What is this Rosetta I am hearing about? What does it actually do?
Okay, I am sure you have heard of Apple adopting the Intel chips. The long and short of it is, the Intel Chips use a completely different architecture, CISC, from the older Motorola PowerPC chips (RISC). You could find out more by googling for “RISC vs CISC”, but here is one site, here or perhaps Wiki.
Now, since they are different architectures, there needs to be some translation so that applications can run.
Rosetta is the key – it allows your intel mac to translate some of the PowerPC applications and run in an Intel Mac environment. (This is similar in concept to what Virtual PC for the Mac used to do on PowerPC macs, albeit the opposite.)
Because it is emulation and translation on the fly, there will be a general performance hit. Rosetta-ed applications typically run slower on an Intel Mac than they do on a native PowerPC processor. However, because the Intel chips are no slouches themselves, the performance hit is usually not so significant for many cases.
Applications that run natively on an Intel processor are known as Universal Binaries – “universal” because they run natively on both the Intel processors and the PowerPC.