cache line is provided per channel). For more information on the independentmemory mode, see “Independent memory mode” on page 55.– Lockstep memory mode:: This mode provides the best memory RAS features.It supports dual-device data correction (DDDC) for x4 SDRAM technology.The memory controller handles all cache lines across the two DDR3 channels(Channel 0 and Channel 1) on each memory channel. Each DDR3 channelprovides 4 x 8 byte data transfers (64 byte cache line is provided per channelpair). For more information about the lockstep memory mode, see “Lockstepmemory mode” on page 59.For more information and DIMM population sequence for independent memorymode, see “Memory mirroring in independent memory mode” on page 56 and“Memory rank sparing in independent mode” on page 58. For more informationand DIMM population sequence for lockstep memory mode, see “Memorymirroring in lockstep mode” on page 60 and “Memory rank sparing in lockstepmode” on page 62.Flash DIMMsThis topic provides information about eXFlash DIMM installation andrequirements.The IBM System x3850 X6 and x3950 X6 server provides support for eXFlashDIMMs. You can use Flash DIMMs in unused DIMM slots for solid state drivestorage on the server. For more information and notes about installing DIMMs, see“Installing a memory module” on page 47. Flash DIMMs are only supported inIndependent memory mode. For more information about DIMM installationsequence for Independent memory mode, see “Independent memory mode” onpage 55. The DIMM installation order for Flash DIMMs follows the independentmode (performance) installation order.When you install Flash DIMM, consider the following information:v RDIMMs must be installed in the server with Flash DIMMs. You cannot installall Flash DIMMs in the server.v RDIMMs must be installed first, then Flash DIMMs can be installed.v When you install Flash DIMMs, do not leave an empty DIMM slot betweeninstalled DIMMs.v For both the 4-socket and 8-socket configurations, one Flash DIMM can beinstalled in each DDR3 channel. A maximum of 8 Flash DIMMs can be installedin each compute book. A maximum of 32 Flash DIMMs can be installed in theserver. In the 8-socket configuration of the server, the Flash DIMMs must beinstalled in the bottom node only.v Mixing of LRDIMMs and Flash DIMMs in the same server is not supported.v Flash DIMMs are supported in Independent memory mode only.v Flash DIMMs are not supported in Lockstep memory mode, memory mirroring,or memory rank sparing.v You can install any configuration of the supported Flash DIMMs (up to 32 FlashDIMMs) in the server.v The same level of firmware should be installed on all Flash DIMMs in theserver.v When you install Flash DIMMs in the server, see “Environment” in the “Serverfeatures and specifications” on page 7 section for the supported environmentinformation for Flash DIMMs.Chapter 2. Installing optional devices 51
