Thank you for contacting us today. I pulled up your system requirements and I do see what you mean. Based on the memory configuration guide found here: http://h20331.www2.hp.com/Hpsub/downloads/Z820_Memory_Configurations.pdf, it does appear that these memory modules are not specified. This could be because the guide came out in 2012 when these memory modules were not available. From our testing we can guarantee that these memory modules are compatible with your system if you are following all other guidelines from that sheet. Please let me know if you have any other questions or concerns.