Category Archives: Operating system


Difference Between RAM and ROM…………

RAM is a volatile memory type, which means that it loses its content once power is removed. This is the reason why it cannot replace ROM, which retains its content even when not powered. The downside of ROM is its much slower speed. Using it to replace RAM would make a computer perform very slow.

Nowadays, RAM is seen mainly as the primary memory of computers and other gadgets like smartphones and tablets. In portable gadgets, the internal memory reserved for applications is often referred to as ROM. But in computers, ROMs retains its original meaning. The chip used to hold the BIOS is a ROM as it isn’t routinely written to; but it is sometimes updated. Optical drives are also called ROMS (i.e. CD-ROM and DVD-ROM) as they do read discs that cannot be written to; but most optical drives also have the ability to write to blank discs.

ROM is used for storing programs while RAM is used by programs to hold temporary data
RAM is a type of memory that can be accessed non-sequentially while ROM is a type of memory that is only read in typical operation
ROM is non-volatile while RAM is volatile
RAM is considerably faster than ROM




Limitation of firewall………..

The top 10 firewall limitations :

  • Viruses. Not all firewalls offer full protection against computer viruses as there are many ways to encode files and transfer them over the Internet.
  • Attacks. Firewalls can’t protect against attacks that don’t go through the firewall. For example, your firewall may restrict access from the Internet, but may not protect your equipment from dial in access to your computer systems.
  • Architecture. Consistent overall organization security architecture: Firewalls reflect the overall level of security in the network. An architecture that depends upon one method of security or one security mechanism has a single point of failure. A failure in its entirety, or through a software application bug, may open the company to intruders.
  • Configuration. A firewall can’t tell you if it has been incorrectly configured. Trained professionals have the talent and experience to properly configure firewalls.
  • Monitoring. Some firewalls can notify you if a perceived threat occurs, however, they can’t notify you if someone has hacked into your network. Many organizations find they need additional hardware, software and network monitoring tools.
  • Encryption. While firewalls and Virtual Private Networks (VPNs) are helpful, they don’t encrypt confidential documents and E-mail messages sent within your organization or to outside business contacts. Formalized procedures and tools are needed to provide protection of your confidential documents and electronic communications.
  • Management. Firewalls stop incoming threats but organizations still require a formalized management, destruction, and archival procedure for their electronic documents. Electronic messages taken out of context can put an organization in financial jeopardy.
  • Masquerading. Firewalls can’t stop a hacker from masquerading as an employee. Hackers have a number of ways to acquire user ids and related passwords.
  • Policies. Firewalls are not a replacement for a strong Security Policy and Procedure Manual. An organization’s security structure is only as strong as its weakest link. Security professionals have the experience needed to help protect your reputation.
  • Vulnerabilities. Like a deadbolt lock on a front door, a firewall can’t tell you if there are other vulnerabilities that might allow a hacker access to your internal network. Organizations frequently rely on Security Vulnerability Assessments to help them manage their risks.




Segmentation is the method of separating or segmenting your data into groups. For instance, if you want to find out how your social media efforts are working, you can check the Analytics panel on the Woopra Desktop Client under Referrers for various social media networks and groups. To analyze specific information on a referrer or visitor, right click on them and choose Analyze to create a custom filtered report.

A segment is a defined portion or section of something larger such as a database, geometric object, or network. The term is used in database management, graphics, and communications.

In a database , a segment is a portion of the database that consists of one or moreextent s. Each extent is in turn made up of units called block s, which are the smallest database units. One or more segments make up a table space .



Difference Between DOS and UNIX………….

The primary advantage of UNIX over DOS is its security. Although it greatly adds to the complexity of the operating system, it is essential for an operating system that is mainly used as a server. DOS was meant to be an operating system for personal computers and sacrificed security to make it easier to use.

There are a couple of usage differences between DOS and UNIX. The first difference is the case sensitivity of UNIX but not DOS. So in UNIX, the files example.exa and Example.exa can exist in the same folder but not in DOS. As long as the filename has the same characters, they would be considered as identical by DOS. The second, and less consequential of the two, is the use of slashes. DOS uses backslashes (\) to separate directories. In contrast, UNIX uses forward slashes (/) in its directory structure. These are just things to remember if you are familiar with one or the other.

The differences between UNIX and DOS are largely attributed to what they were meant to do. Nowadays, UNIX is still used with servers due to its light and performance-oriented nature. Only a handful of people have the ability to work with it. Although DOS was initially meant for personal computers, it has been replaced by more intuitive and easier-to-use operating systems like Windows, OS X, and even Linux. The only niche where DOS is still used is in embedded systems largely due to its very minimal requirements.



