Flash Foundations

Flash Foundations, Part 10: The Future of Flash

Sort each direction in flash as on sale, in qualification or in research, and learn what to specify today.

On this page 25 sections

A roadmap slide is not a product, and neither is a sample or a demonstration. Part 9 showed what the whole stack delivers against its spec sheet. This part looks forward from that stack and asks which directions you can buy.

Flash Foundations, Part 10: the future of flash, with zones written in order, a CXL memory module and a program running on the driveThree equal panels. The first shows four zones, each filled from the left up to a copper write pointer, because a host writes each zone in order. The second shows a processor box joined by two copper lines to a memory module with four chips and gold connector fingers, a CXL module on the PCIe wires. The third shows a drive with two flash chips and a copper program block running beside them.GUIDE / FLASH FOUNDATIONS, PART 10What flash does nextZONES · CXL · COMPUTE ON THE DRIVE01 ZONES02 CXL03 COMPUTEWrite in orderCPUMemory moduleProgramBeside the flash

For most of flash history the firmware layer was static. Engineers tuned garbage collection and read retry for the median drive, validated the result against representative benchmarks, and released logic that ran the same on day one and day one thousand. No single setting fits every drive, because dies, workloads and wear states differ. Vendors are moving to adaptive firmwareAdaptive firmware changes its behavior as the drive ages, for example by adjusting read voltages and refresh rates from measured conditions. that observes each drive and tunes itself, while other work shifts data placement to the host, attaches memory over Compute Express Link (CXL)CXL runs over the same physical layer as PCIe but adds cache-coherent memory access, so it moves cache lines rather than blocks of storage., raises link speeds, and packs more bits into each cell. Every one of those directions changes who manages the data or where it sits. None of them changes the NAND underneath.

Which directions can you buy today, which are still being qualified, and which are research? By the end you can sort a roadmap claim into one of those groups and say what it depends on. Dated claims are fenced “As of October 2026”. Memories built to sit beside NAND, including Optane, which went on sale and ended, belong to Beyond NAND.

Machine learning in SSD firmware

Machine learning (ML)Machine learning in firmware uses small trained models to predict things such as the best read voltage or the next access, in place of fixed tables. in SSD firmware is narrower in drives on sale than the research literature suggests. As of October 2026, four techniques run from production to research, and they share one loop. Figure 10.1 shows the loop. The drive observes itself, then a table, a heuristic or a model decides what to do, the firmware acts on a threshold or a garbage collectionGarbage collection copies the valid pages out of mostly stale blocks and erases those blocks, so there is always free space for new writes. (GC) choice, and the result feeds the next observation.

Machine learning in SSD firmware

Adaptive firmware closes a loop that static firmware leaves open

Telemetry, a decision, an action, and a check on the result

Four numbered steps at the corners of a loop. Step one observes telemetry from the drive: error counts, wear, temperature and the access pattern. Step two decides, using a fixed table, a heuristic or a trained model. Step three acts by adjusting a read threshold or a garbage collection choice. Step four, outlined in copper, checks whether the error rate or write amplification improved, and a copper arrow carries that result back to step one as the next observation. Static firmware stops after the third step and repeats the same decision. Adaptive firmware keeps the fourth step, so the decision can move with the NAND, the workload and the wear state.01 OBSERVETelemetry from the drive itselfError counts, wear, temperature,access pattern02 DECIDEA table, a heuristic or a modelpicks a settingA model can change its answer asinputs change03 ACTAdjust a read threshold or a GCchoiceShift the reference, pick thevictim block04 CHECKDid the error rate or WAFimprove?The result becomes the nextobservationnext observationStatic firmware stops after step 03 and repeats the same decision.stepthe step static firmware lacks
Figure 10.1 · A model changes how step two decides, not the loop itself. Illustrative values.

Static firmware stops after the third step and repeats the same decision. Adaptive firmware keeps the fourth step, so the decision can move with the NAND, the workload and the wear state. A trained model changes only how the second step decides. It extends the heuristics of victim selection in Part 7 and the read retry in Part 8, and it leaves the domain knowledge behind them in place.

Workload classification

Vendors describe workload-adaptive behavior in current consumer and enterprise controllers. Firmware watches access patterns (sequential or random, read-heavy or write-heavy, bursty or sustained) and adjusts GC aggressiveness and read-ahead depth, and on client drives it also adjusts the single-level cell (SLC) cache allocation. Vendors don’t document how much of this is trained inference and how much is simple pattern detection, so the depth of the production behavior is unknown. One controller vendor is specific about the goal. Microchip’s Haija said in a 2022 EE Asia article about the Flashtec NVMe 4016 that an SI engine in the controller lets NAND management algorithms adapt in real time to the workload the SSD sees.

Adaptive read thresholds

Part 8 explains read retry, which tries alternate read reference voltages when the first read has more bit errors than the error-correcting code (ECC) can fix. Some controllers learn good positions for specific blocks over time, which is learning at block granularity. Vendors publish neither the retry tables nor how they update them, so which drives do this, and how much, is unknown.

Predictive GC

Research has studied the idea at length (a 2019 HotStorage paper is one example), yet no vendor publicly documents it in firmware on sale. One Samsung research paper cut write amplification (the write amplification factor, WAF) by up to 43.5% in its best case, where a neural network predicted each write’s future data temperature and a clustering step sent data of similar predicted temperature to the same NAND blocks.

