title: When a program is loaded by the OS into memory from the file system, how does the operating system know how big the program is?
body: <p>When a program is loaded by the OS into memory from the file system,  how does the operating system know how big the program is?</p>
  
  <p>Does it just page in one page from the file system at a time?
  Or is there some sort of hardware or software indicator so that the OS knows how big the program is?</p>