Memory mapping: Difference between revisions

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{{mergeto|Memory-mapped I/O}}

In [[computing]], '''memory mapping''' may refer to:

* [[Memory-mapped file]], also known as <code>mmap()</code>

* [[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 on to disk storage

==See also==

'''Memory mapping''' is a process whereby some item of digital hardware is connected to a [[central processing unit|processor]]'s address bus and data bus in such a way that it can be accessed (for reading and/or writing) exactly as if it were a memory cell.

* [[Port-mapped I/O]], a method complementary to Memory-mapped I/O

{{disambiguation}}

This is used as an alternative to connecting it to an I/O port, especially in [[embedded system]]s.

For example, an [[analog-to-digital converter]] could be memory mapped to a certain address. When that address is written to, the conversion is started; when the address is read from, the data is transferred to the processor.

Sometimes only partial address decoding is used, meaning that the device effectively occupies a much larger block of memory space than is strictly necessary. This can be a problem if the memory space is small (e.g. with a 16-bit address bus which can only address 65,536 different locations).

Memory mapping also hogs the address and data buses if the mapped device is slower than true memory (as for instance, a [[Successive Approximation ADC|successive approximation A-to-D converter]] might well be).

[[Category:Microprocessors]]

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