When purchasing a memory product based on NAND flash, you may have encountered terms like SLC, MLC, or TLC in the product description. But have you ever wondered what they mean and how they can influence your buying decision? Let’s take a closer look to understand SLC, MLC, and TLC in detail.
A NAND flash cell can be programmed with different voltage thresholds, Let us consider a pipe where we are filling water as NAND flash voltage thresholds
SLC (Single Level Cell( NAND flash(
In SLC flash memory, each cell holds a single bit of data, representing either a logic 0 or 1. The cell’s threshold voltage is measured against a specific voltage level—if the voltage exceeds this level, the bit is read as 0; if it falls below, it is read as 1.
Since there are only two levels in this type of flash memory, the voltage margin between them is significantly high, making it easier to read the cell. Additionally, the Bit Error Rate (BER) is lower because voltage disturbances have minimal impact.
Moreover, cell wear is reduced as leakage has a relatively low effect, contributing to better longevity. However, a key drawback is the higher cost—since only two levels are used, the amount of data stored within the same die area is lower compared to other types of flash memory.
When cost is not the primary concern and durability and reliability are the top priorities, SLC is the preferred choice. It is commonly used in enterprise solutions where high endurance and data integrity are critical.
MLC (Multi Level Cell)
Here each cell stores two bits of information i.e. 00, 01, 10 and 11, here we have 4 bands of voltage
As the number of levels increases, reading the cell requires greater accuracy, making the process slower compared to SLC.The Bit Error Rate (BER) is also higher relative to SLC since each cell stores more bits, making it more susceptible to errors. Additionally, charge leakage has a greater impact, leading to increased wear and a shorter lifespan. As a result, the number of Program/Erase (P/E) cycles the device can endure is lower compared to SLC.
This doesn’t mean that MLC has only drawbacks. One of its key advantages is its lower cost compared to SLC. When affordability is a major consideration and factors like reliability or durability are less critical, MLC becomes a suitable choice. It is often used in applications where performance is the primary concern, such as SSDs designed for gaming systems.
TLC (Triple Level Cell)
Each memory cell stores 3 bits of the information. There are 7 levels in TLC against which the threshold voltage is being compared
Since there are more levels, the read operation must be highly precise, making it slower compared to SLC or MLC. Additionally, the Bit Error Rate (BER) is higher, and even minor wear can significantly impact the number of P/E cycles, reducing the overall lifespan.
However, the key advantage of TLC is its lower cost, which is the lowest among SLC, MLC, and TLC. As a result, TLC is commonly used in products where affordability is a major factor, and a shorter lifespan is acceptable.
Coming back to out PIPE analogy , below is how we can represent SLC, MLC and TLC
To summarize, the key parameters on which we can differentiate the three is as below
