Prior to the introduction of SSH in the Cisco IOS, the only remote login protocol was Telnet. Although quite functional, Telnet is a non-secure protocol in which the entire session, including authentication, is in clear text and thus subject to snooping.
SSH is both a protocol and an application that replaces Telnet and provides an encrypted connection for remote administration of a Cisco network device such as a router, switch, or security appliance.
The Cisco IOS includes both an SSH server and an SSH client. This document is concerned only with the configuration of the SSH server component.
Prerequisites
Software
The SSH server component requires that you have an IPSec (DES or 3DES) encryption software image from Cisco IOS Release 12.1(1)T or later installed on your router. Advanced IP services images include the IPSec component. This document was written using c2800nm-advipservicesk9-mz.123-14.T5.bin.
Pre-configuration
You must configure a hostname and a domain name on your router. For example:
router#
router#conf t
Enter configuration commands, one per line. End with CNTL/Z.
router01(config)#hostname router01
router01(config)#ip domain-name soundtraining.net
You must also generate an RSA keypair for your router which automatically enables SSH. In the following example, note how the keypair is named for the combination of hostname and domain name that were previously configured. The modulus represents the key length. Cisco recommends a minimum key length of 1024 bits (even though the default key length is 512 bits):
router01(config)#
router01(config)#crypto key generate rsa
The name for the keys will be: router01.soundtraining.net
Choose the size of the key modulus in the range of 360 to 2048 for your General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes.
How many bits in the modulus [512]: 1024
% Generating 1024 bit RSA keys ...[OK]
Finally, you must either use an AAA server such as a RADIUS or TACACS+ server or create a local user database to authenticate remote users and enable authentication on the terminal lines. For the purpose of this document, we'll create a local user database on the router. In the following example, the user "donc" was created with a privilege level of 15 (the maximum allowed) and given an encrypted password of "p@ss5678". (The command "secret" followed by "0" tells the router to encrypt the following plaintext password. In the router's running configuration, the password would not be human readable.) We also used line configuration mode to tell the router to use its local user database for authentication (login local) on terminals lines 0-4.
router01(config)#username donc privilege 15 secret 0 p@ss5678
router01(config)#line vty 0 4
router01(config-line)#login local
Enabling SSH
To enable SSH, you must tell the router which keypair to use. Optionally, you can configure the SSH version (it defaults to SSH version 1), authentication timeout values, and several other parameters. In the following example, we told the router to use the previously created keypair and to use SSH version 2:
router01(config)#
router01(config)#ip ssh version 2
router01(config)#ip ssh rsa keypair-name router01.soundtraining.net
You can now log on to your router securely using an SSH client such as TeraTerm.
Viewing SSH Configurations and Connections
You can use the privileged mode commands "view ssh" and "view ip ssh" to view SSH configurations and connections (if any). In the following example, the SSHv1 configuration from a Cisco 871 router is verified using "show ip ssh" and a single SSHv1 connection is displayed using the command "show ssh". Notice that we did not enable SSHv2 on this router, so it defaulted to SSH version 1.99. Also note in the output of the "show ssh" command that SSH version 1 defaults to 3DES. SSHv2 supports AES, a more robust and efficient encryption technology. SSHv2 is also not subject to the same security exploits as SSHv1. soundtraining.net recommends the use of SSHv2 and disabling a dropback to SSHv1. Enabling SSHv2 disables SSHv1. This example is included only to demonstrate backwards compatibility:
router04#
router04#show ip ssh
SSH Enabled - version 1.99
Authentication timeout: 120 secs; Authentication retries: 3
router04#
router04#show ssh
Connection Version Encryption State Username
2 1.5 3DES Session started donc
%No SSHv2 server connections running.
router04#
You can also use the command "debug ip ssh" to troubleshoot SSH configurations.
Article Source: http://www.articlesbase.com/computers-articles/how-to-configure-ssh-secure-shell-for-remote-login-on-a-cisco-router-667048.html Article Tags: Ssh, Cisco Training, Telnet, Cisco Router Training, Network Cisco Training,
Remote Login
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Wednesday, December 17, 2008
Simple ways to add videos to you website
There are many different ways through webmasters look to increase the traffic on their websites and blogs. Increasing the number of visitors to their websites is quite reminiscent to adding more money into their pockets. Whether you have an online store to sell products or you simply earn by displaying advertisements on your website, number of visitors on a website work just like oxygen works for a human body.
Therefore, webmasters go to all limits in order to attract more visitors to their website. From adding articles to starting online contests, there are hoards of methods to pull more people to your website. One such tool to increase the popularity of your website is uploading quality videos to your website. Adding this feature will give a new dimension to your site, and will increase the interest of visitors. Apart from uploading videos to your own website, you can add them to several top websites that allow free submissions.
Uploading a video is not as difficult as it may seem on the first glance. Almost all of us have a digital camera of decent quality, which can be used to take pictures and videos of whatever you like. It is important to keep a steady hold on the camera as the success of your video depends on its quality. After successfully making videos, you can transfer them to your PC.
