How the computer industry suppliers are classified

Feb 24th, 2010
by Rashmi.
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The computer industry suppliers can be classified into three groups , namely Hardware Suppliers, Software Suppliers and Service Suppliers.

Suppliers of hardware include Mainframe manufacturers , peripheral vendors, computer leasing firms and used –system dealers.

IBM is one of the major suppliers of mainframe computers.

Peripheral vendors supply tape drivers, disk and diskette drives, printers and other components.

Computer leasing firms finance hardware and software purchase. They may also guarantee or insure the development of a computer system.

Used-system dealers purchase second-hand equipment from computer user’s, rebuild them and sell them at attractive prices.

Similarly, computer users can acquire ready-made software packages from either the vendor or the software house for virtually every application imaginable. Prices depend on the levels of complexity and the state-of-completion.

Services such as system design, programming, education and training, hardware maintenance are available at Service bureaus or computer manufacturers

Preventive Measures for Virus Attack

Feb 24th, 2010
by Rashmi.
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There are three things one can do to prevent virus infection in a computer system. These are:

1. Limit sharing

2. Limit transitivity

3. Limit functionality

Limit sharing

One can limit sharing by limiting information flow so as to form a post office kind of communicating information domains in a network system. In such a system, a

?virus will spread only to those domains which are in the transitive flow path from its initial source.

Limit transitivity

In a system, with unlimited information paths, limited transitivity may have an effect if users do not use all available paths, but since there is always a direct path between any two users, there is always the possibility of infection. As an example, in a system, with transitivity limited to a distance of 1, it is safe to share information with any user you trust without having to worry about whether the user has wrongly trusted another user.

Although isolation and limited transitivity offer solutions to the virus infection problem they are not the ideal solutions in the sense that widespread sharing is generally considered a valuable tool in computing.

Limit functionality

The last option for absolute prevention is limited functionality of the sensitive data sources. Most users do not exploit the general purpose capabilities provided to them, and it would be a substantial advantage for the defender if limited function may be applied. However, all modern software packages allow general purpose function. Such packages include most application programs such as databases, spreadsheets, editors and mailing systems etc.

Audit Trail

Feb 24th, 2010
by Rashmi.
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An audit trail is designed to permit tracing of operation, whether it is related to insertion, deletion or updation of records or processing performed on the computer system. In audit trail, all the operations that a user performs during a log-in session are noted. When a user logs in, the system records the user’s account number and associates it with the terminal from which the user logged in. All operations done from that terminal are attributed to that user account number, till the user logs off.

One way of accomplishing this is by automatically maintaining a transaction log. The details of each transaction are permanently recorded in a separate transaction file on the system itself. The storage of these details is automatic and invisible to the user. Information about the users should also be stored so that it will be clear who conducted the transaction. If the system has an internal clock, each transaction  is also time-shaped to tell when it occurred. Hence, it is easy to determine who submitted the transaction, when it occurred, and what data the transaction contained, and how the database or master file record was modified. In other words, there is a complete trail of the entire transaction and its effect on the system.

Note: But storing transaction log on magnetic disk is not fully reliable. This is because if the system is turned off abruptly, such as through a power failure, before the data are stored on disk, the data may be lost completely.

Another method of performing audit trail is to print a copy of the transaction before executing it. This method will not be having any problem of data loss. Thus, if anything happens, the transaction can be reentered by using the printed transaction list.

Benchmark

Feb 24th, 2010
by Rashmi.
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A benchmark is a sample program used for evaluating the performance of computer-based systems. It helps in the following manner:

1. Determination of the minimum hardware configuration needed t operate the system.

2. Testing the system in an ideal environment to determine comparative timings and then testing the system in a normal environment.

3. Determination of the system’s influence on other programs or systems.

The more elaborate is the benchmarking, the more costly is the performance evaluation. There must therefore be compromise on meets its functional criteria. Benchmarking helps in measuring the following parameters:

1. Response time,

2. Ease of use

3. Reliability of computation  and

4. Adequacy of storage capacity.

Graphical User Interface (GUI)

Feb 24th, 2010
by Rashmi.
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The pictorial representation of information and instructions using GUI’s are more user-friendly and easy-to-understand than textual commands and lifeless screens. Nowadays, GUI (Graphical user Interface) is incorporated within most of the computer operating systems, pioneer among them being the Microsoft’s Windows 9X,2000 and XP.

