It will need to be 8GB minimum, and it will be completely erased as part of this process, so if you’ve got anything on it already make sure you back up the contents somewhere first. The process of creating a bootable USB install drive for OS X 10.11 El Capitan is pretty easy just make sure you meet the basic requirement for the process. If you’re going to use El Capitan on your only computer, it’s wise to install it as a dual-boot system, that way you can easily switch back to Yosemite whenever things get buggy. If you have multiple computers that need the El Capitan upgrade, then a bootable install flash drive will make the process easier and faster, since the install file is over 6 GB in size (about a gig larger than Yosemite was!) and could take some time to download on each computer individually. Whilst the technique of upgrading OS X has grown to be notably the clean way in the Mac App store, many users could be interested in having a bootable install drive of the new OS.
Apple’s latest update to Mac OS X, 10.11 El Capitan, is going to be available to majority of its users this July in a Beta Preview, but developers can get their hand on it right now.
