Yes, they can. All of my blades in production are HS21s although they are still only on dual core CPUs and only have 16GB of RAM. We are getting ready to stage in the upgrades to bring them all to Quad-core CPUs and 32GB RAM. Each of ours have the daughter expansion so they take up two slots. but after a year in production have been flawless. Let me know if you have specific configuration questions.