What on earth is? Broadband

Broadband: that's fast internet access, right? Wrong. Well, wrong as far as the true definition goes, which is why ISPs can call their paltry 128Kbps services 'broadband' in their ads and get away with it.

Strictly speaking, broadband has nothing to do with the internet and it's simply a term that refers to any high-bandwidth connection. Well, we say 'simply' but unless you have a degree in computer science, you're probably still none the wiser.

Bandwidth is a measure of how much data that can be transferred between two points at any one time. Writing has more bandwidth than speech, for example, since you can usually read a page in far less time than it takes to listen to someone read it aloud.

Similarly, a publisher looking to distribute the latest batch of Harry Potter books would opt for a high-bandwidth lorry (lots of copies in the back) over a low-bandwidth motorcycle courier (one copy in his satchel).

When it comes to computers, the introduction of kilobytes (KB) and megabytes (MB) starts to complicate things but the principles are the same.

A hard disk, for example, has much more bandwidth than a floppy disk drive, since it can transfer around 41,000 pages of Notepad text in one second (about 40MB, for those that are interested). A floppy disk drive, on the other hand, can only transfer around 500 pages (about 50KB) in the same amount of time.

Internet connections are much the same. An ordinary telephone line is slow at transferring data and, being low bandwidth, a dial-up modem connection is often called 'narrowband'. An ADSL-converted telephone line or cable TV fibre optic line, however, has lots of bandwidth, hence 'broadband'.

Here comes the 'but': An internet connection may have lots of bandwidth but that doesn't mean its users have access to it. Cable TV companies, for example, use most of their bandwidth for delivering TV programmes and the rest is then shared on a street-by-street basis for internet access.

That internet access might be fast (2Mbps with some ISPs) or it might be slow (128Kbps for others) but since both are delivered over a high-bandwidth connection, they're both technically broadband.

The science
We fibbed a bit when we explained how bandwidth applies to internet connections in order to keep things simple. When it comes to networking (an umbrella term under which all internet connections fall), broadband really refers to how many signals can be sent over a connection at the same time and that depends on the range of available frequencies.

A fibre optic cable TV connection typically has 750MHz of bandwidth, with each TV channel it carries requiring 6MHz a piece. In other words, a cable TV service is limited to around a 100 TV channels.

For internet access, cable TV companies usually devote one channel's worth of bandwidth for downloading and that gives a speed of up to 36Mbps, to be shared between everyone connected to that particular bit of the network.

Less bandwidth is usually given over to uploads, since most people download more data than they upload. Typically, a broadband service downloads at 512Kbps and uploads at 128Kbps and most broadband services are therefore 'asymmetrical' networks.

The basics
Bandwidth isn't an easy concept, so here's a simple analogy. Outside your house, under the road, is a large pipe that carries hundreds of gallons of fresh water a second.

You, however, only have access to a fraction of that amount, since the pipes that connect your taps to it are narrow, but that's still ample for most households.

Similarly, broadband ISPs maintain a 'fat pipe' (no, really) that transfers dozens of megabytes of data each second - lots and lots of bandwidth, in other words. That bandwidth is then shared between the ISP's customers, who are usually allocated 512Kbps each.

Unfortunately, just as a main water supply couldn't maintain its pressure if every household it served turned all of their taps on at once, an ISP's fat pipe lacks the bandwidth to provide every customer's full allocation at the same time.

Fortunately, most internet tasks - web browsing, email and so on - are low bandwidth, which means there's always some spare capacity.

The system isn't foolproof though and if you spend all day, every day downloading enormous files, you're hogging bandwidth. Just imagine how you'd feel if your shower slowed to a drip while your neighbour turned on all of their taps to fill their swimming pool.