Algorithms have long been used by the capital markets industry. In the beginning, and still today, algorithms are created on spreadsheets by some and other more complex methods are used by others. What has evolved is not necessarily the tool used to do the programming, but the complexity of the algorithm itself, both in terms of technological requirements to execute the algorithm and the intelligence weaved into the program.
Multiple markets and the ever evolving market microstructure globally, require algorithms to be intelligent - built with the programmer’s knowledge and an extensive decision tree to provide for when the computer meets or doesn’t meet various parameters. There must also be disparate algorithmic strategies so as not to be seen in the books of the proliferating venues that are queried for liquidity.