You should note that I suggested the use of a file system that performed deferred writes, or that are based from virtual memory, and not a real disk. In any case, the pages just written are still likely to be in RAM, meaning that the write ahead is to RAM, and the read behind is from RAM. The real benefit of using a true file, is that the system can write the data to the file at its leisure, marking pages as clean and ready for reclaimation as necessary. Using a shared memory segment, for example, requires that the processes perform their own scheduling to ensure that the producer does not over-write pages not yet read by the consumer (during a fast network burst, for example). Using a file lets the kernel do this magic for us.