Each file in the system has a set of file attributes. These attributes record all sorts of meta data about a file, most importantly its name and its type (which tells the system how to handle a file, like the more limited four-character file type code on the Macintosh). Other attributes have the file's record size (if fixed for commercial applications), the block size (in multiples of records that tells the MCP how many records to read and write in a single physical IO) and an area size in multiples of blocks, which gives the size of disk areas to be allocated as the file expands.