Note : GUI is a software design that allows you to control your computer by using a mouse pointer,windows and icons.

In systems that use Graphical User Interfaces, everyday tasks—such as running programs, opening files, choosing commands etc. are done using a graphical approach that is very intuitive to new users of computers. Even children of age   6 and above can control computers that uses GUI’S.

The basic element of a GUI is the window. A window is a rectangular area on the screen that displays information from a running program. You can open, close and move windows, and change the size of most windows. You can open several windows at a time, and you can often reduce a window to an enlarge it to fill the entire computer screen.

Within a window all the user interface controls like scrollbars, text boxes, radio buttons, checkboxes, drop-down lists, buttons, etc. are used.

In case of GUIs, the user dialogues are not hierarchical.

Different types of Interview

Feb 24th, 2010
by Rashmi.
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There are two types of interviews. These are:

1. Unstructured

2. Structured

Unstructured Interview

Unstructured interview is an approach in which the questions and the corresponding responses are open-ended. The interviewer can ask questions which may not be directly related to the system under consideration.

Unstructured interviews are conducted with only a general goal or subject in mind, with few specific questions. Conducting unstructured interview has the following advantages:

1. Interviewer has greater flexibility in wording questions to suit the respondent.

2. Unstructured interview may also produce information about the areas that were important.

Unstructured interviews may not work well for system analysis and design, because in this type, interviewee frequently gets off the track, and the analyst must be prepared to redirect the interviewee back to the main goal or subject.

A successful interview is likely to be the one in which the interviewer listens for the greater proportion of the time, giving the interviewees the opportunity to express themselves in an unrestricted manner.

Structured Interview

In structured interview, the interviewer has a specific set of questions to ask from the interviewee. All these questions are prepared in advance and the answer are noted. Structured interviews has the following advantages:

1. Structured interview ensure uniform wording of questions for all respondents.

2. It is also easy to administrate as well as to evaluate the answers.

3. In structured interview, limited training for the interviewer is needed. Hence its results in completing the job is possible in much shorter time. However, the cost of preparation for conducting interview will be much higher.

The success of an interview depends on all the skill interviewer and on his or her prior preparation for the interview.

Structured Interviews are further classified into the following two types:

1. Open-ended interviews

2. Close-ended interviews

Open Ended Interview: It is a type of interview that poses questions which may require a specific or a brief response. Open questions are general questions that establish a person’s viewpoint on a particular subject. For example the question may be:

“In what way is the sales forecast relevant to your activity?”

A question that requires the respondent to express a viewpoint is called an open question.

Close Ended Interview: Close-ended interview poses question in which the response(s) is/are presented as a set of alternatives. Close ended questions are more specific and usually require a specific answer. For example, a close-ended question may be:

“Where do you send your summary of orders?”

System Design and its Characteristics

Feb 24th, 2010
by Rashmi.
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In the system design process, the primary objective is to identify user requirements and to build a system that satisfies these requirements. Design of system is largely the logical design. The logical design can be sketched on a paper or on a computer terminal. The design, also including the physical design elements, describes the data to be  inputted, the processes involved in the manipulation of data and the output.

This system design phase includes the following steps:

1. The analyst should specify the file structures, storage devices etc.

2. The database is also designed in this phase.

3. Hardware cost, capability, speed, error rates, and other performance characteristics are specified.

 4. Changes to be made in the organizational structure of the firm are outlined.

5. Input, output, files, forms and procedures are planned.

6. Finally, standards for testing, documentation and system control are formulated.

A system analyst is an agent for changing the organization

Feb 22nd, 2010
by Rashmi.
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Systems are designed to perform certain required functions – there could be new functions, or modifications of older functions. A system which is being designed will often require changes and re-orientation in the way an organization works. There could be changes in format of input, or reports, additional information to be gathered, new procedures to be followed.

The user who implements the new system has therefore to adopt the changes to interact with information. Changes that a system will result in are often resisted. This is because persons are used-to working in a particular way and find it difficult to change.

New system means new skills have to be learnt, job descriptions may change and so on. Hence the system analyst is the creator of new environments. For this, he has to be a persuader as well as a controller and appropriately named as an agent for changing the organization.