On-device training

Here the model updates itself from runtime data instead of arriving pre-trained from the factory. Training hardware costs controller die area, and a model that changes itself in the field is hard to validate. This form shows up in research papers and conference talks, and it is the least likely to be in a drive a customer can buy. The table sets the four side by side for a buyer.

Technique Status, as of October 2026 What it needs from the controller (editorial reading) Observable benefit
Workload classification Vendors say production, depth not public Standard controller CPU cores with monitoring logic Better sustained performance on variable workloads, less unnecessary GC
Adaptive read thresholds Vendors say production in some drives, tables not published Standard ECC engine with per-block calibration memory Fewer internal read retries and lower tail read latency
Predictive GC Research, no public production use Higher CPU capability, more memory for model state and write history Up to 43.5% lower WAF in the best published case
On-device training Research or early qualification Dedicated ML training and inference silicon, substantial on-chip static RAM (SRAM) Continuous per-drive adaptation, not available in purchasable products

For a buyer the consequence is narrow. The first two techniques are behavior to expect and measure. The last two are not yet a reason to choose a drive.

Zones, placement hints and keys decide who owns the map

Three NVMe extensions move mapping work between the drive and the host. A conventional SSD’s flash translation layer (FTL)The flash translation layer is the firmware that maps host addresses to physical flash locations and hides the rules of erase blocks and wear. owns the map from host addresses to physical NAND (Part 6 covers why), the placement of writes, and GC.

Zoned namespaces and flexible data placement

Zoned Namespaces (ZNS)Zoned Namespaces split the drive into zones that must be written in order, which moves data placement to the host and removes most garbage collection. split a namespace into zones that the host must write in order and reset as a unit, and Part 1 lists the command set. Flexible Data Placement (FDP)Flexible Data Placement lets the host direct writes into separate groups of blocks by lifetime, which lowers garbage collection work without changing the block interface. keeps the ordinary block interface and lets the host tag writes with a placement handle, and Part 6 covers how lifetime hints cut write amplification. Figure 10.2 compares who does the work under each design.

Zones, placement hints and keys decide who owns the map

ZNS moves the most work to the host, and FDP moves less than ZNS

Mapping, placement and garbage collection under three designs

A grid of three designs, in columns, against three jobs, in rows. In a conventional SSD the drive does all three: it keeps the full map, guesses data lifetimes when it places writes, and runs garbage collection itself. With Flexible Data Placement the host tags each write with a placement handle, and the drive keeps the map and runs garbage collection but groups data by lifetime. With Zoned Namespaces, drawn in copper, the host writes each zone in order and resets whole zones, so the drive keeps a much simpler map and the host runs garbage collection.01 CONVENTIONAL02 FDP03 ZNSMappingDriveFull FTL mapDriveFull FTL mapDriveMuch simplermapPlacementDriveGuesses datalifetimesHost hintsDrive groups bylifetimeHostWrites eachzone in orderGarbagecollectionDriveRuns GC itselfDriveStill runs GCHostResets wholezonesthe drive does itthe host does ithost hints
Figure 10.2 · Each design hands the host a different share of the work the FTL does. Illustrative values.

A conventional drive guesses lifetimes and runs GC itself. FDP leaves the map and GC with the drive and supplies the lifetime information the FTL lacked. ZNS goes further. Because the host guarantees sequential writes inside each zone, the drive can use a much simpler map, and GC moves to the host, which copies live data out and resets whole zones. The drive no longer relocates user data to reclaim space. It still runs background media management, including refresh, so it is never idle. Lower write amplification under ZNS follows from this shift in ownership.

Western Digital’s Ultrastar DC ZN540 data sheet describes a 2.5-inch U.2 ZNS SSD aimed at cloud and storage-system builders that can modify their host software, and as of October 21, 2026 the reseller Advanced HPC lists it, in capacities up to 8TB, on a request-a-quote page that shows no price or stock. Meta, Google and Samsung took a related path with FDP, ratified as Technical Proposal 4146 in late 2022. They wanted much of the locality benefit of ZNS with far less host software change. In a kernel storage discussion an engineer from Meta reported that every SSD the company buys has FDP, though it isn’t enabled by default, and hyperscale data placement work has leaned toward FDP.

ZNS needs a zone-aware host, because the file system, database or application has to generate the sequential writes it expects. Linux’s XFS, btrfs and f2fs handle zoned devices natively, and the ZNS authors built a zone-aware backend called ZenFS and ran RocksDB directly on a ZNS SSD through it. Any stack without that support gets no benefit. A reseller lists the drive, but availability is unconfirmed. Microchip’s Haija said in a 2022 EE Asia article that ZNS has had limited traction mainly because of the higher-level pieces needed to make it work at scale, and that SSD and application providers need standards, tools and drivers for more data centers to adopt it. For an enterprise team choosing a platform today, ZNS is worth tracking but not yet worth writing into a specification.

Key value: moving the key index to the drive

NVMe’s Key Value (KV) command set, introduced with NVMe 2.0, exposes store, retrieve, list, delete and exist operations by key. Normally the host writes key-value data to a block device and keeps its own map of keys to block addresses. In a log-structured merge (LSM) tree store such as RocksDB, memtables, Bloom filters and block indexes locate keys in sorted string table (SSTable) files, the file system maps those files to block addresses, and the FTL maps blocks to NAND. Three mapping layers sit between the key and the NAND, and Figure 10.3 shows what a KV drive does to them.

