Flash Comparison Tool

SLC vs. MLC

How Flash Works

In flash memory, information is stored as bits in a group of memory cells referred to as a page.  As the name implies, Single-Level Cell (SLC) flash memory stores one bit of information per cell as opposed to Multiple-Level Cell (MLC) flash memory, which stores multiple bits of information in each cell.  The number of cells required to store a given file will vary with the size of the file.  When programming data, flash memory cannot access information directly at the byte level.  Instead, it must write information to pages (groups of cells) and erase in blocks (groups of pages).  It is precisely because of this compounding effect that wear and tear on a MLC flash drives happens at such an accelerated rate, where multiple bits of information are stored in each cell rather than just one.  Both SLC and MLC cells are equally prone to wear, MLC cells just get more activity. 

The limited number of erase/program cycles, which determine the life cycle of the drive, can be used up extremely quickly depending on the application.  To manage the space in either a MLC or SLC flash drive or even simply save an updated version of a file, a drive will often need to reprogram multiple pages of cells, which requires one or more erase/program cycles for each page. 

Why Flash Deteriorates

To understand why flash memory deteriorates it is important to recall that flash memory uses electrical currents to program data to each cell.  The limited number of erase/program cycles is because the silicon oxide material used to separate cells suffers wear and tear from the electrical currents that are used in programming data to the cells.  This material eventually dissipates to where cells in the drive fail.  

See our “About Emphase” document for a look at some features and benefits of Emphase SLC Flash.

Reliability of SLC                                                                            

Program/Erase Cycles is the number of times data can be written to and erased from a cell.  Due to static wear-leveling, Emphase drives can spread out the wear of all cells in the drive and should the drive detect failure, it will even attempt to do so in a way that all data will be recoverable by doing so on the next erase command.

MTBF (Mean Time Between Failures) is not acomponent's useful life but rather a statistical indicator of reliability.  It is the predicted elapsed time between failures of a system while in use.  An MTBF of 4,000,000 hrs means that of all the drives tested, one failure occurred every 4 million hours of testing.  In simpler terms, this also means that if 400 drives were tested, one failure would occur every 100,000 hours (11+ years). 

*Intel Corporation does not provide this information.

Performance

Read/Write Speed refers to the sustained speeds at which information can be read from and written to the drive.  By design, SLC memory is able to achieve higher speeds because there can only be one bit value of data in each cell whereas it takes more time to sort through the bundled data in MLC flash cells. 

IOPS are the input/output operations that a drive can achieve per second and are most commonly referred to for systems that handle a large volume of small files (typically 4-8KB).  It’s important to note that not all drives are designed to provide high IOPS.  Emphase IOPS specifications are different as they represent how a drive functions at a “broken in” state after several days of burn-in, rather than simply at a brand new state.  It is due to this that our IOPS figures represent drive performance at a highly stable state.   The achievable IOPS for SLC are faster than MLC for the same reasons that sustained Read/Write speeds are faster – it is by technological design. 

Wide-Temperature Rangecan be a critical requirement for many applications.  Due to the design, MLC memory has limited operating temperature ranges, whereas SLC memory is dependable at operating temperature ranges of -40°C to 85°C (-40°F to 185°F).