Windows – Why is the microSD card is so slow

I don't know what device you are using that requires FAT32 or EXT2. Stick with the exFAT format if you can - is my advice.

The tools on the Windows operating system are not specialized enough to format micro SD cards. If you EVER get a message asking or telling you to format using Windows DONT DO IT! The reason is that micro SD cards have two different areas on them when they come from the factory and/or when formatted properly. There is the storage area, of course, for all the files that you store on it and that are visible when examining the folder contents, but there is also another small administrative area that contains a security information specific to the card. When the clumsy Windows formatting is employed to format a micro SD it bull-dozes across the security area and that important information is lost from the SD card. This loss often throws one of many possible errors when the card is in use, or when you try to plug it in somewhere.

Do not freak out just yet. Just get organized to recover the card:

1. Never pull a micro SD card out of a device without "unmounting" the micro SD card first. You can do this on phones and tablets by going to the settings setting on the device and selecting the storage option. Under Storage select "unmounts" and wait a second for it to go gray. Without screwing around go to the "All Running Apps" selection (mine is a little square on the bottom ribbon of the home page) and hit "close all apps." Turn off the device completely through the normal shut-down process. Always insert micro SD cards when the device is powered OFF. ALWAYS remove them UNMOUNTED and with the Power OFF.

2. Download the free SD Formatter software and the user guide from the SD Foundation website. This is the ONLY correct software for formatting micro SD cards. I used this URL: https://www.sdcard.org/downloads/formatter_4/ to get my copy. Browse around the site, you can learn a lot about SD standard. This makes it Sooo easy.

3. I run the software on my Windows 7 computer with the micro SD in a USB converter. Occasionally I might get the error that it is not ready to work or something so I gently pull the USB out and push it back in while the program is running. Select the CORRECT drive from the dropdown and press format. Several warnings will pop up reminding you to check that you selected the right "drive". Check the size information and make sure it is your SD card.

4. Enjoy your reformatted micro SD card. Total cost: $0.00, nada. Micro SD cards are really volatile if you are fiddling around with them outside a "mounted" environment inside the phone or tablet.

I learned all this fiddling around with my new 1024GB (yes folks, 1TB), no, it is not a smaller chip programmed to read large by a device that deletes your information when you get to the "real" capacity of the chip. There are also 512GB and 256GB chips out there if you have a friend at the FAB. It is weird to think that a tiny chip the size of your fingernail holds 1TB. I must be getting old. I think I must have bought twenty different hard drives (the spinning disk type) over the years before I ever purchased one that held even 1 terabyte. A 2TB micro SD chip is on the horizon. 2TB is the maximum supported capacity that the SDXC format will support.

This is a feature of newer cards called the "Ultra High Speed Bus."

It allows the card to transfer data faster.

USB 3.0 is like this too - it has additional pins which allow faster data transfer, but is still backward compatible with things that do not have the additional pins (will fall back to slower speed).

From Secure Digital Wikipedia page:

UHS-II

Specified in version 4.0, further raises the data transfer rate to a theoretical maximum of 156 MB/s (full duplex) or 312 MB/s (half duplex) using an additional row of pins] (a total of 17 pins for full-size and 16 pins for micro-size cards).

Without these extra pins you can only do UHS-I which maxes out at 104 MB/s.

Nice chart on the page comparing all the speeds as well:

Bus interface   Logos          Bus speed                    Spec version    
--------------  -------------  ---------------------------  ------------

Default Speed   SD SDHC SDXC   12.5 MByte/s                 1.01

High Speed                     25 MByte/s                   2.00

UHS-I           SDHC SDXC I    12.5 MByte/s (SDR12)         3.01
                               25 MByte/s (SDR25)
                               50 MByte/s (SDR50, DDR50)
                               104 MByte/s (SDR104)          

UHS-II          SDHC SDXC II   156 MByte/s (FD156)          4.00/4.10
                               312 MByte/s (HD312)         

UHS-III         SDHC SDXC III  312 MByte/s (FD312)          6.0
                               624 MByte/s (FD624)