But your video right now is not in the finished form and you will require software to convert your video file's format into a compatible format. Although, most of the websites that allow video submission accept files in many formats but still you will have to get a file converter. The easiest way to get hold of one is through the internet, where you will easily find good file converter software for free.
MPG-Flash Converter software offers many features to convert file formats. This program compresses your video files into Flash format which is considered to be the best in video files. Then, all you have to do is to update your concerned webpage with a basic HTML code and upload these files to the hosting server system. All this might seem to be a bit hassling, but the results will be outstanding, as the videos will be viewed by viewers without the need to download them. After all, if your video does run at a good streaming rate, then you will lose your viewer immediately.
There are other programs that can convert videos to several other formats as well such as .AVI, .MPEG, .MOV and .SWI. A MOV-AVI file converter is also a great program that can convert files into any desired format. You can also choose to burn them on to your DVD as a built-in DVD authoring tool is also in it. A PSP Converter is also widely used by people who publish video files on the web. Just like audio files, it can convert video files to MP3 format as well.
Converting video is an easy job even for an inexperienced hand, as the features in these programs are self-explanatory. Whether you want to promote your website or you simply want to publish your memorable videos with friends and relatives, uploading videos is a fun job. Things to be kept in mind while uploading videos is that smaller size files will definitely run better. While publishing a video one should make sure that the rate at which it streams is decent as people haven’t got enough time to wait for hours to view your movie.
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How To Safely Download A Screensavers
To download a screen saver is relatively simple. They are usually executable files with the extension "exe". Click these files twice with the left mouse button and the installation begins. The menus window will pop-up asking the user a location for the screen saver to be installed. The standard is usually the folder 'Program Files' on drive C. Sometimes, these executable files are compressed using a popular program called WinZip. These files can be unpacked and extracted using the same programs, ie, WinZip. After unpacking now they can be installed just like the other executable files are installed.
The Internet is the spin-off with a screen saver, which can be easily downloaded and installed. These are organized according to different themes. Some of them are stars, sports, nature, entertainment, politics and the movies. Most of these topics to users the additional option of all screensaver with music and without music. Many users to download the screensaver with the music, and if they do not want the music, they are just off the speakers of their computer. If the speakers are integrated, they have left, click on the speaker icon in the corner right on the screen on the left side and click again to control the option that says, dumb, or drag the volume of the deepest Point possible.
It is easy to download and install the screensaver, it's almost as easy to install, a screen saver, which is infected with a virus or adware or spyware. Such a screen saver may be the data on the user's computer and can also be temporary or permanent loss of data. It may also be too many pop-ups to a court hearing and to the chaos at work. Therefore, it is important for downloading screen savers from a trust. Even after downloading a screen saver from a trust, it is necessary to examine the executable file that was downloaded the screen saver for the virus.
Review of a file against viruses is relatively simple. A click with the right-click the executable file, a pop-up menu. The menu has a scan with ... "Option. On the left, click the option makes the anti-virus software on the user's computer scan and other infections. If the scanner shows that the executable file is infected, should be deleted immediately. Sometimes, the Anti -Virus software is configured to take care of that automatically deleted.
As long as users are careful, they can download screensavers, how many they want and install. However, it is also important that the area of the screen saver on your computer so that the computer is not prevented, with the screen saver. And it is important to have a screen saver, the computer processor can be used with ease, without freezing or slowing down.
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Adobe Photoshop CS3: Top 5 Standout New Features
Upon first digging into Adobe Photoshop CS3, a few features have really popped out at me as incredibly useful. I would like to offer a brief overview of some of these new ways of attacking your creative challenges using the latest version of Adobe's flagship app. PsCS3 will run you about $649 to buy it outright if you do not own any previous versions. If you own Photoshop 7, CS, or CS2, you are eligible for upgrade pricing - looks like $199 for the upgrade. Check Adobe's store on their website for more info. For more information about what comes in the different versions of CS3, and what your suite configuration options are, see my previous post.
My current favorite five new PsCS3 features in order are:
1. Nondestructive Smart Filters
2. Quick Selection Tool & Refine Edge
3. Photomerge with advanced alignment and blending
4. Automatic layer alignment and blending
5. Vanishing Point with adjustable angle
Feature Overviews:
* Nondestructive Smart Filters
Adobe has finally given us non-linear, nondestructive filters. Can I just say "HOORAY!" In the past, you applied filters and effects in a linear order: one filter would alter your image, and the second filter would alter your now altered image, and a third filter would alter the altered altered image. The problem with that workflow is that if you decide you want to slightly tweak the second filter, you'd have to either undo back to that point (losing your subsequent edits), or use the history palette to step directly "back in time" to the point before you added the second filter, add your "revised" second filter and then add your third manually. All too often, you don't quite remember what exact parameters you had set on that third one - or worse, your real world project involved applying 20 filters instead of the 3 in my example and changing the second filter would mean redoing the 18 that follow it. What a drag. Because of this issue, people developed many work arounds (often involving saving off multiple "partially completed" versions of files all over your hard drive with iterative file names, hoping that if you needed to go back to a certain point in time you'd be able to figure out where you needed to be), and while these workarounds were clever and well-conceived in many cases, there was a perfect, real solution, waiting to happen.
