Before an SD card can be used it has to be formatted. In general, they come out of the box pre-formatted, and you can put them straight in the camera and the camera will create any folders it needs automatically. But there are several reasons you might need to format or reformat it. For one thing, formatting is the best way to wipe an SD card clean to free up space. For another, it can repair any filesystem errors that have crept in at some point.
Best practice is to format the memory card in the camera you'll be using it in. But that's not always possible or practical. There might be times you need to format an SD card in computer.
Modern computer operating systems can handle this job well, and I've posted separately on how to format SD cards on Mac using the built-in Disk Utility app. The advantages of that method are that it's using tools already available in the operating system and it works for any kind of storage volume connected to your computer. The downsides are that there are more choices, which means more complications and places where things can get messed up.
In fact, the SD Association goes so far as to recommend against using the tools in your computer's operating system:
It is strongly recommended to use the SD Memory Card Formatter to format SD/SDHC/SDXC Cards rather than using formatting tools provided with individual operating systems. In general, formatting tools provided with operating systems can format various storage media including SD/SDHC/SDXC Cards, but it may not be optimized for SD/SDHC/SDXC Cards and it may result in lower performance.
The SD Association makes available its own app that is designed to perfectly implement their own specifications for SD and microSD cards--they are the ones that set the specifications, after all. Whether the card is SDHC or SDXC, the SD Card Formatter will make sure it's formatted correctly and ready for use. And the filesystem will be optimized for its intended use on an SD card rather than, say, an old-school magnetic hard drive.
The app is called SD Card Formatter, and it's available in Mac and Windows versions. It's free, and you can find it on the SD Association's website.
While it's very straightforward to use, there are a couple of things worth noting, which I'll go into below.
First, though, there are some advantages to using SD Card Formatter over using your operating system's built-in tools. For one thing, it takes the risk out that you'll use the wrong filesystem on the card. For another, it gives you tools that might help repair a corrupted SD card. In short, it ensures that the card is in tip-top formatting shape for use.
The app has just a single small screen, and there are only three things to set.
The first, at the top, is selecting the SD card you want to format. A useful feature is that it will only show you memory cards, so there's not much risk that you'll accidentally format an external hard drive instead (although it shows all memory cards, not just SD and microSD cards).
Just below that, it will show you two related bits of information: card capacity and type.
For card capacity, you'll most likely see slight differences from what you might expect. A 64GB card, for instance, but show as 63.85GB. Or, as you see in this case, a 128GB card shows as 128.46GB. There are a few reasons for those differences, including that the app uses different ways to calculate a gigabyte in its Windows version (base 1024, or 1kB=1024 Bytes) than in its Mac version (base 1000, or 1kB=1000 Bytes). But those variances are normal and aren't anything to get concerned about.
Based on the capacity, the Type field automatically adjusts to SD, SDHC, or SDXC. That's important, because that determines the filesystem the app uses to format. This is something that's laid out in the SD Associations specifications for SD and microSD cards. Cards that are from 4 to 32GB are SDHC, and they're formatted with a FAT32 filesystem. Cards 64GB and larger are SDXC, and they're formatted with the newer, more flexible exFAT filesystem. But with this app, you don't even know that because the app handles it for you.1 You'll see a small icon for the type at right: SD, SDHC, or SDXC.
The next section is where you choose which formatting option to use. In most cases, the Quick Format option, which is the default, will do what you need. This operation is, as it says, quick. It deletes the directory entries but it doesn't dig down into the files themselves. Or, more technically: "It deletes all the file/directory entries by initializing file
system parameters of the card but does not initialize the data written in files." In most everyday cases, this is the option to use.
If your card is showing signs of data corruption of you want a deeper cleanse of sensitive data, you select Overwrite format instead.2 Note that this is not the same thing as data recovery. This is going to wipe everything thoroughly--it's not going to recover any lost photos or videos. For that you'll need a different kind of app.
The Overwrite format operation starts the same way as Quick Format, but then it tackles the data in the files themselves. Or, again more technically: "This option deletes file/directory entries by initializing file system parameters of the card and erase all data by overwriting the user data area completely." This option is more thorough, but it's also much slower. It's a good option if you're trying to salvage a card that has been showing symptoms of data corruption, but it's not the best option for everyday formatting.
There's one other option that's only available in the Windows version (the one I'm using for these screenshots is the Mac version, so it doesn't show up here), and even then only when the card is 8GB or smaller. That's the CHS Format Size Adjustment option. But that is both a specialized function and also one that applies only to smaller cards that are getting rare today. You can find more information about what it does here.
Finally, there's the Volume Label field. That's the equivalent of the Name field if you're using Disk Utility on Mac. It's an opportunity to give the card a friendly name when it shows up in file viewers such as Finder or Explorer. Filling that in is optional, but if you do, keep it simple--with no special characters and only short.
Beyond that, it's just a matter of proceeding with the formatting. You'll get the obligatory warning that you're about to wipe the card.
Once you confirm that that is in fact what you want to do and you want to continue, you might be prompted to enter your computer's admin password so as to get the required permissions to change the filesystem on the card. Then it'll do its thing and display a report on what it has done.
And that's about all there is to it. Your SD card is now ready to use.
- It is technically possible to go against the SD Association specs and, for example, format a 32GB hard with exFAT or a 128GB card with FAT32. But that goes against the specifications and can potentially cause issues with some cameras, so you can't use this app to do it. For that, you'd need to use a different tool such as the built-in formatting tools with the operating system. ↩
- For truly sensitive data, you can also get more specialized data scrubbing apps that can do things like multi-pass overwrite. ↩