sentences:  In 1961 after ten years of intermittent contact Wiseman joined the staff of the University Mathematical Laboratory, Cambridge, now the University of Cambridge Computer Laboratory, as Chief Engineer.He continued working with tunnel diodes and constructed a prototype store capable of running at 250 megahertz, a phenomenal speed for the time.The arrival of one of the world's first mini-computers, the DEC PDP-7 and its type 340 vector display, presented new challenges.