Memory of the future: how does a SSD?

The flash memory is of particular interest. When the traditional hard drives store information on several magnetic platters (platter), where an actuator with a reading head receives information from a rotating disk, SSD the information is stored using a NAND flash. Initially this technology was only available for use on the wire, but SSD manufacturers are not standing still, so now the market stormed actively both wired and wireless SSD.

Consider the principle of operation of SSD. Information is stored in the array of memory cells, which consists of a floating gate transistor. Electrons, depending on the direction the voltage moves between the control gate and the channel of the NAND. When the shutter control voltage is applied, electrons are attracted up, and the resulting electric field helps them to reach the floating gate, breaking the barrier of oxide. Thanks to him, the electrons do not move on the floating gate. So is the programming of the cell.

No moving disks moving parts is one of the main advantages of SSD over hard drives, and that is what gives SSDs to work at speeds markedly superior HDD. For clarity — here’s a summary table of delay time of different types of NAND and HDD.

SLC, MLC, TLC — the number of bits in each cell. In SLC (Single) this single bit in the MLC (Multi) two-bit TLC (Triple), respectively, three bits. Consequently, the MLC stores two times more data than SLC, and this despite the fact that the number of cells of the same. In General, the principle of these types is the same NAND that can be said about stamina.

If, for example, take crystal NAND flash density 16GB, get 16GB SLC despite the fact that in each cell a single bit. Respectively, for MLC it will be 32 GB, but for TLC — 48 GB. However, in the latter case, the crystal NAND still have to cut, the result is equivalent to 32 Gbit MLC.

At TLC this parameter is the best indicator of this type of NAND can withstand wide range of voltage fluctuations. Drives with this type differ affordable price and high capacity — for example, this model from SILICON POWER or a drive SANDISK. But with SLC there are interesting options (SILICON POWER M-Series).

A few years ago to replace planar NAND flash to 3D NAND came. It is less prone to wear due to the lack of supply of high voltage when writing data into the cell. Manufacturers are actively developing this direction, and on the market there are many drives memory 3D NAND. At a cost they are more expensive (A-DATA 512 GB will cost about 7000 rubles, and INTEL — almost 20 000 rubles), but will these drives last longer.

In this case, we get a cylinder with the top layer as a control gate, while the inner layer acts as the insulator. Cells themselves are arranged one above the other, forming a stack. Control logic located under the memory array, freed the area of the chip where later find himself “home” of the memory cell.

With these modern technologies SSD become more productive and have good bandwidth. Was expected to replace NAND will come something else, and 3D NAND is not long in coming. And then who knows where that will lead us to technology.

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