[1] Foundation vs Core Foundation CoreFoundation is a general-purpose C framework whereas Foundation is a general-purpose Objective-C framework. Both provide collection classes, run loops, etc, and many of the Foundation classes are wrappers around the CF equivalents. CF is mostly open-source , and Foundation is closed-source. Core Foundation is the C-level API, which provides CFString, CFDictionary and the like. Foundation is Objective-C, which provides NSString, NSDictionary, etc. CoreFoundation is written in C while Foundation is written in Objective-C. Foundation has a lot more classes CoreFoundation is the common base of Foundation and Carbon. [2] iOS Directories ~/Documents, ~/Documents/Inbox [both will store user generated files that can be exposed to user. Ex. email attachments] ~/Library [files not to user.] ~/tmp [System clears files if app not running. Not backed up by iTunes] [3] Concurrency Operations Operations can be configured to run a block of code synchronously or as
