AppleTalk sharing on the 7200 and mount the 7200’s drive on your iMac’s desktop.

    There are lots of resources on the web that’ll help you through this. Check Apple’s help article

    Once you get your new iMac, Apple’s tech support (free) will help you work out any glitches.

  7. Dave, Sounds pretty straightfoward. I give it a go. Thanks for the assist, I am looking forward to my first 21st century computer! I’ll let you know how it goes.

    Regards, Curtis

  8. You don’t need to use FW target disk mode anymore! You have built in FW networking and you don’t even know it. Okay, so I had to figure this out the hard way, but, it is incredibly cool!

    Connect two machines with an FW cable. You can set up your computer to connect to other computers over FireWire, using the Internet Protocol (IP).

    Connect a FireWire cable to the FireWire ports on the computers you want to connect. Open System Preferences and click Network. Choose Network Port Configurations from the Show pop-up menu. Click New, and then choose FireWire from the Port pop-up menu. You can give the new port configuration a name, such as FireWire. Drag the port configuration to the top of the Port Configuration list. This ensures the port is assigned an IP address using DHCP. Click Apply Now.

    I go back and select the FW network from the main Network tab and use a manual address of for the first machine and for the second machine.

    Now click on your desktop and hit command-K or use the GO menu command. Type in the IP of the other machine and bang there it is! Faster than hell too!

    Have fun!

  9. Target disk mode, originally called SCSI disk mode has been around since 1991.

    As far as I know, the only issue would be OS9 on the host machine and a UFS partition on the target drive.

    There is an article on lowendmac with the details

    Unfortunately when going between a pre-firewire mac like Curtis’ 7200 and a firewire model the best way is a crossover ethernet cable at a blazing 10mbs….



  10. If anyone is feeling REALLY smart, please help! I accidentally used the key combo of “apple+option+Control” and then repeatedly, while holding those down, selected the period key. Slowly, the colors on my monitor changed to a horrible mix of pixellated black, white and neon blues only.

    I can’t seem to get it to restore correctly, and have no idea what this inadvertent key combo caused. If you have any ideas, please email me at and I’ll be forever grateful!

    Note: I can get the monitor colors at a default, if I create an additional user on my computer, but I’d like to fix the monitor in the user name that is set up for me already!

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