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Program and Erase Cycle (P/E)- SSD Technology

In my earlier post, I talked about SSD drives and how they can use an algorithm called Static Data rotation to help prevent premature wear on the drive. Today, I am going to briefly cover the write operations of SSD/Flash Memory.

One of the limitations of flash memory (Which preceded SSD technology) is that while it can be read or programmed a byte or a word at a time in a random access fashion just like regular memory. (RAM)  It can only be erased one “block” at a time. This will set all bits in the block to 1 which is the default state for NAND memory.

Writing a byte to flash memory involves two steps: Program and Erase. (or also known as “P/E”) The block is written to a new cell and the old block needs to be erased.

The programing can be done at cell level (setting it to the “0″ state)  via a process called tunneling while the floating gate is being flooded with high voltage using the on-chip charge pumps.

Erasing can be done only on an entire block (resetting it to the “1″ state), through high negative voltage that is pulling the electrons off the floating gate via process called quantum tunneling. Flash memory is divided in erase segments (often called blocks or sectors).

As usual, I hope this helps…

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