An SD card or secure digital memory card is a solid-state memory format that is used in small, portable devices and other items that accept outside memory sources. You can use an SD card to create an alternate start-up point for your computer to give you a safe, secure method of booting wherever you are. Some operating systems don't support an SD boot, like Windows using an SD with the file system called FAT32. But if you have any model of MacBook or MacBook Pro, you can easily write an SD card to serve as a bootable drive.
Insert an SD card into the card reader on the side of your MacBook and click on the hard drive icon your desktop.
Open the utilities folder and launch the program called Disk Utilities. The Utilities folder is located in the Application folder in the hard drive.
Open the icon for your SD card and format it to have one partition. You can do this through the Disk Utilities.
Insert the installation disc that came with your computer and click on the installation file to open the installation wizard.
Select the SD card as the destination for the install when the wizard prompts you for a location. Proceed through the wizard without changing any of the other options.
Shut down the computer once the installation onto the card has completed. You do not need to remove the card when you turn the computer off.
Turn your computer back on, holding down the Option key, until the computer has started up. You will need to select the SD icon when prompted for a booting location.
Keep your booting SD card clearly labelled so you don't confuse it with another card.
Do not tamper with or alter the system of your computer if you are not completely sure what you are doing or you may need to bring your computer to a professional for repair.