IBM® 00D4980 Compatible Factory Original 8GB DDR3-1333MHz Registered ECC Single Rank x4 1.35V 240-pin CL9 Very Low Profile RDIMM | Your Fiber Optic Solution | Proline
Kingston Technology 8GB 1600MHz DDR3 Reg ECC Single Rank DIMM Memory for HP/Compaq Desktop KTH-PL316S/8G at Amazon.com
Beware of the single rank x16 RAM kits sneaked in some laptop models! The 1Rx16 modules have significantly lower bandwidth compared to the 1Rx8 variants - NotebookCheck.net News