Purpose of board:

• you want play with XTSD chip
• create device with more reliable connector and want still have way to load/save data with uSD shaped connector
• you need just hook wires to SPI signals inside uSD slot

    You receive 1pcs bare PCB without memory chip
  

XTSD chip description by adafruit product: Adafruit SPI Flash SD Card - XTSD 512 MB

This breakout is for a fascinating chip - it looks like an SPI Flash storage chip (like the GD25Q16) but its really an SD card, in an SMT chip format. What that means is that you wire up like an SD card breakout, and use the SD card libraries you already have for your microcontroller. For example, you can use the built in SD library in Arduino, or for CircuitPython we have an sdcard library.

You might be wondering why you'd want such a thing - after all you can't plug it into a computer to get the files off like MicroSD cards. For some use cases, such as data logging in a high-vibration device where you don't want the SD card to come loose, or for when you need to reduce size, or when the microcontroller provides a USB mass storage interface, this chip could very useful.

Compared to plain SPI flash, this NAND memory chip handles all the wear leveling and ECC calculation. You don't have to manually erase blocks, you just write and read them like you would with any SD card.You can clock it up 50 MHz and the 'write speed class' is 8 (although you may not be able to get that fast with plain 1-bit SPI compared to SDIO).

XTST chip order link:

• https://www.lcsc.com/search?q=xtsd