SEO - Relevant Filenames

One of the simplest methods to improve your search engine optimization is to look at the way you name your files. Before writing this tutorial I did lot of research on file names and found that search engines like Google give too much importance to file names. You should think what are you going to put in your web page and then give a relevant file name to this page.
Just try giving any keyword in Google search engine and you will find file names highlighted with the keyword you have given. So it simply proves that your file name should have appropriate keyword.

File Naming Style:

  • The filename should preferably be short and descriptive. It's always good to use same keywords in file name as well as in page title.
  • Don't use file names like service.htm or job.htm. But use actual service name in your file name like computer-repairing.htm
  • Don't use more than 3-4 words in file name and separate them with hyphens rather than underscores. Try to use 2 keywords if possible.

File Name Example:

Here are some file names which should be preferred from SEO as well as from user point of view.
slazenger-brand-balls.html
wimbledon-brand-balls.html
wilson-brand-balls.html
Notice that keywords are separated by hyphens rather than underscores. Google sees file names as follows:
seo-relevant-filename as seo relevant filename(good)
But Google sees
seo_relevant_filename as seorelevantfilename (not good)

File Extension:

It should be noticed that .html, .htm and .php and any other extension do NOTHING for your visitors, and they are simply a means of offloading some of the work of configuring your webserver properly onto your visitors. In effect you are asking your site vistors to tell your webserver HOW to produce the page, not which one?
Many Web masters think that its a good idea to use filename without using extension. It may help you but not a whole lot.

URL Sub-Directory Name:

From Search Engine Optimization point of view URL sub-directory name hardly matters. You try giving any keyword in any search and you will not find any sub-directory name matching with your keywords. But from user point of view you should keep very much abbreviated sub-directory name.

Guru Mantra:

Finally, I will suggest to keep the following points in mind before naming your files:
  • Use web page file name short, simple, descriptive and relevant to page content.
  • Try to use maximum 3-4 keywords in your file name and these keywords should be appeared in your web page title as well.
  • Separate all keyword with hyphen rather than with underscore.
  • Keep your sub directories name as shorter as possible.
  • Keep the file size fewer than 101K though because Google chops almost everything above that.

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SEO - Miscellaneous Techniques

There are various other tips related to SEO. I have not categorised them into any special category so putting in misc category. Go through these tips one by one

Don't do the followings:

  • Don't keep hidden text on your web pages.
  • Don't create alt image spamming by putting wrong keywords.
  • Don't use meta tags stuffing.
  • Don't use frams and flash on your site.
  • Don't exchange yoru links with black listed sites.
  • Don't try to fool your site visitors by using miss spelled keyword.
  • Don't send spam emails to thuasand of email IDs.
  • Don't use too much graphics on your site.
  • Don't create too many doorway pages.
  • Don't try to create duplicate content of pages.
  • Don't submit yoru website many times in a single search engine.
  • Don't use sub-directory depth more than 1-2.
  • Don't create too many dynamic pages. Try to convert them into static pages.
  • Don't bloat your pages with code.
  • Don't nest your pages.

Do the followings:

There are various other tips which can help you to optimize your web site for many Search Engines.
  • Create logs of pages and each page should however contain a minimum of about 200 visible words of text to maximize relevance with Google.
  • Create a Sitemap, Help, FAQ, About Us, Link to Us, Copyright, Disclaimer, Privacy Policy pages on mandatory basis.
  • Create a home page link to each and every web page and provide easy navigation through all the pages.
  • Pay attention to your dynamic page URLs. Google can crawl and index dynamic pages as long as you don't have more than 2 parameters in the URL.
  • Check your complete site for broken links. Broken links will reduce your other pages rank as well.
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SEO - Hiring Experts

Creating, editing, and promoting unique high-quality content is difficult and time consuming. If you are really serious about SEO and you are not getting expected result then better choice is to hire an SEO expert. There are following tasks which should be taken care by SEO experts
  • Code validation and clean up - Ensure that code is SE Friendly and standards compliant.
  • Site Structure - Building a semantic structure/theme and ensure URL's are spider friendly.
  • On Page optimization - Page Title, copy writing, Call to action etc.
  • Quality link building - Securing one way links from relevant sites.
  • Keyword research - Building a list of key-phrases relevant to your business.
  • Creating Quality Content - Build optimized pages around terms discovered through keyword research.
  • Off Page Optimization - Blogs, Press Releases, Article Submissions
If you are confident that you have the required skills then you can take care of doing all the above activities otherwise its worth taking help from SEO Companies or to hire any SEO Specialist.

