Unlike SRAM (cache) or flash (USB drives), DRAM is forgetful. Literally. The capacitors holding your "1"s and "0"s leak charge in milliseconds. JESD79-4D dictates that every single row of memory must be read and rewritten every 64 milliseconds (standard temperature) or 32 milliseconds (hot environment).
: An architectural deep-dive and physical implementation of the JESD79-4D DDR4 standard . Paper Contributions : jesd79-4d pdf
An overview of how DDR4 SDRAM works, including its architecture and the functionality of its components. Unlike SRAM (cache) or flash (USB drives), DRAM is forgetful
Without periodic ZQCS, driver impedance and ODT values drift with temperature, causing signal integrity failures at 3200 MT/s. JESD79-4D dictates that every single row of memory
First published in September 2012, the standard has seen multiple updates (4A, 4B, 4C) to incorporate new features like 3D Stacked SDRAM (Addendum No. 1) and refined timing parameters.
The "JESD79-4D" specifically refers to a revision of the JEDEC standard focused on DDR4 SDRAM. DDR4 is a type of synchronous dynamic random-access memory (SDRAM) with a high bandwidth interface. The "D" in "JESD79-4D" denotes the document revision level, indicating updates or revisions to the standard to reflect advancements in technology, new testing methodologies, or to clarify specifications.
While DDR4 was mature by 2021, JESD79-4D introduced critical bug fixes and clarifications, not revolutionary features. Key updates include: