The download time for a web page, defined as the time it takes for the remote computer to retrieve the data from the web server, is a critical issue in web development. It is assumed that the visitor of the site is there for a reason, whether to access information, communicate with others, or to pursue a personal interest. Very rarely will a site visitor be interested enough to wait longer than 2 or 3 minutes for the entire content of a page to be loaded into the web browser, and more often when this happens the decision will be made to try another online resource. Thus download time can affect the usability of a page, as well as an entire site.
Connection Speed
There are a number of factors that affect the speed at which a web page is downloaded. An obvious one is the speed at which the user is connected to the Internet. Dial-up (modem) connections are peaked for the time being at 53k/sec. In accordance with FCC regulations, download speeds of 56k/sec. are unattainable through a normal phone line. Depending on bandwidth usage and Internet traffic, the modem speed generally averages around 40-42k/sec. The dial-up connection speed is not the only thing a developer must keep in mind when designing web pages scaled for the average modem. Even at a reported connection speed of 53k/sec., a page that is 53k in size can take much more than a second to be displayed. The reason for this is the modem speed states only the data transfer rate and not the time it takes for the computer's processor and software to display the final product. These additional factors will increase the overall time required to display a page.
Graphic Size
Another critical factor in building a web page for speed is the size of any graphics used on the page. In fact, this should be the primary concern of the web developer as the page is being designed. Graphics tend to be the largest elements of a page and their large size tends to create problems when the browser is trying to download and display the file simultaneously. While the modem is designed to transmit, receive, and correct errors in binary data with maximum efficiency, the web browsing software has more limitations in the form of available active memory, processor power, etc. This is what accounts for the "tiling" effect that is noticeable when displaying a web page with large graphics.
Additional Size Issues
There are a number of lesser concerns involved in creating a fast loading web page. One of these is the presence of "bloated" or unnecessary code in the web page itself. The web browser compiles the code "top-down", and the more code there is to tell the browser how to render the page, the slower it will be displayed. With the advent of style sheets, much of the inefficient code that caused loading problems can be avoided, and should be. Another issue is the use of advanced features, like JavaScript, Java applets, Flash media, and Portable Document Format (PDF) documents. JavaScript is compiled by the browser upon page load, so scripts takes time in a similar way that graphics do. More advanced features like Flash or PDF use plugin applications that need to be launched for the contents of the web page to be viewed thus taking additional time to display a page.
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