A FORTRAN callable library is provided for accessing IAM files. This library exists purely for reasons of speed - there is no other snag in choosing to use FORTRAN unformatted I/O instead. No equivalent library is provided for calling from C - this is unnecessary, because the FORTRAN-callable library is mostly just providing wraparounds for the standard C functions fopen, fclose, fread, fwrite, fseek.
The library can be obtained from ROE using ftp.
It requires the Starlink CNF library which can also be got by ftp.