SK hynix said on Tuesday it has completed development of the PQC21 client SSD (cSSD) based on 321-layer QLC NAND flash and has begun supplying customers. The product is the company’s first to combine 321-layer stacking with QLC technology. It applies a QLC method that stores 4 bits in each cell to increase storage capacity per unit area. It will be launched in 1TB and 2TB capacities.

QLC is one of the standards based on the number of bits stored per NAND flash cell, storing 4 bits per cell. It can pack more data into the same area than SLC (1 bit), MLC (2 bits) and TLC (3 bits), making it advantageous for implementing high capacity. However, its write speed is relatively slower, so PQC21 applies SLC caching technology that uses part of the cell area like SLC to supplement write performance.

SK hynix will ramp up supply of PQC21 starting this month, beginning with global IT company Dell Technologies. Dell is a major customer in the AI PC segment, and SK hynix plans to gradually expand partnerships with major global customers from this supply.

It also aims to accelerate efforts to expand its share of the QLC-based cSSD market. According to global market research firm IDC, the share of QLC NAND in the global cSSD market is forecast to rise to 61 percent in 2027 from 22 percent in 2025.

An SK hynix official said, "This supply of a 321-layer QLC-based cSSD will be an important milestone that proves the company’s leadership in the AI PC market." The official added, "We will continue to lead the high-performance NAND solution market based on overwhelming technological capabilities."