Introduction to Computers

Introduction to Computers

The word ‘computer’ is derived from the Latin word ‘computare’ which means ‘calculate’. A computer is an electronic device that takes input (data and program) which is processed to get the desired output (usually called information).

Data is the collection of raw facts that are processed to get information. And information is the data shaped into a meaningful form after processing.

In computer, two kinds of inputs are required to get information. These are data and program or software. A program is a set of instructions containing methodology to process data.

All computers have many characteristics that have made computers powerful and useful. These characteristics are: speed, processing capacity, accuracy, diligent, storage capacity, flexibility, and automatic.

Speed

Computers work at very high speed and are much faster than humans. The speed of computers is measured in terms of milliseconds (1/1000 sec), microseconds (1/1000000 sec), nanoseconds (1/1000000000 sec), or picoseconds (1/1000000000000 sec), that is, one-thousandth, one-millionth, one-billionth, and one trillionth of a second respectively.

Processing Capacity

A computer can process the given instructions. It can perform different types of processing like addition, subtraction, multiplication and division. It can also perform logical functions like comparing two numbers. Furthermore, computers can process any kind of data like numbers, text, images, audio, video etc.

Accuracy

The accuracy of computer system is very high. They either give the correct answer or do not answer at all. In most cases, the errors are due to the human factor. If faulty instructions are provided for processing data, obviously faulty answers will be given.

Diligent

Computers never get bored and tired. They carry out repetitive and voluminous work for hours without variation.

Storage Capacity

Computers can store huge amount of data. To store data, computers have primary and secondary memory systems. With more and more secondary memory systems, which are capable of storing huge amount of data, the storage capacity a computer is virtually unlimited.

Flexibility

Computers are very versatile machines. They can perform the activities ranging from simple calculations to performing complex CAD (computer aided design) modeling and simulation to navigating missiles and satellites. They can be used in different areas like business, education, scientific research, medicine, training etc. Hence, computers are capable of performing almost any task and in any area.

Automatic

Computer is an automatic machine. Everything that is given to computer are processed and done by computer automatically according to the instruction provided.

Block Diagram of Digital Computer

Any computer system has three essential components, namely, input unit, central processing unit (CPU) and output unit. The CPU itself has three components, namely, arithmetic logic unit (ALU), control unit (CU), and memory unit (MU). In addition, computers also have secondary storage devices (also called auxiliary storage or backing storage) that are used to store data and programs on a long-term basis.

Fig: Building blocks of Computer

Input Devices

Input devices are used to transfer data into the memory unit of a computer. This information is then transferred from the memory to the ALU where comparisons and calculations are done and the results are sent back to the memory unit. Some common input devices are: keyboard, mouse, scanner, touch screen, and joystick.

Central Processing Unit (CPU)

The part of the computer that executes program instructions is known as processor or central processing device (CPU). It consists of three components. These components are arithmetic logic unit (ALU), control unit (CU), and memory unit (MU).

            Arithmetic logic unit (ALU) performs fundamental mathematical operations consisting of addition, subtraction, multiplication, and division. In addition, it also performs logical operations that consist of comparisons like equal to, less than, greater than etc.

Control unit (CU) coordinates and controls the operations of a computer system. It controls the activities between memory and ALU and between CPU and input/output devices.

            A memory unit (MU) is also called primary memory or main memory. It holds data for processing, instructions for processing data (program), and information (processed data). The contents of main memory are lost when the computer is turned off. So, it is also called volatile memory.

Output Devices

The results that are stored in the memory can be transformed into a form that can be understood by users of a computer system by means of an output device. Some common output devices are monitor, printer, speaker etc.

Secondary Storage Devices

These devices are also called auxiliary storage devices. These devices are any storage other than main memory. Unlike main memory, these are long-term, non-volatile memory. That is, these devices store and retain the programs and data after the computer is switched off.

            There are two types of secondary storage devices. This classification is based on the type of data access: sequential and random. In case of sequential access devices, the data stored in these devices can only be read in a sequence and to get to a particular point on the media, we have to go through all the preceding points. For example, magnetic tapes are sequential access media. In case of direct-access devices, the data stored can be accessed randomly at any point without passing through intervening points. Magnetic disks and optical disks are most common examples of direct-access devices.

Memory/Storage

The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Basically, there are two types of memory: primary memory and secondary memory.

