SLC vs MLC vs TLC vs QLC

Flash is a non-volatile memory. Flash memory stores information in an array of floating gate transistors, or cells.

NAND memory is a type of Flash memory where all operations are performed per block, similarly to Hard Disk Drives (HDD).

There are four types of NAND:

• Single Level Cell (SLC) - Industrial / Defense Grade
• Multi Level Cell (MLC) - Industrial / Defense Grade
• Triple Level Cell (TLC) - Commercial Grade
• Quad-Level (QLC) - Commercial Grade

Bits per cell.

• SLC NAND stores 1 bit per each cell
• MLC NAND stores 2 bits per cell
• TLC NAND stores 3 bits per cell
• QLC NAND stores 4 bits per cell

By using more granular distinction between charge levels of the floating gate. This reduces design margins and leads to more complex implementation. The added complexity allows the increase of data density, hence lower $/GB. However, the TLC NAND pays the price elsewhere. In comparison to SLC and MLC NAND, it achieves in general 50% of lower transfer rates and >10 times lower write endurance. It also yields lower data reliability and has higher power consumption.

TLC and QLC NAND lower reliability, endurance, and performance implications

Lower reliability of TLC and QLC NAND requires the use of the most powerful Error Correction Code (ECC). The wear-leveling is simply mandatory. Today, the overall data reliability is still not sufficient for TLC and QLC NAND use in general industrial applications.

All NAND Flash has a finite number of Program/Erase cycles (P/E cycles). For a sense of magnitude in differences in write endurance between different NAND:

• TLC NAND and QLC NAND is limited to <800 - 1,000 P/E cycles
• MLC 3,000 P/E cycles
• SLC 30,000 to 100,000 P/E cycles (depending on SLC grade)

When operating in extreme environments, performance is also significantly impacted based on NAND selection, especially in write-intensive applications. Write performance is extremely degraded on applications using TLC or QLC NAND in low or high temperature operating environments. Manufactures quickly begin to throttle performance just to keep SSD on.

SLC and MLC NAND based devices require much less powerful ECC/wear-leveling capability to achieve adequate data and device reliability. They also perform exponentially better in extreme operating environments (starting over 45 degrees Celsius).

Applications

TLC and QLC NAND is therefore used in consumer type of products such consumer media cards, mobile phones, and tablets. You wouldn't stick your mobile phone between the wheels of a F16 and expect it to work... 

SLC and MLC NAND must be used in the majority of defense and aerospace applications to meet professional grade performance and reliability requirements. In addition, the cost of data loss and/or corruption is too great.

MEMKOR only uses SLC and MLC NAND

All MEMKOR products are designed and built for defense and aerospace applications, and therefore are only built with the highest quality SLC and MLC NAND.