Flash RAM - NVMe, 3D XPoint, NAND and NOR

NVMe (non- express) https://searchstorage.techtarget.com/definition/NVMe-non-volatile-memory-express

NVMe (non-volatile memory express) is a host controller interface and storage protocol created to accelerate the transfer of between enterprise and client systems and solid-state drives (SSDs) over a computer's high-speed Peripheral Component Interconnect Express (PCIe) bus.

NVMe provides an alternative to the Small Computer System Interface (SCSI) standard and the Advanced Technology Attachment (ATA) standard for connecting and transmitting data between a host system and a peripheral target storage device. The ATA command set in use with Serial ATA (SATA) SSDs and the SCSI command set for Serial Attached SCSI (SAS) SSDs were developed at a time when hard disk drives (HDDs) and tape were the primary storage media. NVMe was designed for use with faster media.

The main benefits of NVMe-based PCIe SSDs over SAS-based and SATA-based SSDs are reduced latency in the host software stack, higher input/output operations per second (IOPS), and potentially lower power consumption, depending on the form factor and the number of PCIe lanes in use.

3D XPoint https://searchstorage.techtarget.com/definition/3D-XPoint

3D XPoint is memory storage technology jointly developed by and Inc. The two vendors have described this new technology as filling a gap in the storage market between dynamic RAM (DRAM) and NAND flash. How 3D XPoint memory works

In their 2015 announcement of the technology, Intel and Micron claimed 3D XPoint would be up to 1,000 times faster and have up to 1,000 times more endurance than NAND flash, and have 10 times the storage density of conventional memory. Early products are faster and more durable than NAND and denser than conventional memory, but they haven't lived up to the full extent of the vendors' claims.

3D XPoint has a different architecture from other flash products. It's reputed to be based on phase-change memory technology, with a transistor-less, cross-point architecture that positions selectors and memory cells at the intersection of perpendicular wires. Those cells, made of an unspecified material, can be accessed individually by a current sent through the top and bottom wires touching each cell. To improve storage density, the 3D XPoint cells can be stacked in three dimensions.

Each cell stores a single piece of data, making a cell represent either a 1 or a 0 through a bulk property change in the cell material, which modifies the cell's resistance level. The cell can occupy either a high- or low-resistance state, and changing the resistance level of the cell changes whether the cell is read as a 1 or a 0. Because the cells are persistent, they hold their values indefinitely, even when there is a power loss.

While not as fast as DRAM, 3D XPoint has the advantage of being nonvolatile memory. NAND vs NOR

NAND flash memory https://searchstorage.techtarget.com/definition/NAND-flash-memory

NAND flash memory is a type of nonvolatile storage technology that does not require power to retain data.

An important goal of NAND flash development has been to reduce the cost per bit and to increase maximum chip capacity so that flash memory can compete with devices, such as hard disks. NAND flash has found a market in devices to which large files are frequently uploaded and replaced. MP3 players, digital cameras and USB flash drives use NAND technology.

NAND flash offers faster erase and write times than NOR flash, while NAND technology delivers better density at a lower cost per bit. NAND also offers up to ten times the endurance or NOR.

NOR flash memory https://searchstorage.techtarget.com/definition/NOR-flash-memory

NOR flash memory is one of two types of nonvolatile storage technologies. NAND is the other.

Nonvolatile memory does not require power to retain data.

NOR and NAND use different logic gates -- the fundamental building of digital circuits -- in each to map data. Both types of flash memory were invented by Toshiba, but commercial NOR flash memory was first introduced by Intel in 1988. NAND flash was introduced by Toshiba in 1989. NOR flash is faster to read than NAND flash, but it's also more expensive, and it takes longer to erase and write new data. NAND has a higher storage capacity than NOR.

NAND devices are accessed serially, using the same eight pins to transmit control, addressing and data. NAND can write to a single memory address, doing so at eight bits -- one byte -- at a time.

In contrast, older, parallel NOR flash memory supports one-byte random access, which enables machine instructions to be retrieved and run directly from the chip, in the same way a traditional computer retrieves instructions directly from main memory. However, NOR has to write in larger chunks of data at a time than NAND. Parallel NOR flash has a static random access memory (SRAM) interface that includes enough address pins to map the entire chip, enabling access to every byte stored within it.

NOR flash is also more expensive to produce than NAND. That, and its random access function, mean NOR is mostly used for code execution, while NAND is mostly used for .

NOR flash is most often used in mobile phones, scientific instruments and medical devices. NAND has found a market in devices to which large files are frequently uploaded and replaced, such as MP3 players, digital cameras and USB flash drives.

Some devices use both NAND and NOR flash. A smartphone or tablet, for instance, may use embedded NOR to boot up the and a removable NAND card for all its other memory or storage requirements.

More about NVMe https://searchstorage.techtarget.com/feature/NVMe-SSD-storage-costs-wont-hinder-market-takeover

Experts anticipate that NVMe SSD storage will become the predominant solid-state drive standard.

Unlike the Advance Host Controller Interface (AHCI) -- the hardware mechanism that SATA SSDs use for data flow -- the nonvolatile memory express (NVMe) protocol was designed from the ground up to govern solid-state memory. It's optimized for flash-based technology, which positions NVMe to replace AHCI SSDs.

NVMe SSD storage brings an extensive list of enhancements and optimizations to the data storage market, said Walter Hinton, senior director of product marketing for storage technology vendor Western Digital.

"This can dramatically raise the bar for the benefits that can be had from present and coming software," he said.

With the introduction of SSDs, SATA interfaces became a limiting factor; bandwidth thresholds stuck at approximately 600 MBps.