How to install RetroPie on a MicroSD card for Windows and Mac

Format your SD card to work with Raspberry Pi

First things first we need to format the microSD card using FAT32. Insert the microSD card into your microSD card reader and insert the reader into your computer via a USB port. Your microSD card will now show up as a mounted drive on your computer.

Windows Instructions, open up Explorer, locate the microSD card, right-click it, and select Format from the menu.  

The following fields should be set as follows

Filesystem: FAT32

Allocation unit size: Default allocation size

Volume Label: (empty) Just like the picture

Format options: Quick Format


Click START!!!

Mac Instructions, open Disk Utility. Navigate to Applications > Utilities > Disk Utility. Select your microSD card in the left pane. For Yosemite and older, navigate to the Erase tab and select MS-DOS (FAT) as the Format, give it a name, and click the Erase button. For El Capitan and newer, simply click the Erase button, Select MS-DOS (FAT) as the Format, give it a name, and click the Erase button.

Install the RetroPie image (using Windows)

Download and install the Win32DiskImager utility. Follow the instructions here and select the (unzipped) RetroPie microSD-Card Image (.IMG file) that you downloaded earlier.

Installing the RetroPie image (using a Mac)

To do this, we'll use a third-party utility called ApplePi-Baker. Download the most recent version and open the application. ApplePi-Baker requires SUDO (admin) access in order to read/write to your SD card. Therefore, you will be prompted to enter your OSX account password.
After opening the application, select your SD card in the left hand column. Then, click the "Restore Backup" button and select the (unzipped) RetroPie SD-Card Image (.IMG file) that you downloaded earlier. Wait for the process to complete.

Note:

If your Mac recognizes ApplePi-Baker as an "Unidentified Developer"  App you should Open

System Preferences > Security & Privacy > Allow apps downloaded from anywhere.

to allow ApplePi-Baker to be installed.

Finishing up

When the image has finished loading to the microSD card safely eject the card from your computer.

Put the SD card into your Raspberry Pi.

Plug in your keyboard, USB game controller, and HDMI cable.

Finally, connect the MicroUSB power supply.

Always connect the power supply after connecting your other peripherals so that your Pi will detect all of the peripherals properly on boot.

After boot enjoy all the retro gaming goodness :)