1.  reason - the control blocks for processes are larger 
than for threads (hold more 
	state information), so the amount of information to 
move during the thread 
	switching is less than for process context 
switching 
2.  reason - the major reason is that the memory management 
is much simpler for 
threads than for processes. Threads share their memory so 
during mode switching, memory information does not have to 
be exchanged/changed, pages and page tables do not have to 
be switched, etc. This makes the thread context switch much 
cheaper than for processes. In case of processes the memory 
pieces (pages) need to be exchanged, etc. (Will talk about 
the details in few weeks). 
3.  reason - threads do not have to worry about accounting, 
etc, so do not have to fill 
	out all the information about accounting and other 
process specific information in 
	their thread control block, so keeping the thread 
control block consistent is much 
	faster 
 





4.  reason - threads share files,  so when mode switch 
happens in threads, these 
information stay the same and threads do not have to worry 
about it   (similar to accounting information) and that 
makes the mode switch much faster. 
But the most expensive operation is truly the memory 
aspect.