The Octalink bottom bracket was chosen, partly because I wanted to fit a Tiagra chainset at the front. Tiagra as a component quality is the road bike equivalent of a rough and tumble mountain bike. The component group often being used on touring bikes and long range commuters.
Octalinks are Shimano's evolution of the square tapered bracket. Instead of a square taper for the crank arm, the crank arm is splined partly to give better purchase and transmission of the crank arm on to the bottom bracket. Partly to have a patented pattern that other manufacturers couldn't copy and so lock users into one make of component. It's an evolution that works as looking through the parts list it was getting harder and harder to find one that wasn't Octalink or ISIS based. Which in itself is silly becuase the square taper is effectively bomb proof and easier to manufacture. But I guess in a modern world looking for lightness and the next best thing everyone is happy to be tied into one manufacturer.

The chain has been replaced with a SRAM 9 speed, because after mucking around with all those pins on the Shimano I can't be bothered spending another £5 because the pins won't insert straight and break. The powerlink clip makes it much easier to work with and has the advantage of if I change any of the gear ratios I will be able to shorten quickly and easily without fuss.