For much of its history Melbourne has been Australia's largest single centre of manufacturing. Once the gold rushes of the 1850s increased Melbourne's population more than fourfold in a decade and a policy of import protection was implemented in the 1860s, manufacturing became the biggest sector of the Melbourne economy and the main source of employment. Protective tariffs probably contributed to the pre-eminence of manufacturing in Melbourne. So too did government bonuses and subsidies offered to Victorian firms, especially engineering and metal workshops, for locomotives and other railway equipment, water supply and irrigation pipes.
In the 20th century, Melbourne's economy became more diversified. Population growth (fuelled partly by natural increase, but also by overseas immigration and the movement of population from the countryside) and government tariff and infrastructure policies encouraged the development of manufacturing. New manufactured products made some service jobs obsolete (for instance, refrigerators meant that there was no longer any need for ice to be delivered to homes) but the creation of new service jobs helped to offset those which had been lost. These developments were in line with overseas trends and in the 20th century Australia had a service sector which was comparable in size and composition to that of other developed countries.
From the mid-1970s, a globalised 'new economy' created investment and job opportunities in a broad range of industries, such as research and development, transport and distribution, business services, information technology, retailing and high-value manufacturing. In the 'new economy', the offices of an Information Age have replaced the factories of the Industrial Age as key generators of wealth, where skilled workers process and transform information, rather than raw materials, into products (which may be manufactured or finished off-shore). In Melbourne, many of these new workplaces are located in the central business district or in the old inner suburbs, as old buildings have been demolished or remodelled to accommodate new uses.