# SD card

***Copyright © Quectel Wireless Solutions Co., Ltd. 2026. All rights reserved.***

---

SD card (Secure Digital Card) is a widely used portable storage medium with the advantages of small size, large capacity, low power consumption, and ease of use. It is commonly used in mobile phones, cameras, embedded devices, and single-board computers to store system files, applications, and data. It is one of the most mainstream storage solutions in modern mobile and embedded devices.

# Hardware Interface

The Quectel PI M2 smart main board is equipped with a flip-type SD card slot using a 4-bit SDIO interface. The slot has no card-detect switch and does not support hot-plug detection. After inserting an SD card, a rescan or system reboot is required for recognition.

The SD card IO level is fixed at 3.3V, supporting up to SD high-speed mode (50 MHz). UHS-I (1.8V) high-speed mode is not supported. The slot is powered by an onboard load switch (SD_3V3, enabled by default).

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# Usage

## System Recognition

After inserting an SD card, use the following command to confirm whether the system recognizes the device:

```bash
fdisk -l
```

Comparing the output before and after inserting the SD card, you can see that the system has successfully recognized the SD card:

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## Mounting and Unmounting

The SD card is not auto-mounted; manual mounting is required. Create a mount directory and mount (using /mnt/sdcard as an example):

```bash
sudo mkdir -p /mnt/sdcard
sudo mount /dev/mmcblk1p1 /mnt/sdcard
```

Check the files in the mount directory:

```bash
ls /mnt/sdcard
```

Unmount after use:

```bash
sudo umount /mnt/sdcard
```

**Tip:** Unmount the SD card before removing it to prevent data corruption.

## File Operations and Permissions

Normal users may encounter permission issues when accessing the SD card. Change the ownership of the mount point with the following commands:

```bash
sudo chown <username> /mnt/sdcard
sudo chmod 755 /mnt/sdcard
```

Replace ``<username>`` with the current logged-in username. After that, you can read and write files normally in the /mnt/sdcard directory.

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