PPT Slide
Memory-mapped File I/O
- Explicit file I/O (use of open(), read(), write() and close()) is similar to paging to a swap area.
- Paging involves implicit I/O that the programmer isn’t aware of; file I/O involves explicit instructions that the programmer needs to be aware of to perform the I/O.
- Both, however, involve reading and writing disk blocks. The information in the swap area is transient in that the next page of a process that is swapped out will overwrite any earlier page. File I/O is not transient; the file write()s stick.
- Why not use the paging mechanism for use with persistent file data?