> The biggest downside of it is that it requires tight coupling between the programming language and OS, such that you can only use a single programming languag

> The biggest downside of it is that it requires tight coupling between the programming language and OS, such that you can only use a single programming language (or a family of related ones that all share a type system) for all programs on the box. I would point out (from a relatively lay perspective) that while this isn't strictly the case in current popular kernels (Mach/OSX, Windows, Linux), it's still a pretty strong trend. These kernels (AFAIK) are implemented in C and have large ecosystems of C code orbiting them. As such there are many benefits to having a program written in C or at least speaking C's ABI and memory layout. Maybe I'm mistaking the causes for this situation, but most developers are effectively using something that is either C itself, written in C, or speaks C in some way (CPython, JVM, MRI/CRuby, Perl, are notables that are written in C as far as I know). I think that if a language is sufficiently high performance and general purpose, it's fine for it to be the "core" language that other languages are expected to interface with.