Types of Computers 1. Microcomputers These are the smallest family of the computer world. General features are low cost, general usage and high availability. Microcomputers can be further divided as palmtops, laptops and desktops. 2. Minicomputers (workstations) Minicomputers and workstations are higher in capacity than the desktop computers and they are suitable for advanced applications such as technical drawing, animation, video editing etc. Most business organisations use minicomputers to provide a better and efficient service to their customers. 3. Mainframe computers This is a powerful computer system used in large corporate and governmental organisations for high volume and critical data processing. A mainframe is a multiuser computer system where thousands of users can use it at the same time. It can be used via terminals. 4. Super computers Super computers are extremely powerful computer systems that are specifically designed for scientific, engineering and business applications requiring extremely high speeds for massive numeric computations. The use of supercomputers include weather forecasting, military defense systems, climate research, oil and gas exploration, astronomy, large scale data mining etc. The System Configuration Input devices are used to feed data into the system and the CPU processes the data. CPU is unable to hold data while processing. Hence, the RAM holds data while processing take place. Hence the capacity of the RAM directly affects the performance of the computer. The RAM keeps data as electrical signals. When the computer shuts down all data are deleted from the RAM and it does not have the capability to hold data permanently. Secondary storage devices are used to store data permanently in the computer system. Output devices are used to produce the results and communicate them to users. Introduction to Bits and Bytes Computer memory is represented in bits and bytes. The amount of information stored and transferred through a computer ranges into many millions of bytes. 1024 Bytes = 1 Kilobyte (KB) 1024 KB = 1 Megabyte (MB) 1024 MB = 1 Gigabyte (GB) 1024 Gigabyte = 1 Terabyte (TB)
Data entered to the system in a human readable format is converted to a machine readable format, before it is processed and then the output is converted to a human readable format. Advantages of Data Entering Devices 1. Equipment and implementation cost is low 2. Easy to use Disadvantages of Data Entering Devices 1. Data entering speed is very low 2. Error rate is high 3. Types of data that can be entered is limited. Advantages of Data Capturing Devices 1. Data Entering speed is high 2. Error rate is low Disadvantages of Data Capturing Devices 1. Equipment and implementation cost is comparatively high 2. User requires training before using devices. Factors to consider in selecting input and output devices 1. analyse the purpose and usage of the device 2. analyse the intended audience who use the device 3. cost and allocated budget 4. durability, warranty period and after sales services Importance of CPU and its types CPU is the main component that controls devices connected to a computer system and processes instructions given to a computer system. It is the brain of the computer system. Hence the capability of the CPU directly affects the performance of a computer system. Although small in size this is the most
expensive part of a computer system. CPUs are classified based on manufacturer and performance. AMD and Intel brands are the most commonly used processors Factors to be considered when selecting a CPU 1. The clock speed - Clock speed is measured in Hertz (Hz). Greater the Hz number, higher the speed. 2. Number of Cores -The latest inclusion to the CPU industry is the inclusion of more logical CPU (Cores) in one physical CPU. Higher the number of cores, better the performance of the computer system. Intel Core 2 Duo processor has 2 cores and Intel Quad Core processor has four cores inside a physical processor. 3. Processor Architecture - 32 bit or 64 bit processor (bits of data). 64 bit is more powerful than 32 bit. Importance of RAM Random Access Memory(usually referred to as memory of the computer) provides space for the computer to read data on it and write data from it when processing is done by the CPU. When the RAM of the computer is increased, the number of times the CPU must read data from the hard disk will reduce. RAM is many times faster than the hard disk. RAM is volatile, so data stored in RAM stays there only as along as the computer is turned on. Factors to be considered in deciding RAM Capacity 1. RAM capacity should support the CPU. 2. RAM capacity requirement of different software. Different types of drives and media Secondary storage devices hold files that are not currently being used by the CPU. For a file to be used it must be first brought on to main memory. After modifications are done files must be saved to secondary storage so that it can be used again. Secondary storage can be damaged and files on them become corrupted. Hence backups needs to be taken regularly. 1. Read/write media versus Read-only mediaeg:-cd-rw vs CD-R 2. Sequential vs Random Access Storage - In sequential file access method, files are accessed in a sequential manner (Eg:- Magnetic tape). However in random access, wherever the file is located you can go to the exact location directly and retrieve it (Eg: - Hard disks and optical disks). 3. Magnetic vs Optical - A magnetic disk's medium contains iron particles, which can be polarised - given a magnetic charge - in one or two directions. Optical disk is a storage medium from which data is read and to which it is written to using laser beam. 4. Removable and Non-removable media - Hard disk versus Portable drives.
