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_at_siconic.com>
To: <classiccmp_at_classiccmp.org>
Sent: Thursday, May 17, 2001 7:53 PM
Subject: Re: tape drives
> On Thu, 17 May 2001, Richard Erlacher wrote:
>
> > speed control, but it did work. The Coleco ADAM (?) or some other
> > similar setup used a computer-controllable drive. That could have
> > been exploited in such a way as to allow multiple programs to be
> > recorded on the tape.
>
> The ADAM used a digital tape format.
>
> Sellam Ismail Vintage Computer Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger http://www.vintage.org
>
>
Received on Fri May 18 2001 - 00:06:24 BST