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From: sdyer@bbncca.ARPA (Steve Dyer)
Newsgroups: net.micro.6809
Subject: Re: non RS *FIRST* disk???
Message-ID: <669@bbncca.ARPA>
Date: Fri, 13-Apr-84 16:00:45 EST
Article-I.D.: bbncca.669
Posted: Fri Apr 13 16:00:45 1984
Date-Received: Sat, 14-Apr-84 09:30:24 EST
References: <1233@ucf-cs.UUCP>
Organization: Bolt, Beranek and Newman, Cambridge, Ma.
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It is certainly advisable to avoid buying a R/S disk, even as your first (I
didn't take this advise, and only recently sold it off to a true RSDOS
fan.) It will run no faster than a 20 ms step rate, has only 35 tracks, and
is single-sided.  I would advise buying two double-sided TEAC or Shugart
40 track drives--these will read and write ordinary R/S disks.  On the other
hand, it is probably a good idea to buy the Radio Shack disk controller (or
the functionally compatible J&M controller), simply because you will be
able to run the R/S "standard" OS9 operating system.  I recommend two
disks because attempting to use OS9 with only one disk is an exercise
in patience, if not futility, and the new K&R C compiler practically
demands two disk drives.

The R/S controller can support double sided disks, provided you don't use
their 34-pin ribbon cable which uses the "side select" pin as drive 3
select, and which addresses drives at the connector.  What you want is a
cable which passes all pins straight through to the drives.  Thus, the R/S
disk controller, suitable programmed, can support three double-sided
drives, 40 or 80 track.  FHL Flex, and several OS9 disk driver replacements
use this scheme.

Now, if you are interested in performance, the RS controller stinks
(as do many inexpensive non-DMA controllers.)  The controller asserts
HALT to the 6809 during the period that it cannot accept or produce
a byte of data, and disk reads and writes run in a tight lock-step
loop.  But, having this controller will allow you to develop a better
hardware scheme.  
-- 
/Steve Dyer
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