Bandwidth, data, and speed are closely related terms and are sometimes used interchangeably. The amount of bandwidth that a computer connection is allotted determines how much data can be downloaded per second, or transferred from the Internet to the computer. More bandwidth equals more data per second, which translates to more speed. In some cases, a bandwidth limit refers to a speed limit, and in other cases it refers to a data limit.
For example, broadband Internet services sell access plans based on speed, limiting bandwidth according to each plan. Plans with higher limits are more expensive, but faster.
Luckily, many standard plans include unlimited access, so users don’t have to worry about limits in terms of data download. Every time the user visits a webpage, after all, the page must be transferred to the computer, constituting a download. This says nothing of files, programs, videos, and music that someone might download.
A number of online services do impose caps on the amount of data that can be downloaded over a set period of time. Depending on the service, data limits might apply to surfing as well as to downloading files or programs. A bandwidth limit might also apply to personal domains.
Subscribers of mobile broadband (Internet access supplied over cellular towers), commonly have bandwidth limits. Typically, an account is allotted a large block of “free” data, with charges applying for every megabyte downloaded past the allotted amount. If the account is contractual, the allotted amount refreshes or starts over every month. If the account is pay as you go, the limit applies to the segment of time purchased.
There are also limits associated with domains. People who have their own domains often find that the website host service imposes a monthly bandwidth limit on the account. Every time someone visits the website, the account racks up a download deficit that counts against this monthly allowance. The more visitors, the more the allowance is whittled away. If a popular site has a very low limit, the owner might find himself paying extra charges or having to upgrade the plan to increase the site's allotment.
Another example where these limits are found is in USENET newsgroup services. Services that sell access to binary newsgroups where people can share large files typically cap accounts with a limit that prevents downloading more data from the news server than has been allotted for the month. Some newsgroup services offer plans that charge a flat monthly fee for unlimited downloads, eliminating the limit.
People who find themselves regularly watching their bandwidth use may want to consider installing a bandwidth monitor. Many of these programs are free and will keep a running tally of downloads along with displaying real-time connection speeds. Some will also sound an alert at user-configurable points to announce and approaching threshold, allowing users to make better decisions about how to spend the rest of their bandwidth allotment.
Someone who is only concerned about a website’s bandwidth limit should know that most host services feature a built-in monitor accessible through the site’s administration interface. In addition to seeing how much bandwidth an account has left for the month, the host might also provide traffic analysis, information that can help improve the site's content.