Is the CPU on the iMac G4 upgradable? How is it mounted?

According to the Apple Developers Notes for the iMac G4 models, the processor in each is mounted directly to the motherboard. Consequently, it is not feasible to upgrade the processor in any iMac G4 model.

Does the iMac G4 have PCI slots or expansion bays?

No. The iMac G4 is designed to be simple and inexpensive, and consequently, there is no internal expansion other than AirPort for the original and "Spring 2003" models and AirPort Extreme and Bluetooth 1.1 for subsequently released models.

What ports are provided by the iMac G4?

For details regarding the ports for each iMac G4 system, please refer to the ports pages for the original/Spring 2003 iMac G4, iMac G4 17" 1 GHz, and iMac G4 USB 2.0 models.

What is the difference between the Apple speaker minijack and the headphone jack on the iMac G4? Which jack should be used with external speakers?

The Apple speaker minijack is a proprietary 2.5-mm input, whereas the headphone jack is a standard 3.5-mm input.

Apple notes that:

Headphones or externally powered speakers connect to the standard headphone jack. The Apple speaker minijack is designed specifically for use with the Apple Pro Speakers -- it connects to a powerful amplifier built into the system.

In developer's documents, Apple further explains:

Some types of headphones and other audio devices have a 2.5-mm plug. The user should be warned not to plug such devices into the Apple speaker minijack. Doing so could cause damage to the devices.

The Apple Speakers include an internal ROM that enables the computer to identify the speakers. Speakers other than the Apple Speakers should not be connected to the Apple Speaker jack.

Ultimately, Apple Pro Speakers are the only speakers that should be used with the Apple speaker minijack on the iMac G4. All third-party powered speakers should be used with the 3.5-mm headphone jack.

What type of modem is standard with the iMac G4 models?

All iMac G4 models shipped standard with a 56k v.90 or 56k v.92 internal modem.