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What Computers Are All About
A preparatory guide for rookies, Written by Baalendu Dadhich
(Part 2)
A language of two letters (Err.. figures)?
But a computer does not understand human language. So
how to communicate with it? 
Fortunately
this task is not as difficult as it seems. Computers work on the basis of instructions
written in Machine Language. Machine language has only two figures to
communicate everything, and they are 0 and 1. This is why it is called Low
Level Language as well. Computers don't understand anything other
than these two 0s and 1s. So, different combinations of these two figures are
formed to communicate different instructions and it works most accurately! For
example, if you want to write letter 'A' in machine language, you would write
'01000001'.
The problem is, not every one can communicate in this language with the computers. It is very complex, very difficult to master and takes a lot of time to write even the most basic instructions. To overcome this problem, computer technologists came up with Assembly Languages that were a bit easier to understand and master for humans. Following some more advancement in the computer technology, evolution of High Level Languages took place, which made programming a lot easier. BASIC (Beginners All Purpose Symbolic Instruction Code), C, COBOL (Common Business Oriented Language), Pascal and all the modern computer languages such as C++, Visual Basic, Visual C++, Java etc. fall in this category. They are easy for humans to understand and it is convenient to write instructions in these languages. But still, the computer does not understand such raw code. It is just like two foreigners talking to each other in different languages. What do we do in such situations? We hire some interpreters who know both the languages to help them.
The same is applied with computers. We need special programs that convert code written in Assembly Languages or High Level Languages into Machine Language code. These programs are called Translators, Assemblers, Interpreters or Compilers. They have completely solved the problem of communication between computers and programmers.
Do all software acts the same way?
No. There is different software to perform different tasks. They are generally divided into the following two broad categories:
System Software is used for developing or running of a computer system. It consists of Operating System, translators, compilers etc. Application Software is used to develop programs to serve a particular application like word processing (Notepad, Word Pad etc.), financial accounting (Tally etc.), Spreadsheet operations (MS Excel etc.). You may still have confusion about the difference among these types of software. Let's spare a little more time for understanding these very important concepts.
Operating System is the interface between the computer and user. It controls and monitors the entire system. If any other program wants to run on the hardware, it has to piggyback the operating system. Let's take an example. You book a cabin in a ship for a long journey. Now you want to enter your cabin. What do you first do? You board the ship. Without boarding the ship you cannot enter your cabin. Just like this, without using the operating system your application program cannot run on the computer. An operating system is the most basic software that a computer needs to run. A computer could run without application software but not without an operating system. An Operating System is a System Software.
Examples of Operating Systems are Microsoft Windows, Microsoft Windows NT, MS-Dos, Unix, Linux, Sun Solaris etc. Since you are going to study at least two of them in depth, you need to understand the concept properly.
Application Software are programs that perform certain predefined tasks that are separate from managing and monitoring the system. All the games you play over the computer fall in this category. Microsoft Word, using which you write letters or notes is another example of such software. Adobe PhotoShop used for editing images, 3D Max used for creating and editing 3 dimensional images; Oracle used for maintaining databases are all examples of Application software. They have nothing to do with the system and have independent tasks to handle using the computer.
The following graphical representation will give you a better idea as to who is in contact with whom.
How data is stored and processed
Data is represented in the form of bits. A bit is the smallest unit of data stored on a computer. For example, we represent the letter 'A' in the binary form (machine language) as 01000001. You can see that a total of 8 0s or 1s have been used to express the letter 'A' in the machine language. Every 0 or 1 in this group is called a bit. And a group of all these 8 bits is called a byte. So, every character consists of 1 byte of data. If we write 'BILL' in machine language, we will have to use a total of thirty-two 0s or 1s. In other words, the word 'BILL' requires 32 bits, or 4 bytes of data to be written in machine language. Half of a byte (4 bits) is called a Nibble.
1024 bytes make a Kilobyte (KB) and 1024 KB make a Megabyte (MB). Likewise, 1024 MB make a Gigabyte (GB). So what will you do if someone asks you how many binary digits are needed to store 1 GB of data? The answer is simple: 1024*1024*1024*8 = 8589934592 digits.
