CNC, when it was done from paper tape - to some point in the 1980's, used both bi-directional PTRs and Reel to Reel PTRs. The essential function point was probably low operator intervention cycling through one or a few (CNC) programs (G code) : at its simplest execute then rewind . G code defines magic characters to indicate blocks, comments and end of tape; in computing usage the EoT marks are particularly unfunny as they can stop the transport ... (lift leg, cut track ...). The CNC controller would exploit this functionality. The RtR transport was probably the key function point, this model is the only twin capstan unit I am aware of - I suspect it simplified the (reverse) take up system design.
eg https://www.ebay.co.uk/itm/253377485885 a nice unit save that the LHS tension roller is chipped; machine a new one from Nylon 66 stock, 3D print one or take a chance ... The price is quite tasty, but they don't travel well : not MO to UK. The pair of centrifugal motor fans, look like mushrooms, need removed (grub screw) and packed seperately - very easy to shear the moulding. The PT spools are yet again XFU - probably the one thing less common than blank paper tape. Note two capstans, fwd and rev, and two take up hubs etc. But only one optical reader and one brake - configured for forward use. The standalone unit (including its control card) reads in either direction, speed (cps) being 5 x motor frequency (nominally 60 Hz @ 100V). While the unit can be controlled from the front panel switches, it also has remote control capabilities - TTL from the CNC controller proper. My RevEng of both the reader logic and transport board (pdf schematics) are in my Paper Tape Zoo - see https://www.emeritus-solutions.com/papertape/fanuc/visualise.php. And, I would very much like information on the remote control interface ... No manuals, no recollections, no anecdotes, ... I have asked in CNC land. Martin -----Original Message----- From: Paul Koning via cctalk [mailto:[email protected]] Sent: 02 March 2026 15:13 To: [email protected] Cc: Carey Schug <[email protected]>; Paul Koning <[email protected]> Subject: [cctalk] Re: Operating system, on punch cards? > On Mar 2, 2026, at 9:49 AM, Carey Schug via cctalk <[email protected]> > wrote: > > BOS and BPS for the 360 were on punch cards. That would make sense, since those were basic OS for machines with no tape or disk. > the Pitney bowes, later Raytheon, 440 had an operating system on paper > tape. they had a large spool with a biderectional high speed tape drive. That's wild, I never heard of a bidirectional paper tape reader. There is something vaguely like that in the original EL-X1 ALGOL compiler. Since the machine (originally) only had 4 kW of memory, it needed several passes. The intermediate object file tape would have the code on it, then a table of library symbol references at the end because only at that time would the list of needed functions be known. The loader needed to load those functions to resolve references, so rather than make two passes over that tape, the tape was read in reverse direction instead. It's rather strange to look at code that interprets a tape read backwards. paul
