see also http://www.samhallas.co.uk/repository/po_docs/system_x.pdf and http://www.samhallas.co.uk/repository/journals/BTEJ/BTEJ%20V...

and this

https://www.academia.edu/39809466/System_X_The_history_of_th...

by http://www.kingdom-technology.co.uk/malcolmhamer.php