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Tech blog  September 14, 2015

Spec Sheet Cheat Sheet | SSD Overview

Introduction

A solid state drive’s specification sheet can be confusing to understand as there are various core terms and concepts that need to be understood first. In this document, we will be taking a look at what these terms mean and which of them are important when selecting an SSD.

Interface

The very first thing would be to take a look at the interface, which is a fancy way of determining how this device will connect to the computer. At this point, SATA is the standard and most SSDs available at the consumer-level will reflect that. If you don’t know what SATA is, that’s okay. The important thing to know is that most modern computers use the SATA port to connec t their storage drives. We will be publishing an article that takes a deeper look at the different interfaces sometime soon, so if you are interested, look out for that post.

This is what the SATA interface looks like. Source: Wikipedia

Controller

After you have established that the SSD will connect to your computer, you will need to look at various other criteria. ?Beyond peering at the most important items (price and capacity) spec sheets will often contain mostly-unknown words, such as “controller” and “NAND.”

Under the “controller” heading, it will list out a specific brand name -- though only the well-versed users will be able to distinguish between them. The controller acts a s the medium between the user and the flash memory. When the user attempts an operation, such as reading or writing a particular set of data, it is the controller that carries out the operation. The controller can essentially be referred to as the brain of the drive ? that’s the level of its importance. When an SSD is considered to be a top level drive, it is usually because the controller itself is top qu ality. The controller affects the speed for both random and sequential access, as well as the longevity of the drive. Though is it not necessary to look at the controller when buying an SSD, it is important to be aware that they do make a difference in quality and longevity of the drive.

The DRAM occupies the space next to the Controller

Speeds

Another big factor when looking at SSDs are the speeds. When an SSD has its specs listed out, the read and write speeds are separated into sequential and random. The random speed is listed out in IOPS (input/output operations per second) and the sequential speed is listed out as a raw number (ie. 500MB/s). ?Both terms indicate exactly what they mean: the random measures the SSDs ability to read non-sequential data, data that is strewn about the drive. While the sequential measures data that is linear and in large chunks (think large video files). When considering these speeds, it is important to know what sort of performance you expect from your SSD and where you should focus your attention: sequential or random access.

NAND Type

The NAND heading simply refers to what sort of memory configuration is being employed by the drive. For a while, this sort of heading was relatively linear. When a new SSD was released with a higher density, the NAND type number got smaller. SSDs are growing larger in capacity because manufacturers are becoming more efficient in packing more data on smaller and smaller dies(or chips). The number refers to the size of each die. So, if you see an SSD indicating it uses a 64Gb die, then the manufacturers found a way to pack 64Gb (8GB) onto a tiny surface area (94mm 2 in this example) utilizing 19nm nodes. The smaller the number of nanometers, the more densely packed the NAND. The space will also be shared with an acronym: MLC, SLC, and TLC. These acronyms (Multi-Level Cell, Single-Level Cell, Triple-Level Cell) simply refer to how data is written and read from the flash cells and will have a significant impact on the density, endurance, and speed of the drive. There will be an article published that will delve into this subject a bit more sometime soon, so be on that look out for that.

This is a close up view of a NAND cell. The more densely packed, the closer these structures are to each other. Source: Wikipedia

TBW

Reliability is arguably the most important and overlooked feature for a storage device. What good is cutting-edge density and price if the data itself is not protected? When looking through a specification sheet, this metric is usually represented by an endurance rating labeled “TBW” (Terabytes Written). The metric is used as an upper limit of how much data can be written o nto the drive throughout its life. So if, for example, the specs indicate a TBW of 200, it means that the drive can withstand being written with 200 terabytes of data before it risks any complications. This of course means that the higher the rating, the better and more reliable the drive.

Conclusion

As you might notice, upgrading to an SSD is arguably the best available path to increasing overall performance of your device. Knowing what you need and what to expect when buying a new drive will lead to a smarter purchase.

Article by: Israel Imru

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