Both the Dell PowerEdge R720 and the Dell PowerEdge R720XD are 2U rackmount servers. These rackmount servers have the capability of running Intel Xeon E5-2600 series and Intel Xeon E5-2600v2 processors *You must have BIOS revision 2.0.19 update or later installed to use the v2 processors. These rackmount servers also offer twenty-four DDR3 slots for RDIMMS, LRDIMMs, and UDIMMs.
The R720XD weighs in at just a few pounds more than the R720 due to its significant increase in Hard Drive Bays. The R720XD has a few different options for hard drive bays and can hold a staggering twenty-four two and a half inch hard drives or twelve three and a half inch hard drives while the R720 can only hold a maximum of sixteen two and a half inch or alternatively eight three and a half inch hard drives.
For v1 processors, BIOS revision 1.4.8 upped the maximum frequency supported to 1600MHz for both RDIMMs and UDIMMs when using one or two channels at either 1.5V or 1.35V. BIOS update 1.4.8 also upped the maximum default frequency to 1333MHz on a three DIMMs per channel layout for both RDIMMs and LRDIMMs.
While moving up the BIOS update chain, if you are using BIOS update 2.0.19 you will be able to use the Intel Xeon E5-2600 v2 processors and also the LRDIMM will support 64GB because in a patch released before the v2 processors were even compatible they released an update (BIOS update 2.1.2) that made that possible. In a later update (BIOS update 2.4.3) LRDIMMs at two DIMMs per channel will have its max supported memory speed upped to 1866MT/s for 32GB.