Managing connections

Dear Friends,
I want to know if I open a table to view the data a new connection is
opened. If I open another table/execute a query does a another new
connection is opened? As per manual, I know that for a database cluster and
the same port a postgresql instance runs. But if we run multiple SQL
statements from same client machine with same username, does postgresql
creates a new instance? If yes, how to manage memory? (As per my
observations, normally each postgresql instance takes 5-10 MB. So if we have
to manage simultenious 1000 connections, it will require 1000*5MB=5GB +
system memory requirements (approx. 1 GB) = total 6 GB (min.) Does this is
correct?)
Please give the details. I am using Win XP Pro with PostgreSQL 8.3.
Thanks
CPK

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