Zones, placement hints and keys decide who owns the map

A KV drive takes the key map off the host

The mapping layers in a key-value store, with and without KV

Two columns of stacked boxes, one per path. The block path has three mapping layers between a key and a NAND page: the host maps a key to an SSTable block using the memtable, Bloom filter and block index; the file system maps a file to a block address; and the flash translation layer maps that address to a physical NAND page. The key value path, on the right, keeps no key-to-block map on the host, which addresses data by key. The drive holds the key index, drawn in copper, and maps a key to a physical location, and the flash translation layer still places data inside the drive.01 BLOCK PATHHost maps key to SSTable blockMemtable, Bloom filter, blockindexFile system maps file to blockaddressFTL maps block address to NANDpage02 KV PATHHost keeps no key-to-block mapIt addresses data by keyDrive holds the key indexMaps a key to a physicallocationFTL still places data inside thedrivehostdrivekey index
Figure 10.3 · The host stops mapping keys to blocks, and the FTL still maps inside the drive. Illustrative values.

A KV drive keeps the key index itself, so the host no longer maintains or consults a key-to-block map. Physical placement inside the drive stays with the FTL.

Don’t confuse this command set with the large language model (LLM) “KV cache” that some vendors market SSDs for. They share only an acronym. A prototype Samsung described in 2019 is the KV SSD hardware this page can source. Adoption also needs applications written or ported to issue KV operations instead of block I/O, as with ZNS.

Specification changes

As of October 2026, NVM Express published its 2.4 set of specifications on August 4, 2026, updating all eleven documents (Part 1 lists the set). Three command sets were ratified on July 31: ZNS at revision 1.5, KV at revision 1.4, and Computational Programs at revision 1.3. No new technical proposal for any of the three appears in the revision changes document, and they moved only through engineering change notices shared across the whole set. New proposals went into the Base specification and other documents instead, including PCIe bandwidth and IOPS quality of service, subsystem migration, post-quantum cryptography enhancements and a device voltage monitor. That document also gives notice that the August 2027 release plans to obsolete Predictable Latency Mode and NVM Sets. Standards upkeep continues, and the gap remains host software.

CXL after several revisions, with the ecosystem still maturing

Part 1 covers what CXL is. CXL runs over the same PCIe wires NVMe uses, carrying cache-coherent load and store access to memory instead of block commands. It also covers the trap in the drive bay, where a CXL memory module can sit in an NVMe slot. Figure 10.4 repeats the one difference that matters for this part.

CXL after several revisions, with the ecosystem still maturing

The same bay can hold block storage or load/store memory

An NVMe SSD and a Type 3 CXL memory module on one PCIe link

Two columns of three boxes over one shared band. The first column is block I/O in an NVMe SSD: the host sends a read or write command through a queue, the flash translation layer maps the address and the controller moves a block, and the controller posts a completion entry. The second column, in copper, is memory semantics in a Type 3 CXL memory module: the CPU issues a load or a store to an address, the CXL.mem protocol carries the cache line to device memory, and there is no queue, no flash translation layer and no completion entry. The band under both columns says they share the same bay and the same PCIe wires.01 BLOCK I/OThe host sends a read or writecommand through a queueThe FTL maps the address and thecontroller moves a blockThe controller posts acompletion entry02 MEMORY SEMANTICSThe CPU issues a load or a storeto an addressCXL.mem carries the cache lineto device memoryNo queue, no FTL, no completionentrySame bay, same PCIe wiresNVMe SSDType 3 CXL memory moduleblock I/Oload and storenot present
Figure 10.4 · Block I/O moves blocks through a queue; CXL.mem moves cache lines on a load or store. Source: CXL Consortium and NVM Express specifications.

Panel two’s module has no FTL and never appears as an NVMe namespace. For latency-sensitive access patterns it takes data off the block I/O path, and today that data is mostly DRAM expansion. So the question for storage planning is whether a given deployment is short of memory capacity or short of storage.

As of October 2026, CXL has reached revision 4.0 (November 2025), and what matters is where in the stack adoption has happened. Memory expansion devices (Type 3) are in production servers. AMD’s EPYC 4th Gen (Genoa) supported Type 3 expansion at launch, and Intel’s official Type 3 support arrived later, with 5th Gen Xeon (Emerald Rapids). Lenovo’s CXL 2.0 memory primer puts CXL 2.0 memory support on its ThinkSystem V4 servers with Intel Xeon 6 and expects future AMD EPYC processors to support CXL memory. AMD’s own EPYC 9005 (Turin) data sheet cites CXL 2.0 capabilities for memory-intensive tasks without spelling out Type 3 expansion.

Pooling is earlier. XConn announced early production samples of its Apollo CXL 2.0 switch in March 2024, and the CXL Consortium’s FMS 2025 demo list shows an XConn CXL 2.0 switch sharing a memory pool across hosts. In September 2026 Astera Labs said its Leo 2 P-Series for pooling and sharing, with the rest of the Leo family, is sampling with hyperscaler customers, and in November 2025 it described Leo-based CXL memory expansion in a Microsoft Azure M-series preview.

CXL 3.x is further back. The same demo list shows a Panmnesia cluster with CXL 3.x switches as a demonstration. AMD has announced a 6th Gen EPYC (Venice) as its first PCIe 6.0 server CPU. StorageReview reports that Venice supports CXL 3.1 and that its SP7 platforms are due in Q4 2026, and no CXL 3.x platform is confirmed on sale. The table below pairs each version with the platform it needs. The platform and implication columns are an editorial reading, and the deployment column follows the sources above.