Choosing a SEO Expert or Company:

This is most difficult part to choose a correct SEO Expert or SEO Company. But we are giving you few guidelines which can help you for the same.
  • Start searching through your friends and business partners.
  • Post your queries in SEO Forums to get feedback from the community.
  • Check other sites rank which they already have optimized.
  • Don't go for SEO companies doing automated submission etc.
  • Don't go for SEO companies doing Balk Hat tricks.
  • Don't look for cheap SEO because of some pennies you can loss more. But take care, high price also does not guarantee high quality.
  • Take guarantee if possible for a particular rank and any particular search engine.
  • User SEO Expert or Company name in Google to find more information about them.
  • Don't go just because of their fancy site and good article available on their site.
  • Don't go testimonials available on their sites.
I can not list out all the factors here because there may be different situations and different views. So you should be smart enough to think what's bad and what's good.
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SEO - Content is the King

Content is basically includes what you see on the site: the text, graphics and even links to outside world. I would condemn using excessive graphics because they are not Search Engine Friendly plus users feel irritation when they get downloaded specially over a slow netwrok.
Thousands of articles, books and forum entries detail how to make your site search engine friendly, but ultimately, one rule stands above the rest: Content is king. But I will say this rule is past now and I would like to say Unique, high-quality, unduplicated content is the king.
Superior the quality of your content, the higher the ranking you achieve, larger the traffic you gain and greater the popularity of your website. Search engines prefer good quality sites in their index and search results.
A relevant, fresh, and timely content is crucial to attracting and keeping visitors to your web pages. It will help you both draw traffic from search engines and create audience loyalty.

Unique, High-Quality Content:

When people visit a Web site for information, they want your unique spin on a topic. How is your material or content unique? Is that uniqueness obvious and easy to find and to understand? Visitors want unique, high-quality site conten. Its not only your home page content but also all the linked pages should have useful and easy to understand content.
Now a days search engines have become very smart and they are able to understand complete grammer and complete phrase.So while raking a page against other then it matters how rich content is available on a page.
Sites with duplicated, syndicated or free content, who get given red flags by the Search Engines.

SEO Content Writing ( Copy Writing ):

SEO Content Writing (also referred as SEO Copy Writing) involves the process of integrating keywords and informative phrases which make up the actual content of your website.
While writing your web page content following tips may help you in keeping it better than others.
  • The content should be directed for the specified target audience.
  • Keyword density is strictly adhered as per search engine guidelines.
  • Titles should always be eye-catchers, compelling your visitors to read on and want what you have to offer in your website.
  • Don't use confusing and complex language. Use small statements to make your content more understandable.
  • Keep your web pages short and don't put all the content on a single page.
  • Divide your web page content also into short paragraphs.

Other advantages of having great content:

Its not only SEO you have to think about, but also many factors will make your site popular.
  • If your site is having something really unique then people would like to suggest it to their friends.
  • Other webmasters would like to create a link of your site on thier sites
  • Your site visitors will start trusting on your site and they will look forward for the next content and will keep coming again and again.
  • Assuming you have been listed out by any Search Engine but net surfer will click only that page whose content snippet would look more unique and interesting.

Conclsuion:

Creating, editing, and promoting unique high-quality content is difficult and time consuming. But in the end Golden rule of SEO is that Content is the King. Its not just because of a Search Engine but its for your site visitors. A page that is read by people is better than a page that is read by bots.
So write your content after going a serious thought. Keep your title, keywords, link text, meta tags up-to-date and unique and interesting. I am sure you will win.
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SEO - Link Building

Link building is the SEO practice of obtaining links from external web sites to your own to improve both direct referrals ie. people clicking on the links and search engine ranking. Link building is all about increasing your site link popularity.
Web site Crawler will go to a site again and again whose ranking in Search Engine is high. You can verify this fact by putting your site on a high rank site. If your site link is available on a high rank web site then you have 99.99% chances that you site will be indexed witn-in 24Hrs.

