format 
(1) You establish how a hard disk or a floppy disk will store data by formatting it. For instance, a disk used in an IBM-compatible PC would be formatted to use the FAT file system. The format is usually dictated by the operating system; you format a hard drive differently for working with the Windows OS as opposed to the Mac OS, for instance (and a floppy disk formatted in a Mac cannot work in a PC--although a disk formatted by a PC can usually be read by a Mac). You might also format a hard disk or a floppy disk as part of a system recovery process when data on the disk has become corrupted. Formatting does not erase existing data on the hard drive, but it makes it unfindable except with the assistance of a special disk recovery utility or a technical specialist.

(2) A file's format--how its data is presented to an application--is usually dictated by the application with which it was created. Some applications, such as word processors, can use documents created in the file formats of competing applications, usually with little or no loss of data or document-layout details.

(3) A document's format encompasses any or all of the specifications of its layout and presentation: typeface, margins and tabs, number of columns, use of graphical elements, and so on.