Here is the host adapter in its full glory. I think all the circuit really amounts to is a logic circuit to convert the signals going to and coming from the Winchester disc controller into messages which the Beeb can understand via the 1 MHz bus. The blue connector at the top is a 34-way connector to take a ribbon cable to the 1MHz bus. At the bottom is a 50-way connector to attach to a SCSI type hard disc controller which itself either forms part of the hard disc unit or then goes via another cable to the actual hard disc drive.

It is VERY important to get the 50-way cable the right way round otherwise you will get strange whining noises and the ribbon cable will melt!! Believe me, I know!!

The host adapter needs its own power source. In the top left hand corner you can see a famous BeebMaster bodged soldering job as I attempted to attach two wires to go to a power supply.