The major difference between threads and processes is 
1.Threads share the address space of the process that 
created it; processes have their own address.

2.Threads have direct access to the data segment of its 
process; processes have their own copy of the data segment 
of the parent process. 

3.Threads can directly communicate with other threads of 
its process; processes must use interprocess communication 
to communicate with sibling processes. 

4.Threads have almost no overhead; processes have 
considerable overhead.

5.New threads are easily created; new processes require 
duplication of the parent process.

6.Threads can exercise considerable control over threads of 
the same process; processes can only exercise control over 
child processes. 

7.Changes to the main thread (cancellation, priority 
change, etc.) may affect the behavior of the other threads 
of the process; changes to the parent process does not 
affect child processes. 

Process is a program in execution where as thread is a 
seperate path of execution in a program.

process is a execution of a program and program contain set 
of instructions but thread is a single sequence stream 
within the process.thread is sometime called lightweight 
process. single thread alows a os to perform singler task 
ata time similarities between process and threads are: 
1)share cpu. 
2)sequential execution 
3)create child 
4)if one thread is blocked then the next will be start to 
run like process. 
dissimilarities: 
1)threads are not independent like process. 
2)all threads can access every address in the task unlike 
process. 
3)threads are design to assist onr another and process 
might or not might be assisted on one another.

Technically, a thread is defined as an independent stream 
of instructions that can be scheduled to run as such by the 
operating system.
So, in summary, in the UNIX environment a thread: 
o	Exists within a process and uses the process 
resources 
o	Has its own independent flow of control as long as 
its parent process exists and the OS supports it 
o	Duplicates only the essential resources it needs to 
be independently schedulable 
o	May share the process resources with other threads 
that act equally independently (and dependently) 
o	Dies if the parent process dies - or something 
similar 
o	Is "lightweight" because most of the overhead has 
already been accomplished through the creation of its 
process. 


Whereas in case of process, every process has its own 
memory management, two process cannot communicate without 
using IPCS or Sockets, they do not share resources and 
every process has its own process ID(pid).

simply say thread is a light weight process(flow of
execution throw the process code)....
  but process is heavy  weight(heavey weight) process

A programm  in execution,as mentioned is a process.A time
share user program such as a complier is a process.
A thread is contain a peace of code  and each processor
contain the one or more threads.

process
threads

A Thread is a smallest execution unit of the Process.
While a process can have multiple threads.

process is a program in execution whereas thread is a light
wight process and has separate path.

Process is a seprate one and a thread is pa part of any process .Process can't communicate other processes but thread do it easily