Intel Mobile Processor Core i7 vs Core i7 Extreme Edition………….

The Core i7 line-up of processors from Intel is already well known to be very fast. Still, Intel releases processors for utmost performance. These are known as the Core i7 Extreme Edition. The most notable difference between the ordinary Core i7 and the Core i7 Extreme Edition is the unlocked multiplier. The multiplier is directly related to the actual speed that the processor works at. Given an external clock of 133Mhz, the 990X (Extreme Edition) has a multiplier of 26, which results in an actual speed of 3.47Ghz. For most processors, the multiplier is locked to a certain value to prevent users from tampering with it. In the Core i7 Extreme Edition, the unlocked multiplier lends itself nicely to overclocking. With the example above, changing the multiplier to 27 would make the processor operate at almost 3.6Ghz. Proper care should be taken in overclocking a processor as the practice can easily destroy your hardware.

Another major difference between the two is price. The latest Core i7 Extreme Edition processor always claims the $999 price tag. For that amount, most people can already build a complete computer, maybe even two. If price is a factor in choosing or building your computer, an ordinary Core i7 can cost hundreds of dollars less with only a minor decrease in performance.



Change Text on XP Start Button………….

Step 1 – Modify Explorer.exe File

In order to make the changes, the file explorer.exe located at C:\Windows needs to be edited. Since explorer.exe is a binary file it requires a special editor. For purposes of this article I have used Resource Hacker. Resource HackerTM is a freeware utility to view, modify, rename, add, delete and extract resources in 32bit Windows executables and resource files (*.res). It incorporates an internal resource script compiler and decompiler and works on Microsoft Windows 95/98/ME, Windows NT, Windows 2000 and Windows XP operating systems.

get this from h**p://

The first step is to make a backup copy of the file explorer.exe located at C:\Windows\explorer. Place it in a folder somewhere on your hard drive where it will be safe. Start Resource Hacker and open explorer.exe located at C:\Windows\explorer.exe.

The category we are going to be using is “String Table”. Expand it by clicking the plus sign then navigate down to and expand string 37 followed by highlighting 1033. If you are using the Classic Layout rather than the XP Layout, use number 38. The right hand pane will display the stringtable. We’re going to modify item 578, currently showing the word “start” just as it displays on the current Start button.

There is no magic here. Just double click on the word “start” so that it’s highlighted, making sure the quotation marks are not part of the highlight. They need to remain in place, surrounding the new text that you’ll type. Go ahead and type your new entry. In my case I used Click Me!

You’ll notice that after the new text string has been entered the Compile Script button that was grayed out is now active. I won’t get into what’s involved in compiling a script, but suffice it to say it’s going to make this exercise worthwhile. Click Compile Script and then save the altered file using the Save As command on the File Menu. Do not use the Save command – Make sure to use the Save As command and choose a name for the file. Save the newly named file to C:\Windows.

Step 2 – Modify the Registry

!!!make a backup of your registry before making changes!!!

Now that the modified explorer.exe has been created it’s necessary to modify the registry so the file will be recognized when the user logs on to the system. If you don’t know how to access the registry I’m not sure this article is for you, but just in case it’s a temporary memory lapse, go to Start (soon to be something else) Run and type regedit in the Open field. Navigate to:

HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\ Windows NT\ CurrentVersion\ Winlogon

In the right pane, double click the “Shell” entry to open the Edit String dialog box. In Value data: line, enter the name that was used to save the modified explorer.exe file. Click OK.

Close Registry Editor and either log off the system and log back in, or reboot the entire system if that’s your preference. If all went as planned you should see your new Start button with the revised text.[/b]



What is an Operating System…………..

Every computer must have an operating system. Without one your computer is pretty much useless. The operating system is like your computer’s manager. It is the program that manages all the other programs on your computer. The operating system performs the following tasks in addition to many others:

When several programs are open it determines which programs should run and in what order.

It determines the amount of time each program should get.

It manages the sharing of memory among the many programs on your computer.

It handles input and output.

It sends messages to both the program and the user concerning the status of operations and any errors that may have occurred.

The list of responsibilities the operating system has is much longer than the one above. The main thing you need to know is that you cannot use your computer if you don’t have an operating system. Fortunately, the system works in the background and most of the time you will not be aware of what it is doing.

As we continue throughout the textbook you will learn and appreciate more about what an operating system is and what it can do. Back in the early days of computers when there was no such thing as an operating system a computer user could only run one program at a time. Each time they wanted to use the program they had to load one they had written and if something went wrong during the process the user would have to start all over from the beginning. This is because there was nothing within the computer to manage it the way an operating system does today.



Installing Red Hat Enterprise Linux in VMware-workstation.