The real solution to all this is what we have been given in CS3: Nondestructive Smart Filters. In this new version, each filter and effect that you apply to a layer, remains live and continually re-editable, in real time, and the parameters that you adjust will all cascade down through whatever subsequent filters or effects you might have added to your layer. These are savable, movable, copy and pastable, and most importantly scalable.
* Quick Selection tool & Refine Edge
A design mentor of mine once told me "Photoshop is all about the selection. You select something, and then you do something with the selection. Nothing more, nothing less. Remember that, and you'll never go wrong using this app." Almost 10 years later, I must say she was absolutely correct. Using Photoshop is all about "the selection." There are more tools in Photoshop for selecting than for any other single task.
As in just about every version of Photoshop that has ever been released, CS3 has made even greater strides in the area of "making your selection" than comes to memory in recent years. The new Quick Selection Tool used in combination with the Refine Edge palette is about the most helpful and clean way of selecting the edges of an object in your image that I have ever seen. This new revised Quick Selection tool is so smooth. You basically set the parameters of your Quick Selection tool - as if it were a brush - and paint the general area of your image edges (like trying to select just a kid and his soccer ball out of the photo of the big game) and Photoshop is watching what you do, and interpreting what you consider to be the general edges of what you are wanting to select and it figures out what's kid and ball and what's grass and goal posts and sky and crowd and selects just what you want it to. It's VERY fast and clean. Then, you can invoke the Refine Edge palette, and you have seemingly infinite control over exactly how the edges of that selection behave. Check out the palette to the right to get an idea of what you could do to "refine" that edge. With radius, feathering, smoothing, and various display settings, I believe this new combo will cut down on my masking and selecting time in a quantifiable way.
* Photomerge with advanced alignment and blending
Ever tried to stitch together a series of images that you took, that you intended to "put together" into a panorama? Even with some of the stand alone tools that have been available over the years—even those for doing quicktime VR's—are clunky and difficult to use - with mixed results at times. I have always wanted something built into Photoshop to let me do these "photo merges" - I never expected that Photoshop would actually be able to automatically do it for me. This feature floored me. The technologies involved in my number four choice "Automatic layer alignment and blending" are at work here in this feature as well, and the new auto layer alignment features in CS3 are far-reaching and crop up again and again in different areas of the application. It's really one of the revolutionary things about this new version.
All of the things that have made making panoramas a difficult task in the past are all done automatically. The primary among these being 1. those times when you have to actually distort, rotate, skew or transform one of your elements because the perspective is screwy, 2. those times when the sun or lighting or a window made the white balance, color space or over all wash of brightness and contrast different from one image to the next (especially when doing 360's) and of course 3. actually finding and aligning those overlapping areas of consecutive elements. Photoshop CS3 does these all for you and with surprisingly amazing results. It's not just about the typical "panorama" either... I saw a demo of someone standing "too close" to a building, and taking pictures zoomed all the way out, of the front door, windows and window-boxes, front brick walk way, tilting upward and taking a picture of the balcony and roof line of the second floor - in other words, many elements that were WAY out of whack in terms of perspective, lighting and color space, and these 4 or 5 images were distorted, tweaked, rotated, matched, blended, lighting and color density matched... and I was amazed in like 5 seconds, there was this "wide angle" almost "fisheye" photomerge of the front of the building, from brick walkway to roof-line, and it looked incredible.
* Automatic layer alignment and blending
Another powerful application of this new alignment and blending technology is with a series or stack of images of the same subject. Let's say you wanted to take a picture of a statue in a park somewhere, or a huge fountain, or the front of a monument or building. There are always people walking through the frame - if you can't close down the area and still need a picture of the statue, in the park, in it's beautiful setting, but with no people or birds or random elements - what are you to do? In the past, it was a painstaking process of shooting a bunch of images, selecting the "closest" one to your vision of a nice, clean, tourist-less frame, and begin the hours and hours of painting, cloning, healing, brushing etc., to remove all of your "randoms." There are artists who are very good at this process, but I'm fairly certain they would agree that if there was a way to not have to spend all that time, they'd take it. Well, it's here. Photoshop CS3 can take your stack of images and by analyzing all of them, figure out which things are permanent (things that appear in all the images like that building in the distance, the big tree, the sidewalk, and which parts of the image are obscured in one of the frames but not all of them, are healed automatically by borrowing pixels from other images in the stack and building an advanced composite of all the images and doing 90% or more of the work for you. There's even a set of "fuzziness" sliders letting you say "eleminate things that are in X% of the images in the stack or less." This is so impressive to see in action. You have to try it on some of your own images. It's really hard to believe that it's this easy to do this sort of process now. This is one of those new areas that I'm sure we'll see artists finding incredibly creative ways to utilize this feature. Again, this one floored me when I first saw it.
