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The ability to use an SDRAM memory from any manufacturer it is necessary to have a common standard. To enable SDRAM DDR memories to be sourced from any supplier, a standard has been drawn up by, JEDEC, Joint Electron Device Engineering Council.
In this way it is possible to equipment manufacturers to source their components from any manufacturer of DDR SDRAM knowing that they are interchangeable. This is important when it is necessary to be able to state a second source on any components.
This can only be done if they conform to the same standard. Accordingly JEDEC developed their standard JESD79 to enable manufacturers of DDR SDRAM to produce product that was interchangeable.
JEDEC DDR SDRAM Standard JESD79 outline
The JEDEC DDR SDRAM specification or standard defines all required aspects of 64Mb through 1Gb DDR SDRAMs with X4/X8/X16 data interfaces. It includes a whole variety of elements including features, functionality, ac and dc parametrics, packages and pin assignments.
The DDR SDRAM specification is expanded will be expanded to formally apply to x32 devices, and higher density devices as well.
The aim of the JEDEC JESD79 DDR SDRAM Standard is to define the minimum set of requirements for 64Mb through 1Gb, X4/X8/X16 JEDEC compliant DDR SDRAMs.
This enables system designs based on the required aspects of the specification to be supported by all DDR SDRAM vendors providing JEDEC compliant devices.
JEDEC DDR SDRAM Standard JESD79 releases
As with any stanard, the JEDEC 79 standard has undergone a number of updates and revisions to enable it to meet the current requirements, keeping pace with technology:
|JEDEC JESD79 Releases|
|JESD79 Release Verson||DDR Type|
|JESD-1 (June 2000)||DDR|
Updates of the individual JESD standars are of the form JESD-XV, where X is a numeric indicating the standard version or type, and V indicates the version of that standard, e.g. JESD-3F is version F of JESD-3 for DDR3 memories.