Date   : Tue, 26 Mar 1985 15:03:00 PST
From   : "R. MEIER" <rmeier@SU-STAR.ARPA>
Subject: re: CP/M card for Apple ][+

To:mailer!info-cpm@brl-tgr.arpa
From:rmeier@star.arpa

Ed,
       I have been using a Z80 card in my Apple ][+ for a year now without
serious problems.  Specifically, I use a Softcard from Microsoft.  It came
with CP/M 2.2 and runs a 2.1 MHz.  It accomplishes this by using a
nonsymmettric clock that is synchronized with the Apple's internal clock.
The Apple's internal memory is used.  I tried to rewire the card, so as to
double its speed to 3.5 MHz, but this failed intermittently due to the fact
that it exceeded the speed of the Apple's memory and I didn't think it worth
the effort to add wait cycle logic.
       Their Softcard has worked reliably and timing experiments have shown
that it works at a consistent 2 MHz, unlike some cards which use wait cycles
to operate slower than the advertized clock speed.
       My only complaint against this card, is that the CP/M 2.2 that is
supplied with it is rather inefficient in terms of memory and time.  Memory
cycle observations have shown that as many as 300 subroutine calls may be
involved in a single bdos call.  The operating system occupies 20K of memory.
I have dreamed of writing my own unixlike operating system, but I don't
expect that I will ever get the time.
                                       Bob