On the left, right-click the USB flash drive, select Format Disk for Mac. You want to do this before creating the bootable media because there is a good chance that the drive was formatted using a Windows device. If you are on an earlier operating system like Windows 7, XP, etc. The screenshots may look slightly different. For example, in Windows XP 'My Computer' is equivalent to 'This PC' on Windows 10. Step 1: Locate your USB stick under 'This PC', right click on it and select the 'Format' option.
If you can’t see your USB drive in Explorer, search for “Create and format hard disk partitions” to open Windows’ Disk Management console. From here you can see all connected drives – even ones that aren’t currently usable in Windows. If need be you can wipe your USB device and reformat it as required. How to format a USB drive on a Mac Step one To format a USB on a Mac, you can format your drive using Disk Utility. You’ll find this tool in your Applications folder, within the Utilities subfolder – or simply search Spotlight to find it (press Cmd+Space, then type its name).
Step two When Disk Utility opens you’ll see a list of drives in the left-hand pane, with the partitions on each one nested beneath each entry. To reformat your USB disk, click on its name in this pane, then switch to the Erase tab in the main interface (if it’s not already selected) and hit Erase to wipe the drive. How to format a USB drive: which format? If you follow the instructions above then Windows will, by default, format your disk using Microsoft’s NTFS filesystem, while a Mac might suggest the Mac OS Extended filesystem. These formats are sensible defaults because they support all the features of their respective operating systems, such as native compression and encryption. However, neither is suitable if you want to move files back and forth between Macs and PCs: OS X can read NTFS volumes, but it can’t write to them, while Windows in its default configuration can’t access HFS+ disks at all. There are free drivers available, but again these are limited to read-only access.
To use your USB disk on both Windows and OS X, therefore, you’ll need to use a different filesystem. You can choose this from the drop-down menu in Windows' Format. Dialogue, or in the Erase pane of Disk Utility.
In most cases we recommend you select Microsoft’s exFAT format: this will give you full read and write access in both Windows (Vista or later) and OS X (Snow Leopard 10.6.5 or later). If you need compatibility with systems that are older than this, you’ll need to fall back to the ancient FAT32 format. This is supported by all versions of Windows and OS X (as well as Linux), but it has the drawback of not supporting individual files larger than 4GB – which can be a pain if you work with large video files or databases. On a Mac, you can format any disk as FAT32 by simply choosing “MS-DOS (FAT)” from the dropdown menu in Disk Utility before you click Erase. For historical reasons, Windows won’t offer FAT32 as an option if your disk is larger than 32GB, but you can format a disk of any size by opening a Command Prompt and typing format h: /fs:fat32 /q, where h: is the letter of your removable drive and the /q parameter specifies a quick format – assuming you don’t want to wait around for Windows to check each sector of the drive for errors.
How to format a USB drive: allocation unit size. As well as choosing a disk format, Windows also invites you to specify an “Allocation unit size”. Simply put, this determines the size of the chunks in which storage is allocated for your files: if you choose 4096 bytes (the NTFS default), every file that’s saved to that disk will be allocated space in multiples of 4KB. Slicing up disk space in this way isn’t perfectly efficient. A file that’s only 1KB in size will still occupy 4KB of space, while a 5KB file will take up 8KB, and so on. In practice though, most of the files on your USB drive will probably be many megabytes in size, so the impact of wasting a few kilobytes here and there is negligible.
If you plan to save lots of small files to your disk then reducing the allocation unit size might be a good idea. However, this can have a negative impact on performance, especially if you’re using a mechanical disk drive. Splitting up a file into more chunks gives the drive controller more work to do, and makes it more likely that the data will end up fragmented into lots of blocks scattered about your disk, making it slower to access. With a modern flash drive, it’s unlikely you’ll notice much difference either way, so it’s up to you whether you stick to the 4KB standard or pick a smaller allocation unit size.
Assuming Vista or 7 (this should work on XP, 8, 8.1, and 10, as well) and that the disk is not showing up under My Computer at all:. Connect your disk. Run cmd as an Administrator.
Run diskpart.exe. If you need help in this program.
list disk. Find the disk that corresponds to your USB disk. Select disk n where n is the number of the disk. Confirm that you're using the right disk with detail disk. clean (Warning: This command erases the disk's partition information. Any data on the disk will no longer be accessible.).
create partition primary. No size is needed if you want to use the whole disk. active. Marks the partition as potentially bootable. format fs=fat32 quick. You can choose NTFS or exFAT instead of FAT32 if you want.
(Note: Windows 10 limits FAT32 to 4GB. I recommend using exFAT instead, which is essentially a newer version of the same format.). assign. Assigns the disk a drive letter. exit to quit. If you're still having problems with the disk after trying this, you might try omitting the quick from step 9 to do a full format. That will take a very long time and usually isn't necessary, but may help uncover physical damage to the disk.
In some cases you might need to re-initialize the disk. As above, this will destroy the data on the disk (or, rather, your ability to access it). To do that from diskpart.exe:. list disk. select disk n.
attributes disk clear readonly. This command will unset the read-only flag on the disk. You can see the current attributes with attributes disk or detail disk. online disk. Sets the device status to online if it's been disabled.
convert mbr. Converts the disk to MBR format, which will work just fine for most disks. If you've got a USB disk larger than 2 terabytes, however, you'll want to use convert gpt instead. I'm not sure if the above commands are all identical on older OSs (XP).