HP 8GB DDR4 2133MHz ECC Registered Single Rank x4

This high quality latest generation DDR4 memory module is designed for performance systems, servers and multiprocessor computers with ECC Registered technology support. The DDR4 memory provides higher date throughput and lower energy at the same frequency compared to the previous generation. The ECC technology checks transparently and in real time integrity of data stored in the memory. It can find and fix mistakes in a single bit and detect the error in two bits. Some memory controllers can repair large-scale mistakes in conjunction with the ECC memory. Most server boards require memory with ECC support.
The registered memory is equipped with a controller which manages the access to individual memory modules, making it easier for the memory controller and motherboard or processor to work.  

The memory behaves externally as a single module - the register chip - which is responsible for the writing and reading of individual memory cells, and transfers the controller to the results of these operations. This increases the efficiency of the memory access and the processing speed even when using more memory modules simultaneously. Some server boards require registered memory.
The memory has a separately addressable area (Memory rank). Most server chipsets have a limited memory rank or directly specified memory configuration for each slot, so you must track this for future upgrades - if you reach the full rank of memory on the motherboard, you will not be able to add another module even if there are memory slots available.
The "x4" chipset is designed for the most demanding applications, supporting a broad range of professional technologies such as multiple-bit error correction, Chipkill, memory scrubbing and Intel Single Device Data Correction (SDDC), making it ideal for mission-critical applications and servers.