Difference between unit testing and system testing.

Unit Testing	System Testing
It is done in an existing program unit. The program unit can be a function or method.	The purpose of system testing is to identify and correct errors in the candidate system.
It is always done by the programmers.	Such testing is conducted by testers and system analysts.
Unit testing is always preceded by module testing because a program is the combination of the modules.	A system testing is preceded by system documentation and a report is generated on the overall performance of the system.
It uses stub and skeleton where stub are the functions and skeletons are the code inserted inside the function.	It uses term around time, back up and file protection.
It requires less support of H/W during the testing.	H/W support in case of system testing is much require because overall performance of the system is described by the H/W architecture.