Solid State Drives (SSD)

In this video, I will look at Solid-State Drives. Solid-State Drives have become more popular than hard disks as they have better performance. In this video, I will have a look at how they work and what you can use them for.

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Solid-State Drive
Nowadays, Solid-State Drives or SSDs generally come in three different types. These are, Solid-State Drives, PCI Express and M.2. These all essentially use integrated circuits to persistently store data. This means once the data is written, it will still be available if the computer is switched off. Although they look different, they all use the same kind of chips to store data and, thus, are all considered to be Solid-State Drives.

Solid-State Drives became commercially available back in 1991. Back then, to be compatible with existing computers, they used the same connections as hard disks. Thus, the initial Solid-State Drives were functionally the same as hard disks; however, the technology used to store data was different.

Solid-State Drives can also plug into PCI Express slots. These are usually marketed as PCIe SSD. These were a bit more popular in the old days;, however, with the increased use of M.2 Solid-State Drives, they are becoming less popular. Nevertheless, they still get used in server systems, and later in this video I will look at when and why you would use them.

M.2 Solid-State Drives have become very popular. These storage devices use a small circuit board that can easily be installed onto a motherboard. They have become so popular that, in a lot of cases, they replace the other two types of Solid-State Drives.

Regardless of which Solid-State Drive you use, they all use flash storage in order to store data. Before I look at these storage devices in more detail, I will first look at how flash storage works in these devices.

Non-Volatile NAND
Most Solid-State Drives use non-volatile NAND memory. To start with I will look at how a simple cell works. The cell essentially has three parts, the source, drain and gate. I won’t go into too much detail on how they work. Let’s consider the first example where there is no charge in the cell. When power is applied between the source and the drain, there is a gap between them. With no charge in the cell, the power will not be able to jump between the source and the drain.

The other state of the cell is when it contains a charge. When power is applied to the source and the drain, this time the power can jump between them with the added help of the charge in the cell.

No charge is logically equivalent to a zero value being stored in the cell; and a charge being equivalent to a one value stored in the cell. The drain is used to either remove the charge or add charge to the cell. You can start to understand why read and write speeds are different. Reading the cell is quite fast;, however, writing to the cell means either draining or filling the cell with charge which takes more time.

This is a basic design, so let’s look at how the basic design has been changed to allow more data to be stored.

SLC/MLC/TLC/QLC
The cell I have already looked at is called a Single-Level Cell or SLC. Cells like these can only hold two values, but there are also other cells that have been developed. A Multi-Level Cell or MLC is able to store four values. It does this by changing the amount of charge that is stored in each cell. Essentially, it is just a matter of reading how much charge is in the cell. This is not as easy as it sounds, the process takes longer to read data, write data and the cells wear out faster.

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References
“The Official CompTIA A+ Core Study Guide (Exam 220-1001)” Chapter 6 Paragraph 125 - 139
“CompTIA A+ Certification exam guide. Tenth edition” Pages 292 - 294
“Solid-state drive” https://en.wikipedia.org/wiki/Solid-state_drive
“Coding for SSDs – Part 2: Architecture of an SSD and Benchmarking” http://codecapsule.com/2014/02/12/coding-for-ssds-part-2-architecture-of-an-ssd-and-benchmarking
“M.2” https://en.wikipedia.org/wiki/M.2
“Picture: Solid State Drive Inside” https://commons.wikimedia.org/wiki/File:Embedded_World_2014_SSD.jpg
“Picture: Inside SDD” https://upload.wikimedia.org/wikipedia/commons/f/f0/Samsung_SSD_840_120GB_MZ-7TD120--4_LID_REMOVED.JPG
“Picture: Grinder” https://pixabay.com/photos/angle-cutting-fire-grinder-heat-88524/

Credits
Trainer: Austin Mason http://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson http://www.pbb-proofreading.uk

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