Re: Did Commodore cheat with the quad density floppies?

On 1/10/2019 3:46 PM, Gerrit Heitsch wrote:
>
> Well, if you want to have identical drives but be able to adress them 
> seperatly and use a 34pin Shugart cable, then you have 2 choices:
>
> 1) Modify the cable between the 2 drives. Advantage: Only one cable 
> necessary. Disadvantage: Special cable needed. Probably involved 
> manual labour at least at the beginning => price.
>
> 2) Each drive gets its own cable to the controller card and the pinout 
> of the 2 connectors on the card decides which drive is which. 
> Advantage: Simple 1:1 cable. Disadvantage: You need one cable per drive.
>
I would concur.  I can only thus assume that the cost to flip the wires 
was less than the cost for the second set of wires, single IDC conn (the 
other would be needed either way), and the 2 extra IDC headers on the 
FDD card (to support 4 drives) outweighed the early manual cost of 
flipping wires.  Probably a safe assumption, given the cost to lay out 
the 2 extra conns on the FDD controller would have driven up cost 
quickly (PCB space, etc.)

I would also assume that putting a single drive on a cable would allow 
people the naive but wrong assumption that a second drive could be 
connected by just adding the conn and putting a second drive on the 
cable.  The twisted cable prevents that assumption.

And yes, Mike is right, other resources online noted the concern around 
power (or, maybe to put another way, IBM wanted to hit a price point on 
the PSU, and the selected PSU would be marginal with 2 drives on at the 
same time - concerning the heavy initial current motors take when they 
spin up)

Jim