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.

Process :Generally heavy weight by, the PCB holds kernel
objects the values generally referred as state information.

A application can be divided into two types in design phase:

1.Process - may affect application/program architecture
2.Threads - didn't affect architecture

Threads typically are spawned for a short-term benefit where
as process for long-term even the thread share its own
process address space is never larger than 4GB.

A single process may hold "n" threads so exchanging value
between process; then the cpu spend most of its time for
swapping it leads to thrasing definitely.


Threads easily exchange their locale variables within its
scope but exchange value between process stolen more cpu cycles.