This memory is very specialized to fit into the Alienware R12 computer. You can’t mix this with other memory so if you had 4 slots and 2 were taken as was my case you must match the memory perfectly by using the exact same size modules and speed as well as model number. They must be exact in the R12. If you own one of these beast of a PC’s and want to go from the stock 32gb to 64gb like I did these memory modules work perfectly. The first boot after installing will take a long time as any addition of memory is checked bit by bit by the bios before it posts. It took about 7 minutes to boot and gave me the message that memory size has changed and I had to except the change in the bios and save it. After saving the new configuration the PC boots in 5 seconds to windows reflecting the 64gb.