Does Squid move objects from disk to RAM?

[Brett Glass <squid-users@xxxxxxxxxxxxxx>]

In a typical multilevel cache (e.g. the ones we see on 
microprocessors), data that's fetched from a lower level cache is 
kept in higher levels of cache in case it's used again. Due to the 
principle of locality of reference, this practice usually pays off. 
However, in my use of Squid I haven't seen TCP_MEM_HITs when an 
object that's in the cache is accessed multiple times, even in 
rapid succession.

Does Squid "promote" objects from disk to RAM? And if not, why not? 
If it doesn't, restarting a Squid cache could cause a substantial 
loss of performance, because objects which were previously in RAM 
won't be restored to it and will be fetched more slowly thereafter.

--Brett Glass