What are Solid State Drives

What is a Solid State Drive?

A Solid State Drive is a storage device which emulates a rotating hard disk drive but is made from semiconductor components. Typically SSD are made using NAND flash memory, but a DRAM based device would also be considered a solid state drive. The 2.5” form factor is most popular, but flash cards and modules such as CompactFlash, SD Card, mSATA all the way up to PCIe boards are also SSD.

Since a SSD has no moving parts, it handles shock and vibration much better that a rotating disk drive. Without the spindle motor needed to rotate platters and an actuator to move the heads to the correct location, a SSD generally uses much less power than its mechanical HDD counterpart.

What does a Solid State Drive do?

A Solid State Drive replaces a hard disk drive in applications which require one of the following attributes:

The most popular SSD form factor is 2.5” and has a SATA interface. A 2.5” SSD is installed similar to a regular hard disk drive. The host computer system doesn’t know the difference between the SSD and hard disk drive. It is formatted and used as normal. In the case of the 2.5” SSD, the faster performance and better battery life are the main differences which will be experienced by the user.

What is a Solid State Drive Used for?

A Solid State Drive is used to provide better performance and/or lower power usage than a hard disk drive in an existing computer system. It is also used for new computer or embedded system designs which require smaller physical size, removability, lower power, higher performance and/or a lower absolute price if low capacity needed.

There is a growing trend in the notebook market to install SSDs instead of hard disk drives. Recently an industry analyst firm shows the total SSD memory capacity equal to ~16% of hard drive usage. This is a rapidly growing trend since 2 to 3 years prior this percentage would be in the low single digits.

How do Solid State Drives Work?

A Solid State Drive emulates a hard disk drive in a host computer or embedded system. It does this with a specially designed controller which has the same electrical interface as a rotating hard disk drive. In many cases it has the exact same connector and physical form factor as the hard drive as well.

Other circuitry of the controller manages the NAND flash memory which stores the data of the SSD. While the controller function appears relatively straight forward, there are many behind the scenes issues with NAND flash management and it requires a great deal of planning to create a reliable SSD controller.

How long do Solid State Drives last?

The life of a SSD depends on the application which it is being used. Unlike rotating hard disk drives which SSD were designed to replace, the SSD memory has a finite number of endurance/erase cycles. This makes the management of data written to the SSD extremely important. As an example, a consumer 2.5” SATA SSD could last for decades in low intensity application, but may only last a few weeks in a high intensity data logging application.

There are also different types of NAND flash memory which range from the highest reliability and cost Single Level Cell (SLC) to the lowest cost and reliability Tri Level Cell NAND. It is important when choosing a SSD to select the one which is right for the application.

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