Discussion on storage devices (floppy disk, hard disk, CD-ROM, DVD, Flash Drive, External Hard Disk) Floppy disks - 3.5" single sided disks. Not used any more. Holds up to 1.4MB data. Limited capacity and slow, although cheap. Hard disk - Pack of disks permanently sealed inside a disk drive. The read/write heads do not actually touch the surface of the disk but fly over it on a cushion of air. It is possible to have more than one hard disk. The main one is called master and the second is called slave. Hard disk have tracks and sectors. Disk formatting means formatting tracks and sectors. CD ROM/ Digital Versatile Disk / Blu-ray Flash Memory - Electrically-Erasable Programmable Read-only Memory. Pen Drive/USB Drive/Flash drive have capacity ranging up to 32/64 GB. External Hard Disk - These are disks extending up to 500GB. Discussion on OS Operating system is the main and the most important program. A computer cannot do anything until the OS is loaded in to the main memory or RAM. When a computer is turned off, the OS is deleted from the main memory and CPU does not do anything. BIOS is the program used by a computer to get the computer system started after turning on a computer. BIOS is a set of programs, which controls the PC hardware and is stored in a memory chip on the motherboard. This chip is a Read Only Memory chip which keeps in contents even when the power is off. The ROM contains instructions for activating the CPU and OS during the boot up process of a computer. Components of OS The basic components of all operating systems consist of 4 managers and the user interface which will work closely in order to provide needed services. User Interface - The user interface provides the communication link between user and computer. They are either The Command-Line Interface or Graphical User Interface. Memory Manager - This is related to the management of computer memory. Virtual memory makes the system appear to have more memory than actually available by sharing it between competing processes as they need it. The main functions of the memory management system includes keep tracks of available memory, checks validity of request for memory, preserves allocated space to the operating system in main memory, allocates memory for execution and de-allocates memory after certain time. File Manager - This controls and supports all the files in the system. The main functions of a file manager include keeping track of each file, user policy for storing files and utilising storage spaces, allocates files for manipulation by operating the file and de-allocates files when the files are not in use. Process Manager - A job is a collection of instructions that is submitted for execution to the operating system. The important function of process manager is to keep track of the status of each job during execution and direct processor from execution of one job to another one. Device Manager - The device manager is a software that monitors utilisation of all peripheral devices of the system such as printers, terminals and disk drives. The main functions of device manager are
tracking the status of each device, determining which process will get a device and for how long, allocating a device and de-allocating a device. Advanced Features of OS Multitasking this refers to multiprogramming on single user operating systems such as those in microcomputers. This allows one person to run 2 or more programs concurrently on a single computer. Virtual Storage (Virtual Memory) Virtual Memory is a storage on the computer s hard disk that the operating system uses in conjunction with Random Access Memory (RAM). Time Sharing The time sharing capability allows many users to share computer processing resources simultaneously. Each user is allocated a tiny slice of computer time. Multiprocessing This is a capability of an operating system that allows to link 2 or more CPUs to work in parallel. While multiprogramming uses one CPU for concurrent processing, multiprocessing uses multiple CPUs for simultaneous processing. Networking Computer network is a collection of computers. There are two types of computers in a computer network. A client computer is a computer that requests services from a computer network. Server computer is a powerful computer that provides services and controls the network. (Refer http://www.ics.uci.edu/~ics143/lectures.html for detailed discussion on operating system) Discussion on Utility Programs / System Support Programs A utility program is one that supports the user to us the computer, an application or a development environment. These applications play a supporting role and typically perform a limited number of tasks. The following are typical example for utility programs. - System monitors These are performance monitoring and security monitoring programs. - Anti-virus Software that protects the computer from malicious attacks. Antivirus software scans for virus and removes them. - Backup Backup software enables copying files or databases so that we can restore the original after a data loss due to equipment failure or a catastrophe. - Disk compression Agent This allows to save disk space by compressing files, or improve performance by changing the level of compression on the files. - ScanDisk Scan disk runs automatically in the event the operating system is shut down improperly. It detects corruptions when they are most likely to occur and corrects them.
