SK Hynix announced today that its first solid-state drive PQC21 based on 321-layer QLC NAND flash memory has officially started supply and will be shipped to Dell starting this month.PQC21 is a client SSD, available in 1TB and 2TB capacity options, using M.2 2230 form factor, suitable for space-constrained devices such as laptops and mini hosts.
QLC is a four-layer unit. Each storage unit can store 4-bit data. Compared with a single-layer unit, the storage density is higher, but there are trade-offs in speed and durability.
The product is built by stacking hundreds of billions of QLC cells in a 321-layer 4D structure. It uses a PUC architecture to place peripheral circuits under the memory cell array, thereby reducing the chip size.
PQC21 also uses DP chip packaging technology, which can integrate multiple 321-layer NAND chips into a single chip, further increasing the storage density per unit area.
At the same time, the product is equipped with an SLC cache function, which can first write data to the faster SLC area and then transfer it to the QLC storage area, effectively improving writing performance.
As early as August 25, 2025, SK Hynix announced that it had completed the development of 321-layer 2Tb QLC NAND flash memory and put it into mass production. This is the first time in the world to achieve the application of QLC technology with more than 300 layers.
In November of the same year, SK Hynix announced the mass production of the world's first 321-layer 1Tb TLC 4D NAND flash memory, further consolidating its technological leadership in the field of high-stack-layer NAND.
According to data from market research firm IDC,QLC NAND flash’s share of the global cSSD market is expected to grow significantly from 22% in 2025 to 61% in 2027.
A relevant person in charge of SK Hynix said: "The supply of 321-layer QLC solid-state drives is an important milestone."