Primary Memory

Primary memory is the memory is the memory that can be directly accessed by the CPU. Different types of primary memories are RAM (Random-access Memory), ROM (Read-only Memory), PROM (Programmable Read-only Memory), EPROM (Erasable Programmable Read-only Memory), and EEPROM (Electrically Erasable Programmable Read-only Memory).

RAM (Random-access Memory)

This is also called main memory. The term RAM refers to read and write memory, that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.

It is also defined as a type of computer memory that can be accessed randomly that is any byte of memory can be accessed without touching the preceding bytes. There are two types of RAM: dynamic RAM (DRAM) and static RAM (SRAM). These two types differ in the technology they use to hold data. DRAM needs to be refreshed thousands of times per second. SRAM needs to be refreshed less often.

ROM (Read-only Memory)

Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. Once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike RAM, ROM retains its contents even when the computer is turned off. Hence, ROM is nonvolatile.

PROM (Programmable Read-only Memory)

A PROM is a memory chip on which data can be written only once. Once a program has been written into a PROM, it remains there forever. Unlike the main memory, PROMs retain their contents when the computer is turned off.

The difference between a PROM and ROM is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or a PROM burner. The process of programming a PROM is sometimes called burning the PROM.

EPROM (Erasable Programmable Read-only Memory)

An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased.

EEPROM (Electrically Erasable Programmable Read-only Memory)

An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off.

EEPROM is similar to flash memory (sometimes called flash EEPROM). The principle difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster.

Flash Memory

It is a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS stored on flash memory chip so that it can easily be updated if necessary.

Cache Memory

The cache memory is placed between CPU and main memory. It is a semiconductor memory and consists of static RAM. It is a special and very high speed memory used to increase the speed of processing by making current program and data available to the CPU at a rapid rate. It stores programs and data which are to be currently executed by the CPU. It is used to reduce the average access time for programs and data, which are normally stored in the main memory.

As the CPU processes data, it looks first in the cache memory and if it finds the data there, it does not have to do the more time-consuming reading of data from larger main memory.

Cache memory is placed at two or three levels. They are also called first-level cache (L1), second-level cache (L2), and third-level cache (L3). An L1 cache is on the same chip as the CPU or microprocessor. L2 and L3 are usually a separate static RAM chip. Cache within the CPU is called internal cache and the cache outside the CPU is called external cache.

Secondary Memory

These devices are also called auxiliary storage devices. These devices are any storage other than main memory. Unlike main memory, these are long-term, non-volatile memory. That is, these devices store and retain the programs and data after the computer is switched off.

There are two types of secondary storage devices. This classification is based on the type of data access: sequential and random. In case of sequential access devices, the data stored in these devices can only be read in a sequence and to get to a particular point on the media, we have to go through all the preceding points. For example, magnetic tapes are sequential access media. In case of direct-access devices, the data stored can be accessed randomly at any point without passing through intervening points. Magnetic disks and optical disks are most common examples of direct-access devices.

Magnetic Tape

It is a magnetically coated strip of plastic on which data can be stored. Storing data on tapes is considerably cheaper than storing data on disks. Accessing data on tapes, however, is much slower than accessing data on disks. Because, tapes are so slow, they are generally used for long-term storage and backup.

Magnetic Disk

Magnetic disks store data on disks rather than in tapes. The most popular magnetic disks are floppy disk and hard disk.

Floppy disk is a soft magnetic disk that is commonly used to move files between different computers, load new programs onto the computer, or store backup of data and small programs. It is slower to access data than hard disks and have less storage capacity, but is less expensive and portable. It is not very reliable and can be damaged easily. Floppies come in two basic sizes: 5.25 inch and 3.5 inch. 5.25 inch was common before 1978 and can hold 100KB and 1.2MB of data. The most common were 360KB and 1.2MB. 3.5 inch can hold 1.44MB of data. Now days, floppies are used infrequently.

Hard disk is a magnetic disk on which we store computer data. It holds more data and is faster than floppy disks. It can store several gigabytes (GB) of data. A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks and a track location that cuts across all platters is called a cylinder.

Optical Disk

Optical disks are the storage medium from which data is read and to which data is written by lasers. There are two types of optical disks: CD (compact disk) and DVD (digital versatile disk). CD can hold vast amount of information such as videos, music, animation, text etc. it is portable and its capacity usually ranges from 650 to 750MB. It is more reliable for long-term storage. DVD is primarily used to store movies or music. However, it can hold any type of information. It is similar to a CD but has a larger capacity. It can store about 17GB of data.