* Vanishing Point with adjustable angle
One of the most powerful new features of Adobe CS2 was the vanishing point feature. One limitation it had was that you only had one set of right angles to work with in the vanishing point interface. Adobe took it one exponential step further by adding multiple, adjustable angle perspective planes to this vanishing point feature. What this enables you to do is copy, paste and clone in far more complex image planes than just the "clone parts of a building in perspective" job that the first iteration of this feature offered (impressive and powerful, but not very flexible). One of the big examples Adobe is pushing with this feature is to simulate 3D packaging and work on multiple planes at various angles in the same image. Like an open box for a new product, or even for experimenting with your final package art by seeing it in its real-world context. Again I think this feature has so many far reaching implications for inventors, prototypers, 3D modelers, visual effects artists... and can give Photoshop artists the ability to render full blown mockups of product packaging art for clients in a whole new way - getting us to sign-off, green-light and on to the next project at hand much more quickly. I like that a lot.
There are numerous new features in the application, especially when you dig down deep into the Photoshop Extended editions (sounds like a Peter Jackson DVD...) and as the week progresses here, I'd like to look into some of what PsCS3 Extended has to offer. The versions of PsCS3 that are available are the Film & Video, Medical & Science, AEC (Architecture, Engineering & Construction), and Manufacturing editions.
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Key Steps To Creating An Adobe Dreamweaver Web Site
Adobe Dreamweaver has brought the business of web development within the reach of everybody. However, it is still a sophisticated piece of software with numerous floating palettes which can be a little off-putting for the new user. So, in this article, we aim to show you how to find your way through the maze of features and create a basic Dreamweaver web site.
It is very important that you design and sketch out how you want the site to work and what information will be available for users to navigate their way through. It is also a good idea to keep your first project simple. Once you have completed a basic version of your site, you can look to expand your knowledge and expertise and then add enhancements to the site.
Next, create a folder somewhere on your hard disk or desktop which will contain all of the files which will make up your site. Dreamweaver refers to this folder as the "local root folder". It should contain nothing but the files pertaining to your web site and will become a mirror image of your actual site when the site goes live.
Next, create a folder inside the "local root folder" which will hold your images. This will help you to avoid ending up with "broken images" on your site, where visitors are presented with an empty box instead of the actual image.
Now, finally, we launch Dreamweaver and create a new web site by choosing New Site from the Site menu. Click the Advanced tab ("Advanced" here simply means manual, so don't be intimidated.) You will notice a series of categories on the left of the screen. Only the first two categories need to be completed: Local Info and Remote Info.
Local Info relates to your version of the site. In this window, first enter a name for the new site. Next, click on the yellow folder icon next to the box marked "Local Root Folder" and browse for the folder you created earlier. Repeat this step to identify the "Default Image Folder".
The second piece of information is Remote Info. In this section, you tell Dreamweaver how to connect to the server hosting your web site. Set you Access Method to Local/Network if you are working on an intranet site then browse to locate your intranet server. Choose FTP if you are working on a public website for the internet and enter your FTP login details in each of the boxes. This information will be supplied by your web hosting company.
The next step is to create all of the pages in your website arranged in the appropriate sub-directories. Don't put any content in the pages at this stage, just create and save each page into your local root folder. This is done, so that later, when you create links on any page, the page that you link to will already exist, so you can just point to it and automatically create the correct link.
Naturally, you will want to ensure that there is some consistency within your pages with some elements that remain the same as visitors move from page to page. One of the best ways to achieve this is to create at least one Dreamweaver template. Templates contain the basic design and layout that you want each of the pages to have as well as editable regions which can be modified each time you apply the template to a page.
Having finished your template or templates, you are ready to build the web pages that will constitute your site. Simply open each page, choose Modify - Templates - Apply Template to Page and then add the text, images etc. that make up the page.
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Operating Systems: File Systems
File systems are an integral part of any operating systems with the capacity for long term storage. There are two distinct parts of a file system, the mechanism for storing files and the directory structure into which they are organised. In mordern operating systems where it is possibe for several user to access the same files simultaneously it has also become necessary for such features as access control and different forms of file protection to be implemented.
A file is a collection of binary data. A file could represent a program, a document or in some cases part of the file system itself. In modern computing it is quite common for their to be several different storage devices attached to the same computer. A common data structure such as a file system allows the computer to access many different storage devices in the same way, for example, when you look at the contents of a hard drive or a cd you view it through the same interface even though they are completely different mediums with data mapped on them in completely different ways. Files can have very different data structures within them but can all be accessed by the same methods built into the file system. The arrangment of data within the file is then decided by the program creating it. The file systems also stores a number of attributes for the files within it.
