This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Frank, As a machine is on, more and more things get cached. After a reboot, the cache is completely empty so everything you do is a disk access. This has the effect of making things signicantly slower until enough is cached again.