thrashing is caused by an excessive amount of page swapping between the main memory and secondary storage.
but how does the OS detect the problem(thrashing)?
and how to fix it?

and

what's the purpose of modified bit serve in demand paging?
is it want it to be loaded faster???... it seems that demand paging introduce the concept of loading partial of program into the memory and when begins the pages'll be loaded into the memory as they'r e needed.

Hello,

I am not sure how the OS is going to detect thrashing. I know that I can detect it by looking at logs, and looking at the size of the swap file, and seeing what is going on in real time. If your logs show that the CPU is waiting, and your I/O systems are busy, you know something is not right.

As for your bitserve question, I no longer have my OS book handy to look that information up. Sorry there.

Christian

that's ok
thanks anyway