All files have a name by which they can be accessed by the user. In most modern file systems the name consists of of three parts, its unique name, a period and an extension. For example the file 'bob.jpg' is uniquely identified by the first word 'bob', the extension jpg indicates that it is a jpeg image file. The file extension allows the operating system to decide what to do with the file if someone tries to open it. The operating system maintains a list of file extension associations. Should a user try to access 'bob.jpg' then it would most likely be opened in whatever the systems default image viewer is.
The system also stores the location of a file. In some file systems files can only be stored as one contigious block. This has simplifies storage and access to the file as the system then only needs to know where the file begins on the disk and how large it is. It does however lead to complications if the file is to be extended or removed as there may not be enough space available to fit the larger version of the file. Most modern file systems overcome this problem by using linked file allocation. This allows the file to be stored in any number of segments. The file system then has to store where every block of the file is and how large they are. This greatly simplifies file space allocation but is slower than contigious allocation as it is possible for the file to be spread out all over the disk. Modern oparating systems overome this flaw by providing a disk defragmenter. This is a utility that rearranges all the files on the disk so that thay are all in contigious blocks.
Information about the files protection is also integrated into the file system. Protection can range from the simple systems implemented in the FAT system of early windows where files could be marked as read-only or hidden to the more secure systems implemented in NTFS where the file system administrator can set up separate read and write access rights for different users or user groups. Although file protection adds a great deal of complexity and potential difficulties it is essential in an enviroment where many different computers or user can have access to the same drives via a network or time shared system such as raptor.
Some file systems also store data about which user created a file and at what time they created it. Although this is not essential to the running of the file system it is useful to the users of the system.
In order for a file system to function properly they need a number of defined operations for creating, opening and editing a file. Almost all file systems provide the same basic set of methods for manipulating files.
A file system must be able to create a file. To do this there must be enough space left on the drive to fit the file. There must also be no other file in the directory it is to be placed with the same name. Once the file is created the system will make a record of all the attributes noted above.
Once a file has been created we may need to edit it. This may be simply appending some data to the end of it or removing or replacing data already stored within it. When doing this the system keeps a write pointer marking where the next write oparation to the file should take place.
In order for a file to be useful it must of course be readable. To do this all you need to know the name and path of the file. From this the file system can ascertain where on the drive the file is stored. While reading a file the system keeps a read pointer. This stores which part of the drive is to be read next.
In some cases it is not possible to simply read all of the file into memory. File systems also allow you to reposition the read pointer within a file. To perform this operation the system needs to know how far into the file you want the read pointer to jump. An example of where this would be useful is a database system. When a query is made on the database it is obviously ineficient to read the whole file up to the point where the reuired data is, instead the application managing the database would determine where in the file the required bit of data is and jump to it. This operation is often known as a file seek.
File systems also allow you to delete files. To do this it needs to know the name and path of the file. To delete a file the systems simply removes its entry from the directory structure and adds all the space it previously occupied to the free space list (or whatever other free space management system it uses).
These are the most basic operations required by a file system to function properly. They are present in all modern computer file systems but the way they function may vary. For example, to perform the delete file operation in a modern file system like NTFS that has file protection built into it would be more complicated than the same operation in an older file system like FAT. Both systems would first check to see whether the file was in use before continuing, NTFS would then have to check whether the user currently deleting the file has permission to do so. Some file systems also allow multiple people to open the same file simultaneously and have to decide whether users have permission to write a file back to the disk if other users currently have it open. If two users have read and write permission to file should one be allowed to overwrite it while the other still has it open? Or if one user has read-write permission and another only has read permission on a file should the user with write permission be allowed to overwrite it if theres no chance of the other user also trying to do so?
Different file systems also support different access methods. The simplest method of accessing information in a file is sequential access. This is where the information in a file is accessed from the beginning one record at a time. To change the position in a file it can be rewound or forwarded a number of records or reset to the beginning of the file. This access method is based on file storage systems for tape drive but works as well on sequential access devices (like mordern DAT tape drives) as it does on random-access ones (like hard drives). Although this method is very simple in its operation and ideally suited for certain tasks such as playing media it is very inneficient for more complex tasks such as database management. A more modern approach that better facilitates reading tasks that arent likely to be sequential is direct access. direct access allows records to be read or written over in any order the application requires. This method of allowing any part of the file to be read in any order is better suited to modern hard drives as they too allow any part of the drive to be read in any order with little reduction in transfer rate. Direct access is better suited to to most applications than sequential access as it is designed around the most common storage medium in use today as opposed to one that isnt used very much anymore except for large offline back-ups. Given the way direct access works it is also possible to build other access methods on top of direct access such as sequential access or creating an index of all the records of the file speeding to speed up finding data in a file.
On top of storing and managing files on a drive the file system also maintains a system of directories in which the files are referenced. Modern hard drives store hundreds of gigabytes. The file system helps organise this data by dividing it up into directories. A directory can contain files or more directories. Like files there are several basic operation that a file system needs to a be able to perform on its directory structure to function properly.
