why does compiler matter? slack8.1 & current
 

i read that packages in current directory might not work in slack 8.1 system because 8.1 packages got compiled with gcc2.9 and current 3.1 or above

i'm wondering if packages are binary files, why would it matter?
and also, when i want to upgrade to 9.0, wouldn't it matter for the same reason?
thanks

Well, the binaries produced by the two compilers are incompatable, and 9.0 will/does have a different version of glibc, another incompatability.