How to increase Link Popularity ?

There are various ways of increasing your web site link popularity. I'm listing out some important tips which are easily doable.
  • Submit your site in popular search engines manually. Don't go for automated submission.
  • Get your site listed in Open Directory Projects like dmog.org, yahoo.com. Getting listed in these directories will give your site a boost in link popularity and improve search engine ranking in other search engines.
  • Provide high quality content - people will naturally link to your site if you have what they want and no where is available.
  • Leverage your personal relastions with other webmasters. Put your site link on their sites. One way links often count for more than reciprocal links.
  • Particiapte in Link Exchaneg Program. Find top 20 sites doing the same business and contact them for reciprocal links. Link exchange between unrelated sites might affect the ranking of websites in the Search Engine.
  • If you are subscribed in a forum and forum does not have any restriction to keep your site link as your signature then it can help you to increase your site popularity.
  • Submit your site to bookmark sites like DIGG, and Slashdot etc. Before submitting please go through their spam policy.
  • Write good articles in blogging sites and give few references of your links with-in that article.
  • Keep providing good content to your site visitors. Try to keep them busy on your site. If possible create forums, news letters, blogs etc.
There are other ways but you need to spend some dollars to go for such alternative.
  • Buy a place on high rank website where you can put your link.
  • Subscribe for google's Adwords program to drive traffic towards your site.
  • You can go for alternative advertising option to increase the number of hits on your site which will result in your site link popularity.

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Search Engine Optimization (SEO)- Summary

This is the end of this tutorial and I hope now you have a good knowledge and at least you would need any other help to optimize your web site.
We have covered almost all major concepts related to Search Engine Optimization. Now you are familiar with most frequently used SEO related terminology as well.
You have learnt how to optimize keywords, title, alt, mata tags, anchor and other text from SEO point of view. You also have learnt importance of having good content in your web site and in Miscellaneous Techniques chapter we have suggested you other important points which will help you to optimize your web site
So in brief ethical strategies for acheiving optimal ranking in the search engines are:
  • All Pages Must Conform with W3C Standards
  • Keyword Density is Never Abusive
  • Always Include: Robots.txt, Sitemap.xml, & Urllist.txt
  • Keywords are Prominent in the Title, META tags, & Headings
  • ALT Tags and Title Tags are Not Forgotten
  • Nomenclature is Fundamental to Being Indexed
I have listed down various good resources for SEO on the next page so if you want to do further study on SEO then you can go ahead.
Please send us your feedback at webmaster@tutorialspoint.com.
Keep visiting to us, Happy Learning!
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SEO - Title Optimization

Hope you understand the meaning of HTML TITLE tag which is put inside head tag. The page title (not to be confused with the heading for a page) is what is displayed in the title bar of your browser window, and is also what is displayed when you bookmark a page or add it to your browser Favorites.
This is the one place on a web page where your keywords MUST be present. Correct use of keywords in the title of every page of your website is extremely important to Google - particularly for the home page. If you do nothing else to optimize your site, remember to do this!
The title shouldn't consist of much more than about 9 words or 60 characters, with your keywords used at the very beginning of the title. Since Google is looking for relevant keywords in the title, this means you should NOT include your company name in the title unless your company name is very well known.
Improper or nonexistent use of titles in web pages will keep more websites out of top rankings on Google than any other factor except perhaps for a lack of relevant content on a page or a lack of quality links from other websites that point to your site.

