All Power Macs prior to 1997 used PowerPC 60x-series processors, and 4-digit model numbers (e.g. Power Mac 8600). In 1997 the first third-generation ("G3") Power Macintosh was introduced, using the PowerPC 750 processor. From this model onward, Apple no longer used a numbering scheme to identify their Power Mac models, but instead referred to them by their PowerPC processor generation number (i.e. G3, G4, and G5). Later models based on the same generation of PowerPC processor relied on descriptive characteristics to differentiate them, e.g. the color scheme ("Power Macintosh G3 - Blue and White") or a technical feature of a particular model ("Power Mac G4 - Gigabit Ethernet"). This same identification scheme was used in the
iMac,
PowerBook, and
iBook lines of Macintosh computers.
The marketing name was changed from
Power Macintosh to
Power Mac with the introduction of the G4 models, meaning all G3 and earlier models are Power Macintoshes, while all G4 and G5 models are Power Macs. Not all Apple documentation follows this rule, but the vast majority does.
source:
wiki