The problem about block size

[程笑]

Hi,
I have established a Hadoop cluster with one NameNode and two DataNodes.
Now I have a question about block size. I site the block size for 64MB.I stor 
one text file (50MB) on the HDFS. Whether this text file  is splited? If not, 
the text file stor on which DataNodes? I user MapReduce to comput the text 
file, how many maps will process this file?
Please forgive my poor English.
Best regards! 
Cheng Xiao