Best Practices for Creating Titles:

Here are some best practices you should follow for creating titles on pages:
  • Each page should have a unique title.
  • If practical, try to include your Primary Keyword Phrase in every title of every page.
  • Begin the title of your home page with your Primary Keyword Phrase, followed by your best Secondary Keyword Phrases.
  • Use more specific variations to your Primary Keyword Phrase on your specific product, service, or content pages.
  • If you must include your company name, put it at the end of the title.
  • Use the best form, plural or singular, for your keywords based on what WordTracker says is searched on more often.
  • Don't overdo it - don't repeat your keywords more than 2 - 3 times in the title
  • Make sure the <title> tag is the first element in the <head> section of your page - this makes it easier to find by Google.
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SEO - Optimized Metatags

There are two important Meta Tags and they are the meta description and meta keyword tags. Some search engines may display the meta description as part of the search results, but the meta keywords tags should not appear in search results.
The general consensus among SEO experts is that meta tags are dead. Even so, many of these same experts continue to use meta tags in their own sites.
For Google adding the Description Meta Tag won't result in a boost in the Search Engine Results Pages (SERPs), but the description might be used for the description for your SERP listings in Google. Yahoo says they use the Keyword Meta Tag when it ranks a page. So it makes sense to add one for Yahoo and any other minor search engines that still use.

What do the Meta Tags Look Like?

You can add following in the head section of the web page:
<meta name="keywords" 
         content="KEYWORD1 KEYWORD2 KEYPHRASE1 etc. 
         about 30 to 40 unique words">

<meta name="description" 
         content="An accurate, keyword-rich description 
         about 150 characters">

Meta Description Tag Tips:

There are few important tips for good meta description tags:
  • Use keywords in your meta description tag.
  • Try not to repeat the words overly often, but try to use multiple syntaxes of your key words.
  • There should not be more than 150 chracters in a description meta tag of a single web page.
  • Use a different meta description tag for each page, as each page is different and stands a better chance of being found if you place a good title and description on it.

Meta Keywords Tag Tips:

There are few important tips for good meta keywords tags. Please refere to previous chapter on identifying good keyword.
  • Use synonyms
  • Use unique keywords
  • No need to repeat any given phrase.
  • You can repeat any word an unlimited amount of time as long as each time it is part of a different phrase.

Robots Meta Tag:

The important Meta Tag that you may need sometime is the Robots Meta Tag which looks like this:
meta name="robots" content="noindex,nofollow">
Using above meta tag you can tell to a spider or robot that you do not want some of your pages indexed or that you do not want your links followed.
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SEO - Optimized Keywords

We are discussing everything in Web context so in web terminology a keyword is a term that a person enters into a search engine to find specific information. Most people enter search phrases that consists of between two and five words. Such phrases may be called search phrases, keyword phrases, query phrases, or just keywords. Good keyword phrases are specific and descriptive.
There are following concepts related to Keywords which helps in optimizing keywords on a web page.

Keyword Frequency:

This is calculated as how often does a keyword appear in a site's title or description. You don't want to go overboard with frequency, however, since on some engines if you repeat a word too many times, you'll be penalized for "spamming" or keyword stuffing.
In general though, repeat your keyword in the document as many times as you can get away with, and up to 3-7 times in your META tags.

Keyword Weight:

This refers to the number of keywords appearing on your Web page compared to the total number of words appearing on that same page. Some search engines consider this when determining the rank of your Web site for a particular keyword search.
One technique that often works well is to create some smaller pages, generally just a paragraph long, which emphasize a particular keyword. By keeping the overall number of words to a minimum, you will increase the "weight" of the keyword you are emphasizing.

Keyword Proximity:

This refers to the placement of keywords on a Web page in relation to each other or, in some cases, in relation to other words with a similar meaning as the queried keyword.
For search engines that grade a keyword match by keyword proximity, the connected phrase .home loans. will outrank a citation that mentions .home mortgage loans. assuming that you are searching only for the phrase "home loans".

Keyword Prominence:

A measure of how early or high up on a page the keywords are found. Having keywords in the first heading and in the first paragraph (first 20 words or so) on a page are best.

Keyword Placement:

WHERE your keywords are placed on a page is very important. For example, in most engines, placing the keywords in the Title of the page or in the Heading tags will give it more relevancy. On some engines, placing keywords in the link text, the part that is underlined on the screen in a browser, can add more relevancy to those words.

Best Places to Put Keywords:

Here is a list of places where you should try to use your main keywords.
  • Keywords in the <title> tag(s).
  • Keywords in the <meta name="description">
  • Keywords in the <meta name="keyword">
  • Keywords in <h1> or other headline tags.
  • Keywords in the <a href="http://yourcompany.com">keywords</a> link tags.
  • Keywords in the body copy.
  • Keywords in alt tags.
  • Keywords in <!-- insert comments here> comments tags.
  • Keywords contained in the URL or site address, e.g., http://www.keyword.com/keywordkeyword.htm.