Humans are not the only ones to have memory!
So how are these stored and where? The answer is Memory. We have earlier noted that Hard Disk Drive, Floppy Disk Drive, Tape Drive, Read Only Memory and Random Access Memory are all ways of storing data. Let's know some more about them.
Hard Disk Drive (HDD) or Magnetic Disk is a thin, circular metal plate coated on both sides with a magnetic material. Since the plates are made up of metal (unlike floppy disks that are made of breakable material), it is called 'Hard' disk. A disk pack consists of a number of these disks, three or more, mounted about half an inch apart from each other on a central shaft that rotates at the speed of 2,400 or more revolutions per minute (rpm). Each disk consists of a number of invisible concentric circles called Tracks. A set of corresponding tracks in all the surfaces is called a Cylinder. Outer surface of the top and bottom disks cannot be accessed. All the disks of a disk pack move simultaneously, in the same direction and at equal speed. Even though the length of each track is different, the number of characters stored in each track is same.
A hard disk having 6 disks with 100 cylinders, 50 sectors per cylinder and 500 bytes per sector can store 500 bytes*100 tracks*10 surfaces * 50 sectors = 25,000,000 bytes that is equal to 25 MB.
Hard disks generally fall into two categories: Small Computer System Interface (SCSI) that has a fast data writing and retrieval speed and Intelligent Device Electronics (IDE) that has comparatively slower speed but much cheaper than SCSI drives. Our cost effective PCs generally use hard disks of the IDE category.
Floppy Drive is made up of flexible plastic material. This plastic base is coated with an iron-oxide recording substance. Data is recorded as tiny invisible magnetic spots on this coating. Each floppy diskette is packaged in protective paper or plastic envelope. These are mainly used for the purpose of backup and transportability of data, for small data volumes. Floppies mainly come in two different capacities- 1.2 MB and 1.44 MB.
When formatted the floppy gets divided into Tracks, and tracks get further divided into Sectors. Sectors have their own capacity in terms of storing the data, which depends upon the type of floppy. While storing the data, if the sector is full, the data storing is done in the next sector and so on.
The floppy with the capacity of 1.2 MB and a size of 5 1/4 inch is a double-sided one having 80 tracks per side and 15 sectors per track. The other type of floppy (1.44 MB) has a size of 3 1/2 inches, is double sided having 80 tracks per side and 18 sectors per track.
Read Only Memory (ROM) is a small memory that is an inseparable part of a computer as it has the minimum operating system (Basic Input Output System, more known as BIOS) to allow the computer to boot (begin operations). As is clear with its name, a user has no access to its contents and they cannot be changed. When we switch on the computer, it is the ROM that first gets into action. Unlike Hard Disk or Floppy Disks, information stored on ROM can be accessed directly by CPU. You must have noted that before your Operating System appears on the screen, many little tasks are performed in the computer. One such task is to check all the hardware connected to the computer. Such responsibilities are pre-written in the ROM that plays its role till the Operating System takes over. ROM is a non-volatile storage medium i.e. information stored here will never be erased unless it is physically damaged. Its capacity is measured in Kilobytes.
Random Access Memory (RAM) has a very important role in the operations of a computer. This is called Primary Memory and Main Memory, as all the programs that run on a computer have to access CPU via RAM. Parts of these programs are first loaded into RAM from where they interact with CPU for further processing. Unlike ROM, information can be stored as well as retrieved from it. It is a volatile storage as information stored here will be erased during a power failure or after the system is switched off. Information stored on RAM too, like ROM, is accessed directly by the CPU. Its capacity is measured in Megabytes. Generally our systems have RAM in the range of 4 to 256 MB.
If RAM is called Primary Memory, Hard Disk storage drive is called Secondary Memory. The reason is simple- though they can store programs but none of them could be executed directly from them and sent to the main memory for execution. Hard Disks are generally used in the range of 200 MB to 8.4 MB.
There are two more forms of memories used in computers. Cache is a very fast memory placed in between the main memory and the CPU. We know that each instruction is to be fetched by CPU from main memory. Ironically, RAM (main memory) is comparatively slower than CPU, so it holds CPU whenever CPU refers to RAM. Cache memory acts as a buffer (temporary storage medium) and fetches chunk of contents from main memory to be used by CPU. Cache memory is very fast and very expensive, so our systems have very small amount of it. Registers are another temporary storage medium.
