Re: Did Commodore cheat with the quad density floppies?

----- Original Message ----- 
From: "Gerrit Heitsch" <gerrit@laosinh.s.bawue.de>
To: <cbm-hackers@musoftware.de>
Sent: Tuesday, January 08, 2019 4:05 PM
Subject: Re: Did Commodore cheat with the quad density floppies?


> On 1/8/19 9:48 PM, smf wrote:
>> On 06/01/2019 13:16, Gerrit Heitsch wrote:
>> 
>>>
>>> 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.
>> 
>> That would require you to interrupt communication with one drive while 
>> starting or stopping the motor on another.
>> 
>> As starting a motor takes an appreciable amount of time, it makes sense 
>> to overlap them.
>> 
>> If starting the motor while the drive isn't selected causes problems, 
>> then that is a design error.
> 
> It doesn't cause problems, it just means that you need 2 control lines 
> per drive, one to select the drive and one to control its motor.
> 
> That's only possible if you limit the number of drives on a 34pin cable 
> to 2 while the shugart spec allows 4.
> 
>  Gerrit

Could you show us an example or two of desktop systems that actually _had_ four internal full height drives on the same cable, as opposed to IBM's two internal and two external? Why is four drives on one cable instead of 2 + 2 such an important issue for you and silverdr?

Note that the PC's A/B drive selects and drive B's motor control do follow the sacred Shugart standard; it's only drive A's motor signal that's non-standard to allow independent control; just jumper it to pin 16 if you must.