Memory configuration (Supported)
2GB, 4GB and 8GB ECC or non-ECC unbuffered DIMM
Your picture shows 10600R as well as the extra chip in middle of stick.
"Registered" ("buffered"), improves signal integrity (and hence potentially clock rates and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, e.g. PC3-10600R. Typically modules with this designation are actually ECC Registered, but the 'E' of 'ECC' is not always shown. Whereas non-registered (a.k.a. unbuffered RAM) may be identified by an additional U in the designation. e.g. PC3-10600U.
The HP Workstation z220 won't work with "Registered" ("buffered") memory.