pt60 run for maximum employees ?

hi all ,

As w are having nearly 1400 employees , so i want to run PT60 for them , so system is not picking all employees it is going to overflow error , so kindly let me know , a standard sap server with 8 GB capacity of RAM can pick how many employees and if we want to run for more employees what we need to do the process ....?

Regards,

Jwala.