It needs to be able to create a file. This is also covered by the overview of peration on a file but as well as creating the file it needs to be added to the directory structure.
When a file is deleted the space taken up by the file needs to be marked as free space. The file itself also needs to be removed from the directory structure.
Files may need to be renamed. This requires an alteration to the directory structure but the file itself remains un-changed.
List a directory. In order to use the disk properly the user will require to know whats in all the diretories stored on it. On top of this the user needs to be able to browse through the directories on the hard drive.
Since the first directory structures were designed they have gone through several large evolutions. Before directory structures were applied to file systems all files were stored on the same level. This is basically a system with one directory in which all the files are kept. The next advancement on this which would be considered the first directory structure is the two level directory. In this There is a singe list of directories which are all on the same level. The files are then stored in these directories. This allows different users and applications to store there files separately. After this came the first directory structures as we know them today, directory trees. Tree structure directories improves on two level directories by allowing directories as well as files to be stored in directories. All modern file systems use tree structore directories, but many have additional features such as security built on top of them.
Protection can be implemented in many ways. Some file systems allow you to have password protected directories. In this system. The file system wont allow you to access a directory before it is given a username and password for it. Others extend this system by given different users or groups access permissions. The operating system requires the user to log in before using the computer and then restrict their access to areas they dont have permission for. The system used by the computer science department for storage space and coursework submission on raptor is a good example of this. In a file system like NTFS all type of storage space, network access and use of device such as printers can be controlled in this way. Other types of access control can also be implemented outside of the file system. For example applications such as win zip allow you to password protect files.
There are many different file systems currently available to us on many different platforms and depending on the type of application and size of drive different situations suit different file system. If you were to design a file system for a tape backup system then a sequential access method would be better suited than a direct access method given the constraints of the hardware. Also if you had a small hard drive on a home computer then there would be no real advantage of using a more complex file system with features such as protection as it isn't likely to be needed. If i were to design a file system for a 10 gigabyte drive i would use linked allocation over contigious to make the most efficient use the drive space and limit the time needed to maintain the drive. I would also design a direct access method over a sequential access one to make the most use of the strengths of the hardware. The directory structure would be tree based to allow better organisation of information on the drive and would allow for acyclic directories to make it easier for several users to work on the same project. It would also have a file protection system that allowed for different access rights for different groups of users and password protection on directories and individual files.Several file systems that already implement the features ive decribed above as ideal for a 10gig hard drive are currently available, these include NTFS for the Windows NT and XP operating systems and ext2 which is used in linux.
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A file is a collection of binary data. A file could represent a program, a document or in some cases part of the file system itself. In modern computing it is quite common for their to be several different storage devices attached to the same computer. A common data structure such as a file system allows the computer to access many different storage devices in the same way, for example, when you look at the contents of a hard drive or a cd you view it through the same interface even though they are completely different mediums with data mapped on them in completely different ways. Files can have very different data structures within them but can all be accessed by the same methods built into the file system. The arrangment of data within the file is then decided by the program creating it. The file systems also stores a number of attributes for the files within it.
All files have a name by which they can be accessed by the user. In most modern file systems the name consists of of three parts, its unique name, a period and an extension. For example the file 'bob.jpg' is uniquely identified by the first word 'bob', the extension jpg indicates that it is a jpeg image file. The file extension allows the operating system to decide what to do with the file if someone tries to open it. The operating system maintains a list of file extension associations. Should a user try to access 'bob.jpg' then it would most likely be opened in whatever the systems default image viewer is.
The system also stores the location of a file. In some file systems files can only be stored as one contigious block. This has simplifies storage and access to the file as the system then only needs to know where the file begins on the disk and how large it is. It does however lead to complications if the file is to be extended or removed as there may not be enough space available to fit the larger version of the file. Most modern file systems overcome this problem by using linked file allocation. This allows the file to be stored in any number of segments. The file system then has to store where every block of the file is and how large they are. This greatly simplifies file space allocation but is slower than contigious allocation as it is possible for the file to be spread out all over the disk. Modern oparating systems overome this flaw by providing a disk defragmenter. This is a utility that rearranges all the files on the disk so that thay are all in contigious blocks.
Information about the files protection is also integrated into the file system. Protection can range from the simple systems implemented in the FAT system of early windows where files could be marked as read-only or hidden to the more secure systems implemented in NTFS where the file system administrator can set up separate read and write access rights for different users or user groups. Although file protection adds a great deal of complexity and potential difficulties it is essential in an enviroment where many different computers or user can have access to the same drives via a network or time shared system such as raptor.
Some file systems also store data about which user created a file and at what time they created it. Although this is not essential to the running of the file system it is useful to the users of the system.
In order for a file system to function properly they need a number of defined operations for creating, opening and editing a file. Almost all file systems provide the same basic set of methods for manipulating files.
A file system must be able to create a file. To do this there must be enough space left on the drive to fit the file. There must also be no other file in the directory it is to be placed with the same name. Once the file is created the system will make a record of all the attributes noted above.
