How SD card works?

How SD card works

Based on NAND Flash memories, they allow you to store and exchange files between smartphones, cameras and laptops. Available in various formats, they support encryption

Small and light, they find space inside smartphones, digital cameras and camcorders and even laptop computers. The SD card is an extremely versatile mass storage device that finds space inside many hi-tech devices of everyday use. Born in the very first years of the new millennium, this technological standard spread rapidly all over the world and is now used for the most diverse purposes: from exchanging files between users (such as a USB stick), to saving photos and videos recorded with multimedia devices (various cameras, smartphones and tablets).

What is an SD card?

What is an SD card

The SD card (acronym for Secure Digital ) meets the technological and format standards imposed by the SD Association , an organization based in California (United States) created in January 2000 by Panasonic SanDisk and Toshiba and which today counts on the membership of over a thousand manufacturers of mass memories from all over the world. The idea behind SD cards is to create mass storage devices that are small in size and, at the same time, are capable of providing high storage capacity.

SD cards are distinguished by size (“regular” SD, miniSD and microSD) and file writing and reading speed (in this case SD memories are divided into six “classes”) while always using memories made with NAND Flash technology. There is also an additional SD card format, called ” nanoSD “, which is however a proprietary format developed by Huawei and presented at the launch of the Mate 20 smartphone in October 2018. These are cards 45% smaller. compared to microSD, which have the same dimensions as telephone nano-SIMs.

Types of SD cards

Types of SD cards

Within the family created by the SD Association we now find three different types of SD cards: Full SD , miniSD and microSD . As the names imply, the biggest distinction lies in format and size.

The standard SD card is rectangular in shape (even if one vertex is cut off), measures 32×24 millimeters and can be purchased in various “cuts” of storage capacity (from a few hundred megabytes to a few terabytes). Given these characteristics, it is often used as an extremely light portable hard disk (but be careful to store it carefully, otherwise you risk losing it very easily).

The miniSD and microSD were introduced respectively in 2003 and 2005 to meet the needs of the growing market for mobile and portable devices. Irregular in shape (although both resemble a rectangle) they measure 20×21 millimeters the first and 15×11 millimeters the second. Also in this case, SD cards can be purchased in storage capacity cuts of different sizes: depending on whether you are dealing with ordinary SD cards, with SDHC memories (acronym for Secure Digital High Capacity , with space ranging from 2 to 32 gigabytes) or card SDXC ( Secure Digital Extended capacity , with capacity from 32 gigabytes up).

Another discriminating factor is that of the speed of writing and reading data. The SD Association has established minimum requirements that Secure Digital cards must meet if they want to fall into one of the six existing classes: Class 2 (minimum write / read speed of 2 megabytes per second); Class 4 (minimum write / read speed of 4 megabytes per second); Class 6 (minimum write / read speed of 6 megabytes per second); Class 10 (minimum write / read speed of 10 megabytes per second); UHS Speed ​​Class 1 (acronym UHS-1, with a minimum write / read speed of 10 megabytes per second); UHS Speed ​​Class 3 (acronym UHS-3, with a minimum write / read speed of 30 megabytes per second).

The card SD UHS (acronym for Ultra High Speed ) are characterized by a bus for more efficient data transfer compared to the one mounted by the “normal” SD cards and for this reason are able to achieve higher read and write speeds peaks compared to past.

Inside the SD card

Inside the SD card

An SD card is a solid state mass storage medium. This means that, like RAM or SSD hard drives, it has no moving parts inside, thus favoring its endurance and life expectancy. In particular, SD cards – both the standard ones, both the miniSD and the micro SD cards – make use of NAND Flash memories , which stores data by electrically charging (or unloading) the various memory cells inside it. Particularly fast, NAND Flashes belong to the family of EEPROM memories (acronym for Electronically Erasable Programmable Read Only Memory , “programmable and electronically erasable read only memory”).

SD 8.0 cards: the fastest

Since 2000, the transfer speed of SD cards has steadily increased thanks to two factors: the use of more advanced memory chips and the connection via faster buses . This development trend continues today and the latest standard published by the SD Association (the SD 8.0 standard) brings the maximum data transfer rate of these cards to 3,940 megabytes per second . That is, just under 4 gigabytes per second.

To achieve this speed, however, the card reader must be connected to the motherboard via two dedicated lines of the PCIe 4 bus (with the PCIe 3 bus, and two dedicated lines, the speed stops at 1,920 MBps). The new SD 8.0 cards remain backwards compatible with previous readers, which will read and write them at a limited speed. The maximum speed of 4 gigabytes per second will be useful to go hand in hand with the evolution of smartphone cameras : 8K videos, perhaps with a high framerate, can in fact be written and read smoothly on an SD card only if the latter will have the sufficient transfer rate .

What makes the SD card safe?

The name chosen by the SD Association is, of course, not accidental. The Secure Digital card allows users to protect data within them by encrypting a move designed by the standard creators so as to allow the film and music producers to distribute their content via SD cards without fear that users could then realize copies pirate. The technology behind this feature of SD cards is called CPRM (acronym for Content Protection for Recordable Media ) and was developed by the company specializing in IT interoperability solutions 4C entity .

The fact that SD cards allow you to encrypt your data doesn’t mean they do it by default . In order for a user to be able to protect their data, a Media Identifier and a Media Key Block (MKB) must be created on the SD memory. These are cryptographic keys that will then be used by the “reader” device to decrypt the data contained within the SD card.

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