postgreSQL query via JDBC in different OS taking different running time?

Hi,

I want to know the reason behind the case:

My query processes from JDBC (Java Program) to PostgreSQL. I use system time by invoking java function, I collect one time unit before the query statement perform and second after the execution of query statement. 

I found 85 ms time unit in DOS (win7) (laptop 4cores). both Java and PostgreSQL installed and invoked on the same machine, respectively.

On the other hand, I use same process (separate installation) on linux on 8 cores physical machine with 2times greater then laptop. 

I found 150 ms. (which is a question for me because the time in Linux environment should give me half of the time taking on laptop)

I also make same setting  of postgresql.conf in the linux setup, which is available same in the win7  setup, because win7 setup gives better performance of the query.

What do u suggest me, where I need to make performance tuning? which configuration setting must need to modify in the linux?

 * laptop RAM 4 GB and Linux machine 32 GB