Once a file has been created we may need to edit it. This may be simply appending some data to the end of it or removing or replacing data already stored within it. When doing this the system keeps a write pointer marking where the next write oparation to the file should take place.
In order for a file to be useful it must of course be readable. To do this all you need to know the name and path of the file. From this the file system can ascertain where on the drive the file is stored. While reading a file the system keeps a read pointer. This stores which part of the drive is to be read next.
In some cases it is not possible to simply read all of the file into memory. File systems also allow you to reposition the read pointer within a file. To perform this operation the system needs to know how far into the file you want the read pointer to jump. An example of where this would be useful is a database system. When a query is made on the database it is obviously ineficient to read the whole file up to the point where the reuired data is, instead the application managing the database would determine where in the file the required bit of data is and jump to it. This operation is often known as a file seek.
File systems also allow you to delete files. To do this it needs to know the name and path of the file. To delete a file the systems simply removes its entry from the directory structure and adds all the space it previously occupied to the free space list (or whatever other free space management system it uses).
These are the most basic operations required by a file system to function properly. They are present in all modern computer file systems but the way they function may vary. For example, to perform the delete file operation in a modern file system like NTFS that has file protection built into it would be more complicated than the same operation in an older file system like FAT. Both systems would first check to see whether the file was in use before continuing, NTFS would then have to check whether the user currently deleting the file has permission to do so. Some file systems also allow multiple people to open the same file simultaneously and have to decide whether users have permission to write a file back to the disk if other users currently have it open. If two users have read and write permission to file should one be allowed to overwrite it while the other still has it open? Or if one user has read-write permission and another only has read permission on a file should the user with write permission be allowed to overwrite it if theres no chance of the other user also trying to do so?
Different file systems also support different access methods. The simplest method of accessing information in a file is sequential access. This is where the information in a file is accessed from the beginning one record at a time. To change the position in a file it can be rewound or forwarded a number of records or reset to the beginning of the file. This access method is based on file storage systems for tape drive but works as well on sequential access devices (like mordern DAT tape drives) as it does on random-access ones (like hard drives). Although this method is very simple in its operation and ideally suited for certain tasks such as playing media it is very inneficient for more complex tasks such as database management. A more modern approach that better facilitates reading tasks that arent likely to be sequential is direct access. direct access allows records to be read or written over in any order the application requires. This method of allowing any part of the file to be read in any order is better suited to modern hard drives as they too allow any part of the drive to be read in any order with little reduction in transfer rate. Direct access is better suited to to most applications than sequential access as it is designed around the most common storage medium in use today as opposed to one that isnt used very much anymore except for large offline back-ups. Given the way direct access works it is also possible to build other access methods on top of direct access such as sequential access or creating an index of all the records of the file speeding to speed up finding data in a file.
On top of storing and managing files on a drive the file system also maintains a system of directories in which the files are referenced. Modern hard drives store hundreds of gigabytes. The file system helps organise this data by dividing it up into directories. A directory can contain files or more directories. Like files there are several basic operation that a file system needs to a be able to perform on its directory structure to function properly.
It needs to be able to create a file. This is also covered by the overview of peration on a file but as well as creating the file it needs to be added to the directory structure.
When a file is deleted the space taken up by the file needs to be marked as free space. The file itself also needs to be removed from the directory structure.
Files may need to be renamed. This requires an alteration to the directory structure but the file itself remains un-changed.
List a directory. In order to use the disk properly the user will require to know whats in all the diretories stored on it. On top of this the user needs to be able to browse through the directories on the hard drive.
Since the first directory structures were designed they have gone through several large evolutions. Before directory structures were applied to file systems all files were stored on the same level. This is basically a system with one directory in which all the files are kept. The next advancement on this which would be considered the first directory structure is the two level directory. In this There is a singe list of directories which are all on the same level. The files are then stored in these directories. This allows different users and applications to store there files separately. After this came the first directory structures as we know them today, directory trees. Tree structure directories improves on two level directories by allowing directories as well as files to be stored in directories. All modern file systems use tree structore directories, but many have additional features such as security built on top of them.
Protection can be implemented in many ways. Some file systems allow you to have password protected directories. In this system. The file system wont allow you to access a directory before it is given a username and password for it. Others extend this system by given different users or groups access permissions. The operating system requires the user to log in before using the computer and then restrict their access to areas they dont have permission for. The system used by the computer science department for storage space and coursework submission on raptor is a good example of this. In a file system like NTFS all type of storage space, network access and use of device such as printers can be controlled in this way. Other types of access control can also be implemented outside of the file system. For example applications such as win zip allow you to password protect files.
