DBMS packages-4

Today we continue our discussion on DBMS Packages. Software packages called Data Base Management System (DBMS) has been developed long before micro-computers to handle the problems of maintaining and integrating large volumes of data on large machines. The most important distinguishing feature of a DBMS package on personal computers is that it provides a very high level language interface which can be learned by a user who is not a computer programmer. We have already talked some important command in our previous post. Today we will talk on other command like quit, use custlist etc….

 

..QUIT

Next day when we start the dBASE III programme, we must first indicate which file we want to use, otherwise dBASE III will not know which file we are interested in. The command for this is

 

..USE CUSTLIST

Now let us say we want to query on the customer data for extracting different types of information. Here is a sample list to illustrate how easy it is. 
 

One has to learn only few additional features to see how sales and receipt transactions can be used to update amount due for each customer. The dBASE III package also has REPORT command for producing user specified reports. With the command verbs, dBASE III also provides conventional programming features like IF-THEN-ELSE, WHILE-DO. A complete set of dBASE III programmes can be designed to implement a medium sized application in a couple of weeks.

 

DBMS packages

In our last post we have discussed on Data Base Management System (DBMS) and today we are going to talk on DBMS packages.

 

Like other DBMS packages, dBASE III provides features for: 

1.      Creating data files on a computer.

2.      Maintaining these data files by way of providing functions for adding, deleting editing and updating a give set of data items.

3.      Generating reports based on the data files created through dBASE III

4.      Querying on those data files.

 

To develop an understanding of the features provided by dBASE III package, let us take a specific application and see how it could be implemented in dBASE III. Suppose we are operating a small business house which has 1000 customers. We are interested in maintaining a list of these customers and using this list for our day-to-day business operations. Obviously we will have to create a file which contains data about these 1000 customers. In this file there will be one record for each customer. Thus, we will have a file containing 1000 records.

Personal Computer and its uses-1

INTRODUCTION OF PERSONAL COMPUTER AND ITS USES

Computers were first used in management and business applications in centralized data processing departments. These departments were manned by computer specialists who were the only persons allowed access to the machines. Later terminals were provided to users for certain applications. However, cost, complexity, size and the need for special environment control did not permit computer users to have computers at their work places. All this has changed with the advent of micro-computers. For example market type is also change now a day than before. New days companies are using trade show booths where they have banner stands, table skirts and pipe and drape. Same way, computers are changing day by day with the use of new technology being invented and introduced in the market. Marketing exhibitions and trades shows are best way to introduce new technology to people.

 

MICRO-COMPUTERS

Micro-computers are computers which have their entire Central Processing Unit (CPU) on single integrated circuit ‘chip’ (called a micro-processor). Today powerful micro-computers are available which cost as little as $ 500. These micro-computers can do many of the jobs earlier done by large computers which cost many times this amount. In addition, because they are small enough to sit on a desk and do not require extensive environmental control, they can be used in most reasonably dust-free environments. Field tests on machines used in projects such as the Computer Literacy Project for Secondary Schools of the Education Ministry have shown this.

 

This ready availability for users has enabled a large number of entirely new applications to be undertaken. It has also increased user interest in computing since users can be directly in control of their data unlike the situation with centralized computing. Due to these factors and the fact that micro-computers can be used at home and schools for education and entertainment there has been a spectacular increase in their numbers since their first arrival as hobby kits in the U.S. Several million micro-computers are used in management applications around the world today. In India the projections are that by 1990 a few lakhs of these machines will be installed.

Classification Of Computers

 

In the 1970s computers were classified into three categories, namely, super-computers, large computers and mini computers. But the invention of the micro-processor which gave birth to micro-computers in the late 70s has drastically changed the computing scene. A wide range of computers are available today in the market ranging from a personal computer to a super computer.

 

A personal computer (PC) is a micro-computer which has its entire central processing unit on a single micro-processor chip. A PC provides a main memory capacity upto 640 kilo bytes and a processing power of 0.5 MIPS. It supports one or 2 diskette drives of 360 KB each for random access secondary memory. A PC usually comes with a standard key board, a visual display unit and a dot matrix printer. A PC is usually operated by a single user.

 

A super mico-computer has its entire central processing unit on a very powerful micro-processor, provides a main memory capacity of upto 16 mega bytes, has a processing power of 2 to 3 MIPS, supports Winchester disks of capacity 20 to 80 mega bytes and allows simultaneously access to multiple users. Today’s super micro is actually replacing yesterday’s mini computers which provide almost the same computing power it nit less, but based on a different technology.

Operating Systems-1

We are talking computers in management. We talked evaluation of computers and computer softwares in our previous talk. We talked about operating system in our last post, today we continue with that. We talked the drawback of idling the CPU was overcome with the introduction of overlapped processing.

For example why not take up input operation of job 2 and the output operation of job 1 simultaneously? This and similar considerations gave rise to the concept of multi-programming. A multi-programming operating system handles multiple jobs simultaneously by overlapping the input, output and processing cycles of various jobs.

This operating system was introduced along with third generation computers and is still very popular. It has replaced the earlier batch processing (serial) operating system. With multi-programming a CPU’s utilization is increased and hence jobs get executed faster on an average. However a multi-programming operating system is more complex hardware to support it.

Other types of operating systems which are popular today are multi-processing operating systems and real time operating systems. A multi-processing operating system uses multiple CPU’s to process multiple jobs. A real time operating system is a very different type of operating system, because it is used for different type of applications, i.e., real time applications such as airlines reservations, process control, etc.

Utilities

Utility programmes are those which are very often requested by many application programmes. mailing leads and marketing list are few example of such utility programmes which are used in large by industry. A few examples are:

SORT/MERGE for sorting large volumes of data and merging them into a single sort list like mortgage mailing list.

