Flash memory is a storage chip, that can preserve data without the need for an external power source. The flash memory can be of the NOR or the NAND type. The NAND flash cell can further be classified as the SLC(Single-level cell), MLC(multi-level cell), TLC(Triple level cell), and QLC(Quad level cell).
MLC vs SLC
The main difference between MLC and SLC is that the cell structures generate significantly varying outputs. Their storage capacity is not equal, this is in contrast to their almost identical appearance. The cost of each product is influenced by the amount of semiconductor material used. This quantity depends on the performance specifications.
MLCs are of commercial grade and are used in USB flash drives and compact flash cards. They have a block size of 128 Kbyte. The cells are structured in such a way that there are multiple bits in a flash module. The short lifespan of MLC is because of low resistance to high temperatures.
SLCs are used in embedded systems and are of industrial grade. This explains their expensive rates. They make use of high-grade flash technology that makes them the best option for industrial applications. This allows SLC to be operable at high temperatures without any significant leakage loss. It has a block size of 64 Kbyte.
Comparison Table Between MLC and SLC
| Parameters of Comparison | MLC | SLC |
| Expansion | It is known as a multi-level cell. | It is known a single-level cell. |
| Storage | It has the capacity to store two bits per cell. | It can store one bit per cell. |
| Performance | The read and write performance is lower. | The operation is faster and more reliable. |
| Cost | It is not very expensive and is easily affordable. | It is very expensive and unsuitable for the usual market. |
| Endurance | The endurance meets acceptable standards. | Endurance is very good. |
What is MLC?
MLC can interpret multiple ranges of values. This is commonly denoted as four distinct categories. They are 00,01,10 or 11. Each of these numerical values corresponds to a stage of the MLC. The value 00 represents a fully programmed condition.
The values 01 and 10 correspond to the partially programmed and partially erased conditions. At the other end of the scale, the value of 11 denotes a fully erased condition.
The MLC flash memories are available in thirty-two and sixty-four megabits per second. The former has a read speed of 120 nanoseconds, while the latter takes 150 nanoseconds. There is a subclass called the eMLC, or the enterprise MLC.This is a variety of the MLC that has enhanced performance.
They are capable of more write cycles than the average MLC flash. It is the optimal solution given its positive output and affordable price range in comparison to the SLC flash. It also reduces the margin of error during operation.
This is related to the write the lesser the number of write cycles, the greater is the scope of errors to occur. The high threshold of power consumption of an MLC flash is owed to two key reasons-the primary reasons is the necessity for different voltage levels and lack of technology.
What is SLC?
The bit value of the SLC flash, also known as the voltage level, is either 0 or 1. The value of 0 represents a programmed state, whereas 1 donated an erased state. In every cell, a single charge is needed to read and write a unit of data.
The SLC has a density of sixteen megabits per second, with a read speed of hundred nanoseconds. Since there are no fluctuations or different requirements in relation to the voltage levels, the power consumption is significantly lesser. This in turn impacts the speed of its data analysis and the probability of errors occurring.
SLCs are popular for their high quality of endurance. They have a long-life span due to the presence of a small number(two ) of voltage levels. The program and erase cycles are limited because, with each change in the voltage level, the cell memory is altered permanently. With time the degradation of the cell is inevitable.
The security for data logging is assured in this type of flash memory. It eliminates the risk of data loss due to uncertain external influencing factors. The operating temperature of the SLC flash lies between -40 to 85 degrees C. They have a higher tolerance to fluctuating temperature ranges, shock, and vibration.
Main Differences Between MLC and SLC
- The MLC is otherwise called a DLC-Double level cell. In contrast, SLC is a single-level cell.
- MLC has high-density data storage, making retrieval rates slow. In comparison, data retrieval in SLC is faster as it stores 0 or 1.
- Due to a lack of partial programming, the performance of MLC is slower. In SLC, this increases the speed of performance and its efficiency.
- MLC targets the mainstream market and is affordable. The SLC is expensive as it caters to a specialized client category.
- On average, the MCL can give an output of 10000 P/E cycles. The performance of an SLC can meet ten times that of an MLC flash.
Conclusion
The difference in performances of the MLS and SLC flashes can be summarized in certain core aspects. They are durability, reliability, data storage, program and erase cycles, tolerance levels, and economical characteristics.
While the MLC may not be able to compete in the industrial category, it is ideal for the everyday consumer. This is because there is a vast gap in the requirements of flash memory in the commercial and industrial sectors. A key point to note is that the power consumption of SLC is lesser in comparison to MLC.
The selection between the two options depends on the short-listed needs of the user. If the deciding factors are performance and durability, the SLC flash is a good choice. If the selection depends on the ranking of cost and density/capacity, then MLC flash is more suitable.
References
- https://ieeexplore.ieee.org/abstract/document/5572846/
- https://ieeexplore.ieee.org/abstract/document/6298208/
- https://www.usenix.org/legacy/event/fast/tech/full_papers/Grupp.pdf