C Programming – Memory Management

An Overview of Your Computer

Your computer system consists of two parts: hardware and software. The hardware consists of all the physical parts of the machine. It illustrates that your computer's hardware consists of the physical components of your PC. The software is everything else. Software comprises the programs and data that interact with your hardware. The C language is an example of software.

The System Unit and Memory

The system unit is the large, box-shaped component of the computer. This unit houses the PC's microprocessor. You might hear the microprocessor called the CPU, or central processing unit. The CPU acts like a traffic cop, directing the flow of information throughout your computer system. The CPU is analogous also to the human brain. When you use a computer, you are actually interacting with its CPU. All the other hardware exists so the CPU can send information to you (through the monitor or the printer), and you can give instructions to the CPU (through the keyboard or the mouse).

The CPU also houses the computer's internal memory. Although the memory has several names, it is commonly referred to as RAM (random-access memory). RAM is where the CPU looks for software and data. When you run a C program, for example, you are instructing your computer's CPU to look in RAM for that program and carry out its instructions. C uses RAM space when it is loaded.

RAM is used for many things and is one of the most important components of your computer's hardware. Without RAM, your computer would have no place for its instructions and data. The amount of RAM can also affect the computer's speed. In general, the more RAM your computer has, the more work it can do and the faster it can process data.

The amount of RAM is measured by the number of characters it can hold. A character in computer terminology is called a byte, and a byte can be a letter, a number, or a special character such as an exclamation point or a question mark. If your computer has 640,000 bytes of RAM, it can hold a total of 640,000 characters.

You want as much RAM as possible to hold C, data, and the system programs. Computer RAM is relatively inexpensive, so if your computer has less than 640K bytes of memory, you should consider purchasing additional memory to increase the total RAM to 640K. You can put more than 640K in most PCs. There are two types of additional RAM: extended memory and expanded memory (they both offer memory capacity greater than 640K). You can access this extra RAM with some C systems, but most beginning C programmers have no need to worry about RAM beyond 640K.

RAM is volatile; when you turn the computer off, all RAM is erased. Therefore, you must store the contents of RAM to a nonvolatile, more permanent memory device (such as a disk) before you turn off your computer. Otherwise, you lose your work.

Bell Labs first developed the C programming language in the early 1970s, primarily so Bell programmers could write their UNIX operating system for a new DEC (Digital Equipment Corporation) computer.

Until that time, operating systems were written in assembly language, which is tedious, time-consuming, and difficult to maintain. The Bell Labs people knew they needed a higher-level programming language to implement their project quicker and create code that was easier to maintain.

Because other high-level languages at the time (COBOL, FORTRAN, PL/I, and Algol) were too slow for an operating system's code, the Bell Labs programmers decided to write their own language. They based their new language on Algol and BCPL. Algol is still used in the European markets, but is not used much in America.

BCPL strongly influenced C, although it did not offer the various data types that the makers of C required. After a few versions, these Bell programmers developed a language that met their goals well. C is efficient (it is sometimes called a high, low-level language due to its speed of execution), flexible, and contains the proper language elements that enable it to be maintained over time.

In the 1980s, Bjourn Stroustrup, working for AT&T, took the C language to its next progression. Mr. Stroustrup added features to compensate for some of the pitfalls C allowed and changed the way programmers view programs by adding object-orientation to the language. The object-orientation aspect of programming started in other languages, such as Smalltalk. Mr. Stroustrup realized that C++ programmers needed the flexibility and modularity offered by a true OOP programming language.