tape drives

That doesn't really matter, since folks figured out soon enough that whatever you could shove through the head was digital enough. The guys clever enough to design passive filters and write code to match easily figured out what the fastest frequency they could reliably shove onto the tape was and then toggled an F/2F code into the input where F was half that rate. It worked GREAT! The issue I was addressing was that the computer could control the tape movement. Perhaps it was an earlier machine that had the electronically controlled audio cassette drive (Commodore?). Nevertheless, if you run the tape by the heads even if the tape isn't being pressed against it, with any tension at all you should be able to pick up a signal burst on the order of 2 khz at the accelerated speed. That can be a record mark. The fellow who designed the original set of 6502 computer boards I used managed to build a nominally 5600 bps audio cassette interface channel in a PCB area about the size of a dime, using only one port bit in and out. If one wrote to tape while it was in the fast transport speed (which not all transports can do) then you could easily detect that there was signal, while the program, written at slow speed (1-7/8 ips ?) didn't pass the filter. That can be done with the right transport. Dick ----- Original Message ----- From: "Sellam Ismail" <foo(a)siconic.com> To: <classiccmp(a)classiccmp.org> Sent: Thursday, May 17, 2001 7:53 PM Subject: Re: tape drives