A method of managing memory mapped input/output (I/O) for a run-time environment is disclosed, in which opaque references are used for accessing information blocks included in files used in a dynamic run-time environment. The information block is stored in a shared memory space of pages that are each aligned on respective boundaries having addresses that are each some multiple of two raised to an integer power. The opaque reference used for the dynamic run-time environment includes at least an index, or page number reference into a page map of references to the pages of the shared memory space, and an offset value indicating an offset into the referenced page for the beginning of the storage of the information block. Control bits of the opaque reference indicate information such as the mapping mode, e.g., read-only, read-write, or private. Pages which are modified by a process may be written back to a backing store of the file based on control bits which indicate that a page has been modified.