Below is the exact response we got back from Innodisk.
Fixed die and non-fixed die are terms that Innodisk uses to differentiate two types of the exact same module.
In regards to the 8GB DDR4-2666 1Gx8 UDIMM VLP module, a part number with the following will represent:
M4UI-8GS1VC0K-C (fixed die part number)
- The letter "C" appended at the end shows and denotes that the module is built from the Samsung 18nm C-die IC.
- If this part number is selected, then we will provide and supply only C-die ICs for the longevity and duration that Samsung will support producing this IC. The current long term Samsung roadmap shows that this IC is going to be built by Samsung until 2022 but this is a reference as they can always change their mind down the road. Once the C-die goes EOL, then we will not provide the module with part number M4UI-8GS1VC0K-C.
M4U0-8GS1VCIK (non-fixed die)
- The 4th character "0" means that the module is a running non-fixed die. We don't show the C-die at the end of the part number. If the C-die goes EOL, and Samsung migrates to the next generation of the IC which will be the M-die, then Innodisk will perform a running change from the C-die to the M-die to continue everlasting supply and longevity of the module with part number M4U0-8GS1VCIK .
As of right now, both M4UI-8GS1VC0K-C and M4U0-8GS1VCIK are built to the same exact specifications in terms of the C-die and corresponding PCB.