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A memory-mapped file is a segment of virtual memory [1] that has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on disk, but can also be a device, shared memory object, or other resource that an operating system can reference through a file descriptor.
File-backed mapping maps an area of the process's virtual memory to files; that is, reading those areas of memory causes the file to be read. It is the default mapping type. Anonymous mapping maps an area of the process's virtual memory not backed by any file, made available via the MAP_ANONYMOUS/MAP_ANON flags.
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
For example, a C++ compiler inserts vtables, type info objects and many temporary and anonymous objects that are active during a program's execution. In a Java program, the memory footprint is predominantly made up of the runtime environment in the form of Java virtual machine (JVM) itself that is loaded indirectly when a Java application ...
A Data Mapper is a Data Access Layer that performs bidirectional transfer of data between a persistent data store (often a relational database) and an in-memory data representation (the domain layer). The goal of the pattern is to keep the in-memory representation and the persistent data store independent of each other and the data mapper itself.
In embedded system programming, it is very common to have memory-mapped I/O where reads and writes to memory trigger I/O operations, or changes to the processor's operational mode, which are highly visible side effects. For the above example, assume for now that the pointers are pointing to regular program memory, without these side-effects.
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Instead of using standard input and output as with an anonymous pipe, processes write to and read from a named pipe, as if it were a regular file. All POSIX systems, Windows, AmigaOS 2.0+ Shared memory: Multiple processes are given access to the same block of memory, which creates a shared buffer for the processes to communicate with each other.