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iMac G3 Q&A - Updated February 23, 2009

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Is the CPU on the iMac G3 upgradable? How is it mounted? Are third-party processor upgrades available?

Unfortunately, the CPU on the iMac G3 is not mounted on a ZIF socket like the models in the Power Macintosh G3 series. The tray-loading iMac G3 models -- those with 233 MHz, 266 MHz, and 333 MHz processors -- have the processor soldered to a processor daughtercard, and the slot-loading iMac G3 models -- those with 350 MHz and faster processors -- have the processor soldered directly to the motherboard.

The processor daughtercard in the tray-loading iMac G3 models also contains the ROM. Consequently, the only feasible way to upgrade the processor in these models is to replace the original processor daughtercard with a processor daughtercard that contains both a faster processor and an original ROM. To upgrade the processor in the slot-loading models requires one to replace the entire motherboard with a motherboard equipped with a faster processor.

A number of processor upgrade card companies -- FastMac, Newer Technology, PowerLogix, and Sonnet -- released upgrade cards for the tray-loading iMac G3 models that essentially were original iMac G3 daughtercards with the original processor removed and a faster one soldered in its place. Sonnet, perhaps most interestingly, also added a handy Firewire "400" port to their upgrade cards.

Specs on these upgrade cards for the tray-loading iMac G3 models -- all long ago discontinued -- are listed on the "By Compatible System - iMac G3" page of the archived "Pre-Intel Upgrade Cards" section of EveryMac.com, but also are referenced below for your convenience:

Upgrade Card

Processor

FastMac G4/466 (iMac)

466 MHz PowerPC 7400 (G4)

Newer iMAXpowr G3 466

466 MHz PowerPC 750 (G3)

Newer iMAXpowr G4 433

433 MHz PowerPC 7400 (G4)

PowerLogix iForce 400

400 MHz PowerPC 750 (G3)

PowerLogix iForce 500

500 MHz PowerPC 750 (G3)

PowerLogix iForce G4 400

400 MHz PowerPC 7400 (G4)

PowerLogix iForce G4 450

450 MHz PowerPC 7400 (G4)

PowerLogix iForce G4 500

500 MHz PowerPC 7400 (G4)

Sonnet HARMONi G3 500/FireWire

500 MHz PowerPC 750 (G3)

Sonnet HARMONi G3 600/FireWire

600 MHz PowerPC 750cx (G3)


Although it required swapping the entire motherboard, FastMac also offered an "upgrade card" for the slot-loading models with 350 MHz, 400 MHz, 450 MHz, and 500 MHz processors (except the "Early 2001" Flower Power/Blue Dalmation systems and presumably the later "Summer 2001" systems as well).

Given the other limitations of the tray-loading iMac G3 models, it does not make financial sense to invest much in a upgrade card. However, if you locate an extremely cheap iMac G3 upgrade card and you like to tinker with old Macs, you probably would enjoy the experience.

Alternately, a motherboard swap for the slot-loading models makes even less financial sense, but if you don't mind the risk of killing a slot-loading iMac G3 entirely, and you have a lot of hardware experience, overclocking it is an option.



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