The organization of memory can vary among compilers and programming languages. In most cases, the goal of memory management systems is to make the limited resource of memory appear infinite (or at least more abundant) than it really is. The goal is to free the application programmer from having to worry about where his memory will come from. In the oldest days of mainframes, when each byte of memory was precious, a programmer might account each address in memory himself to ensure that there was enough room for the instructions, heap, and data. As programming languages and compilers were developed, algorithms to handle this task were developed so that the computer could handle its own memory issues.
Today, even assembly programmers do not have to worry about memory allocation because current assemblers can handle that task. Memory allocation algorithms are good enough at their job that it isn't worth a programmer's time to manually allocate memory. There are a few different ways that languages solve the problem of memory allocation. In general, it is simply a matter of providing the programmer with memory that is known to be required at compile time including space for global data values and the code itself. The more difficult problem is how to provide flexible data memory that may or may not be needed when the program actually executes.
The approach that C takes is to make available to the the programmer special functions that manage memory allocation. These methods are called malloc(int) (memory allocate) and free(void *) . The basic idea is that whenever the programmer needs a specific amount of additional memory, he calls malloc(int) with the integer being the number of bytes of memory needed. The function returns a pointer to a block of memory of the requested size. When the programmer is done with a particular block of memory, he may call free(void*) to let the memory management library know that the particular block of memory isn't needed anymore by passing the pointer to that block to the function. If the programmer is diligent about returning (freeing) memory that isn't needed anymore, then he will enjoy an abundant supply of memory without having to count individual bytes. On the other hand, if a programmer repeatedly requests memory but does not free the memory back to the system, the memory allocator will eventually run out of memory and program will then crash. Thus, it is essential for passages of code that frequently request memory allocations to free these allocations as quickly as they can. Un-freed memory blocks are not fatal in very infrequently executed parts of code; however, the longer a program runs, the more potential there is for a problem. In general, a program that allocates but does not free memory, is said to have a memory leak.
Other languages handle the problem of memory allocation automatically. Java allocates the memory for new data on the fly using the keyword new instead of the function malloc, but the more important difference is that freeing takes place automatically. Part of the Java system called the garbage collector detects memory that can be safely freed and does so. In this manner, Java programs do not suffer memory leaks in the way a C program might.
"This is the entire course organized at Rice University for all the basic lessons for using an MSP430. It is designed for the use of an eZ430 tool and is still under construction."