CXL version Memory semantics Deployment, as of October 2026 Platform needed Storage implication
1.1 Type 3 memory expansion Production Intel 5th Gen Xeon (Emerald Rapids) or later, AMD EPYC 4th Gen (Genoa) or later Byte-addressable memory expansion
2.0 Type 3 expansion, pooling through a CXL switch (tree topology) Expansion supported on Xeon 6 servers; pooling silicon sampling with hyperscalers (Astera Labs, September 2026) Xeon 6 or later, plus a CXL switch for pooling Memory pools allocated to several compute nodes
3.x Multi-level fabric topology No CXL 3.x platform confirmed on sale; switches shown in demonstrations; Venice SP7 platforms due Q4 2026 (StorageReview) Full ecosystem alignment Fabric-attached memory pooling, not yet deployed

For most enterprise environments, CXL isn’t yet a storage architecture decision. Fully exploiting CXL 2.0 pooling needs specific processor and platform support, and most enterprise fleets still run on older platforms. If a customer asks whether to build storage architecture around CXL, the field engineer’s answer is not yet for storage and yes for memory capacity. Qualify CXL-capable platforms where a workload needs more memory than the dual in-line memory module (DIMM) slots give. Don’t make a deployment depend on CXL if it must also run on older servers without native CXL support.

PCIe 6.0 and 7.0 signal at the edge of the channel

Part 1 gives the generation ladder. PCIe 6.0PCIe 6.0 uses PAM4 signaling at 64GT/s per lane. The signal loses more strength on the board, so the channel must be short or use retimers. reaches 64 gigatransfers per second (GT/s) per lane by changing the signal and leaving the clock alone. PCIe 5.0 and earlier use Non-Return-to-Zero (NRZ) signaling, which has two voltage levels and one bit per symbol. PCIe 6.0 switches to four-level pulse amplitude modulation (PAM4), which carries two bits per symbol at the same clock frequency and without a proportional rise in signal edge rate. The generation also introduces FLIT (flow control unit) modeFLIT mode, introduced with PCIe 6.0, sends data in fixed-size units protected by forward error correction instead of variable-length packets.. It restructures the protocol around fixed-size units that carry forward error correction (FEC). PAM4’s smaller noise margin makes FEC necessary. Figure 10.5 shows the levels.

PCIe 6.0 and 7.0 signal at the edge of the channel

PAM4 fits four levels where NRZ fits two, so each eye is smaller

Signal levels at equal amplitude

Two panels side by side compare signal levels at the same amplitude. The first panel is NRZ, used through PCIe 5.0: two voltage levels, one bit per symbol, and a single full-height eye between them. The second panel is PAM4, used by PCIe 6.0: four voltage levels, two bits per symbol, and three stacked eyes that each have about one third the height of the NRZ eye, with the middle eye in copper because it carries the one-third label; all three eyes are the same height. Because the eyes are smaller, PAM4 has less noise margin, which is why PCIe 6.0 adds forward error correction and demands a cleaner channel.01 NRZ2 levels, 1 bit per symbol10full eyeSymbol value on the left02 PAM44 levels, 2 bits per symbol32101/3Symbol value on the leftLess noise margin: PCIe 6.0 adds FEC.signal leveleye openingPAM4 eye with the 1/3 label
Figure 10.5 · At the same amplitude, each PAM4 eye is about one third the height of the NRZ eye. The copper eye carries the 1/3 label; all three are the same height. Source: Quarch, Gen5 versus Gen6 PCIe; EDN, PAM4 basics; levels drawn to scale for equal amplitude.

Four levels in the same amplitude sit closer together than two, so each of the three eyes is one third of the full amplitude. That cuts the noise margin to roughly one third of what NRZ provides. Therefore the channel between the SSD and the host must be cleaner, with tighter impedance control and differential pair matching, better connectors, and more sophisticated receiver equalization. A PCIe 5.0 physical layer (PHY) cannot simply be clocked up to PCIe 6.0, and controllers need new analog front-end designs validated at the tighter tolerances. Insertion loss is tighter too. The channel target dropped from 36dB at Gen5 to 32dB at Gen6, which limits the trace lengths and connector transitions a board can use. Both generations share a 16GHz fundamental frequency.

Form factor follows the channel. Quarch judges it quite likely that the U.2 and U.3 connector will not go to Gen6, given its age and the small benefit of pushing it to PAM4 margins, and expects the EDSFF connectors to appear in Gen6 versions. EDSFF, the Enterprise and Datacenter Standard Form Factor covered in Part 1, was designed for data center mechanics and can meet the tighter interconnect requirements.

Part 1’s landscape section covers the first PCIe 6.0 data center SSDs (the Micron 9650 and Samsung PM1763), so this part turns to the controllers behind the next wave. Marvell’s Bravera SC6 is a PCIe 6.0 x4 enterprise controller with 16 NAND channels, and Marvell expects it to sample to partners in the fourth quarter of 2026. Phison showed its X3, which it claims reaches up to 28GB/s sequential, and told Tom’s Hardware at Computex 2026 that it will sample to customers in December 2026 and ship in volume in mid-2027. Both are controllers, so no drive yet carries these figures. A Gen6 x4 link carries about 30GB/s after FLIT overhead, as Part 1 explains. The 28GB/s sits below that because a drive can’t read faster than its link and rarely reaches it.

