Servlet config is a private area for every servlet.Any 
variable stored there is accessible to only that servlet 
while sevlet context is a shared area for every servlet in 
an application.In an aaplication every servlet can access 
the variable stored in servlet context.

Servlet Context :
In servlet programming, the servlet context is the
environment where the servlet runs. The servlet container
creates a ServletContext object that you can use to access
information about the servlet's environment.

ServletConfig:
A servlet configuration object used by a servlet container
used to pass information to a servlet during initialization.

Servlet context is a context for all servlets under the web 
application.in the web application there is only one 
context.and all the servlets communicate each other through 
context and it uses context parameters
In the web application each servlet have one servlet config 
object it uses init parameters.

servlet config is used to obtain configuration data when it
is  loaded in to the application server.
for each servlet servlet config will be indipendent and the
configuration of a servlet is intialized in the servlet
config file.

servlet context is used to obtain the information about the
environment in which it is running.one application have only
one servlet context file.through this servlet context file
we can acces servlets in that application.

servlet context hold the info about application and servlet
config hold the servlet info.