Finding Keywords:

There are many different ways to find keywords for your website. Some good keyword ideas are:
  • Words people would search for to find your product or service.
  • Problems your prospective customers may be trying to solve with your product or service.
  • Keyword tags on competitors websites.
  • Visible page copy on competitors websites.
  • Related search suggestions on top search engines.
  • By using an online tools like: Google Keyword Tool
  • By analyzing your website carefully and finding out proper keywords. This task can be done by expert SEO Copywriters.
  • Pay attention to stemming for your keywords - Particularly to what the root word is and what Google considers to be a match for that word when optimizing pages over time.
  • You can do brainstorming to identify correct keywords for your site.
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SEO - Web Site Domain Name

When you start thinking of doing a business through internet, first thing which you think about is your web site domain name. Before you choose a domain name you should consider the followings:
  • Who would be your target audience?
  • What you intend to sell to them. Is it a tangible item or just text content?
  • What will make your business idea unique or different than everything else that is already on the market?
Many people think it is important to have keywords in a domain. Keywords in the domain name are usually important, but it usually can be done while keeping the domain name short, memorable, and free of hyphens.
Using keywords in your domain name give you a strong competitive advantage over your competitors. Having your keywords in your domain name can increase click through rates on search engine listings and paid ads as well as make it easier to Using your keywords in get keyword rich descriptive inbound links.
Avoid buying long, and confusing domain names. May people separate the words in their domain names using either dashes or hyphen. In the past the domain name itself was a significant ranking factor but now search engines have advanced it is not very significant factor anymore.
Keep two to three words in your domain name it will be more memorable. Some of the most memorable websites do a great job of branding by creating their own word. Few examples are eBay, Yahoo!, Expedia, Slashdot, Fark, Wikipedia, Google...
You should be able to say it over the telephone once and the other person should know how to spell it and they should be able to guess about what you sell.
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Laserdisc


Videodisc, also known as laserdisc, thin circular platter that contains video and audio information similar to, but with greater storage capacity than, a compact disc. Videodiscs are used primarily in the entertainment industry to store and play movies and in education to contain information such as an encyclopedia.
The videodisc is made of clear plastic and is coated with a thin photosensitive material. Its diameter ranges from 12 to 30 cm (5 to 12 in). A videodisc contains a series of microscopic pits burned into it by a laser. Each pit represents the number 1, and each smooth area (untouched by the laser) represents the number 0. These 1s and 0s, called binary numbers, are used to store the information in a format compatible with the electronic circuitry of a computer. The sequence of microscopic pits is arranged in tracks that spiral into the center of the disc. These tracks are small enough to fit nearly 500 of them in the period at the end of this sentence. For mass duplication of a particular disc, a mold is made from a master disc, and subsequent discs are made from imprints of the master.
A finished videodisc can be placed in a laserdisc player designed to read the information encoded upon it. A low-power laser illuminates the disc as it spins, and the resulting reflected patterns made by the series of pits and smooth areas are focused onto a detector. The detector decodes the patterns into binary numbers, which are then translated by electronic circuitry into the original video and audio signals.
Schemes for encoding and compressing video signals, such as motion joint photographic expert group (JPEG) or motion picture expert group (MPEG and MPEG2), have enabled large amounts of video information to be stored on a single disc. Compression techniques identify a recurring series of numbers that represent a particular piece of information and replace that series with a single number to save space.
Compression technology, along with techniques that correct information when it is improperly stored or transferred from the disc, have made optical storage systems, such as videodiscs and compacts discs, useful for personal computer systems. This technology will allow the production of a new generation of optical storage media known as Digital Video Discs (DVD).
A DVD is a high-density compact disc encoded with MPEG2 video and audio information. These discs will initially contain about 136 minutes of video and audio information. The DVD will offer superior resolution for video information and will support both standard and high-definition television formats. Eventually, a higher-density version of the DVD will contain about nine hours of video and audio information.
The main drawback with optical storage media such as videodiscs is that new information may not overwrite information that has been burned into the disc. Magnetic tape, such as the kind used in VCRs, has the distinct advantage of being able to record and rerecord, but it lacks the resolution and durability of videodiscs. The videodisc is more resistant to heat and scratches, and produces higher-resolution images with better quality sound.
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Compact Discs (CDs)


