Much as you may have been satisfied with the way iCloud synced your data in the past, if you’d hoped for comprehensive file syncing between your Mac, iOS devices, and the cloud, you were likely frustrated. Prior to OS X 10.10 Yosemite, iCloud’s file storage was sandboxed, meaning that you could only access files created with a specific application by that application. You could, for example, launch Pages and access the Pages files you stored in the cloud, but you couldn’t use that same app to open TextEdit files stored in iCloud.
Enter iCloud Drive. Taking its cue from Dropbox, which is a simple file repository accessible from any app, Apple has changed the way iCloud manages files.