DDR3 1066Mhz PC3-8500 HP Memory
DDR is short for double data rate, DDR3 ram comes in a few varieties. PC3-8500, PC3-10600, & PC3-12800. The most popular of this type was the PC3-10600. The fastest DDR3 memory is PC-3 12800, but generally PC-3 8500 will be the cheapest and is very popular for memory upgrades.
When servers are being upgraded they're generally adding to what is currently in the system, so servers that came with PC-3 8500 often simply add more instead of replacing all the memory in the system. Some of the popular servers that used PC-3 8500 are HP ProLiant DL360 G6 1U server and the ProLiant DL380 G6 2U servers.