One of the biggest problems in computing is the speed of access to data. Only the RAM is fast enough that the CPU can run from it. Fortunately, with the arrival of NAND Flash memory, new standards have appeared that solve the dilemma of capacity versus speed.
NVDIMM – Non-volatile memory on DIMMs for DDR
Non-volatile memory can be divided into two types according to its level of access in the hierarchy. On the one hand, we have the classic NAND Flash of SSD units, which is accessed through PCI Express and SATA I / O interfaces and which are in a hierarchy below the RAM memory for access.
The other type of non-volatile memory is that with which the CPU can communicate making use of the interfaces with which it accesses the RAM, which are much faster and allow access to said memory with lower latency, since it does not have to go through the IOMMU, and not have to use uneven paths to copy data where the bandwidth is usually that of the slowest bus.
An example of the second type was Intel Optane memories, well, the JEDEC has created with DDR4 NVDIMM-P a type of non-volatile memory that uses the interface of DDR4 memory. This allows the CPU to see the non-volatile memory module as part of the RAM and access data faster than a classic SSD, even faster than an NVMe PCIe SSD.
NVDIMM-P Technical Specifications
The first and most important thing is that as it is non-volatile memory, data will not be lost if the system is turned off. Which is ideal for servers, which have to be running 100% of the time and where data loss is a problem. Thanks to the NVDIMM-P it will be possible to return to the previous state. Furthermore, it is widely useful for multitasking with many programs, as it allows the operating system to send data from RAM to the NVDIMM quickly.
Furthermore, sharing the same bus as DDR4 memory allows very fast copies from RAM to NVDIMM-P and from NVDIMM-P to RAM. On the other hand, since graphics cards have access to RAM through their DMA drives that allow them to access RAM through the PCI Express port, the NVDIMM-P can also be used by standard GPUs without additional hardware. for DirectStorage.
The NVDIMM-P modules have access to both NAND Flash memory and DRAM memory mapped within the memory addressing, a particularity that makes it unique compared to previous NVDIMM standards from the JEDEC.
A number of JEDEC standards are known as NVDIMMs. Apart from the new NVDIMM-P there are other NVDIMM standards which are as follows:
- NVDIMM-F: It is an SSD disk with a DDR interface, inside there is no memory of any kind so it is a DRAMless SSD. Connected to a DDR4 interface, it can exceed 200 GT / s and does not require an external power supply.
- NVDIMM-N: It combines DRAM and an SSD in a single DIMM, but requires an external power supply. When the computer is turned off it makes a backup copy of the RAM to the SSD and when it is turned on it does the reverse. During normal computer operation, the hardware does not have access to the non-volatile memory of the NVDIMM-N
The new NVDIMM-P standard is therefore a combined version of these two standards and it is expected that Samsung will manufacture the modules with DDR4 interface and later Micron those with DDR5 interface. Are we going to see them on the PC or will their high price make them only available for certain markets in particular?