How do Computers Work

Volumes can be written about the working methodology of a computers, and each component will have to be dealt as a different subject. But I will try to do my best in giving a simple yet logical insight about the workings of these machines. Here, I assume that you have an access to a computer and are aware of what a monitor, mouse and a keyboard does.

The computers that we use have mainly two important components, the hardware and the software. The hardware consists of the motherboard (with the processor integrated into it), the hard disks, the RAM and many other peripheral devices like CD ROMs, floppy drives etc. The most important component of the software part however, is the system software, i.e. the operating system. Various other application softwares, like the most common Microsoft Office package, runs on the system software.

Let us now start with the basics. When we switch on the computer, the processor executes the BIOS routines stored in the ROM (Read Only Memory). During its execution, all the peripheral devices attached to the computer are checked, the operating system is loaded and various other operations are started. In short, the computer comes to life. If you are using a Linux operating system, you can manually select the components and software that you want for that particular session, during the booting up process.

Now let's come to the execution part. When you double click on an icon to select a software, you are sending an instruction to the CPU. The CPU responds by executing a series of other instructions that are required to start the program. The software is then loaded from the hard disk into the RAM. Cache memories, that do not have much space, also hold in the instructions and provide a faster access to the CPU. Instructions, as well as data, are stored in the computer's memory in bits of 0's and 1's. All these instructions are executed by the processor and the processor has a faster access to the cache memory. In general, a processor can access the primary storage devices like the cache memory and the RAM directly, but does not have direct access to the secondary storage devices like the hard disk. The data that it stores or retrieves into or from the hard disk is done via the RAM.

When we make a single click on an icon in a computer, 'n' number of instructions are executed. So you must be wondering, how can the execution of all these instructions take place at such a fast rate? Remember, when you bought your computer, the vendor must have given you the details like processor speed. It is normally in GHz. So what does that mean though? Well, every processor works in synchronization with the clock cycle. By clock cycle, I mean a waveform (consider square waveform) that keeps on pulsating. Each instruction is executed with the rise and fall of the clock cycle. Some instructions may take more than one clock cycle for their execution. Now what is mentioned as the speed of the CPU, is the frequency of the clock cycle, i.e. the no. of clock cycles that is produced by the processor in one second. A processor with a speed of 1.7 GHz can produce 1.7 x 10⁹ clock cycles in one second. Now, if one instruction is executed with the rise and fall of the clock cycle then consider the number of instructions that can be executed in one second. Yes, you are right, that is a very large figure.

Many times, it often happens that when we start executing too many softwares at a time, the computer hangs. The reason is the RAM. The RAM has a certain storage capacity, but it is far less than the storage capacity of the hard disk. Each program that you execute takes a certain portion of the RAM and the execution of too many softwares or large softwares, gives rise to a condition in which the RAM cannot hold the data anymore. It may have no place left to execute the instructions given by the CPU. In such cases, the process can take up some free space from the hard disk, but again, the processor cannot access the hard disk directly. The result is that your computer hangs.

The next important thing, that has probably already struck your mind, is that how can information be stored in the form of 0s and 1s. Your computer memory comes in multiples of bytes. One 0 or 1 makes a bit. 8 bits make a byte, 1024 bytes make a kilo byte, 1024 kilo bytes make a Mega Byte and 1024 Mega Bytes make a Giga Byte. Hectic stuff, no?

So, if you have 120 Giga Bytes of hard disk space then you can store a total of '120 x 1024 x 1024 x 1024 x 8' bits of data. That is again, a very large figure. Now, hard disks and computer chips contain millions of transistors. A transistor in its off state, is designated as a 0 bit and in its on state is designated as 1. Each character, symbol or instruction has a specific pattern of bits and it is stored in that form, in the hard disk. This means that storing a single character, at a particular location in the hard disk, means switching on and off, a lot of transistors and each of this is done with an instruction that is executed by the CPU.

The designing of the hardware and software for these processes is indeed a complex task. Here, I have just dealt with the execution and storage of data and the instructions in a computer, but understanding the entire working of each and every component would probably take a lifetime.