Squid memory usage

Hi The school has a proxy server with 512Mb of memory. The only major service running on it is Squid. The server acts as a proxy for approx 35 machines. Will squid (depending on demand) use all available memory or are there self imposed limits? Are there other ways of tuning squid? Should I really mess about with squid.conf!? For example, what does this actually result in ? cache_mem 320 MB Thanks in advance for any help Mike Rees Ysgol Glanymor School Heol Elfed Burry Port Llanelli SA16 0AL Tel 01554 832507 Fax 01554 832424 mike@glanymor.carms.sch.uk