when specifying commit=nrsec in fstab, does that mean data does not get written to disk until that time has passed ? so where is the data until then ? in memory ?

and if it is that simple, why would someone bother creating a program (noflushd) that does the same thing while a very effective method already exists ?

what other methods of write caching are available on linux ? and are the write caching algorithms in linux kernel are better than programs with their own cache algorithms ? are there significant advantages to have a system-wide write cache ?

can read-cache be configured on linux ? the size and/or time, separately for libraries/code and data ? or percent allocated for each category ? I know that all unused memory is used for cache in linux, but I do not know what is stored there and how it is decided to be stored there, and it sounds like a good idea to be able to control what gets stored there.