To what do the words 'i386, i586, PPC, Alpha, Sparc' refer?
All software is written for a particular computer system architecture. Software written for a particular architecture does not run on another distinct architecture. Think Apples and IBMs. Intel (i386, i586) refers to the system architecture of what is commonly called the Personal Computer or PC. This is the type of computer system architecture used in the majority of personal computers. i386 means 386 or above and i586 means pentium or above.
Sparc refers to the system architecture of Sun Computers. PPC refers to the Power PC system architecture, mostly Apple computers. Alpha refers to the system architecture of Digital Equipment Computer systems. ia64 refers to the architecture of Intel-based 64 bit computer systems.