This section covers installing a fully virtualized Red Hat Enterprise Linux 5 guest.  the steps are interchangeable and different steps are noted.

Procedure : Creating a fully virtualized Red Hat Enterprise Linux 5 guest with virt-manager

1.Start the new virtual machine wizard

Pressing the New button starts the virtual machine creation wizard.

Press Next to continue.

2.Name the virtual machine

Provide a name for your virtualized guest. Punctuation and whitespace characters are not permitted in versions before Red Hat Enterprise Linux 5.5. Red Hat Enterprise Linux 5.5 adds support for ‘_‘, ‘.‘ and ‘‘ characters.

Press Next to continue.

3.Choose a virtualization method

Choose the virtualization method for the virtualized guest. Note you can only select an installed virtualization method.

Press Next to continue.

4.Select the installation method

Red Hat Enterprise Linux can be installed using one of the following methods:

  • local install media, either an ISO image or physical optical media.
  • Select Network install tree if you have the installation tree for Red Hat Enterprise Linux hosted somewhere on your network via HTTP, FTP or NFS.
  • PXE can be used if you have a PXE server configured for booting Red Hat Enterprise Linux installation media. Configuring a sever to PXE boot a Red Hat Enterprise Linux installation is not covered by this guide. However, most of the installation steps are the same after the media boots.

Set OS Type to Linux and OS Variant to Red Hat Enterprise Linux 5 as shown in the screenshot.

Press Next to continue.

5.Locate installation media

Select ISO image location or CD-ROM or DVD device. This example uses an ISO file image of the Red Hat Enterprise Linux installation DVD.

  1. Press the Browse button.
  2. Search to the location of the ISO file and select the ISO image. Press Open to confirm your selection.
  3. The file is selected and ready to install.

Press Next to continue.

6.Storage setup

Assign a physical storage device (Block device) or a file-based image (File). File-based images must be stored in the /var/lib/libvirt/images/ directory. Assign sufficient space for your virtualized guest and any applications the guest requires.

Press Next to continue.

7.Network setup

Select either Virtual network or Shared physical device.

The virtual network option uses Network Address Translation (NAT) to share the default network device with the virtualized guest. Use the virtual network option for wireless networks.

The shared physical device option uses a network bond to give the virtualized guest full access to a network device.

Press Next to continue.

8.Memory and CPU allocation

The Memory and CPU Allocation window displays. Choose appropriate values for the virtualized CPUs and RAM allocation. These values affect the host’s and guest’s performance.

Virtualized guests require sufficient physical memory (RAM) to run efficiently and effectively. Choose a memory value which suits your guest operating system and application requirements. Remember, guests use physical RAM. Running too many guests or leaving insufficient memory for the host system results in significant usage of virtual memory and swapping. Virtual memory is significantly slower which causes degraded system performance and responsiveness. Ensure you allocate sufficient memory for all guests and the host to operate effectively.

Assign sufficient virtual CPUs for the virtualized guest. If the guest runs a multithreaded application, assign the number of virtualized CPUs the guest will require to run efficiently. Do not assign more virtual CPUs than there are physical processors (or hyper-threads) available on the host system. It is possible to over allocate virtual processors, however, over allocating has a significant, negative effect on guest and host performance due to processor context switching overheads.

Press Next to continue.

9.Verify and start guest installation

Verify the configuration.

Press Finish to start the guest installation procedure.

10.Installing Red Hat Enterprise Linux

Complete the Red Hat Enterprise Linux 5 installation sequence.

A fully virtualized Red Hat Enterprise Linux 5 Guest is now installed.


What is Linux……..

Linux is a free Unix-type operating system for computer devices. The operating system is what makes the hardware work together with the software. The OS is the interface that allows you to do the things you want with your computer. Linux is freely available to everyone. OS X and Windows are other widely used OS.

Linux gives you a graphical interface that makes it easy to use your computer, yet it still allows those with know-how to change settings by adjusting 0 to 1.

It is only the kernel that is named Linux, the rest of the OS are GNU tools. A package with the kernel and the needed tools make up a Linux distribution. Mandrake , SUSE Linux,Gentoo and Redhat are some of the many variants. GNU/Linux OS can be used on a large number of boxes, including i386+ , Alpha, PowerPC and Sparc.


Differences Between Paging and Segmentation………..



Physical unit

Logical unit


invisible to the user programs

Visible to the user programs


Fixed length

Variable length


virtual memory scheme

memory management scheme


one-dimensional address

Two dimensional address

Address space

#Page, frame#

Limit , base


Not easy



Not easy



Internal fragment

External fragment


Static linking

Dynamic linking


Dynamic loading

Dynamic loading




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