I worked for a couple of years on clearing tech and have worked in trading tech. The two sides are didn't share much in the way of systems but clearing tech came first and enabled e.g. direct exchange data feeds. Clearing is the quintessential PG "schlep" problem, relatively easy math, an administrative hassle to set up accounts and connectivity. Dominated by a few big players and "enterprise" software vendors that no one is really happy with.
Some of the systems from the 1970's are still in production. Our technology counterpart from one of the main US CCP's [1] (and a really nice guy) told us he was running a mainframe emulator on his Windows box to service requests in 2010. Wish I could remember what the mainframe was.
[1] http://en.wikipedia.org/wiki/Central_Counterparty_Clearing
Edit: fixed mispaste, link, clarified
But I'm not sure what your question is in response to. Was there a suggestion of a link? I didn't see algorithmic trading mentioned, simply a description of the automation of trade processing that has occurred over the years (vs automation of the trade decision making process).