Generations of Programming Languages - 1 st Generation languages Machine language / 1940-1950s - 2 nd Generation language Assembly language /1950-1958 - 3 rd Generation language High level language / 1958-1985 - 4 th Generation language 4GL, AI / 1985 to to-date Basic Concepts in Programming Languages - Complier Compiler is a program that translates the instructions of higher-level languages in to a machine language. The complier translates the entire source code and translates it at once to the object program. - Interpreter This translates higher level language into machine language but takes one statement of higher-level language at a time, translate it into machine language and execute it immediately. - Assembler An assembler is a computer program used to translate a program written in an assembly language in to machine language. - Source Program This is the original program written by a programmer using a specific programming language. - Object Program The object program is equivalent of the source program translated in to machine language by a language translator like complier or assembler. Object program can be executed directly by the computer since it is in machine language. Factors to be considered in selecting system software - Features necessary features to match your needs. - Fit Compatibility with other IT products you already have and whether it supports the IT Strategy. - Future In line with future trends and get customer support - Flexibility ability to modify based on business changes - Budget software matches the budget - Return policies Ability to return the software/ availability of trial period - Training and Documentation availability of training and documentation Discussion on General Purpose Software - Word Processing - Spread sheets - Presentation Software - Web Browsers - Email Clients :- Microsoft Outlook, Eudora, Pegasus
- Personal Information Managers - Multi Media Players Discussion on Application Specific Software These are packages available to support specific applications of end users in various fields such as science and engineering, education and commerce etc. Discussion on Commercial Software, Freeware, Shareware & Open source Commercial Software These software are available to be purchased at a price. Eg MS Office, MS Windows Freeware Freeware are downloadable and distributable software free of charge Shareware This is a proprietary software that is provided to users without payment on a trial basis and is often limited by any combination of functionality, availability and convenience. Open Source These are software whose source code is published and made availableto the public, enabling anyone to copy, modify and redistribute the source code without paying royalties or fees. Open source code can evolve through community cooperation. Discussion on DBMS A database is an integrated collection of logically related tables (records or files) consolidated into a common pool that provides data for one or more multiple uses. Data hierarchy A field holds one fact (Eg:-Employee ID) A record is collection of related fields (Eg:- Employee Y Information) A table is a collection of related records (Eg:- Employee table) A database management system (DBMS) should be there to create databases, access and control. A DBMS is an independent program that can communicate with application programs and databases. Advantages Reduce data redundancy, increased consistency, greater data integrity, improved data access to users, improved data security, reduced costs. Disadvantages Complex, difficult and time consuming, higher initial costs, cumbersome conversion, initial training required, and damage to database affects all applications. Discussion on SQL SQL is the standard language used for creating and querying relational databases. SQL commands can be classified in to 3 types. Data Definition Language (DDL) CREATE, ALTER, DROP
Data Manipulation Language (DML) UPDATE, INSERT, MODIFY Data Control Language (DCL) used to control a database including administering priviledges. Eg: - SELECT Employee_ID, Employee_Name FROM Employee WHEREEmployee_Salary> 50,000 ORDER BY Employee_ID ASC GROUP BYEmployee_JOIN_DATE HAVING>01/01/2014 Advantage of Twisted Pair Cable 1. Easy to use 2. Lower cost Disadvantage of Twisted Pair Cable 1. Beyond 100m the signal becomes poorer. Only suitable for short distance. Coaxial Cable Single copper conductor in the middle. A plastic layer provides insulation between the center conductor and braided metal shield. Very rarely used computer network. Can transmit signals up to 500 meters. Fiber Optic Cable This consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. Advantage of Fiber Optic Cable - No electrical interference - Capability to carry out information at vast speeds - Possibility to include more services Disadvantages of Fiber Optic Cable - The cost is too expensive - Implementation is difficult and requires special skills. Radio Waves The transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Microwave Electromagnetic waves having frequencies between 1-300 GHz are called microwaves. Microwaves require line-of-sight transmission and reception equipment. To increase the distance of transmission, a
