bert@aiva.ed.ac.uk (Bert Hutchings) (07/15/87)
A recent question about CRT memories in comp.arch reminded me of the old LEO III and its engineers' store monitor. This was a small CRT with a square-wave brightness modulation and two sinusoidal X and Y coordinate modulations for each bit position in a word. The main X and Y sweeps displayed 16 words of 48 bits at a handswitch-selected address, and a stored 1-bit suppressed the small sinusoidal X modulation for that bit position. Since the X and the Y modulations were 90 degrees out of phase, each bit actually showed up on the little screen as a 1 or as a Lissajous 0. The engineers were very cruel, and used to tell ignorant visitors truthfully about binary encoding and that the main store was ferrite cores, then falsely that the cores stored a 1 when they were edge-on or 0 when they were face-on, and showed them the store monitor to prove it, claiming it was just a camera.