Equijoins in Oracle

Feb 22nd, 2010
by Rashmi.
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Equijoins are also commonly known as simple joins, or inner joins. Given two or more tables, an equijoin will return the results of these tables where a common column between any given pair of tables has the same value (an equal value). Equijoins are typically joins between foreign keys in one table to a primary key in another table.

Equijoin :  A join between two tables where rows are returned if one or more columns in common between the two tables are equal and not NULL.

Pre-Oracle9i Equijoin Syntax

The boss, King, gets his employee report with only the department ID on it, because the query used for the report is based on only the EMPLOYEES table. When the company was smaller, he knew automatically that department 100 was the Finance department, and so on. But now, with almost 30 departments in the company, he needs to see the department name in the report. That information is in the DEPARTMENTS table. Janice will join the two tables on the common column, DEPARTMENT_ID, and produce a report that is much more readable:

     select employee_id "Emp ID", last_name || ', ' ||
         first_name "Name", department_name "Dept"
     from employees e, departments d
     where e.department_id = d.department_id;
 

Notice that table aliases are used. You've already seen quite a few column aliases in previous examples, and tables can be aliased also, either for clarity or for performance reasons. In this case, the aliases are necessary to identify which columns in which table are to be compared in this query. Typically, the column names match, but that is not a requirement for columns that are matched in a WHERE clause.

King tells Janice that the report looks good, but he also wants to see the full job description for each employee. Janice adds another table to the query and expands the WHERE clause. She also adds an ORDER BY clause to ensure that the report stays in employee ID order:

     select employee_id "Emp ID",
       last_name "Name", department_name "Dept",
       job_title "Job"
     from employees e, departments d, jobs j
     where e.department_id = d.department_id
       and e.job_id = j.job_id
     order by employee_id;

Tip : To join together n tables, you need at least n-1 join conditions to avoid undesired Cartesian products, resulting from combining every row of one table with every row of one or more other tables

King is still not satisfied with the report because it’s too long. He wants to see only information about the Finance and Purchasing department people on a regular basis. Janice updates the query one more time to add another WHERE condition to the query:

     select e.employee_id "Emp ID",
       e.last_name "Name", d.department_name "Dept",
       j.job_title "Job"
     from employees e, departments d, jobs j
     where e.department_id = d.department_id
       and e.job_id = j.job_id
       and e.department_id in (30, 100)
     order by e.employee_id;

Janice already knew the department numbers to use with the IN operator.

Join Syntax in Oracle

Feb 22nd, 2010
by Rashmi.
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So far, we have been dealing with only one table at a time in our SQL query examples. But typically the information needed to satisfy a user query requires more than one table. In new SQL 1999, you can not only  join two or more tables in a number of different ways, but can also use two different syntax forms to perform these joins. As of Oracle9i, the standard form  for join syntax is supported. Prior to Oracle9i, Oracle used a proprietary syntax that wasn’t always compatible with the ANSI standard.

Join : To combine two or more tables in a query to produce rows as a result of a comparison between columns in the tables.

Oracle’s proprietary syntax, which is still supported in Oracle9i and Oracle 10g for backward compatibility with existing code, put all of the join conditions in the SELECT statement’s WHERE clause. It also relied on relatively obscure methods to indicate certain types of join operations. The newer syntax relies more heavily on concise yet descriptive keywords to clearly indicate what operation is being performed. We’ll cover both the old and new syntax in this chapter; as a DBA or developer, you’ll most likely see new applications using the new syntax and plenty of existing applications that use the old syntax.

Tip:  All new SQL code should use the SQL:1999 or SQL:2003 standard syntax for readability and cross-platform compatibility

There is no performance benefit to using one syntax over the other; the same kind of join using either syntax will translate into the same internal SQL engine operation. One of the biggest benefits is the ease with which the new syntax can be written and understood. The join conditions are now separated from theWHERE clause and placed in the FROM clause. The WHERE clause, if one even exists, ends up being much cleaner because it’s used only for filtering the rows being returned from the query, instead of being intertwined with table join conditions.

