Memory Mapped File Quirks [Greg] - BCL Team Blog - Site Home - MSDN Blogs

Memory Mapped File Quirks [Greg] - BCL Team Blog - Site Home - MSDN Blogs:

Recall that when you create a view of a memory mapped file, Windows aligns the view to virtual memory page boundaries. E.g., if your page size is, say, 4096 bytes, a memory-map view can only be 4096, 8192, 12288, ..., N × 4096 bytes large.

As our data file is smaller than a memory page, we get a view that is as large as a memory page (if the size of virtual memory pages on your machine is not 4096, then the output will also differ accordingly). The memory-map view contains the data supplemented with zeros. When we use a stream reader to read this data, we only reach the EOF mark when we get to the end of the entire view, not to the end of the original data.