architechute kinda means the guts of the processor.
while all x86 processors understand the same machine code.
(where x is a variable and in linux can be anything between 3 and 6)
386's are very olv processors
486's still quite old
586's (never actually seen 1, but they exist)
686's are the modern ones in all new computers (athlons, pentium 2,3,4 (not sure bout 1)
basically, when you see these numbers for rpm's or whatever, its letting you know what porcessor architechutre the compiler has optimiesed the code for.
usually optimisations are set to 386 or 686.
686 optimisation runs faster on modner computers, but will not run on old 386's
386 optimisation is set when a program may be used on an old 386, for example if sum1 wants to turn an old pc into a router or proxy.