7 has AltiVec acceleration as an option (for example, I still use the G5-specific version).
None of the actual classic OS cares, however. This is why, for example, you can use a 7447A with 9.2.2, but you can't with 10.0-10.3.4: those try to initialize the AltiVec portion of the G4, but only 10.3.5 and up can handle later G4s. Mac OS 9, however, treats any supported CPU essentially as a generic PPC.
The G3 is very fast at certain operations, being essentially a pumped-up 603, and it was specifically tuned for Mac OS in a way that no other chip was (i.e., IBM sat down, figured out what instructions were most heavily used in the OS, and put them in hardware). The downside is that it lacks some of the more advanced bus and caching features of the G4, but (like it superseded even fast 604es) for most consumer workloads this is irrelevant.
None of the actual classic OS cares, however. This is why, for example, you can use a 7447A with 9.2.2, but you can't with 10.0-10.3.4: those try to initialize the AltiVec portion of the G4, but only 10.3.5 and up can handle later G4s. Mac OS 9, however, treats any supported CPU essentially as a generic PPC.
The G3 is very fast at certain operations, being essentially a pumped-up 603, and it was specifically tuned for Mac OS in a way that no other chip was (i.e., IBM sat down, figured out what instructions were most heavily used in the OS, and put them in hardware). The downside is that it lacks some of the more advanced bus and caching features of the G4, but (like it superseded even fast 604es) for most consumer workloads this is irrelevant.