There are many different file systems currently available to us on many different platforms and depending on the type of application and size of drive different situations suit different file system. If you were to design a file system for a tape backup system then a sequential access method would be better suited than a direct access method given the constraints of the hardware. Also if you had a small hard drive on a home computer then there would be no real advantage of using a more complex file system with features such as protection as it isn't likely to be needed. If i were to design a file system for a 10 gigabyte drive i would use linked allocation over contigious to make the most efficient use the drive space and limit the time needed to maintain the drive. I would also design a direct access method over a sequential access one to make the most use of the strengths of the hardware. The directory structure would be tree based to allow better organisation of information on the drive and would allow for acyclic directories to make it easier for several users to work on the same project. It would also have a file protection system that allowed for different access rights for different groups of users and password protection on directories and individual files.Several file systems that already implement the features ive decribed above as ideal for a 10gig hard drive are currently available, these include NTFS for the Windows NT and XP operating systems and ext2 which is used in linux.
http://www.articlecity.com
video
http://www.youtube.com/watch?v=iHYiG-H-bKw
Get FREE Internet Access on Your Computer
Will mobile internet ever be possible? Mobiles phone service providers give you access to the internet or at least that is the claimed. However, there are issues of boundaries, availability of good signals, telephone memory which affects down load speeds and the most prohibitive aspect is the cost.
You can have access to the internet via your computer on the move using s data card with a starting price of nearly £50 per month for limited access. Unlimited access via data card can cost as much as £150 per month. WEBAROO soon to be on the market is about to change all that. This device in conjunction with a computer or other mobile tool for the first time gives you the ability to have "Web on your computer on the move". This clever little tool does Google searches on the underground, on a plan, on top of a mountain or even in the wildest part of the Amazon jungles. How does Webaroo add the power of internet to your computer? Cutting edge compression technology which is the core of this device saves the internet on the hard drive of your computer or on your memory chip of your computer. The whole internet is compressed into 2 gigabytes of memory and it is thereafter yours to take it with you to where you want to take your computer. What are the benefits of this technology? There are no wifi issues to be concerned about. There are no costs for the use of internet on the move. You simply have free internet at your finger tips on your computer to use as you please. You can access useful information like maps, encyclopedia and even news stories. Short comings of Webaroo? You don't have access to the entire web. Your access to the web is limited to the internet as seen by Google. The amount of information being help does depend on the memory of your computer. Depending on the popularity of your search term, the search results are limited to the first few pages as opposed to the entire search results for your chosen term. Updates are only possible when the machine is hooked up to the internet the next time. Finally, Webaroo is not just another internet device or tool to fit neatly in a niche that has remained available for a long while. It is innovation itself. Webaroo; for the first time, has made it possible for people to have internet on their computer and in their pocket at its very first attempt. And, all that technology, information and system for free on your computer and on the move. Because of this achievement, Webaroo is therefore a very serious contender on the market with a myriad of possibilities. Webaroo is very good news for the market because it will encourage other suppliers in the market to come up with even more innovative products. Cheaper internet access via your computer on the move is really needed and I hope that Webaroo makes big inroads into that area by its very presence.
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You can have access to the internet via your computer on the move using s data card with a starting price of nearly £50 per month for limited access. Unlimited access via data card can cost as much as £150 per month. WEBAROO soon to be on the market is about to change all that. This device in conjunction with a computer or other mobile tool for the first time gives you the ability to have "Web on your computer on the move". This clever little tool does Google searches on the underground, on a plan, on top of a mountain or even in the wildest part of the Amazon jungles. How does Webaroo add the power of internet to your computer? Cutting edge compression technology which is the core of this device saves the internet on the hard drive of your computer or on your memory chip of your computer. The whole internet is compressed into 2 gigabytes of memory and it is thereafter yours to take it with you to where you want to take your computer. What are the benefits of this technology? There are no wifi issues to be concerned about. There are no costs for the use of internet on the move. You simply have free internet at your finger tips on your computer to use as you please. You can access useful information like maps, encyclopedia and even news stories. Short comings of Webaroo? You don't have access to the entire web. Your access to the web is limited to the internet as seen by Google. The amount of information being help does depend on the memory of your computer. Depending on the popularity of your search term, the search results are limited to the first few pages as opposed to the entire search results for your chosen term. Updates are only possible when the machine is hooked up to the internet the next time. Finally, Webaroo is not just another internet device or tool to fit neatly in a niche that has remained available for a long while. It is innovation itself. Webaroo; for the first time, has made it possible for people to have internet on their computer and in their pocket at its very first attempt. And, all that technology, information and system for free on your computer and on the move. Because of this achievement, Webaroo is therefore a very serious contender on the market with a myriad of possibilities. Webaroo is very good news for the market because it will encourage other suppliers in the market to come up with even more innovative products. Cheaper internet access via your computer on the move is really needed and I hope that Webaroo makes big inroads into that area by its very presence.
Did you find this article useful? For more useful tips & hints, Points to ponder and keep in mind, techniques & insights pertaining to Google Ad sense, Do please browse for more information at our website :-
http://www.reprintarticlesite.com
http://computertips.reprintarticlesite.com
http://www.articlebasement.com
video
http://www.youtube.com/watch?v=3lNqqryPBNU
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