Dos Tutorial

What is Database?

What is Database Hosting?

What is Database Normalization?

What is Process?

Dos Tutorial

Before you begin this tutorial, please make sure that your prompt is C:\> If it is not, please do the following:

Directions:

1. Type: c:
2. Type: cd..

This should place you into the C:\> working directory.

NOTE: DOS is not case sensitive; therefore, a command can be entered in with CAPITAL LETTERS, lower-case letters, or a MiXtuRe of the two.

Hardware and Software Differences

There are two parts to a computer system, the hardware and the software. Hardware refers to the physical components of a computer. An example of hardware components would be the monitor, keyboard and mouse. Software represents the programs which contain a set of instructions written to perform a certain task on the computer.

What is DOS?

DOS stands for Disk Operating System. DOS controls the computer’s hardware and provides an environment for programs to run. This system program must always be present when working with your computer.

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Why You Need DOS

There are a variety of reasons why you need DOS. A few of them are listed below to satisfy your curiosity.

1. DOS controls the flow of information between you and the computer (translator).
2. DOS allows you to store information on your computer.
3. DOS allows you to retrieve information stored on your computer.
4. DOS interprets and translates the software you have on your computer.
5. DOS gives you access to all its function (i.e. saving, copying, and printing files).

Set the Date and Time

Most computers on campus have an internal clock that will automatically set the date and time for you when you turn the computer on. However, if your computer does not have this feature or your computer has two floppy drives, you will need to do the following steps to set the date and time.

Directions:

1. Type the date like this: 1-15-97
2. Press the return key (enter key).
3. Type the time like this: 8:46
4. Press return.
5. Notice that the C:\> prompt will appear.

DOS marks the date and time on everything you do. It is important to periodically check the date and time if you have an internal clock to see if it is correct. If you have a two floppy system, it is important to enter the correct date and time when you turn the computer on.

NOTE: Baynan sets the date and time for you automatically when you Login.

Check the Date and Time

DOS will let you check or change the date and time once it has been set. The procedure to do this is as follows:

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Directions:

1. Type: date and press return.
2. If the correct date is displayed, simply press return. If the date is incorrect, type the correct date and press return.
3. Type: time and press return.
4. If the correct time is displayed, simply press return. If the time is incorrect, type the correct time and press return.

Directory Command

The DIRECTORY command is like a table of contents in a book. This directory will list the following information:

• Filenames
• File extensions
• Size of each file
• Date and time the file was last updated

Directions:

1. At the C:\> type: dir and press return.
2. The list of files will scroll up and off the screen.

NOTE: At the end of the listing, there is a line that shows the number of bytes free on the hard drive.

Scroll Through the Directory Listing

When you type the DIR command and press return, the files begin to scroll vertically on your screen. If you have a lot of files it is difficult to read each one. By holding down the Control Key (CTRL) and the letter S at the same time, you are able to freeze the listing to view your files. When you are finished, press the spacebar for the list to continue.

NOTE: You must return to the C:\> before entering your next command.

Pause a Directory Listing

You can add a PAUSE command to your directory command which will allow you to view your directory one screen at a time.

Directions:

1. Type: dir/p and press return.
2. The screen freezes after it fills the screen with the files that are listed first in the directory.
3. Press the spacebar to continue listing you files.
4. Continue to press the spacebar until you return back to the C:\> prompt.

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View a Wide Listing of Files

When you need to quickly view your files, you can add a /W to the directory command. This will display your files into five columns on the screen.

Directions:

1. Type: dir/w and press return.
2. DOS will list only the name of you file and the file extension on the screen.

NOTE: Use this command when you are not concerned with looking at the file size or the date it was created.

Recall a DOS Command

The F3 function key can be used to recall the last DOS command you typed in. If you would like to retrieve a previously entered command, you can also press the up arrow key continuously until you reach the desired command you were looking for.

NOTE: You can also type out each letter in your last command by using the right arrow key or the right cursor key. After you use the F3 key to recall a command, you can use the backspace key to edit any part of the command or add to your command.

Print a Directory Listing

You can print a list of your files in your directory by instructing DOS to send the information to your printer.

Directions:

1. Type: dir>prn and press return.
2. The > symbol stands for output. The PRN stands for printer.

NOTE: You can print a wide listing of your files by typing dir/w>prn

Laserjet printers and other sheetfeeder printers will not eject the page after the dir>prn command. You must take the printer off-line and press the form feed button. Remember to press the on-line button when you are done in order to continue using the printer.

