A SSD Technology a Day (8) – eMLC and MLC-HET

This entry is part 9 of 9 in the series One SSD Technology a Day

In the 2nd post off this series we have explored the differences between SLC and MLC and saw that the main issue with MLC is endurance which in the past prevented their use for enterprise applications. Because of the increased capacity of MLC is a right fit for enterprise use, flash memory manufacturers looked for a way to increase the endurance characteristic of MLC memories. When analyzing the reasons why MLC cells fail sooner than SLC the main culprit was the tight reference voltage that after a numbur of flash write cycles is being overlapped by the actual charge left in the cell leading to an incorrect value being read from that cell. When that happens a few times the cell is being marked as bad.
The solution was to try to make the programing cycles more precise in order to increase the interval around reference levels from and allow more room for error when the memory cell degrades. Also the silicon dies are being tested and only the ones having better endurance characteristics are selected for enterprise use. This flash memory has been marketed as eMLC or MLC-HET (high endurance).

eMLC reference levels - Image courtesy of www.tomshardware.com

This memory has improved endurance over consumer grade MLC with one downside that programming increases in order to allow for more precise reference levels.
The average Write cycles for this type of memory is between 10K and 30K times.

This post comes to you from the shores of Lake Michigan in Muskegon where we are spending the weekend at a cottage in the company of good friends. In order to continue this SSD saga I found myself forced to write this using the WordPress iPhone app much like the character played by Robin Williams in the movie RV. Please excuse any spelling errors that you might find.

Series Navigation<< A SSD Technology a Day (7) – Intelligent Bad Block Management

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