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
4GB RDIMM 2133MT/s Single Rank x8 DDR4 PC-2133P Memory // STI Kansas City
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
MemoryMasters Compatible 4GB 1333MHz DDR3 Single Rank DIMM Memory for Desktops (KTD-XPS730BS/4G) - Walmart.com
Kingston Technology 4GB 1333MHz DDR3 Single Rank DIMM Memory for Lenovo Desktop KTL-TCM58BS/4G at Amazon.com
647871-B21 HPE 4GB PC3L-10600R Single Rank X4 DDR3 Memory