Check for a Single File

Instead of using the directory command to look for one particular file, you can type the name of the file after the DIR command at the C:\> prompt.

Directions:

1. Make sure that you are at your C:\> prompt.
2. Type: dir format.com (filename.extension) and press return.
3. The screen will display a listing of the file or a file not found message.

Check for a Group of Files

The * symbol is referred to as a wildcard and stands for any character or group of characters. This is helpful when you want to list files that start with a particular letter or group.

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Directions:

1. Type: dir c* and press return.
2. All filenames that begin with the letter C will be listed.
3. Press the F3 key.
4. Backspace twice and replace C* with A* and press return.
5. All filenames that begin with the letter A are listed.

List Files with the Same Extensions
You can also use the wildcard character * to look for a group of files with the same extension.

Directions:

1. Type: dir *.bat and press return.
2. All files with the .bat extension are listed.
3. Press the F3 key.
4. Backspace three times and replace the .bat extension with the .sys extension and press return.
5. All files with the .sys extension should now be listed.

Clear the Screen

When the screen get full of information, you may want to clear it. To do this, type CLS at the C:\> prompt and press return.

Create a File with DOS

Directions:

1. Type: copy con Quick.ltr and press return.
2. Type this message in the following format:

Bob

Sales are up 15%.

Good Job!

Craig

3. Press the F6 function key (^Z) and press return.
4. DOS gives you a message that 1 File(s) has been copied.
5. Type: dir q* and press return.
6. Now you can see the list of files beginning with the letter Q.

NOTE: You can also use the COPY command to print a file by typing: copy quick.ltr prn and press return.

Copy a File

You can use the COPY command to copy one file to another.

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Directions:

1. Type: copy quick.ltr quick2.ltr and press return.
2. DOS will tell you one file has been copied.
3. Type: dir q* and press return.
4. You should have two files listed with different names.

NOTE: Filenames cannot be more than eight characters in length. File extensions cannot be more than three characters in length.

Copy a File with a New Extension

You can also use the COPY command to copy the file with a different filename extension.

Directions:

1. Type: copy quick.ltr quick.bac and press return.
2. Type: dir q* and press return.
3. Three files should be listed.

Type a File with DOS

If you need to check the contents of a particular file or any DOS file, you will need to use the TYPE command.

Directions:

1. Type: type quick2.ltr and press return.
2. DOS prints the contents of the file.

NOTE: Never use the TYPE command with files that have the .com, .exe, .sys, and .bas extensions. These are program files and will only display junk on the screen.

Rename a File

The RENAME command lets you rename a previous file with a new name.

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Directions:

1. Type: ren quick2.ltr sales.ltr and press return.
2. Type: dir *.ltr and press return.
3. DOS lists only two files that have the .ltr extension: quick.ltr and sales.ltr.

Rename a Group of Files

With the wildcard character *, you can also use the RENAME command to change a group of files.

Directions:

1. Type: ren *.ltr *.bob and press return.
2. Type: dir *.bob and press return.
3. You should have two files listed with a .bob extension.
4. Type: dir *.ltr and press return.
5. There should be no files found with .ltr extensions.

NOTE: You can also rename a group of files that have the same name but different extensions. Type the RENAME command then the filename followed by the dot and the wildcard, space and then type the new filename followed by a dot and the wildcard character. It will look like this: filename.* newfilename.*

Create a Subdirectory

To create a subdirectory, you will need to use the MAKE DIRECTORY command, a.k.a. MD. The MD command is useful for organizing files on your hard drive. With subdirectories, you can create and store related files together. For example, one subdirectory could be used to store all word processing files and another for all spreadsheet files.

Directions:

1. Type: md \info and press return.
2. Type: dir *. and press return.
3. Notice the *. will list only the subdirectories.

Move to a Subdirectory

Once you have created a subdirectory, to move to that directory, you will use the CHANGE DIRECTORY command, a.k.a. CD.

Directions:

1. Type: cd \info and press return.
2. Type: cd and press return.
3. The name of the directory is listed.

Set the DOS Prompt

You can set or change the standard system prompt to display the name of the directory or subdirectory you are currently working in.

Directions:

1. Type: prompt $p $g and press return.
2. The DOS prompt tells you that you are working in the C directory (drive) and in the Info subdirectory.
3. Type: dir and press return.
4. The single dot stands for the current directory. The double dots stand for the parent directory (root). The dots are often referred to as place markers.