Compact discs (CDs), which may be found in over 25 million American homes, not to mention backpacks and automobiles, first entered popular culture in the 1980s. But their history goes back to the 1960s, when an inventor named James Russell decided to create an alternative to his scratched and warped phonograph records—a system that could record, store, and replay music without ever wearing out. The result was the compact disc (CD). Made from 1.2 mm of polycarbonate plastic, the disc is coated with a much thinner aluminum layer that is then protected with a film of lacquer. The lacquer layer can be printed with a label. CDs are typically 120 mm in diameter, and can store about 74 minutes of music. There are also discs that can store 80, 90, 99, and 100 minutes of music, but they are not as compatible with various stereos and computers as the 74–minute size. The information on a standard CD is contained on the polycarbonate layer, as a single spiral track of pits, starting at the inside of the disk and circling its way to the outside. This information is read by shining light from a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The light from the laser follows the spiral track of pits, and is then reflected off either the pit or the aluminum layer. Because the CD is read through the bottom of the disc, each pit looks like a bump to the laser. Information is read as the laser moves over the bumps (where no light will be reflected) and the areas that have no bumps, also known as land (where the laser light will be reflected off the aluminum). The changes in reflectivity are interpreted by a part of the compact disc player known as the detector. It is the job of the detector to convert the information collected by the laser into the music that was originally recorded onto the disc. This invention brought 22 patents to James Russell, who today says he working on an even better system for recording and playing back music.
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CD-ROM

In computer science, acronym for compact disc read-only memory, a rigid plastic disk that stores a large amount of data through the use of laser optics technology. Because they store data optically, CD-ROMs have a much higher memory capacity than computer disks that store data magnetically. However, CD-ROM drives, the devices used to access information on CD-ROMs, can only read information from the disc, not write to it.

The underside of the plastic CD-ROM disk is coated with a very thin layer of aluminum that reflects light. Data is written to the CD-ROM by burning microscopic pits into the reflective surface of the disk with a powerful laser. The data is in digital form, with pits representing a value of 1 and flat spots, called land, representing a value of 0. Once data is written to a CD-ROM, it cannot be erased or changed, and this is the reason it is termed read-only memory. Data is read from a CD-ROM with a low power laser contained in the drive that bounces light—usually infrared—off of the reflective surface of the disk and back to a photodetector. The pits in the reflective layer of the disk scatter light, while the land portions of the disk reflect the laser light efficiently to the photodetector. The photodetector then converts these light and dark spots to electrical impulses corresponding to 1s and 0s. Electronics and software interpret this data and accurately access the information contained on the CD-ROM.
CD-ROMs can store large amounts of data and so are popular for storing databases and multimedia material. The most common format of CD-ROM holds approximately 630 megabytes (see Byte). By comparison, a regular floppy disk holds approximately 1.44 megabytes.
CD-ROMs and Audio CDs are almost exactly alike in structure and data format. The difference between the two lies in the device used to read the data—either a CD-ROM player or a compact disc (CD) player. CD-ROM players are used almost exclusively as computer components or peripherals. They may be either internal (indicating they fit into a computer’s housing) or external (indicating they have their own housing and are connected to the computer via an external port).
Both types of players spin the discs to access data as they read the data with a laser device. CD-ROM players only spin the disc to access a sector of data and copy it into main memory for use by the computer, while audio CDs spin throughout the time that the audio recording is read out, directly feeding the signal to an audio amplifier.
The most important distinguishing feature among CD-ROM players is their speed, which indicates how fast they can read data from the disc. A single-speed CD-ROM player reads 150,000 bytes of data per second. Double-speed (2X), triple-speed (3X), quadruple-speed (4X), six-times speed (6X), and eight-times speed (8x) CD-ROM players are also widely available.
Other important characteristics of CD-ROM players are seek time and data transfer rate. The seek time (also called the access time) measures how long it takes for the laser to access a particular segment of data. A typical CD-ROM takes about a third of a second to access data, as compared to a typical hard drive, which takes about 10 milliseconds (thousandths of a second) to access data. The data transfer rate measures how quickly data is transferred from the disk media to the computer’s main memory.
The computer industry also manufactures blank, recordable compact discs, called CD-Rs (compact disc-recordables), that users can record data onto for one-time, permanent storage using CD-R drives. Compact disc-rewriteables (CD-RWs) are similar to CD-Rs, but can be erased and rewritten multiple times. Another technology that allows the user to write to a compact disc is the magneto-optical (MO) disk, which combines magnetic and optical data storage. Users can record, erase, and save data to these disks any number of times using special MO drives.
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Hard Disk