PCI-SIG released the PCIe 7.0 specification to members on June 11, 2025. It runs at 128GT/s raw. The Signal Integrity Journal’s reprint of the announcement lists PAM4 and FLIT-based encoding and up to 512GB/s bidirectional on an x16 link. A ratified interconnect gives an SSD roadmap nothing to buy yet, and every SSD named in this part runs PCIe 6.0 or below.

Flash beside the accelerator and compute on the drive

Two directions move flash closer to where the compute runs, and both are earlier than anything above. Figure 10.6 places them against an ordinary SSD.

Flash beside the accelerator and compute on the drive

Both directions move flash closer to where the compute runs

Where the computing sits relative to the flash

Three rows place the computing relative to the flash. In a standard SSD, a thick arrow carries all the data from the flash across the PCIe link to the host, which does the computing. In computational storage, the SSD holds a program, drawn in copper, next to the flash, and a thin arrow carries only the result to the host. In High Bandwidth Flash, a stack of NAND dies sits directly beside the accelerator with a short link between them, outside the NVMe path altogether.01 STANDARD SSDData crosses the PCIelink, and the host doesthe computing.02 COMPUTATIONAL STORAGEA program runs next tothe flash, and only theresult crosses thelink.03 HIGH BANDWIDTH FLASHStacked NAND sitsbeside the accelerator,outside the NVMe path.Hostall the dataFlashHostresult onlyProgramAcceleratorno NVMe pathFlash stackhost or acceleratorflashprogram on the data
Figure 10.6 · Computational storage moves compute into the drive, and HBF moves flash beside the compute. Illustrative values.

A standard SSD sits at the top of the figure and moves data to the host, which does the computing. Computational storage, in copper, moves a program to the data. High Bandwidth Flash leaves the NVMe path altogether and puts the flash beside the accelerator.

High Bandwidth Flash (HBF) is NAND stacked to sit beside an SI accelerator as a larger, slower tier next to HBM. It doesn’t sit behind an NVMe controller. As of October 2026, Sandisk and SK hynix released the first HBF specification through the Open Compute Project. It covers the host interface, electrical guidelines, reliability and packaging guidance for the die stack, and a software guide for reads and writes. By SK hynix’s own figures, stacks are 8-high or 16-high, hold up to 512GB, and come in three grades from 0.4 to 3.0TB/s over the Universal Chiplet Interconnect Express (UCIe) link. A published specification is not a part on sale. Sandisk’s 2025 announcement targeted first samples in the second half of 2026 and first SI-inference device samples in early 2027, and neither company’s August release names a product on sale. Beyond NAND’s guide on High Bandwidth Flash covers the specification, where HBF’s bandwidth comes from, and its limits in depth.

Computational storage moves processing to where the data lives. For large datasets where data movement dominates total processing time, offloading compression, encryption, filtering or search to the SSD cuts traffic across PCIe and reduces host CPU load. It is built for defined jobs. Blocks and Files reported in November 2022 that ScaleFlux’s CSD 3000 compresses and decompresses data transparently to the host, and a March 2024 report says the company supplied the CSD 2000 and CSD 3000 then. No later status was found. In those drives the engine does one fixed job. SNIA’s model is wider. An engine can be a CPU or an FPGA running configurable functions, and the table below lists that general-purpose case as research. NVMe’s Computational Programs command set standardizes how a host offloads a program. Beyond NAND covers other emerging memories, including Optane and phase-change memory.

More bits or more layers: the cost curve and the scaling limit

Cost per gigabyte follows how many good bits a wafer yields, and Part 4 owns the die density numbers. Wafer cost, yield and test cost go unpublished, so this section charts only what is public, which is bit density (bits stored per unit area). Layers were the main lever, and Part 4 covers the limits of a taller stack. Bits per cell is the other lever, and Figure 10.7 puts both on one scale.

More bits or more layers: the cost curve and the scaling limit

A 5-bit 3D die holds about 41 times the bits per area of planar

Bit density as a multiple of a planar 2-bit die; density printed above each bar

A bar chart of bit density as a multiple of a planar 19 nanometer two-bit die, which holds 0.567 gigabits per square millimeter. A 128-layer triple-level cell die is about 14.9 times denser at 8.47 gigabits per square millimeter, a 176-layer die about 19.4 times at 11.01, and a 232-layer die about 26.5 times at 15.03. A 192-layer die with five bits per cell, in copper, is about 41.1 times denser at 23.3. The figure shows area per bit, not price: wafer cost, yield and test cost are not published.Density multiple of the planar die (×)010203040500.567Gb/mm²1×19nm planar2 bits8.47Gb/mm²14.9×128LTLC11.01Gb/mm²19.4×176LTLC15.03Gb/mm²26.5×232LTLC23.3Gb/mm²41.1×192L5 bitsDie, layers (L) and bits per cellplanar dietriple-level cell5-bit cell
Figure 10.7 · The 5-bit die is denser than every triple-level die on this chart, with fewer layers than the 232-layer die. Source: Kanda 2013 (planar), TechInsights (TLC dies), Khakifirooz 2023 (5-bit die); multiples derived by dividing densities.

