@author: there's room for improvement
I enjoy reading articles which discuss new server models (which is rare enough, the articles not the servers) but the article doesn't really show that the author really know much about the stuff he's writing about. Two examples:
"The machine comes with two processors standard, but if you want the full memory addressability of the system and the full I/O capability, you need all four processors to be plugged in because the memory controllers and PCI-Express 3.0 controllers are on the die, not on the mobo. This is exactly the case with all Xeon E5-4600 machines, not just those made by HP."
Well, since it's unsurprisingly not just the case for HP XEON E5-4800 machines, the author may have wanted to use the industry-known term for that: it's called 'NUMA' (Non-Uniform Memory Architecture, each CPU has its own local memory). And this is nothing new for the XEON E5-4800, the 2-socket variant (E5-2000) is NUMA as well as are it's predecessors (XEON 5500/5600 series). As are all AMD multiprocessor Opterons since the beginning of time btw.
"The system has an embedded Smart Array P420i/ZM RAID 0 and 1 disk controller, which can be upgraded with models with 1GB or 2GB of write cache and RAID 5 support."
Yes, the P420i can be upgraded with FBWC memory modules which add RAID 5 capability. However, it may be worth mentioning that via an Smart Array Advanced license RAID 6/ADG can be added as well, aside from unlocking further functionality.
As a final note, HP puts out detailed spec sheets (called 'quickspecs' in HP speak) for most of its business products, and a search for them on Google helps to avoid to copy little and often incomplete and incorrect information from the HP homepage.