The 32GB card shown below is Class 4, denoted by the 4 inside the letter C – this indicates that it can write at 4MB/s.

The speed rating of an SD card should be printed either on the card itself or on the packaging. Equally, write speed will also affect how well any programs which save large quantities of data run – so it’s important to use a good-quality card. The faster you can read data from the card, the faster your Raspberry Pi will boot, and the faster programs will load. The speed of an SD card will also directly affect how fast your Raspberry Pi runs, in just the same way as the speed of a hard drive affects how fast a conventional desktop computer runs. If you want to store 4K video from your digital camera, it is important not just that the card is big enough to hold it, but also that you can write it to the card fast enough to keep up with the huge amount of data coming out of the camera.

SD cards have a speed rating – how fast you can read or write data to the card – and as card sizes have increased, so have speed ratings. However, the fact that SD cards are now so commonplace sometimes conceals the fact that not all SD cards are created equal. SD card speed ratings, and why they matter Prices have plummeted to the point where smaller size cards are practically given away for free, and at the same time storage capacity has increased to the point where you can store a terabyte on your thumbnail. Without an SD card to store the operating system, Raspberry Pi is pretty useless*! Over the ensuing eight years, SD cards have become the default removable storage technology, used in cameras, smartphones, games consoles and all sorts of other devices. Since we first launched Raspberry Pi, an SD card (or microSD card) has always been a vital component.

Sdspeed review