system of repeaters can be installed with each antenna. Microwaves are used in cellular phones, satellite networks and wireless LANs. Infrared Infrared signals, with frequencies from 300 GHz to 400 GHz can be used for short range communication. Infrared signals cannot penetrate walls. Used in short distance communication between devices such as keyboards, mice, PCs and printers. Satellite Communication A satellite network is a combination of nodes that provides communication from one point on the earth to another. A node in the network can be satellite, an earth station or an end user terminal or telephone. Ring Topology The nodes of the networks is connected to two other nodes in the network and with the first and last nodes being connected to each other. Data is transmitted in a circular manner. Bus Topology Nodes are arranged along a side length of cable that can be extended at the ends. Star Topology Has a central node that connects each of the other nodes by a single, point-to-point link. Tree Topology Combines the characteristics of linear bus and star topologies. Personal Area Network PAN can be used for communication among the personal devices themselves or for connecting to a higher level network and the internet. PAN can be wired or unwired. The reach of PAN is few meters. Wide Area Network WANs are networks that generally span distances greater than one city. Some WANs are commercial, regulated while others are privately owned. Internet is an example of WAN. Local Area Network A LAN is a system for interconnecting two or more communicating devices within 2000 feet usually intra-organizational, privately owned, internally administered. LANs are usually medium to high speed and connects a large number of intelligent devices to share corporate resources. Metropolitan Area Network MAN is a large computer network that spans a metropolitan area. Its geographic scope falls between LAN and WAN. MANs can span up to 50 km. MANs provide internet connectivity to LANs.
Internet Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide. The internet carries a vast array of information resources, services, most notably the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support electronic mail. Internet has given rise to Voice over Internet Protocol (VoIP) and IPTV, newspaper websites, blogging and e-commerce. Intranet Intranet is the term for a collection of private computer networks within an organisation. An intranet uses network technologies as a tool to facilitate communication between people or work groups to improve the data sharing capability and overall knowledge base of an organisation's employees. Extranet An extranet is a computer network that allows controlled access from the outside for specific business or educational purposes. Extranets are extensions to, or segments of, private intranet networks that have been built in many corporations for information sharing and e-commerce. The level of access to the resources within the network can be set at different levels. Network Protocols A network protocol defines rules and conventions for communication between network devices. Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged in to messages sent and received, enhances the performance of the network communication. Internet Protocols TCP/IP is used to connect hosts on the internet. IP takes care of the communication. TCP takes care of the communication between application software and the network software. HTTP and FTP are additional protocols that are packaged with a TCP/IP suite. File Transfer Protocol FTP is the protocol used for exchanging files over the internet. FTP uses internet's TCP/IP protocol to enable data transfer. FTP is mostly used to download or upload a file from the server. Domain Names When you publish your website, there should be a proper naming system to identify your website from other websites. eg:-www(service).casrilanka (name of the website).lk (domain category) Search Engines Search engine is a special website that provides searching facility in the web. It sorts by the key words from millions of websites. Eg:- Yahoo, Google.
Electronic Mail Email service provider allows to create an account for each user, to send and receive emails. Depending on the service provider, the maximum capacity of the email account differs. Email client software such as Microsoft outlook and eudora are available. Telecommuting Telecommuting is working from a remote location not in the same space as coworkers or people. News Group Newsgroup are a globally shared / distributed set of online forums where users can post messages to each other. Newsgroups can either be public or restricted. Discussion on Social Media Eg:-facebook, twitter and linkedin. These are used for business as well. Chat and Messaging Services Online chat is a way for 2 or more computer users connected to the internet to communicate with each other in real time. Skype is a commonly used chat software. There are 3 types of chat facilities available. - Text Chat - voice Chat - Video Chats/video conferencing Cable Modems Modems are used to convert digital computer signals into a analogue form to travel over a telephone line and vice versa at the other end. Wireless USB Modems (USB Dongles) Used to connect computers to the internet with a wireless USB modem. Has different data speeds. Network Interface Cards This is the card that physically makes the connection between the computer and the network cable in a LAN, to provide a dedicated, full-time connection to a network. Wireless LANs Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the access points. Long distance wireless communication takes place through cellular telephone technology, microwave transmission or satellite. Very useful for building where cabling is difficult.