Even after decades of evolution in computing, the hard disk drive remains the primary means of fast data storage and retrieval in computer systems of all sizes. The disk itself consists of a rigid aluminum alloy platter coated with a magnetic oxide material. The platter can be rotated at speeds of more than 10,000 rpm. A typical drive consists of a stack of such platters mounted on a rotating spindle, with a read/write head mounted above each platter. Early hard drive heads were controlled by a stepper motor, which positioned the head in response to a series of electrical pulses. (This system is still used for floppy drives.) Today’s hard drives, however, are controlled by a voice-coil actuator, similar in structure to an audio speaker. The coil surrounds a magnet. When a current enters the coil, it generates a magnetic field that interacts with that of the permanent magnet, moving the coil and thus the disk head. Unlike the stepper motor, the voice coil is continuously variable and its greater precision allows data tracks to be packed more tightly on the platter surface, increasing disk capacity. The storage capacity of a drive is determined by the number of platters and the spacing (and thus number) of tracks that can be laid down on each platter. Capacities have steadily increased while prices have plummeted: In 1980, for example, a hard drive for an Apple II microcomputer cost more than $1,000 and held only 5 MB of data. As of 2007 internal hard drives with a capacity of 500 GB or more cost around a $150.00.

Data is organized on the disk by dividing the tracks into segments called sectors. When the disk is prepared to receive data (a process called formatting), each sector is tested by writing and reading sample data. If an error occurs, the operating system marks the sector as unusable (virtually any hard disk will have at least a few such bad sectors). The set of vertical corresponding tracks on the stack of platters that make up the drive is called a cylinder. Since the drive heads are connected vertically, if a head is currently reading or writing for example sector 89 on one platter, it is positioned over that same sector on all the others. Therefore, the operating system normally stores files by filling the full cylinder before going to a new sector number.
Another way to improve data flow is to use sector interleaving. Because many disk drives can read data faster than the operating system can read it from the disk’s memory buffer, data is often stored by skipping over adjacent sectors. Thus, instead of storing a file on sectors 1, 2, and 3, it might be stored on sectors 1, 3, and 5 (this is called a 2:1 interleave). Moving the head from sector 1 to sector 3 gives the system enough time to process the data. (Otherwise, by the time the system was ready to read sector 2, the disk would have rotated past it and the system would have to wait through a complete rotation of the disk.) Newer CPUs are often fast enough to keep up with contiguous sectors, avoiding the need for interleaving. Data throughput tends to decrease as a hard drive is used. This is due to fragmentation. The operating system runs out of sufficient contiguous space to store new files and has to write new files to many sectors widely scattered on the disk. This means the head has to be moved more often, slowing data access. Using an operating system (or Parts of a typical hard disk drive. Many hard drives have multiple heads and platters to allow for storage of larger amounts of data. Users can periodically reorganize their hard drive so that files are again stored in contiguous sectors. Files can also be reorganized to optimize space rather than access time. If an operating system has a minimum cluster size c4K, a single file with only 32 bytes of data will still consume 4,096 bytes. However, if all the files are written together as one huge file (with an index that specifies where each file begins) that waste of space would be avoided. This is the principle of disk compression. Disk compression does slow access somewhat (due to the need to look up and position to the actual data location for a file) and the system becomes more fragile (since garbling the giant file would prevent access to the data in perhaps thousands of originally separate files). The low cost of high capacity drives today has made compression less necessary.
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