see also http://www.samhallas.co.uk/repository/po_docs/system_x.pdf http://www.samhallas.co.uk/repository/po_docs/system_x.pdf and http://www.samhallas.co.uk/re

see also http://www.samhallas.co.uk/repository/po_docs/system_x.pdf http://www.samhallas.co.uk/repository/po_docs/system_x.pdf and http://www.samhallas.co.uk/repository/journals/BTEJ/BTEJ%20Vol%203%20Part%204%20Jan%201985%20System%20X.pdf http://www.samhallas.co.uk/repository/journals/BTEJ/BTEJ%20V... and this https://www.academia.edu/39809466/System_X_The_history_of_the_development_of_the_UKs_first_computer_controlled_telephone_switching_system https://www.academia.edu/39809466/System_X_The_history_of_th... by http://www.kingdom-technology.co.uk/malcolmhamer.php http://www.kingdom-technology.co.uk/malcolmhamer.php