AIM was set up by the London Stock Exchange in 1995 to help faster-growing companies raise cash. The junior exchange started trading with 10 members.
Now, 650 companies are quoted compared with 2,500 on the main market.
AIM offers tax breaks to encourage retail investors and also has looser regulations to make floating easier for smaller companies.
Firms quoted on the main market must be vetted by the LSE, have three years of trading records and at least 25 per cent of their shares on the market, and also ask shareholders to approve substantial acquisitions or investments.
None of these regulations apply to AIM companies, which only need to employ a nominal advisor - usually a stockbroker.
In contrast, main market firms need a sixstrong team consisting of a stockbroker, corporate advisor, bank, auditor, lawyer and financial public relations outfit.
Brokers can cost £20,000 a year - or £30,000 if they also act as a corporate advisor - and financial PR firms charge between £15,000 and £25,000.
The costs of being quoted depend on the size of the company and the amount of deals being done, but a busy main market firm can easily run up annual bills of £350,000 to £400,000.
On AIM, the cost of being quoted is generally regarded as being 50 per cent less than the junior exchange.
*Amco contractor Andrews Sykes plant Artisan developer/house builder Asite architectural website Cape materials Connaught FM *Darby glass producer *Dimension Resources quarrying/fabrication Enterprise FM/utility or Interior fit-out contractor James Halstead flooring manufacturer James R Knowles construction lawyer Maclellan FM Mears FM Montpellier contractor *NBA Quantum consultant Propan Homes house builder *Pipehawk ground penetrating radar *Samuel Heath bathroom products manufacturer Send modular housing *Stenoak roads contractor Telford Homes house builder Tricorn products *Tolent contractor Water Hall quarrying Weeks consultant Wigmore FM *AIM construction sector