A planar 19nm die with two bits per cell held 64Gb on 112.8mm² (Kanda et al., JSSC 2013), so its density was 0.567Gb/mm². TechInsights’ densest triple-level cell (TLC) dies reach 8.47Gb/mm² at 128 layers, 11.01 at 176 and 15.03 at 232. That 232-layer die is about 26.5 times denser, so the same bits need about one twenty-sixth of the silicon. Intel reported (Khakifirooz et al., ISSCC 2023) a 192-layer die with five bits per cell at 23.3Gb/mm², about 41 times the planar die. Dividing out the bits per cell isolates the rest. A TLC die stores 1.5 times the bits per cell of the planar die, so the 232-layer die gets about 17.7 times from geometry. Geometry here means layer count, array efficiency and where the CMOS sits. Intel’s 5-bit cell gives 2.5 times from bits and about 16.4 times from geometry, a little less than the 232-layer die’s 17.7 times. Vendors and processes differ across these dies, so the split is only a reading aid. Part 4’s table spans TLC from 5.95Gb/mm² at 96 layers to 23.52 for SK hynix’s 321-layer die, and the top figure is about four times the bottom one.

Figure 10.7 charts area per bit and leaves price out. A denser die puts less silicon under each bit, but every added layer adds process work, so whether the bit gets cheaper depends on wafer cost and yield, which vendors don’t publish.

Each added bit doubles the number of states a cell must tell apart in the same voltage window, as Figure 10.8 shows, and Part 2 covers the progression from single-level to quad-level cells.

More bits or more layers: the cost curve and the scaling limit

Each added bit doubles the states in the same voltage window

States a cell must tell apart, by cell type

A bar chart of the number of states a cell must tell apart, by cell type and bits per cell. Single-level cell, one bit, has 2 states, multi-level cell 4, triple-level cell 8, quad-level cell 16, and penta-level cell, five bits, 32, drawn in copper. Each added bit doubles the number of states that must fit in the same voltage window, so the margin between neighboring states shrinks with every step.States per cell0102030402SLC1 bit4MLC2 bits8TLC3 bits16QLC4 bits32PLC5 bitsCell type and bits per cellstates per cellPLC, the 5-bit cell
Figure 10.8 · PLC needs 32 states where QLC needs 16, so the margin between states shrinks again. Source: Blocks and Files, SK hynix split-cell 5-bit flash (states per cell).

Figure 10.8’s copper bar is penta-level cell (PLC)PLC stores five bits per cell using thirty-two voltage levels, which packs more data into the same silicon but leaves very little margin between levels. flash, with five bits and 32 states. In Intel’s ISSCC 2023 paper on a 192-layer die with five bits per cell, a slide labels the step from four bits to five as 25%, and the conclusions claim 24% higher bit density than the best reported quad-level cell (QLC) densities. With 32 states to tell apart, guard bands tighten, raw error rates rise, and low-density parity-check (LDPC)LDPC is a code whose decoder passes confidence messages back and forth until the errors resolve. It corrects more errors than BCH, especially with soft input. error correction has more to correct. A January 2026 report says PLC had not gone commercial, so any endurance number for it is a guess. SK hynix’s split-cell design takes another route. It uses six states in each of two half-cells instead of 32 states in one cell, and pays for that in structural complexity.

Reports from January 2026 found no commercial PLC products on sale. Part 2 lists who has shown PLC work, and SK hynix presented 5-bit multi-site cell results at the International Electron Devices Meeting (IEDM) in December 2025. A research paper is not a production qualification, and none of these results shows the ECC and retention margin PLC needs working at volume. PLC remains a candidate for archive tiers that are rarely read, where capacity per die counts for more than endurance or speed. Timing is the open question. Will PLC reach volume production before taller stacks or bonded-die refinements give a better cost curveThe cost curve follows cost per gigabyte as die density rises, through more layers and more bits per cell. Public per-generation figures are scarce.? Industry roadmaps over the next couple of years will start to answer that.

Where one preprint says NAND goes next

In October 2026 a perspective paper called “The future of 3D NAND flash technology” was posted to arXiv. Most of its authors are university researchers at Georgia Tech and other schools, and one group is at Applied Materials. Two work in Samsung Electronics’ Advanced Device Research Laboratory, and Samsung supported the work in part. That makes it an academic and vendor-adjacent view of the road ahead. I read it as a framework and won’t treat it as proof that any of it works in a drive, and it isn’t a Samsung product announcement either. Everything in this section sits at the research end of Figure 10.11.

Its argument starts from the physics already covered in this series. With stacks heading toward kilolayer heights, the authors say process integration and lithography no longer set the pace of scaling. Charge spreading sideways inside the storage film, interference between neighboring cells, read disturb, the limit on current through a long polysilicon string, self-heating and threshold voltage spread each get worse with height. Its point is that no single one stops scaling. Together they eat the operating margin a little more each generation, and it calls this a margin-limited regime. Part 4 and Part 8 cover the same mechanisms from the die and the ECC side.

Figure 10.9 lists the two sets side by side, as the paper presents them.

Where one preprint says NAND goes next

One preprint lists four density levers and four use tiers

Both lists are the paper’s; it does not cross them in a table

Two columns of four boxes. The first column lists four density levers from the preprint: vertical, lateral, logical and architectural scaling. The second column, in copper, lists the four use tiers it names: cold storage, active storage, high bandwidth flash with big accelerator memory, and compute in memory. The columns are offset and no line joins them, because the paper presents the two lists separately and does not pair them.01 DENSITY LEVERSVerticalMore layersLateralFiner blocks in the planeLogicalMore bits per cellArchitecturalCircuit placement, die bonding02 USE TIERSCold storageDensity and retentionActive storageThroughput and enduranceHBF and accelerator memoryPackaging and access pathCompute in memoryThe array does the arithmeticdensity leveruse tier
Figure 10.9 · The preprint is not peer reviewed. It does not pair the two lists, and neither list is a product plan. Source: “The future of 3D NAND flash technology,” arXiv preprint, October 2026.

