Introduction to Programming Languages/Memory Management


The memory in a computer is organized in a hierarchical way. The lowest level memory unit is a register, followed by the cache memory, then the RAM, hard driver, and so on. This organization of the computer's memory is specially useful because most programs need more memory than they are supposed to use.

Program variables are the link between abstractions represented by a program and the computer physical memory units. For instance, in C, you can use the keyword `register` to give the compiler a hint that a variable will be frequently used.

There are also other ways to specify where a variable should be stored. In dynamic typed languages (such as PHP, Javascript, or Python), the programmer cannot tell where a variable should be stored; the interpreter makes that decision. In statically typed languages (such as C and C++), on the other hand, the programmer can tell, based on the type of a variable, where the compiler should store each variable.

The compiler (or the Operating System, for that matter) can put variables in one of three places within the program's memory: static memory, stack, or heap. The following sections will cover with more details these three types of memory.