What's the use of "-march" & "-mtune" option in GCC?

[SWang]

When excute "gcc --target-help",it print

...
  -march=CPU[,+EXTENSION...]
                          generate code for CPU and EXTENSION, CPU is one of:
                           i8086, i186, i286, i386, i486, pentium, pentiumpro,
                           pentiumii, pentiumiii, pentium4, prescott, nocona,
                           core, core2, corei7, k6, k6_2, athlon, k8, amdfam10,
                           generic32, generic64
                          EXTENSION is combination of:
                           mmx, sse, sse2, sse3, ssse3, sse4.1, sse4.2, sse4,
                           avx, vmx, smx, xsave, movbe, ept, aes, pclmul, fma,
                           clflush, syscall, rdtscp, 3dnow, 3dnowa, sse4a,
                           svme, abm, padlock, fma4
  -mtune=CPU              optimize for CPU, CPU is one of:
                           i8086, i186, i286, i386, i486, pentium, pentiumpro,
                           pentiumii, pentiumiii, pentium4, prescott, nocona,
                           core, core2, corei7, k6, k6_2, athlon, k8, amdfam10,
                           generic32, generic64
...

Is that means it can compile a program run on above CPUs?
But if it can do so, what's the differences among GCCs compiled for different targets(such as i386-linux-gnu,i486-linux-gnu...).

[gerard4143]

Well yes and no. Yes the GCC compiler offers these options but you need GCC set up for the chip family to have them available as valid options...Gerard4143

[SWang]

Thank you.