Motorcars on Fire

Feb 21st, 2010
by Rashmi.
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Of late, it has been observed  that Automobiles running on the roads in Metro Cities sometimes catch fire. Many times the occupants escape unhurt but many times there are no so lucky. Daily one or the other car of different make catch fire in the city. By the time the fire brigade arrives on the scene of fire, the car is almost reduce to ashes.

One reason of fire –brigade not reaching the scene of  accidental fire of automobile is that city roads are unduly crowded all the times and secondly the location of the fire stations which may or may not be near the scene of fire. The experts advises that the automobile purchased from the show room should be used as it is without making any changes in its electrical system or wiring. They recommend that factory fittings should not be altered. People who use extra horns, lights, music systems etc are prone to accidental car fires on the road. Earlier it was thought that high atmospheric temperature as in summer leads to such fire but that has been proved wrong as cars are catching fire in severest of winter also.

To keep your car driving safe on the road the following tips  may be useful :

  • Car  should be used/ driven with the factory fittings without any tampering/ alterations
  • No extra wiring should be got done to add any CD changers, music system, extra  horns or extra lights.
  • The car should be got serviced timely from the factory workshop.
  • Two fire extinguishers should be kept handy in the car in case of any eventuality.
  • Petrol cars need not be changed to LPG or CNG to save some money
  • A medium hammer which can break the window & wind screen should be kept below the front seat adjacent to the driver.

 God bless everyone – Happy & Safe  Driving !!

PBX, PABX & EPBAX

Feb 21st, 2010
by Rashmi.
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The three are abbreviations of three small Automatic Telephone Exchanges which have been in use in the corporate sectors and small offices.

PBX – stands for “Private Branch Exchange “

PABX – stands for “Private Automatic Branch Exchange “

EPBAX –stands for “Electronic Private Automatic Branch Exchange “

All are small automatic telephone exchanges having ten lines to hundred lines. Earlier PBX, PABX were used now EPBAX is commonly used in private offices, where upto hundred telephone lines are taken on lease or rent from Automatic Telephone Exchange run by the government. These are installed in the office compound Electronics Items & Equipments. It is maintained by one Technician/ Engineers who visits the office from time to time to keep the EPBAX healthy and running condition. In the office, one operator is kept to operate it hassle free to provide uninterrupted telephone communication between the office people and various clients located anywhere in the city or country.

Different duties performed by System Analysts

Feb 21st, 2010
by Rashmi.
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System Analyst has the following duties to perform :

  1. Estimate personnel requirements, cost and time for system’s implementation.
  2. Review and approve proposed system’s solutions
  3. Perform resource planning and scheduling for system’s personnel.
  4. Develop, implement and enforce procedural standards for performing tasks of system analysis and design.
  5. Evaluate performance of system’s personnel and report on personnel activity to management.
  6. Plan and direct acquisition, training and development of system’s personnel.
  7. Assist in programs to educate management/ users in data processing and system’s capabilities and requirements.
  8. Define requirements for analytical studies. Also, set procedures for documenting current system operations.
  9. Perform interviews and data gathering by other means.
  10. Apply correct technology to solution of problems.
  11. Prepare specifications for system’s improvements.
  12. Define system’s security and control procedures.
  13. Develop system’s testing and conversion plans.
  14. Fulfill administrative reporting requirements.
  15. Supervise other project personnel as required.
  16. Develop and design file structures, forms and reports.
  17. Guide programmers and procedure writers.
  18. Evaluate results of program and procedure tests.
  19. Document results of design and testing.
  20. Assist in system testing and implementation.

STROUGER SYSTEM

Feb 21st, 2010
by Rashmi.
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 Automatic Telephone Exchange Strouger System

During the decades 1950’s 1960’s & 1970’s all the Telephone Exchange in Delhi were automatic and were using Strouger System which was imported from Belgium. This system was of minimum Ten Thousand lines which means Ten Thousand people could talk to each other at a time. There were nine such telephone exchanges which in different locations of Delhi to cover the  entire population of Telephone Users in the Capital.

Graham Bell created history by inventing the Telephone System by Scientific who created  Automatic Telephone  Exchanges also helped the humanity  in a very way.

In this system Uniselectors , two motion Selectors like Group Slectors final Selectors,Bank, Wipers, Relays,Carriage Assembilies Paul & Rachet Assembilies Ringers, Routiners & Battery Rooms were used to run these Automatic Telephone Exchanges.

