Performance vs. Scalability

 systems capability to provide a certain response time is performance . to process some data or to serve specified users  performance should be good.

when there is increase in the number of users we cannot meet our performance goals ,that time we can think of scalability.

When there is increasing amount of load on a system/device we can increase its performance either by adding extra hardware or by upgrading the current system configuration this is known as scalability. 

performance is a software quality metric. where as , Scalability refers to the characteristic of a system to increase performance by adding extra hardware or by upgrading the current system configuration.