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Kioxia and Western Digital announced their eighth-generation BiCS FLASH 3D NAND, with 218 active layers, on March 30, 2023. The headline’s “1TB TLC” is a unit error: the announced TLC die was 1Tb—about 128GB of raw capacity—not a 1TB SSD. The companies said samples were shipping to limited customers; they did not announce a retail drive, price, or consumer availability date. Kioxia’s announcement
What Kioxia and Western Digital announced
The companies described an eighth-generation BiCS FLASH technology, commonly called BiCS8, built with 218 active layers. The announcement covered both 1Tb TLC and 1Tb QLC NAND, each with a four-plane architecture. Kioxia said samples had begun shipping to limited customers, making this a NAND technology and component milestone—not the launch of a finished consumer SSD.
| Specification | Announcement |
|---|---|
| Generation | Eighth-generation BiCS FLASH (BiCS8) |
| Layer count | 218 active layers |
| Memory types | 1Tb TLC and 1Tb QLC |
| Plane architecture | Four planes |
| NAND I/O | More than 3.2Gb/s, in Kioxia’s wording; commonly rendered as about 3.2 GT/s |
| Density claim | More than 50% higher bit density, claimed by Kioxia versus the previous generation |
| Performance claim | 20% improvement in write performance and read latency, claimed by Kioxia versus the previous generation |
| Availability at announcement | Samples shipping to limited customers; no retail SSD announced |
The company’s release also says I/O speed improved 60% over the previous generation. These are technology-level company claims, not independent benchmarks of a finished drive. The release does not supply a full test table, workload, queue depth, or measurement method for its write-performance and read-latency comparison. Kioxia’s release
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The lowercase b means bits; the uppercase B means bytes. Eight bits make one byte, so 1Tb equals 128GB in decimal units before formatting and other capacity conventions. Tom’s Hardware identifies the announced TLC component as a 1Tb, four-plane device—roughly 128GB of raw NAND capacity per die, not a 1TB drive. Tom’s Hardware’s technical coverage
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A 1TB-class SSD could combine multiple NAND dies, a controller, firmware, and spare capacity, but the announcement did not specify a particular SSD design or die count. Raw NAND capacity and the capacity a drive reports to its user are not necessarily identical because manufacturers also account for formatting, bad-block management, and spare area.
What 218 layers means—and what it does not
In 3D NAND, memory cells are arranged in vertical layers. “218-layer” refers to the active layers in the NAND array; it is not a count of dies in an SSD, a capacity rating, or a measure of memory channels. Layer count alone does not determine a drive’s speed, endurance, or cost.
BiCS8’s design is not simply a taller stack. Kioxia and Western Digital describe a combination of vertical and lateral scaling, cell shrink, and wafer bonding intended to increase bit density and improve performance and manufacturing economics. The companies claim more than 50% higher bit density than their prior generation, but the announcement does not make layer count a linear proxy for that gain.
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How CBA wafer bonding fits in
CBA means CMOS directly Bonded to Array. The companies manufacture the CMOS circuitry and NAND cell array on separate wafers, then bond them together. That lets each structure be made using processes suited to its role, rather than requiring the logic and array to be optimized as one structure. Kioxia attributes density and I/O improvements to this approach alongside scaling and architectural changes. Kioxia’s explanation of BiCS8
CBA is an architectural and manufacturing choice; it does not by itself guarantee a particular SSD’s endurance or sustained write speed. Those depend on the specific NAND, controller, firmware, spare capacity, thermal design, and workload.
What four planes and 3.2 GT/s tell you
Four-plane parallelism
A NAND die is divided into planes that can support internal parallel operations. Four planes can provide opportunities for concurrency, but the benefit a drive realizes depends on its controller, command scheduling, die organization, and workload. The four-plane configuration belongs to the announced device; it should not be conflated with later discussion of a related eight-plane design.
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Interface rate is not SSD throughput
Kioxia states that NAND I/O exceeds 3.2Gb/s; technical coverage commonly expresses this as about 3,200 million transfers per second, or 3.2 GT/s. That is a NAND-device interface rate, not a finished SSD’s sequential read or write speed. Tom’s Hardware discusses a theoretical peak of about 400MB/s per NAND interface under its assumptions, but that is not a guaranteed application or drive result. Tom’s Hardware’s interface-rate context
A finished SSD’s throughput depends on how many dies and channels operate in parallel, the controller, the PCIe/NVMe link, cache behavior, queue depth, and thermals. A NAND I/O figure cannot establish that a drive will sustain any particular speed.
TLC and QLC are different choices
The announcement covers both TLC and QLC; they are not interchangeable descriptions of one part. TLC stores three bits per cell and generally offers a stronger endurance and sustained-write position than QLC. QLC stores four bits per cell, which can support greater density and lower cost, but often relies more heavily on caching and workload management. The specific 1Tb TLC part is one example in the BiCS8 family, not a specification for every variant.
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How it compares with the previous generation
Kioxia and Western Digital announced a 162-layer, sixth-generation 3D flash technology in February 2021. BiCS8’s 218 active layers mark a later generation, but that difference does not translate directly into an equivalent percentage increase in speed, capacity, or endurance: the newer technology also changes scaling and architecture. Kioxia’s 162-layer announcement
What the announcement means for SSD buyers
In March 2023, the companies did not name a retail SSD using this NAND or publish a consumer price, finished-drive benchmark, controller pairing, or mass-market availability date. Sampling to limited customers is not evidence that a drive is on sale, that production yields are established, or that a particular product uses the announced die.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchBiCS8 could support future SSDs and other storage products, but the announcement did not say when buyers would encounter it in a specific product. Kioxia’s current consumer lineup includes the EXCERIA PLUS G4 and EXCERIA PRO, but its product pages do not establish that either uses the exact 218-layer die announced in 2023. Kioxia’s SSD lineup · EXCERIA PLUS G4 specifications
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For a concrete example of why product-level identification matters, Western Digital’s PC SN8000S data sheet specifies 162-layer BiCS6 TLC, not the 218-layer BiCS8 technology. It is a separate comparison product, not proof of BiCS8 use. Western Digital PC SN8000S data sheet
When comparing drives, use the finished product’s specifications and independent testing rather than a NAND layer-count headline. Relevant factors include PCIe compatibility, capacity, TLC or QLC type, controller and DRAM or HMB design, sustained writes after cache exhaustion, endurance rating, cooling, warranty, firmware support, and price per usable terabyte.
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