are viewing this page via a piece of software known as a 'browser'.
The page itself is downloaded as a series of instructions. It is not a complete entity, such as a picture or an image.
The set of instructions is used by the browser to assemble the page. That is, to set the text positionally, to determine its font, size and colour, to place images where they are intended, create menus - a complete re-build of the page on your computer to the initial page design. This is known as 'rendering' a page, and should look the same from all browsers. So far, this page has rendered 3 font sizes, in two colours, and placed a compass image in the top-left corner.
There are international standards and specifications that control these parameters so that whatever browser or computer you have, we will all see the same page the same way.
That is the theory.
This is the real world, and things don't work like that.
Oh, no, they really, really, really don't work like that.
The degree to which browsers wander off and interpret the instructions their own way has lead to a whole new industry in 'browser compatibility'.
The main browsers are Internet Explorer, Firefox, Safari, and Opera. There are many others. Each browser has gone through revisions and changes, sometimes to add new features, but mostly to correct previous blunders and bugs.
Where the browsers differently interpret page instructions there is usuallty a change in the visual appearance of that page. Microsoft's Internet Explorer (all versions) is the worst for deviating from the specification. It has errors and bugs that have been so well documented that there are industry standards for dealing with 'IE variations'. These bugs are even built into some web creation software to make things look OK on Internet Explorer and wrong on all the other specification compliant browsers.
With Internet Explorer having about 70% of the market (and falling) there is a certain arrogance at Microsoft, and its allies, to set themselves as the market leaders and claim their bugged system to be the industry standard. Many banks, and other dominant institutions, have their software written by Microsoft devotees with this notion of arrogance. Should you visit their web site with a browser other than IE you will be informed that you are running an 'incompatible' browser and you are advised to correct this sloppy attitude, and mend your sinful ways if you wish to view any more of their precious pages.
Other, more forgiving, web sites will be aware of the possibility of users wishing to use a browser of their own choice. They may warn that some features will only be available to some browsers, or they may have built in tolerance to deal with the variations. A web page is capable of detecting the current browser, and if containing sufficiently clever instructions, can modify the page assembly instructions to work around the known bugs in that browser. With the permutation of available browsers and their revisions, this is a pessimistically daunting task for any web site designer and this task is very rarely implemented.
Not all browsers, or versions of the same browser, are suitable for all computer operating systems. As an example - Apple's Safari browser was originally developed for the Mac range of computers. They then created a version for Microsoft Windows. Windows has many incarnations - Vista, XP, 2000, 98, etc. These again can only tolerate certain versions of Safari. I know for a fact Windows 2000 cannot cope with Safari revisions above 3.0.3, but XP and Vista can. Or, put another way, the people developing Safari decided not to support Windows 2000 when they advanced from version 3.0.3.
Certain add-on features, and new developments, can only be 'rendered' on later versions of browsers. An example of this is Google Maps - only works on Internet Explorer 6, 7 ... - not 5 or below.
Internet Explorer is integrally bound to a Microsoft Windows Operating System. Up until Windows 7 they cannot be divorced. Internet Explorer has hopelessly poor performance and security partly because of its tight binding to Windows.
Firefox, Opera and Safari and free-standing programs that are not a part of an operating system. They are free - no payment costs or license fee. They can be installed, uninstalled, upgraded and updated without integration to the operating system. On the Past Pages development computer I have IE, Firefox, Opera and Safari all loaded on the same PC. I sometimes have all 4 up and running at the same time for comparison purposes. A computer is not limited to running one browser. They are very clever when they install - they detect existing favourites and bookmarks and load them so that there is a continuity of browsing habits. If you have only ever used Internet Explorer, and spend a lot of time on the internet, I would recommend one of the alternatives.
Some high minded web designers have the arrogance to to favour one particular browser and will issue notices similar to This page is best viewed with Browser X . These are the worst kind of web sites as they want to impose their preferences on the user. For more on combating this attitude click the following button -
So, in summing up - the hardware that you are operating cannot cope with all operating systems, and operating systems cannot cope with all browsers. Browsers can have different page rendering qualities and come in different revisions to cope with new features, leaving the old versions blind to the new features. It is therefore not surprising to see that none of us are experiencing the same thing when we fire up our sparkly bits of whizzy technology to go surfing the web.
As a desperate gesture to publicise the incompatibility issue many organisations have produced Browser Compatibility charts.
These are not always singing the same song, and show variations. For one thing, they do not show that I can run Safari 3.0.3 on Windows 2000 Pro.
The charts do not indicate performance. As a general rule Firefox, Opera and Safari are faster at page rendering than Internet Explorer and usually leave Internet Explorer trailing in the dust. The developers of Firefox and Opera seem to make the best effort to have a browser that will work on most computers and operating systems.
Below is a selection of such charts, pirated from other well meaning sites in June 2008.
Most statistics charts will show Internet Explorer having the lion's share of browser use. This is not because it is the best. This is not because it is the most 'popular' - a term indicating that the users have tried the alternatives and prefer one against the others. It has the top spot because it comes with every new installation of Windows and the users cannot be bothered to find anything better.
As time marches on these charts will lose their relevance to today, but they give an indication of the mess we have.
Early reports (August 2009) of Windows Internet Explorer 8 indicate that it is a disaster. It apparently consumes vast amounts of system recources and has quirks that prevent it from rendering many legacy web sites. Rather than complying with industry standards it is wandering further from the path of compliance.
For a really brutal look at the mind-boggling complexity of this issue follow this link, and have a very stiff drink at hand.