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Move to the Parent Directory

DOS has a quick way to move from the current directory back to the parent directory.

Directions:

1. Type: cd.. and press return.
2. You will return back to the C:\> prompt.

Copy a File into a Subdirectory

The COPY command lets you copy files from one directory to another.

Directions:

1. Type: copy sales.bob \info and press return.
2. Type: dir \info and press return.
3. Notice that a copy of Sales.bob is copied into the subdirectory Info. The original file is also in the root directory.

Copy a Group of Files into a Subdirectory
When copying a group of files from the root directory into a subdirectory, it is necessary to use the wildcard character * along with the COPY command.

Directions:

1. Type: copy quick.* \info and press return.
2. DOS will list the files being copied.
3. Type: dir \info and press return.
4. Three files should be listed in the Info subdirectory.

List Files in a Subdirectory

The CHANGE DIRECTORY, a.k.a. CD, command will let you list files in your subdirectory from your hard drive.

Directions:

1. Type: cd \info and press return.
2. Type: dir and press return.
3. All files in the Info subdirectory are listed.

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List Files in the Root from a Subdirectory

The DIRECTORY command is also used to get a listing of all the files in the root directory while in a subdirectory. The backslash character \ represents the root directory.

Directions:

1. Type: dir \ and press return.
2. All the files in the root directory are listed.

Select the Directory List
To look for a specific filename extension, you can use the SELECTED DIRECTORY command.

Directions:

1. Type: dir \*.bat and press return.
2. Only the files with the .bat extensions are listed.
3. Press the F3 key.
4. Backspace three times.
5. Type: sys and press return.
6. Now only the files with the .sys extensions are listed.

List Subdirectories

Directions:

1. Type: dir \*. and press return.
2. All the subdirectories are listed.

NOTE: The backslash character \ directs DOS to read from the root directory. The *. requests the listing of the subdirectories.

Delete a Single File

Periodically it is a good idea to delete files from the hard disk which are no longer needed or used. DOS makes it easy to remove these files with the DELETE command, a.k.a. DEL.

Directions:

1. Type: cd.. and press return.
2. The prompt shows you that you are back in the root directory.
3. Type: del sales.bob and press return.
4. Type: dir Sales.bob and press return.
5. Sales.bob is no longer listed because it has been deleted.

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Delete a Group of Files

By using the wildcard character * you can delete a group of files from you hard drive.

Directions:

1. Type: del quick.* and press return.
2. Type: dir quick.* and press return.
3. All Quick files have been deleted.

Delete all Files in a Subdirectory

There are two rules you will need to follow before removing a subdirectory.

RULE 1: All files in the subdirectory must be deleted.

NOTE: Never type DEL *.* when you are in the root directory. It will destroy all DOS files that are necessary to boot and operate the computer.

Directions:

1. Type: cd \info and press return.
2. Type: dir and press return.
3. Three files should be listed.
4. Type: del *.* and press return.
5. DOS will ask you if you are sure? (Y/N)
6. Type: Y and press enter.

Now that your subdirectory is empty, you can delete the subdirectory (see rule 2 below).

Remove a Subdirectory

RULE 2: You cannot be in the subdirectory that you wish to remove. You will need to return to the root directory (C:\> prompt).

Directions:

1. Type: cd.. and press return.
2. You should be back in the root directory.
3. Type: rd \info and press return.
4. Type: dir *. and press return.
5. Notice that the Info subdirectory is no longer listed.

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Format a Floppy Disk

Before you can use a disk, you must format it.

Directions:

1. At the C:\> prompt type: format a:
2. The A drive will be the drive that you insert your disk into; hence, the a: after the Format command and press return.
3. You will be prompted with the message: "Insert new diskette for drive A: and press enter when ready."
4. Now insert the disk you wish to format and press return.
5. Once this formatting process is done, the following message will appear: "Format Completed." Then you will be prompted for a volume label. Simply press return again.
6. Now you will be asked if you would like to format another disk (Y/N)? Press N.

NOTE: If you receive a message like: "Track 0 bad" or "Disk unusable," your disk may be the wrong capacity. You can get help with this error message by typing:

Help Format

Change the Default Drive

To change from your hard drive to a floppy drive, you will need to indicate this change as follows:

Directions:

1. Put a floppy disk into drive A.
2. Type: a: and press return.
3. Your prompt should change to A:\>
4. Type: dir and press return.
5. You are now able to see all the files on the floppy.
6. To change back to your hard drive, you will need to reverse this procedure.
7. Type: c: and press return. Now your prompt should be C:\>

Diskcopy Command

Sometimes there is a need to copy all the files on one floppy diskette to another floppy. First you will need a blank formatted disk (refer to section on formatting disks.)