Four ways to add density

Density now comes from four levers pulled at once, the paper says:

  • Vertical scaling adds more layers, and Part 4 covers what a taller stack costs.
  • Lateral scaling is finer partitioning of the array into blocks and sub-blocks in the plane, which fits more independently addressable units into the same die area.
  • Logical scaling puts more bits in each cell, which raises capacity per layer and narrows the margin between states, as Figure 10.8 shows.
  • Architectural scaling is where the peripheral circuits sit and how dies are joined, from circuits beside the array to circuits under it to separately made wafers that are bonded, as in the bonded interface section of Part 4.

Four tiers of use

On the other side, the paper splits demand into four tiers that want different things from the same NAND:

  • Cold storage wants the most bits per die and long retention, and it tolerates modest endurance. The authors expect charge-trap flash to stay the choice here through the kilolayer transition.
  • Active storage for SI training and inference wants sustained throughput and endurance. The paper suggests latency-sensitive inference buffers may run cells in an SLC-like mode, and it names ferroelectric NAND as a candidate for this tier.
  • High bandwidth flash and big accelerator memory change the packaging and the access path and leave the cell alone. The first puts NAND dies and a controller behind a wide on-package interface. The second lets GPU threads start storage reads directly.
  • Compute in memory uses the array itself to do multiply-accumulate work for neural-network inference, which needs uniform, well-separated conductance levels.

How I read the two lists together

The paper presents the vectors in one place and the tiers in another, and it doesn’t cross them in a table. Putting them side by side is my reading. Cold storage keeps leaning on the vertical and logical levers, because bit density is what it buys. Active storage leans the other way on the logical lever, trading bits per cell for speed and margin. The last two tiers are decided by the architectural lever and by system design more than by the cell. Their own summary is that future NAND will likely “evolve as a portfolio”, with no single successor to the charge-trap cell.

What this changes for a specification

Nothing yet. The paper calls charge-trap flash the most mature 3D NAND technology and says ferroelectric NAND is particularly well suited to the active-storage and compute-in-memory tiers, though its demonstrated endurance, 10⁴ to 10⁶ program/erase cycles, falls short of enterprise targets. The authors suggest a hybrid, with ferroelectric cells for high-reliability blocks and charge-trap cells for bulk capacity, as the nearer-term route. No product like that is on sale, so it belongs with the other rows in the bottom stage. If a vendor cites this paper, ask which of the four levers or tiers the claim is about, and whether the result is a lab demonstration or a qualified part.

In the field: telling products from roadmap

A vendor deck says a drive supports a feature. Whether it does depends on the product, the host and the platform, and the answer lives in logs and labels. Figure 10.10 orders the two questions that decide it.

In the field: telling products from roadmap

Two questions sort a claim: can you buy it, can you run it

Product first, then host and platform

A decision tree with three outcomes. The first question asks whether you can buy a drive or module today. If not, the item is a specification or samples only, so watch it and do not specify it. If yes, the second question asks whether your host software and platform support it. If they do not, wait for host or platform support. If they do, the outcome, in copper, is to qualify it against your workload.Can you buy a drive or moduletoday?NoYesSpecification or samplesonly: watch, do not specifyDoes your host software andplatform support it?NoYesWait for host or platformsupportQualify it against yourworkloadquestionwatch or waitqualify
Figure 10.10 · A feature you can buy but cannot run still belongs on the watch list. Illustrative values.

The first question separates a part you can buy from a specification or a sample. The second separates a part that works in your stack from one that needs host software or a platform you don’t run, and four checks answer both.

Read the device, not the press release

A connector that looks identical can hide an NVMe 1.4, 2.0 or 2.4 device, and ZNS, KV and Computational Programs are optional command sets (Part 1 lists them). Whether a given drive implements one is a firmware question, so read Identify. For Streams, the Optional Admin Command Support (OACS) field reports Directives and a Directive Receive Identify command confirms them, and data sheets often omit Streams or FDP support, so confirm it during qualification (Part 6).

Read the bay, not the connector

An E3.S bay can hold a CXL memory module, and Identify will not describe it. Read the JEDEC module label for media type, CXL revision, capacity and connector width (Part 1). A platform CPU that doesn’t speak CXL won’t bring the module up as memory.

Check host support before blaming the drive

A drive that supports FDP hints but receives untagged writes gains nothing, and a ZNS drive needs a zone-aware stack. Both are host work, so a missing benefit is often a missing host feature.

Separate a model shift from wear

If learned models reach drives on sale, a drive’s behavior may change when the model shifts, even with no wear and no hardware fault behind it. Telling the two apart requires knowing what the adaptive system optimizes and what NAND physics predicts at that wear level. Compare the drive with its cohort at equal wear, using the SMART fields that Part 8 owns. Tools measure the outcome. ioTraX covers real-time I/O behavior, TriageIO covers fleet-level SMART telemetry, and IOSpeX covers error log extraction. Knowledge of the physics and firmware from this series says what the outcome means.

What to specify today and what to watch

For a product manager or field engineer making storage decisions in 2026, the relevant question is what is production-ready for this deployment. Figure 10.11 sorts the directions in this part into four stages by how far each is from a purchase order, as of October 2026.

