Different between NSData and NSMutableData in iPhone

Question

What is the difference between NSData and NSMutableData?

Answer 1

From the Stack Overflow tag-wikis:

nsdata

The NSData class is an apple class for holding generic data. Often used when reading/writing from and to files, and the internet.

nsmutabledata

NSMutableData (and its superclass NSData) provide data objects, object-oriented wrappers for byte buffers.

Answer 2

NSData is fixed after creation.

NSMutableData, as the name implies, allows operations that change the contents (appendBytes:, appendData, setData:...).