Questions on Caching Only NameServer

[amran at isp.time.net.my]

Hi all

Currently, I'm having a very high load on my DNS servers and slowliness on
the external DNS queries.
So, I would like to install a Caching only NameServer on my site. It will
obtains information from another server (Root or a Zone Master) when asked
by a host query and then saves (caches) the data locally. On a second or
subsequent request for the same data the Caching Server will respond with
its locally stored data until the time-to-live value of this data expires at
which time the Caching Only NameServer will refresh the data from another
Name Server (Root or Zone Master). 
The primary purpose of a 'caching' DNS server is to reduce the high load on
my Primary & Secondary DNS and to increase the speed of response to DNS
queries especially on sites with slow links. 
Questions :
1) Where does the caches data being stored in the Caching Only NameServer ?
Is it in the memory or harddisk ? What is the best specifications to setup
the server?
2) What will happen to the caches data if  I killed the services, reboot or
down the server?
3) What is the best products to run a Caching Only NameServer ?
Thanks.