FILE_BYTES_WRITTEN and HDFS_BYTES_WRITTEN

[psdc1978]

When an hadoop MapReduce example is executed, at the end of the example  
it's showed a table with all the information about the execution, like the  
number of Map and Reduce tasks executed, the number of bytes read and  
written.

In this information it exists 2 fields FILE_BYTES_WRITTEN and  
HDFS_BYTES_WRITTEN. What's the difference between these 2 fields?

Thanks,
Pedro