JEDEC DDR4 Revision B Spec: What’s different?

The JEDEC JC42.3 committees have issued the B version of the DDR4 specification. This version is several years in the making as the original JESD 79-4 DDR4 SDRAM specification was released in September 2012 and the A version published in November of 2013. Those of us in JEDEC have been using the task group version of this spec for several years, finally it is available to non JEDEC members. So what is new and exciting about this B revision? Let’s take a look! Ballouts A X32 ballout was added so we can get a 32 bit bus in a single package. Provisions were also added for a 2 die stack in this configuration. Editorial Updates Several changes to make things clearer. This is in response to ambiguities and misunderstandings that have happened over the years with the A version Single Rank Dual Die per package This specifies how to put 2 x8 die to create a x16 configuration. 8GB,16GB and 32GB addressing was also specified. Targeted Row Refresh Contrary to popular belief TRR is NOT in the final B version. It was for a while, but then removed. Originally, this was in response to the Row Hammer issues of DDR3. Looks like the DRAM vendors found another way to reduce RH failures for DDR4 other than making the Memory Controller babysit frequently accessed Rows. DDR4 does exhibit fewer Row Hammer failures….but it still has some Row Hammer failures (that’s a whole different article!) 3DS Although there is a separate specification for 3DS, the B version does add additional CAS/CW latencies for 3DS. Post Package Repair This is enabled/disabled in...
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