These exchanges were using 52Volt D.C as power for these exchanges which was Generated  in house from Lead Acid Accumulator or from 220VOLTS A.C Mains which was converted into 52Volt D.C by means of Rectfiers fitted in the exchanges. Ringers used to provide required frequencies for various tones like Dial-tone & Number Un-obtainable tone to the Subscribers. Routiners were used to check the Telephone Exchange Racks & Instruments for satisfactory working of these exchanges. The Instrument & Equipments used were mostly Indigenized and supplied by ITI Bangalore.

This Strouger System was satisfactory except one drawback that to establish a call between Subscriber “A” to Subscriber “B”, the equipment & instrument used were engaged till the cal lasted between two subscriber and was not available to other subscriber till the two subscriber has finished their conversation.

During 1970, this drawback was overcome by using another system known as X-Bar system in which when two subscriber were connected telephonically, the entire Instruments & Machinery was disengaged and the two subscriber were connected through two simple wires and the disengaged equipments & machinery were available for the use of other subscribers.

Shell in Linux

Feb 21st, 2010
by Rashmi.
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A  Linux shell is the program which interprets what you type on the command line and decides what to do with that. A shell can be invoked in a non-interactive way, for example to execute a pre-typed list of commands contained in a text file (a “shell script”). Think of a shell as the equivalent of the DOS “command.com” (command-line interpreter) and the shell script comparison with their DOS cousins, the Linux shell and scripting are on steroids.

There are several shells available on the Linux system (if you installed them):bash (“Bourne Again” shell), sh (Bourne shell, standard on many UNIX systems), csh (C shell, with a syntax akin to the “c”programming language, available on most UNIX systems), pdksh (public domain korn shell), tcsh (tiny C shell, often used on small systems), sash (stand-alone shell could be used when librates are not available) ,ash,zsh and perhaps a couple more.

The default shell on my system (and most probably on yours too) is bash, which is an excellent and standard shell, and I really cannot see a reason why a newbie like myself would want to change it. Bash is fully backwards-compatible with the bourne shell (the most popular shell on UNIX) and incorporates many enhancements and best features from other shells. From a newbie perspective, the different shells are included with Linux for historical reasons and backwards-compatibility of shell scripts that may require a particular shell to run. [Some shells may be useful if you write programme targeted for specialized “embedded” devices, that might run a “tiny” shell.]

                      You can determine the shell you are running using:

                      Echo $SHELL

                      If you wanted to try another shell, type,or for example:

                     Tcsh

                     Which will start the tiny c shell. When done,type

                      Exit

Which will return you to previous shell (using exit on your will log you out). You can find how many shells you stacked on each other by displaying the “shell level” environmental variable:

                         Exho $SHLVL

                       In the above command, the “$” means “expand the value of a shell environment variable”,”SHLVL” is the variable name, and “echo” is a command that prints things.

The shell for each user is specified as the last field in the password file/etc/password. If you really wanted to change it, edit (as root) this file and replace the “/bin/bash” with the shell of your choice.

Network File System (NFS)

This is great for direct access to files that reside on another Linux computer. For mounting of a remote filesystem as NFS,first check if the NFS services is enabled (use the program setup). NFS also requires permission from the other computer. To configure the permission on the server machine, run as root:

                   Netconf

                   And adjust the setting under “Exported File Systems” menu.

If you prefer to do it manually, the permission are set in the file/etc/exports. My /etc/exports looks like this:

                /usr hacer (ro)mars(ro)

               /home hacker(rw)mars(rw)

               /mnt hacker(rw)mars(rw)

              This gives the machines called hacker and mars the permission to mount the directories/usr/(read-only access),/ home and /mnt (read-write).

This gives the machines called hacker and mars the permission to mount the directories/usr/(read-only access),/home and mnt (read-write).

       If you set up your NFS  properly, you should now be able to mount a network directory using a command like this:

Mount-t nfs mars:/home/mnt/mars_home

This mounts the contents of the directory/home/on a machine called “mars” into the directory /mnt/mars_home/(which must exist and be empty).

Many operating systems know NFS, but MS Windows doesn’t. Therefore MS Windows remote shares have to be dealt with differently.

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