Did you know that the quality differs for each SD card? Companies optimize SD Cards for price or performance which leads to different grades of SD Cards. We will discuss why different SD Card grades exist, what grades can be distinguished and why they are important.
This post is the final part of a three part mini series about SD Cards with some in depth information.
- Part 1 – How to classify SD Cards and choose the right Card for an application
- Part 2 – How does flash memory work
- Part 3 – What are Card grades and why are they important
- Why do different SD Card grades exist
- What grades can be distinguished
- Why are SD Card grades important
If you need an overview or a quick reminder on the topic, this info graphic should serve you well.
Why do different SD Card grades exist
In Part 2 we explained how flash memory works and how it is produced. Additionally we mentioned that although manufacturers pay meticulous attention to all parameters, not all dies (single flash memory chips) are of the same quality. Some dies may even be defective.
Most SD Card manufacturers do not produce their own flash memory and other components. They buy the wafers from a different company. Then they test each wafer to determine the quality of each single die. The result is a wafer map that shows the quality of each die on the wafer. Interestingly dies in the middle of the wafer tend to perform better than dies towards the edge.
In order to maximise the income from each wafer, the production company sells as many dies as possible. As a result they use the dies that fail to reach their quality standards for their cheaper retail products.
The application determines the required quality of the SD Card. You can easily swap out the SD Card of your camera if it fails. However this is not the case if you plan to install an SD Card in a satellite. Such a Card should have the highest possible lifespan and work in a much higher temperature range than your average Card.
What grades can be distinguished
Although there are no official SD Card grades it is possible and probably necessary to distinguish between consumer grade (or retail) Cards and industrial grade (or OEM) Cards.
Consumer grade Cards
Manufacturers optimize consumer grade SD Cards for price. Consequently the customer can get two completely different Cards even when buying the same Card from the same retailer. Since the main focus is to produce a Card for the cheapest possible price the production company will use any parts they have available. Some times these Cards do not even reach the specifications that are printed on top.
Furthermore the risk of getting a poor quality Card is higher when you buy an unbranded Card. Hence if you are buying a consumer grade Card you should aim for one of the commonly known brands like SanDisk or Kingston to increase your chances of getting a good reliable SD Card.
Industrial Grade (OEM) Cards
OEM means means Original Equipment Manufacturer. In contrast to consumer grade Cards, OEM Cards have a fixed Bill of Materials (BoM). Therefore the quality of two cards is more similar. The manufacturer optimizes them for performance and reliability. For this reason the price can be higher (up to 50 times for special applications).
The manufacturer tests that these industrial grade Cards reach their quality specifications.
Be aware that industrial grade is no official or global standard. Therefore each company interprets it differently. For some companies it means better performance or reliability, for others it means extended temperature range.
Why are SD Card grades important
Consumer grade Cards are likely to fail sooner or later. Although you might get away with using a consumer grade SD Card for your camera or Desktop Raspberry Pi, it is very frustrating once the Card stops working. The defective Card can damage the Pi and you need to replace the Card. Further it means loss of data and several hours of work to copy all your backups (that you should always make) onto a new Card.
Industrial grade Cards are far more reliable and yield a better performance. For this reason many companies use them for projects where the Card is not easily accessible.
Also if you are working on any larger scale project that involves SD Cards it is crucial to reduce the risk of an SD Card failing, to keep maintenance costs at a reasonable limit.
The Raspberry Pi is gaining popularity for use in embedded devices. In this case if the SD Card breaks, the whole device is defective.
Raspberry Pi recently released a tool to test the SD Card speed. This is handy to check if the SD Card you bought is up to standard. Check out our (very easy) video to learn how to set up and use the tool.