What to specify today and what to watch

Four stages separate what is on sale from what is still a roadmap

As of October 2026, from purchasable to research

Four rows run from most to least mature. The top stage, in copper, is production, which you can buy and deploy today: vendor-described adaptive firmware, retry calibration, Flexible Data Placement, CXL memory expansion and PCIe 6.0 enterprise SSDs. The second stage is narrow use, listed or sampling for a defined use: Zoned Namespace drives, computational storage for fixed jobs and CXL 2.0 memory pooling. The third stage is sampling or demonstrated, so not on sale as products: PCIe 6.0 controllers, CXL 3.x switches and platforms, and High Bandwidth Flash, whose specification is published and whose samples are targeted. The bottom stage is prototype or research, several years out or with no timeline: Key Value drives, learned models beyond retry tables, on-device training and penta-level cell flash.ProductionBuy and deploy todayVendor-described adaptive firmware andretry calibration, FDP, CXL memoryexpansion, PCIe 6.0 enterprise SSDsNarrow useListed or samplingZNS drives, computational storage forfixed jobs, CXL 2.0 memory poolingSampling ordemonstratedNot on sale as productsPCIe 6.0 controllers, CXL 3.x switches andplatforms, High Bandwidth Flash samples(targeted)Prototype or researchYears out or no timelineKV drives, learned models beyond retrytables, on-device training, PLCproduction, buy todaylater stages
Figure 10.11 · The stage says how far a direction is from a purchase order. Source: Derived: the status column of this part’s technology table, as of October 2026.

The top stage is where a specification can name a feature today. At the bottom stage it should not. Below, a table adds what each direction depends on and when to expect it.

Technology Status Practical timeframe (editorial estimate) Ecosystem dependency
Workload-adaptive GC and classification Vendor-described, consumer and enterprise firmware Now None
Flexible Data Placement Production, hyperscale Now Host placement hints (RocksDB, Ceph, application layer)
ZNS drives Data sheet and reseller listing Reseller-listed for drives, several years out for broad enterprise Zone-aware host software (f2fs, btrfs zoned mode, RocksDB through ZenFS)
KV command set drives Prototype (Samsung, 2019) Several years out for broad enterprise KV-native application or database layer
CXL 1.1 memory expansion Production, specific platforms Now on Emerald Rapids or Genoa servers or later Intel 5th Gen Xeon or AMD EPYC 4th Gen, or later
CXL 2.0 memory pooling Type 3 on Xeon 6; pooling silicon sampling with hyperscalers Now for expansion, a few years out for broad pooling Xeon 6 or later, CXL switch fabric
PCIe 6.0 SSDs (data center) Production, enterprise Now from Micron and Samsung; a Tom’s Hardware guide of October 6, 2026 lists no PCIe 6.0 consumer M.2 drive New controller silicon, PAM4 and FEC, EDSFF connector
Computational storage for fixed jobs ScaleFlux compression drives, as of March 2024 Now for fixed jobs; no later status found Workload-specific integration
High Bandwidth Flash Specification published, samples targeted for 2026 and 2027 No product on sale Accelerator and package ecosystem
Per-drive learned models beyond retry tables Research, not publicly documented in drives on sale No firm timeline Controller silicon with inference capability
On-device training Research or early qualification Several years out Silicon area budget, validation framework
CXL 3.x fabric topology Switches demonstrated, no platform confirmed on sale Several years out Full platform and switch ecosystem
General-purpose computational storage Research, NVMe command set ratified No firm timeline Host software ecosystem maturity
Penta-level cell flash Research and demonstration No firm timeline Error correction and retention margin

What does not change

Charge still sets a threshold voltage, pages still can’t be overwritten in place, blocks still erase whole, and error correction still absorbs what the cells get wrong. Smarter firmware, a zoned namespace or a CXL bay changes the workload the NAND sees and where the bookkeeping happens, not those limits. A feature that can’t be traced to one of those layers needs checking before anyone calls it a fact.

The dated items to watch are Marvell’s Bravera SC6 sampling to partners in Q4 2026, Phison’s X3 sampling in December 2026 and shipping in volume in mid-2027, AMD’s Venice SP7 platforms in Q4 2026, Sandisk’s High Bandwidth Flash samples targeted for the second half of 2026, and the August 2027 NVMe release that plans to obsolete Predictable Latency Mode and NVM Sets. Each is a forecast, and a date that passes without the matching product on sale is the signal to note.

What does not change

The future of flash rests on every part below it.

The last part, resting on the nine below it.

Ten boxes are stacked from top to bottom in series order: Part 1, Standards & Interfaces; Part 2, The Physics of Flash; Part 3, From Cell to Die; Part 4, 3D NAND Stacking; Part 5, The Controller; Part 6, The Flash Translation Layer; Part 7, Garbage Collection & Wear; Part 8, Error Correction & Integrity; Part 9, Performance & Endurance; Part 10, The Future of Flash. Part 10 is highlighted. It is the last part and has no arrows leaving it; it builds on the whole stack above it.01Standards & Interfaces02The Physics of Flash03From Cell to Die043D NAND Stacking05The Controller06The Flash Translation Layer07Garbage Collection & Wear08Error Correction & Integrity09Performance & Endurance10The Future of FlashThis partBuilds on itOther part
Figure 10.12 · Part 10 closes the stack and builds on all nine earlier parts. Source: Eyes on Flash series map.

This is the end of the series. For the memories built to sit beside NAND, read Beyond NAND and its guide on High Bandwidth Flash. Where each family sits closes that series and places them by job. To watch the mechanisms from this series move, open the labs.

Sources

Primary is the original paper, standard or datasheet. Secondary is a review, a vendor summary or a news report. Measured is my own test data.

Show all 48 sources, 22 primary