The ease with which a piece of software can be made to run in a new environment (compiler, operating system or computer). The most important factor is the language in which the software is written and the most portable language is almost certainly C (though see Vaxocentrism for counterexamples). This is true in the sense that a C compiler is available for most systems and is often the first compiler provided for a new system. This has led several compiler writers to compile other languages to C code in order to benefit from its portability (as well as the quality of compilers available for it). The least portable type of language is obviously assembly code since it is specific to one particular (family of) processor(s). It may be possible to translate mechanically from one assembly code (or even machine code) into another but this is not really portability. At the other end of the scale would come interpreted languages which rely on the availability of a portable interpreter written in a lower level language.