As an official download chart is launched, BBC News Online asks the music industry what the impact will be for singles.
Rock band Muse recently sold 5,000 copies of a song on the internet
Official music download websites could replace record shops as the public's preferred places to buy singles within five years, one of the UK's leading music industry figures has said.
The singles chart is under threat in its current form, Peter Jamieson, executive chairman of the British Phonographic Industry, which represents UK record companies, told BBC News Online.
A new chart drawn from the legal download sites such as Mycokemusic.com, Napster and iTunes will be launched officially on 1 September. Test charts start this week, with the Pixies' Bam Thwok heading the chart.
On Monday the BPI said that it would not be a competitor to the singles charts, because the new chart had a "much broader range" that included exclusive songs and non-single tracks from albums.
"It's very difficult to say at this stage if and when downloads are going to take over from physical formats like CDs," he said.
"When Steve Jobs launched iTunes two weeks ago he said he expected downloads to have five per cent share of the US singles market in two years time," he said.
Last year the BPI's chairman Peter Jamieson said the demand for legitimate downloads would grow over the coming years and digital sales figures were likely to challenge those from shops, Mr Jamieson said.
"Don't ask me where, in five years time, it will end up - be it 50-50 or 60-40 in whichever direction," he said.
"But I see both of them as being significant businesses."
He also said the growth rate would depend on how much money the industry put into new services.
"But we are, as a music industry, responding to that consumer preference."
Mr Jamieson said: "It's our job to make sure that the charts are good, reflect popular taste and are a sensible marketing tool for the industry."
But they were currently under threat "because there isn't a good enough or strong enough download avenue".
Christina Aguilera came top of the first official download chart in April
They were also under threat because "the decline in physical singles sales is becoming more noticeable", he said.
Online successes have given the industry evidence that such ventures can attract fans in large numbers.
An estimated 5,000 fans last year bought a new track by rock band Muse for 99p - nine weeks before the album was released, industry magazine Music Week reported. It could have charted in the Top 40, analysts said.
The reformed Pixies' decided to release Bam Thwok - their first song in 12 years - not through a record company but through Apple's iTunes music service.
Download services like Kazaa - where fans swap songs for free - would have to be eradicated "in due course", Mr Jamieson said.
"But I think you've got to grow viable legitimate alternatives so you can genuinely say to the consumer 'hey, stop stealing.'"
"It's got to be pretty easy for the consumer to do it properly before they will respond to you.
"I'm quite confident that once we have enough appropriate services out there, there will be - for all the right reasons - a drift towards them."
Some within the industry want the new chart to be revealed on a Friday - rather than a Sunday - to boost weekend business.
There are also proposals to reduce the wait between a single first being played on the radio and being available to buy.
More two-track, cheaper CD singles are also likely to appear, while others are expected to be released as DVD singles to give fans more material.