Directions:

1. Type: diskcopy a: a: and press return.
2. When asked to put in the source disk, put in the diskette that has the information you want to copy into drive A and press return.
3. Wait a few seconds. When asked to insert a target disk, take out the diskette from drive A and insert the blank floppy disk and press return.
4. Once this process is complete, you will be prompted to write to another duplicate diskette (Y/N). Press N.
5. Then you will be prompted to copy another disk (Y/N)? Press N.

NOTE: If your machine has two floppy disk drives, insert the original (source) disk into drive A and the blank (target) disk into drive B. Then type: DISKCOPY A: B:

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Copying a File from the Hard Drive to a Floppy Disk

Sometimes there is a need to copy a file from the hard drive onto a floppy disk. This is helpful if you would like to have an extra copy of a certain file as a backup or to transport the copied file to another computer.

Directions:

1. Type: copy <insert filename here> a: and press return.
2. Wait for a few seconds, notice the red light on the floppy drive. Never attempt to remove a disk from the disk drive while this red light is on.
3. To check to see if the file was copied, type a: at the C:\> prompt and press return.
4. Type: dir and press return.

What is a Database?

One of the technology terms that most people have become accustomed to hearing either at work or while surfing the internet is the database. The database used to be an extremely technical term, however with the rise of computer systems and information technology throughout our culture, the database has become a household term.

The definition of a database is a structured collection of records or data that is stored in a computer system. In order for a database to be truly functional, it must not only store large amounts of records well, but be accessed easily. In addition, new information and changes should also be fairly easy to input. In order to have a highly efficient database system, you need to incorporate a program that manages the queries and information stored on the system. This is usually referred to as DBMS or a Database Management System . Besides these features, all databases that are created should be built with high data integrity and the ability to recover data if hardware fails.

Types of Databases

There are several common types of databases; each type of database has its own data model (how the data is structured). They include; Flat Model, Hierarchical Model, Relational Model and Network Model.

The Flat Model Database

In a flat model database, there is a two dimensional (flat structure) array of data. For instance, there is one column of information and within this column it is assumed that each data item will be related to the other. For instance, a flat model database includes only zip codes. Within the database, there will only be one column and each new row within that one column will be a new zip code.

The Hierarchical Model Database

The hierarchical model database resembles a tree like structure, such as how Microsoft Windows organizes folders and files. In a hierarchical model database, each upward link is nested in order to keep data organized in a particular order on a same level list. For instance, a hierarchal database of sales, may list each days sales as a separate file. Within this nested file are all of the sales (same types of data) for the day.

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The Network Model

In a network model, the defining feature is that a record is stored with a link to other records - in effect networked. These networks (or sometimes referred to as pointers) can be a variety of different types of information such as node numbers or even a disk address.

The Relational Model

The relational model is the most popular type of database and an extremely powerful tool, not only to store information, but to access it as well. Relational databases  are organized as tables. The beauty of a table is that the information can be accessed or added without reorganizing the tables. A table can have many records and each record can have many fields.

Tables are sometimes called a relation. For instance, a company can have a database called customer orders, within this database will be several different tables or relations all relating to customer orders. Tables can include customer information (name, address, contact, info, customer number, etc) and other tables (relations) such as orders that the customer previously bought (this can include item number, item description, payment amount, payment method, etc). It should be noted that every record (group of fields) in a relational database has its own primary key. A primary key is a unique field that makes it easy to identify a record.

Relational databases use a program interface called SQL or Standard Query Language. SQL is currently used on practically all relational databases. Relational databases are extremely easy to customize to fit almost any kind of data storage. You can easily create relations for items that you sell, employees that work for your company, etc.

Accessing Information Using a Database

While storing data is a great feature of databases, for many database users the most important feature is quick and simple retrieval of information. In a relational database, it is extremely easy to pull up information regarding an employee, but relational databases also add the power of running queries. Queries are requests to pull specific types of information and either show them in their natural state or create a report using the data. For instance, if you had a database of employees and it included tables such as salary and job description, you can easily run a query of which jobs pay over a certain amount. No matter what kind of information you store on your database, queries can be created using SQL to help answer important questions.

