[karmakaze]

The basic difference is that the API is a specification at a level higher than the hardware, e.g. source language. An application binary interface specification is at the machine code level. Often compilers, linkers, and operating system conventions all all tied together and the libraries and calling programs follow the same rules.

Note that there can be more than one. Typically the C calling convention was commonly used where the caller pushes data onto the stack, calls a function, and upon return the caller pops the data it pushed. The advantage of this is for variable length argument lists there's less chance of mismatch. A 'pascal' convention was popular on Windows and OS/2 where the called function would use a single instruction to return and pop N bytes. It also made the code slightly smaller as the callers didn't need the pop instructions. That ABI was specific Windows and OS/2 GUI interfaces but compilers would also let you choose for your own libs--I don't know/remember what the kernels used.