MATLAB Programming

Accessing Files with Memory-Mapping
Benefits of Memory-Mapping
The principal benefits of memory-mapping are efficiency, faster file access, the
ability to share memory between applications, and more efficient coding.
Faster File Access. Accessing files via memory map is faster than using I/O
functions such as fread and fwrite. Data is read and written using the
virtual memory capabilities that are built in to the operating system rather
than having to allocate, copy into, and then deallocate data buffers owned by
the process.
MATLAB does not access data from the disk when the map is first constructed.
It only reads or writes the file on disk when a specified part of the memory
map is accessed, and then it only reads that specific part. This provides faster
random access to the mapped data.
Efficiency. Mapping a file into memory allows access to data in the file as
if that data had been read into an array in the application’s address space.
Initially, MATLAB only allocates address space for the array; it does not
actually read data from the file until you access the mapped region. As a
result, memory-mapped files provide a mechanism by which applications can
access data segments in an extremely large file without having to read the
entire file into memory first.
Efficient Coding Style. Memory-mapping eliminates the need for explicit
calls to the fread and fwrite functions. In MATLAB, if x is a memory-mapped
variable, and y is the data to be written to a file, then writing to the file is
as simple as
x.Data = y;
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