Storing a Database

Databases can be very small (less than 1 MB) or extremely large and complicated (terabytes as in many government databases), however all databases are usually stored and located on hard disk or other types of storage devices and are accessed via computer. Large databases may require separate servers and locations, however many small databases can fit easily as files located on your computer's hard drive.

Securing a Database

Obviously, many databases store confidential and important information that should not be easily accessed by just anyone. Many databases require passwords and other security features in order to access the information. While some databases can be accessed via the internet through a network, other databases are closed systems and can only be accessed on site.  

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What is Database Hosting?

Database hosting providers deliver services that enable you to run data and database-intensive applications.  The underlying server can either be exclusively used for databases or other applications such as a website, all of which depend on your requirements.  This type of hosting is particularly useful for clients with a need to run programs such as CRM (Customer Relation Management) and ERP (Enterprise Resource Planning) software or custom-built applications.  Because they typically require more memory, customers often turn to database hosting solutions to increase the speed and reliability of their applications.

The Benefits of Database Hosting

A database server is an intriguing piece of software as it has the ability to store tons of information.  Unlike the average web server application, this type of server stores information in tables, which consists of columns and rows.  Through the use of a database, users can get the information they need in a matter of minutes.  For example, Google aims to keep its online searches below a half a second, all made possible by the more 3 trillion pages in its extensive database.  What makes a database such a good source of retrieval is that it mainly pulls data out of memory opposed to a hard disk drive, something it does up to 10 times faster.  Since the database is the core of the entire application, it tends to have more RAM and therefore, functions much faster than the typical web server.

Downside of Database Hosting

Similar to the software application side of a dedicated server, a database server calls for heavy administration.  For this reason, it may be a good idea to go with a managed service if you lack the experience this type of hosting requires.  A managed service will get you a package where the hosting provider handles some or even all of the database server administration on your behalf.  These services generally range from simple management operations to more demanding tasks such as system security patching.  If your plans call for a complete database server but you do not have time or skill needed to maintain it, you might be interested in a managed solution or at least one that allows you to purchase some sort of service upgrades to ease the pain of administration.

Do You Really Need Database Hosting?

While there are tremendous benefits involved, database hosting is not made for everyone.  For example, if you simply have a need to run a small online business with shopping carts and other e-commerce features, you can probably get by with a normal web hosting package that provides you with access to multiple databases opposed to the entire server.  It is imperative to keep in mind that there are significant differences between database hosting and simply having access to one, or even multiple databases.  In this type of arrangement, the database system is the most essential element of the entire application as this is where all the processing is handled.   True, there are similarities, but the MySQL database server is an entirely different animal than the Apache web server.

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What is Database Normalization?

Database normalization is the process of organizing data into distinct and unique sets.

The purposes of normalization are to:

• Reduce or eliminate storage of duplicate data
• Organize data into an efficient and logical structure

The process of normalization involves determining what data should be stored in each database table.

By tradition, the process of normalization involves working through well-defined steps, called normal forms.

In First Normal Form (1NF) you eliminate duplicate columns from the same table, create separate tables for each group of related data, and identify each row with a unique column or set of columns (the primary keys).

In Second Normal Form (2NF) you remove subsets of data that apply to multiple rows of a table, place them in separate tables, and create relationships between these new tables and the original tables through the use of foreign keys.

In Third Normal Form (3NF) you remove columns that are not dependent upon the primary key.

Additional normal forms have been defined, but are less commonly utilized. These advanced normal forms include Fourth Normal Form (4NF), Fifth Normal Form (5NF), Boyce Codd Normal Form (BCNF), and Domain-Key Normal Form (DK/NF).        

Computer systems of today have been built and programmed to perform multiple task at the same time. While running a user program, a computer can also be reading a disk and printing on a terminal or printer.  These are computers with multitasking operating system.  In a multiprogramming system, the CPU also switches from program to program, running each for tens or hundreds of milliseconds.  In all reality, at any instant of time, the CPU is running only one program, in the course of one second; it may work on several programs, thus giving the users the illusion of parallelism.

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WHAT IS A PROCESS?
 
According to Gary Nutt (2000). “A process is a schedulable unit of computation that requires certain entities (resources) be allocated to it in order for it to execute.  The process specifies its resources needs to the process manager part of the OS and the process manager then causes resources to be allocated and the process be executed in conjunction with the execution of other process. In other words, the process manager creates the process abstraction by implementing a software environment in which one program in execution can be distinguished from other programs in execution, and in which process are able to gain exclusive control resources or selectively share them with one another”.
 
