- written by Phil Muck, Dataram Memory Blog Team Member
Not all DIMMs are created equal. That is where the JEDEC Memory Module committee JC-45 comes into play. The JEDEC JC-45 committee is comprised of major DRAM manufacturers such as Samsung, Hynix and Micron and major DIMM manufacturers such as Dataram. The committee is responsible for the creation of memory module standards, including various DIMM types such as Unbuffered DIMMs, Registered DIMMs, Buffered DIMMs, Low-Profile DIMMs and SODIMMs.
DIMM families such as DDR, DDR2, and DDR3 were all developed and standardized by JEDEC. Future DIMMs such as DDR3 Load Reduced and DDR4 are now in development.
Before a DIMM becomes a JEDEC standard memory module, months of up-front development take place. All the topics listed below are reviewed and discussed. If changes are required, adjustments to the design are made and the review process is repeated. The final design is voted on and approved by the JEDEC members before a DIMM becomes a JEDEC standard.
- DIMM Configuration
- Connector Pin Outs
- DIMM Dimensions
- PCB Traces Topologies
- Clock Stub Lengths
- Impedance Controls
- Power Plane
- PCB Stack-Ups
- System Verification
Non-JEDEC compliant DIMMs may have an initial low up-front cost, but the long term costs of unstable systems errors, system crashes and downtime outweighs that initial saving. Skipping any of the above steps could have devastating consequences to the data integrity of your workstation, servers and blades. Incorrect PCB stack-up may cause crosstalk issues. Incorrect impedance may cause signal integrity issues. Inadequate power plane designs may cause random ECC errors. A DIMM is more than some DRAMs on a PCB. A correctly designed DIMM has hundreds of hours of engineering behind it.
Why use JEDEC compliant DIMMs? DIMMs developed in accordance with JEDEC memory module standards assures 100% compatibility in today’s computer servers, desktop systems, telecommunication and other consumer and business applications. A DIMM manufacturer that is an active JEDEC member understands the steps required to make a reliable DIMM and they also understand the consequences of taking shortcuts.