http://wiki.squid-cache.org/SquidFaq/InstallingSquid#head-56167774a7ab4b9ec2fb1b0bd20a74b4d984776c It says essentially this: Can Squid benefit from SMP systems? Squid is a single process application and can not make use of SMP.But what about Posix threads & Async IO? (./configure --enable-async-io=2 ...)? Don't they take advantage of multiple CPUs/cores/cache_dirs?