In website evaluation, bandwidth refers to the amount of data that can be transmitted from your web server to your customer's computer. It is important because every web page consists of data (the HTML or page file, as well as the graphic files and others) that must be transmitted. The larger the amount of data on a web page, the longer it takes to transmit - and the longer your customer waits to be able to see the page.
A beautiful home page full of lush graphics may look great on your developer's 18 inch LCD monitor - but if it takes 2 minutes to download that page on a slow bandwidth connection (like a dial-up modem that uses a phone line), your customer will never see it, because customers won't wait.
A usable website takes the bandwidth requirements into account.
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