Transfer programmes for transforming contents from one medium to another, e.g., disk to tape, tape to disk, etc.

Language translators

A language translator is system software which will translate a computer programme written by humans into a machine understandable form. The most elemental form of programming uses only the binary digits 0, 1 which is directly understood by the electronic circuits. A programme written using only binary digits is called a machine language programme.

 

Assembly language provide a significant improvement over machine language. Assembly language programmes are written using mnemonic codes like ADD, STORE, etc., rather than their machine language representations in binary digits. Therefore programming in assembly language is easier. Active directory and active directory management or active directory tool can be made with such programming. However, it needs to be translated into machine language codes. This translation is done by an assembler. Both machine language and assembly language programmes are machine dependent. This means that a programme written for one machine cannot be used in another machine.

 

High level languages, which are closer to English overcame the drawback of machine dependence. A few high level languages are FORTRAN, BASIC, PASCAL, COBOL etc. These languages relive the programmers from being machine specific. However a programme written in a high level language needs to be translated into machine language codes before execution. This translation is done either through compilers or through interpreters.

 

A compiler is a translator which reads an entire programme written in a high level language and coverts it into machine language codes. An interpreter on the otherhand, is a translator which interprets statement by statement, any programme written in a high level language. An interpreter is a very effective tools for programme development as it checks for errors statement by statement in an interactive mode. Exchange Management and Exchange Tools require interpreter.  This allows the programmer to correct the errors statement by statement as he enters them. A compiler on the otherhand, will request the user to enter the entire programming statement and then it will check for errors. Basic language provides a compiler and an interpreter.

 

Other language such as Fortran, cobol and Pascal had only compolers initially. However interpreters for these high level languages are also becoming available, partly due to the popularity enjoyed by micro-computers in the field of computing.

COMPUTER SOFTWARE

Today we are going to discuss on Computer Software part. This is a most important topic for Computers. Computer software consists pf sets of programmed instructions which enable the hardware units to perform. Programming a computer to perform has always been a very difficult task. The first electronic computer was programmed using wired panels. Today’s computers are programmed using software.

 

Computer software can be broadly classified into two categories – System Software and Application Software. System software is a set of instructions to the machine hardware to interpret and execute application software. Application software is a set of programming instructions for specific applications like payroll accounting, inventory control, etc. System software consists of language translators [called compilers (compiles program-wise), interpreters (compiles like-wise) and assemblers (converts semi-machine-language, macro-instructions, to machine language)], operating systems, utilities and special purpose software.

 

Computer software or just software is a general term used to describe a collection of computer programs, procedures and documentation that perform some tasks on a computer system. “Software” is sometimes used in a broader context to mean anything which is not hardware but which is used with hardware, such as film, tapes and records. 

We will discuss on languages translator in next post.

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Input and Output Devices-4

Still today we have discussed for different types of the computer hardware devices. Form last few days we are talking on input and output devices which is most important part of the computer hardware. The input or output units of a computer system establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them are discussed in this note.

Most recent trend for data input is towards source data automation. The equipments used for source data automation capture data as a by-product of a business activity thereby completely eliminating manual input of data. Some examples are:

1. Magnetic ink character recognition devices are used by the banking industry to read the account numbers on cheques directly and do the necessary processing.
2. Optical mark recognition devices can sense marks on computer readable papers.

This king of device is used by academic and testing institutions to grade aptitude tests where candidates mark the correct alternatives on a special sheet of paper. These answer sheets are then directly read by the optical mark recognition devices and the information sent to a computer for processing.

Input and Output Devices-3

We talked about input or output units of a computer system. Input and output establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them we are discussing here. We talked about hard disk in our previous post. Today we are going to talk about printer.

 

A printer is a peripheral which produces a hard copy of documents stored in electronic form, usually on physical print media. Printers are purely output devices. Printers are classified into line printers and dot matrix printers. A line printer prints one line of information simultaneously, whereas a dot matrix printer prints one character at a time. A dot matrix printer uses a 5 X 7 or 7 X 9 dot matrix formation to represent each character. Dot matrix printers therefore provide a broken appearance to the characters, whereas a line printer provides a better quality output. A line printer has a speed of about 2000 lines per minute whereas a dot matrix printer has a lower speed of approximately 100 characters per second. If we talke about credit card printer than they need to have a merchant accounts with which credit card processing done. In big shopping mall credit card machine are available there.  With credit card software  and credit card terminal they use credit card printer  to for day to day functions.

Daisy wheel printers and letter quality printers are also character printers. But they produce excellent quality output. However, they are more expensive and slower than dot matrix printers. All the printers discussed so far are called impact printers as they make physical contact with paper while printing. A no impact printer on the other hand transfers information to paper without any physical contact. Example of no impact printers is laser printers, xerographic printers, electrostatic printers, etc.

 

Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless or Ethernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time.

Input and Output Devices-1

Still today we have already discussed different computer hardware parts. In our last talk we have discussed on magnetic disk. The Diskettes and Winchester disks provide random access memory on micro-computers. A diskette is a smaller disk of 5¼ inch in diameter. It provides a storage capacity of 360 KB and an average access time of 180 milli seconds. Today we are going to discuss one other and important part of computer hardware and that is input and Output devices.  

 

Input and Output Devices 

The input or output units of a computer system establish the communication between the system and its users. A large number of input and output units are available in the market. A few of them are discussed in this note.

 

Punched card is the most ancient (few decades old) input medium. Instruction and data punched on cards are transmitted into a computer through a card reader. A printed card had survived a whole century because of its simplicity. But it is on its way out now. Punched cards are being replaced by terminals which provide direct data entry. In next post we will discuss briefly on input and output devices.

 

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