Subject: PC floppy cable twists...
From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
Date: Thu, 20 Oct 2005 17:48:04 +0100
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>
.... discussion about this on another list got me curious - what *was*
the point of that cable twist in a (IBM clone) PC floppy cable, when
every other system on the planet was using straight-through cables?
1) Great, it means both drives in a system can be jumpered for the same
ID - but someone's still got to go in and jumper/modify the last drive
in the chain so that it's terminated, so it's not like the twist
eliminates messing around with jumpers.
Jumpers were not messed with. Drive arrived, plugged in and go. Cost
of delivering service was by then high enough that giving the drive away
to avoid the call was actually becomming loss avoidence!
2) when the twist was introduced, there were presumably
no clone
machines around (it was there from day 1 IIRC) - and wouldn't the
addition of a second floppy drive to an IBM machine have been a field
service call anyway? So it's not like it was the general public changing
jumpers, but a trained engineer...
There was no jumper change. All had pullups and they are sized to allow
two in parallel without problems.
3) IBM seemed to use a very small range of drives in
the PC / XT / 286
days, so it's not like there'd be a million jumper combinations to
figure out. If a customer tried to add their own drive rather than
buying through IBM, surely IBM couldn't care less if they struggled to
figure the drive jumpers on their 'non-standard' unit out?
2 is greater than 1. Cost to stock two is greater than one.
It's got me curious as it seems like a hack that
doesn't completely
solve any kind of problem whilst introducing a difference between IBM
and the rest of the industry.
cheers
Jules
You missed the most basic reason. One part, one bin, one stocking number
and less standing stock. Logistics of warehousing costs and space not
electrical design.
Everyone seems to forget or even miss that not too long after the PC was
introduced and clones appeared the costs of producing, stocking and servicing
them were under great pressure. Anything that cost, even pennies, could put
a vendor at risk. Why did some vendors disappear?
Allison