Modern capital markets are almost invariably hosted on computer-based electronic trading platforms; most can be accessed only by entities within the financial sector or the treasury departments of governments and corporations, but some can be accessed directly by the public. As an example, in the United States, any American citizen with an internet connection can create an account with TreasuryDirect and use it to buy bonds in the primary market, though sales to individuals form only a tiny fraction of the total volume of bonds sold. Various private companies provide browser-based platforms that allow individuals to buy shares and sometimes even bonds in the secondary markets. There are many thousands of such systems, most serving only small parts of the overall capital markets. Entities hosting the systems include stock exchanges, investment banks, and government departments. Physically, the systems are hosted all over the world, though they tend to be concentrated in financial centres like London, New York, and Hong Kong.