Disk Images, or DMGs, are a common way to compress large files on Mac computers, including apps. Because these files can often be a few gigabytes in size, a USB flash drive is usually the fastest way to get the file to your Mac computer. If the file has been downloaded to a Windows PC, you will need to make sure the USB flash drive is formatted in FAT32 -- a format that both the Windows PC and the Mac computer can both read. Most USB flash drives already use this format, but if yours doesn't you can quickly format it in Windows.

Using a Windows PC

Step 1

Insert the flash drive into the USB port on a Windows PC. Wait two or three seconds for the PC to recognize the drive.

Step 2

Go to the Windows desktop, launch File Explorer from the Taskbar and select "Computer." If you are in the Windows Start screen, simply type "computer" and press "Enter" to open File Explorer on the desktop.

Step 3

Select "This PC" or "Computer" from the left pane in File explorer to reveal the flash drive in the Devices With Removable Storage section.

Step 4

Right-click the flash drive unless you are absolutely certain it can be read by both a Mac and a Windows computer. Select "Format," then click "OK." If the File System menu says "FAT32," click "Close." If it instead says "NTFS," change it to "FAT32" and click "Start." This formats the drive in FAT32 so it can be read by both a Windows and Mac computer.

Step 5

Locate the DMG file on your computer and drag it onto the flash drive's icon in File Explorer. When the transfer is complete, remove the flash drive from the USB port.

Using Another Mac

Step 1

Insert the flash drive into the USB port of a Mac computer that has the DMG file you need. Launch Finder. After a couple of seconds the drive appears in the left menu of the Finder menu. If Mac OS X doesn't recognize the flash drive, it prompts you to format it and the Disk Utility app opens. Select "ExFAT" in the Format menu of the Partition tab only if you want to use the flash drive on a Windows PC. Otherwise select "Mac OS Extended (Journaled)" if you plan to use the flash drive only with Mac computers.

Step 2

Locate the DMG file in the Finder. Drag the file onto the flash drive icon in the Finder's left menu.

Step 3

Hover the cursor over the drive's icon in the Finder and select "Unmount" when the file transfer is complete. Alternatively, drag the icon from the desktop onto the Trash icon.

Installing From the Flash Drive

Step 1

Insert the flash drive into the USB port of the destination Mac computer.

Step 2

Launch Finder and then double-click the flash drive's icon in the left menu of the Finder window. Drag the DMG file onto the desktop or any folder in Finder. Double-click the transferred file to launch it on the Mac.

Step 3

Right-click the DMG file on the USB flash drive if you don't need to use the file again and select "Move to Trash." Select "Empty Trash" from the File menu to completely remove it from the flash drive.