SD Standard Overview

An Introduction to SD Standards

SD standards enable manufacturers to deliver high-performance products that enhance the experience of millions of people every day who listen to music, record videos, take photos, save data and use a mobile phone.

As the industry standard, the SD standard is utilized across multiple market segments of the portable storage industry, including mobile phones, digital cameras, MP3 players, personal computers, tablets, printers, car navigation systems, electronic books, and many other consumer electronic devices.

"Universal, portable and convenient SD standards lead the market today and will continue to evolve with the future of the digital world."

There are three defined form factors for SD Card; Standard Size, miniSD and microSD. As microSD took the place of miniSD, recently two form factors, shown in table below, have been used as widespread form factors. Original SD Card (alias non UHS-II Card) has the first-row pins including 3.3V VDD that are used for bus interface such as Default Speed, High Speed and UHS-I modes. Standard Size Card has 9 pins (two VSS) and microSD has 8 pins (one VSS).


A new pin layout on the second-row was introduced to support the UHS-II bus interface and also support UHS-III for the two form factors. 1.8V VDD is included in the second-row pins and then UHS-II/UHS-III Cards require two power supply voltages 3.3V and 1.8V.

Before defining 2nd Row of UHS-II, Non UHS-II microSD Card extended two optional antenna pads for contactless applications but antenna pads will interfere the second row of UHS-II/UHS-III Cards. NFC (Near Field Communication) Interface was defined alternatively that use Single Wire Protocol via a pad on the second row.


Form Factor SD microSD
Dimension SD Card SD Card
Card Capacity Type SD, SDHC, SDXC SD, SDHC, SDXC
Physical Number
of pins
9 pins(non UHS-II card)
+8 pins(UHS-II and UHS-III card)
8 pins(non UHS-II card)
+9 pins(UHS-II and UHS-III card)
Operating Voltage 2.7V - 3.6V(non UHS-II card)
VDD1:2.7v-3.6v/VDD2:1.70V-1.95V(UHS-II and UHS-III card)
Write-protect Switch YES NO


NAND technology showed amazing progress that provided exponential memory capacity increase. Much faster bus interface speed is required in accordance with increase of memory capacity to shorten access time to such capacity card.


UHS-II and UHS-III can provide much higher bus speed than UHS-I using Low Voltage Differential Signal (LVDS) on the second-row pins. The first-row interface enables UHS-II/UHS-III Cards to maintain interoperability with conventional interface host devices.


UHS-II and UHS-III Pin Layout

SD Standard Memory Cards

Simplified Specification Downloads

Simplified versions of selected SD memory card specifications are available for download by developers. To get access to the full specifications, simply join the SD Association.

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