4 ms·

I'm so confused. I can't find a good explanation of how applications and/or the OS "see" these DIMMs. How does my OS/app see this? Is it accessed like regular

I'm so confused. I can't find a good explanation of how applications and/or the OS "see" these DIMMs. How does my OS/app see this? Is it accessed like regular DRAM memory... except slower and persistent? Or would my OS see it as a "normal" drive... except one that's really fast and happens to be connected via a DIMM slot instead of PCIe/SATA/whatever?

sethhochberg 8y ago
Your operating system will see them as storage, not regular DRAM. Intel has released SDKs for developers to use if their applications need to be able to interact with persistent memory in any kind of detailed way (say, if you develop a database product, or a filesystem). http://pmem.io/pmdk/ http://pmem.io/pmdk/ It is very likely that generic kernel support will come for use in Linux and Windows directly, building on top of the existing DAX systems in those operating systems (DAX - direct access - APIs being used for IO to memory-like devices, bypassing cache layers which are useful for more traditional storage types). This would allow a user to create a regular old storage volume in their NVDIMM for general use. https://www.kernel.org/doc/Documentation/filesystems/dax.txt https://www.kernel.org/doc/Documentation/filesystems/dax.txt Do note that NVDIMMs aren't a drop-in replacement for regular DRAM DIMMS, despite using the same bus and electrical subsystem. You'll need proper hardware support on your motherboard and CPU, since memory controllers are on CPU these days.
- JohnBooty 8y ago
  That's a fantastic summary. Thank you!
- twic 8y ago
  > Your operating system will see them as storage Do you mean it will present them to userland as storage, rather than see them as storage? Seeing them as storage implies to me that the DIMM emulates an AHCI, which i don't think is the case.
  - sethhochberg 8y ago
    Correct yeah, I probably oversimplified that part a bit. The kernel will be fully aware that your NVDIMM is NVDIMM, none of the technical details available so far suggest there will be any kind of emulation of legacy storage protocols.

sethhochberg 8y ago

Your operating system will see them as storage, not regular DRAM. Intel has released SDKs for developers to use if their applications need to be able to interact with persistent memory in any kind of detailed way (say, if you develop a database product, or a filesystem). http://pmem.io/pmdk/ http://pmem.io/pmdk/ It is very likely that generic kernel support will come for use in Linux and Windows directly, building on top of the existing DAX systems in those operating systems (DAX - direct access - APIs being used for IO to memory-like devices, bypassing cache layers which are useful for more traditional storage types). This would allow a user to create a regular old storage volume in their NVDIMM for general use. https://www.kernel.org/doc/Documentation/filesystems/dax.txt https://www.kernel.org/doc/Documentation/filesystems/dax.txt Do note that NVDIMMs aren't a drop-in replacement for regular DRAM DIMMS, despite using the same bus and electrical subsystem. You'll need proper hardware support on your motherboard and CPU, since memory controllers are on CPU these days.

JohnBooty 8y ago
That's a fantastic summary. Thank you!
twic 8y ago
> Your operating system will see them as storage Do you mean it will present them to userland as storage, rather than see them as storage? Seeing them as storage implies to me that the DIMM emulates an AHCI, which i don't think is the case.
- sethhochberg 8y ago
  Correct yeah, I probably oversimplified that part a bit. The kernel will be fully aware that your NVDIMM is NVDIMM, none of the technical details available so far suggest there will be any kind of emulation of legacy storage protocols.