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-1

A large computer provides a main memory capacity of up to 32 mega bytes, a processing power of 10 MIPS and supports a large number of disks and tapes. Disk capacities range from 100 MB to 1000 MB. It also allows simultaneous access to multiple users and supports a large number of input and output devices.

 

A super computer is the largest computer system available in the market. It provides a main memory capacity of up to 64 mega bytes and a processing speed of 20 MIPS. It also supports a large number of disks and tapes of enormous capacity for providing random access and serial access secondary memory. A super computer also allows multiple users to interact with the CPU simultaneously through multiple types of input devices. It also provides outputs in a variety of forms and supports a large number of output devices. Customer Relation Management System owner says that for their clients who are selling blinds, roller shades and woven wood shades online; they need to use high configuration computers.

Personal computers are used by managers for their own computing needs. Availability of a large number of user-friendly software packages on PCs have made them effective tools to support managerial decision-making. PCs have also encouraged distributed data processing. A super micro is used for commercial data processing and managerial applications. A large computer is necessary for very large data processing and data management applications. A large computer is necessary for very large data processing and data management applications. A super computer is primarily used for highly scientific and research purposes.

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.

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-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.

 

roman shades, vertical blinds, window blinds

Magnetic Disk-2

Each recording surface is divided into a series of concentric circles called tracks and each track is further divided into sectors. The capacity of each sector whether it is on the inner most track or outer most track is a constant. One important characteristic of a disk drive is the access time which represents the time needed to access the desired record from a disk. Access time consists of two components, namely, seek time and rotational delay. Seek time represents the time required to seek the desired track on the desired recording surface. This involves a movement of the access arm, which supports the read/write head. Rotational delay represents the time required for the rotating disk to position the desired sector under the read/write head. Access times of 35 milli seconds are common. Disk packs are classified into three types, namely, removable disks, fixed disks and Winchester disks. 

A removable disk pack, as the name indicates, can be transported and replaced. A fixed disk pack on the other hand, cannot be removed or transported or replaced. However, it provides a quicker access time. A disk storage capacity of 600-1000 MB is very common. Winchester disks are a special type of hard disks and are supported mainly by micro-computers. A Winchester disk provides a storage capacity in the range of 10 MB – 80 MB.

Magnetic Disk-1

Last time we talk about magnetic tape. Today we are going to discuss on Magnetic Disk which is important device and part of the computer hardware. Magnetic disk was invented to overcome the sequential processing requirement of magnetic tape data. It is helpful to visualize a magnetic disk as a LP record. An access mechanism moves the read/write head to the desired surface on the disk to provide random access of data. A disk pack is a collection of individual disks stored vertically one atop the other and mounted on a disk drive. The disk drive rotates the disk pack at a constant speed. There is enough room in between the spinning disks to allow access arms with read/write heads to move to any storage location.

 

Each disk in a disk pack has two recording surfaces, except the first and last disks which have only one recording surface. Thus a disk pack with 10 disks provides 18 recording surfaces. Such a disk pack also has 9 access arms. Each access arm supports two read/write heads, one read/write head to access the lower recording surface of the top disk and the other read/write head to access the upper recording surface of the bottom disk.

Magnetic Tape

As a part of our talk on computer management, today we are going to talk about Magnetic Tape. A magnetic tape is very compact medium for storing a large amount of data. A standard tape reel is 2400 feet long, ½ inch wide and can store up to anywhere from 20 MB to 150 MB depending on the recording density it permits. A magnetic tape is mounted on a tape drive which has a read/write head. ISP or hosting service provider provides managed hosting services. Data stored and data management is handled by data center.

The density of a magnetic tape refers to the amount of information stored in one inch of its tape length and is measured in bits per inch (bpi). Standard tapes come with 800 bpi or 1600 bpi, even though tapes with 6250 bpi are also common. A text book of 600 pages with 50 lines per page and 40 letters per line can be accommodated in less than 20 feet of a tape of density 6250 bpi. Imagine how much data can be stored in a 2400 feet tape? These technologies can store huge volume of data in small amount of space, same time the risk of data lost also increase. When planning is going on for data stored or data management, management needs to plan about disaster recovery. Data safety and data recovery is very much important for any computerize management system.

The major advantage of a tape is its economical storage of large volumes of data and a quick transfer of its contents to CPU. However it has a major disadvantage namely it permits only a serial access of data. This is because the read/write head is fixed and immovable. As a result the tape has to be moved physically over the read/write head till we come to the desired location to access the required data.