Hi, I'm Jewel with Kingston Technical Support and would like to offer some clarification. Part numbers KVR1333D3S9/4G and KVR13S9S8/4G are essentially the same, except for the DRAM chips used to make them. KVR13S9S8/4G is single rank and uses high density DRAM (4Gbit) while KVR1333D3S9/4G is dual rank and uses lower density DRAM (2Gbit). Both memory when purchased New from a valid reseller carry a lifetime warranty. Part KVR13S9S8/4G is the newer version that is the replace by part of KVR1333D3S9/4G. The only issue to consider between these two modules is the density of the DRAM, older computers may not support high density or single rank 4GB modules. If the system supports single 8GB modules it should support single rank 4GB modules. If you get part number KVR1333D3S9/4G, you do not have to worry about it but it is always best to check compatibility. This can be done by giving us a call or looking up your system in our Memory Search (http://www.kingston.com/us/memory/search/options/). For any further assistance with our products, please call us at 1-800-435-0640 (USA and Canada only) M - F 6am - 6pm PT and I or another available Technician will assist you.
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