Recently,i just learn the mameo's file system?As we all know.there is RAM/ROM,but i want to know more about this.

Just like
1.the swap on the device:when the RAM is low or other situation, the the file will be stored in swap?
2.The file system contains dirty,clean RSS and soon on,what is the different between them?

Thanks

Br,
Jackie

I think you're messing things up, first of all "file system" may refer to a disk, or the software used to store data on the disk. I'm assuming you mean the latter.

the N900 has at least those different file systems:
/ -> should be "rootfs"
/home -> ext3
/home/user/MyDocs -> vfat
swap
/tmp -> tmpfs
/proc -> procfs
etc. etc., you should see all of them by logging via terminal and typing "mount".

Now, since I can't understand the second question at all, I'll answer to the first one: the swap file system is used when the system is low on memory. Memory "pages" (blocks of .. 64kb?) which are not used for some time are copied there and removed from RAM. It is not used to store "files", it's a very lower level memory management thing. You don't know, and shouldn't care, if the system is storing there a "file", a program, a network buffer, etc. When a process tries to access to that memory again, it is copied back to RAM for use.

the other FSs exist to serve different purposes, i.e. tmpfs is a ram disk which is lost upon reboot, procfs is a virtual file system used to access processes infos organized like in a FS (i.e. /proc/<process number>/fd/ contains the open file handles for that process)

A better/fuller explanation can probably be found on wikipedia