The process manager as a major part of the operating system, provides software that creates models for each resource and for the way the process uses the CPU and other  
 
Process scheduling and multitasking allows multiple applications and other processes to run concurrently, using either co-operative multitasking or pre-emptive multitasking (William Buchanan) 2000.  This method requires that applications check the message queue periodically and give up control of the applications.
 
PROCESS MODEL
 
In the process model, all runnable software on the computer is organised in a sequential process.  A process is just an executing program, including the current values of the program counter, registers, and variables, each process as its own virtual CPU. In reality, the real CPU switches back and forth from process to process. To understand the system, it is easier to think about a collection of processes running parallel, than to try to keep track of how the CPU switches from program to program. This switching back and forth is called multiprogramming.
 
Due to the switching back and forth of the CPU among the processes, the rate at which a process performs its computation will not be uniform and probably not even reproducible if the same process is run again.  Thus process must not be programmed with built-in assumptions about timing. For example, an I/O process that starts a magnetic tape in motion, executes an idea loop 1000 times to let the tape getup to speed, and then issues a command to read the first record. If the CPU decides to switch to another process during the idea loop, the tape process might not run again until after the first record was already past the read head. When a process has critical real-time requirements like this, that is, certain events must occur within a specified number of milliseconds, special measures must be taken to ensure that they do occur. (Tenenbaum, 1992)

PROCESS HIERARCHIES
 
Operating systems, which operate on process concept, do provide some ways to create all the process needed. In systems designed for running single application, it may be possible to have all the process that will ever be needed be present when the system comes up. However, in most systems, a way is needed to create and destroy process as needed during operation.
 
In UNIX, processes are created by FORK system call, which create an identical copy of the calling process.  After the fork system call, the parent continues running, in parallel with the child. The parent can then fork off more children, so at any instant it may have several executing children.  The children can also execute FORK, so it is possible to get a whole tree of processes, arbitrarily deep.
 
In MS-DOS a system call exists to load a specified binary file into memory and execute it as a chid process. In contrast to UNIX, in MS-DOS this call suspends the parent until the child has finished execution, so the parent and the child do not run in parallel.
 
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PROCESS STATE
 
Processes are independent entities with each process having its own program counter and inter state but processes often need interaction with other processes.  A process may generate output that another process uses as input. In Tenenbaum (1992) example, in the shell command
 
Cat chapter1 chapter2 chapter3 | grep tree
 
The first process, running cat, concatenates and output three files.  The second process, running grep, selects all lines containing the word “tree.” Depending on the relative speeds of the two processes (which depends on both the relative complexity of the programs and how much CPU time each one has had), it may happen that grip is ready to run, but there is no output waiting for it. It must then block until some input is available.
 
A process is blocked logically because it cannot continue, but typically because it is waiting for input that is not yet available. It is also possible for a process that is conceptually ready and available to run to be stopped because the operating system has decided to allocate the CPU to another process for a while. These two conditions are completely different. In the first case, the suspension is inherent in the problem (you cannot process the user’s command line until it has been typed). In the second case, it is a technicality of the system (not enough CPUs to give each process its own private processor).  

The three basic states a process may be are:
 
Running state: at this state, a process is utilising the CPU at a particular point in time

Ready state: this is a state whereby, though the process is runable, it is temporarily stopped by the operating system to allow another process to run
 
Blocked state: it is a state whereby a process cannot run until some external events happens, e.g. a process waiting for another process to provide input.

The three states are illustrated in the diagram below

Transitions between processes states, in running, ready and blocked

Four transitions are possible among these three states. Transition 1 occurs when a process discovers that it cannot continue. This process in some system execute a system call, BLOCK, to get into blocked state. Also when a process reads from a pipe or special files and there is no input available, the process is automatically blocked. Transition 2 and 3 occur through process scheduling without the process knowing about it. Transition 2 occurs when the system decides that that the process has run long enough, and it is time to let another process run on the CPU. Transition 3 occurs when all the other processes have had their share and it is time for the first process to run again. Transition 4 occurs when the external event for which a process was waiting happens. if no other process is running at that instant , transition 3 will be triggered immediately, and the process will start running; otherwise it may have to wait in ready state for a little while until CPU is available.