The powerhouse
Central Processing Unit of a computer is also called the brain of the system. RAM is in fact a part of CPU. It has three main interactive components:
We have already talked about RAM. Arithmetic and Logical Unit contains a large number of electronic circuits used to carry out arithmetic and logical computations. These computations are carried out with the special purpose storage locations, called Registers. Main part of the ALU that performs computations is called Adder, because a computer performs all operations (subtract, multiplication and division) through additions. Subtraction is nothing but a complimentary addition (a-b = a + (-b)), multiplication is repeated addition and division is repeated subtraction.
Control Unit is that portion of the CPU, which controls each operation. It synchronizes and sequences operations of the CPU for ensuring correct execution of programs. It has a special Register called program counter that contains the details for the next instruction to be fetched from the processor memory.
A few available types of CPUs are Intel, Alpha, RISC and PowerPC. In microcomputers such as IBM PC- compatible machines, the CPU is the microprocessor.
Microprocessor is the crux of the CPU that actually processes data under the given instruction set. It is an integrated semiconductor circuit designed to automatically perform lists of logical and arithmetic operations. It receives raw data and instructions to produce meaningful output.
Looking after their assets
As we all know, different sorts of data are stored on a computer's disk. There can be different ways in which data is stored and retrieved. Take an example of Videotape that stores images or films. How do you access a particular program recorded on it? By forwarding or reversing the tape till it reaches the point where the program is recorded. This process takes some time as many different tasks are related to it. On the contrary, when you access a particular program recorded on a CD you don't need to forward or reverse it. You just have to choose the program from the menu and immediately start watching it. Why?
The reason is, a videotape is a sequential data recording media while a CD not. Computer Hard Disk or Floppy too is not sequential media as you can access any data recorded upon them at any physical location just by clicking a mouse or writing its path at the command line.
A question must have occurred to your mind as to how the computer knows exactly at which place it should store a particular data and exactly from which place on the disk should it retrieve the data? This task is taken care of by a File System that keeps records for all the data existing at each and every part of the disk.
Among the file systems, FAT (File Allocation Tables), NTFS (New Technology File System), HPFS (High Profile File System), CDFS (Compact Disk File System) etc. are the most commonly used ones. They all have different ways to store, retrieve and manipulate data. You will learn about them in detail in your next guides. Here it is sufficient for you to know that File systems are Operating System dependent. MS-Dos (Fat 16), Windows 95 (Fat 32), Windows NT (Fat 16 or NTFS), Unix, Linux all have their own, specific file systems.
They can have a social gathering too!
When many computers are connected to each other (Such connections could be made in different ways including cable, microwave links, satellite links etc. You will learn about them in Networking Essentials Guide, later) to communicate and share data, the entire setup is called a 'Network' of computers. Just like all telephone connections belonging to the same service providing company form a network of telephones, all computers, either connected to a central location or to each other, form a computer network. It is especially useful for companies where the same data is used by many users spread across departments, locations, cities and even countries. In such a situation, we only need to store our software or information on one central location and all the member computers of the network, irrespective of their physical location, can access it. There are hundreds of other advantages of networking that you will learn with the passage of time.
Windows NT, Unix, Linux, Novel NetWare, OS/2, VAX/VMS, Sun Solaris and MDS Quantel are a few examples of operating systems capable of providing networking facility.
Finally, Internet too is a global network. In fact, it is a network of networks that works in the same manner a network in our office does. You can exchange information with computers the world over via Internet as if they are a part of your office network (provided you have access to it, of course). The big difference between simple local networks and Internet, however, is; the Internet is not controlled by any company or managed from any central location.
Relax- your preparatory phase is now over.
I am sure, you must now be feeling a bit more comfortable with the vocabulary of information technology and the technicalities involved with as simple an operation as running a PC. You have spared quite some time for reading all this stuff. Now, I feel you have developed the basic understanding of computers and are prepared to dig a little deeper!