When a PC has 1.5 Gigabytes of RAM available to it, and is showing a KDE desktop running Mepis6.0 (uses Ubuntu engine), with nothing special happening, why is it necessary that we should ever hear a disk access other than when some new window or application is opened the first time that session?

A click on the Konqueror icon brings a dandy little series of crunches, with a repeat performance when the window is closed. Same is true of almost any action.

This is not about me desiring a life sans disk crunches. I already know that the algorithms that manage desktop response and memory are subtle and sophisticated, and probably would tax most users understanding. Maybe this is something specific to KDE - I don't know.

Given that the entire set of running services plus applications of interest, and all the temporary files they could generate could fit in the RAM I would have expected that one could compute at length, with the hard drive spun down on standby much of the time.

So - for those who know, do tell

mmmmmmmmmm???!!! Never heard my disk go crunchy-crunch. I have got a squeaky CD-RW drive though.

Linux is a complex OS.
There are a lot of processes running in the background, although they'll mostly be idle. There will also be cron jobs running from time to time (eg updating the locate database, compressing and rotating log files etc.).

You can see what process are running with the ps -Al or top command. So it is normal for disk activity to occur at seemingly random intervals. Do not worry about it!