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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.
The main difference between System V shared memory (shmem) and memory mapped I/O (mmap) is that System V shared memory is persistent: unless explicitly removed by a process, it is kept in memory and remains available until the system is shut down. mmap'd memory is not persistent between application executions (unless it is backed by a file).
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.
Memory-mapped I/O, an alternative to port I/O; a communication between CPU and peripheral device using the same instructions, and same bus, as between CPU and memory; Virtual memory, technique which gives an application program the impression that it has contiguous working memory, while in fact it is physically fragmented and may even overflow ...
In computing, an input–output memory management unit (IOMMU) is a memory management unit (MMU) connecting a direct-memory-access–capable (DMA-capable) I/O bus to the main memory. Like a traditional MMU, which translates CPU -visible virtual addresses to physical addresses , the IOMMU maps device-visible virtual addresses (also called device ...
Programmed input–output (also programmable input/output, programmed input/output, programmed I/O, PIO) is a method of data transmission, via input/output (I/O), between a central processing unit (CPU) and a peripheral device, [1] such as a Parallel ATA storage device. Each data item transfer is initiated by an instruction in the program ...
In computer science, a memory map is a structure of data (which usually resides in memory itself) that indicates how memory is laid out. The term "memory map" has different meanings in different contexts. It is the fastest and most flexible cache organization that uses an associative memory. The associative memory stores both the address and ...
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.