volatile variable

programming A variable in a computer program which can be

modified by processes other than the program. For example, a

variable that stores the value of a timer chip (either because

it is located at the address of the hardware device or because

it is updated on interrupts) needs to be volatile to be

useful.

A static variable, on the other hand, maintains its value

until the program changes it or it is no longer needed. In

addition, volatile variables can be held in the stack

whereas static variables are usually stored in a program's

data segment.

(1995-05-17)