Although you've seen variables in the previous pages, you may wonder what they are exactly. Part of a computer is called RAM, or random access memory. This is a volatile medium for storing information. That is, it all disappears when you shut off the machine. The computer sees this memory as a long string of single characters, or bytes, each numbered. In PHP, however, you cannot actually get to memory at this level. You must use a variable. You provide a name, and PHP takes care of matching the name to physical memory.
You do not need to let PHP know about a variable before you ...