Re: Did Commodore cheat with the quad density floppies?

----- Original Message ----- 
From: <silverdr@wfmh.org.pl>
To: <cbm-hackers@musoftware.de>
Sent: Monday, January 07, 2019 6:58 AM
Subject: Re: Did Commodore cheat with the quad density floppies?



> On 2019-01-06, at 14:16, Gerrit Heitsch <gerrit@laosinh.s.bawue.de> wrote:
> 
>>>> Given two daisy-chained drives with the motor on/off signal on pin 16, how would you individually turn each separate motor on or off?
>>> A jumper of course, it's a PC & so it's full of them. One more won't
>>> hurt :-)
>>> 
>> ??
>> A normal daisy chain cable directly connects all lines, including  the motor on/off line, of the two drives together in parallel; how could a jumper anywhere turn on one motor while leaving the other turned off?
> 
> A drive that turns on the motor without the drive select line being active too has a design flaw. Properly designed drives would let you control the motor only if the DS line is active too. Yes, you would have to set the jumper for DS properly for each drive.

Precisely that. And the drive could be positioned anywhere on the chain too.
-----

Yes, and if wishes were horses beggars would ride. Although some modern direct-drive drives do have this option, the drives of the day did not; as a matter of fact some contemporary 8" drives were driven with a constantly-on 120 (or 240)V. line-powered motor, albeit often with a head-load solenoid. 

What I find slightly offensive is denigrating the IBM engineers of the day (by putting "engineers" in quotes for example) for devising an IMO very clever way of working around this 'shortcoming' without having to modify all the drives as you would have them do.

The alternative of turning on the motor with the DS signal would mean delaying access until the motor came up to speed; imagine disk-to-disk copy with relatively crude belt-driven motors starting and stopping with every access...

It's so easy to sit back and criticize the decisions and choices made in the distant past without fully taking into account the constraints that influenced them.