Hardware

Hardware, in the computer world, refers to the physical components that make up a computer system. It refers to objects that you can actually touch. There are many, many different kinds of hardware that can be installed inside and connected to the outside of a computer. However, there are several standard pieces of hardware that can be found as part of nearly every computer:

• Motherboard
• Central Processing Unit
• Random Access Memory (RAM)
• Power Supply
• Video Card
• Hard Drive
• Optical Drive
• Sound Card
• Network Interface Card (NIC)
• Keyboard
• Mouse
• Printer
• Monitor
• Speakers

Software

A computer needs both hardware and software for its proper functioning. Hardware (components like input, processing, output, and storage that can be physically handled) alone cannot perform any particular function without software.

Software is a computer program (set of instructions) that causes the hardware to do work. The software acts as an interface between the user and the computer. Software as a whole can be divided into a number of categories based on the types of work done. The two primary software categories are system software and application software.

System Software

System software includes operating systems (OS) and utility programs that operate and maintain a computer system and provide resources for applications programs. System software consists of low level programs that interact with the computer at a very basic level. System software also includes software like compilers, assemblers, debuggers, and file management tools.

            Operating systems are the most important programs that run on a computer. An operating system manages and coordinates the functions performed by the computer hardware. Every general purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from input devices, sending output to output devices, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. Most commonly used operating systems include Microsoft Windows, MS-DOS, UNIX, Solaris etc.

            Utility is a program that performs a very specific task, usually related to managing system resources. Operating system contains a number of utilities for managing disk drives, printers and other devices.

Application Software

Application software (also called end-user programs) includes programs designed to help people to perform specific functions. Depending on the work for which it was designed, application software can manipulate text, numbers, graphics, or a combination of these elements. Application software can be a program used for accounting control in business, a program used for engineering design etc. Some basic examples are word processors, spreadsheets, presentation graphics, image processors, and database management systems (DBMS).

            A word processor is a program that enables us to perform word processing functions. Word processors use a computer to create, edit, and print documents. Of all computer applications, word processors are the most common. A word processor enables you to create a document, store it electronically on a disk, display it on a screen, modify it by entering commands and characters from the keyboard, and print it on a printer. Some of the commonly used word processors are Microsoft Word, WordStar, WordPerfect, AmiPro etc.

A spreadsheet is a table of values arranged in rows and columns. Spreadsheet applications or spreadsheets are computer programs that let you create and manipulate spreadsheets electronically. In a spreadsheet application, each value sits in a cell. You can define what type of data is in each cell and how different cells depend on one another. The relationships between cells are called formulas and the names of the cells are called labels. These applications also support graphic features like charts and graphs. The most famous spreadsheet applications are Microsoft Excel and Lotus 1-2-3.

            Presentation Graphics enable users to create highly stylized slides for presentation. This software includes functions for creating various types of charts and graphs and for inserting text in a variety of fonts. Some popular presentation graphics software are Microsoft PowerPoint, Lotus Freelance, Graphics, Harvard Presentation Graphics, etc.

            Image processors or graphics programs enable you to create, edit, manipulate, add special effects, view, print, and save images. Image processors include paint programs, draw programs, and image editors.

            A DBMS is a collection of programs that enable you to store, modify, and extract information from a database (a systematically arranged collection of computer data). Some examples of DBMS are Microsoft Access, Oracle, Sybase, DB2 etc.

Firmware

Firmware is a combination of software and hardware. Computer chips that have data or programs recorded on them are firmware. Perhaps the most familiar firmware is the basic input output system (BIOS) chip. These chips commonly include the following:

• ROMs (read-only memory)
• PROMs (programmable read-only memory)
• EPROMs (erasable programmable read-only memory)

Firmware in PROM or EPROM is designed to be updated if necessary through a software update.

The BIOS chip on a computer motherboard holds instructions that, upon powering up, initialize the computer system.

Computer Peripherals

Auxiliary equipment used for computer input (keyboard, mouse, scanner, etc.), output (printer, plotter, speaker), storage (floppy drive, hard disk, CD drive), communication (microphone, modem, router), or other functions under the direct control of a computer is called peripheral device.

            A peripheral device is attached to a host computer but not part of it, and is more or less dependent on the host. It expands the host’s capabilities, but does not form part of the core computer architecture (CPU and memory).

Peripheral devices can be external (such as a mouse, keyboard, printer etc.) or internal (such as CD-ROM drive, sound card, internal modem etc.). Internal peripheral devices are often referred to as integrated peripherals.