>
>Subject: Re: PC floppy cable twists...
> From: "Teo Zenios" <teoz at neo.rr.com>
> Date: Thu, 20 Oct 2005 14:51:46 -0400
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>
>----- Original Message -----
>From: "Allison" <ajp166 at bellatlantic.net>
>To: <cctalk at classiccmp.org>
>Sent: Thursday, October 20, 2005 2:35 PM
>Subject: Re: PC floppy cable twists...
>
>
>>
>> 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
>
>The original clone makers still had a huge profit margin so a few pennies
>would not have mattered until the huge 1989-91 shakeout where pretty much
>everybody started competing on nothing else but price (and purchasing power
>benefits). I remember advertisements (early 90's ?) where DELL was comparing
>its server to Compaq and it was thousands less for the same spec machine.
But it did matter. It was only a matter of time that some vendors that
were bleeding from the eyes tossed in the towel or were gobbled up.
one of the major steps was to move to offshore production to reduce
product costs.
>From inside the industry it was already apprent by the late 80s that
costs were under pressure. The clone companies often had a great
advantage as they were smaller and less burdened than IBM, DEC and
others. By '91 some were already dead or dieing.
Allison
>
>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
>
>Subject: OT: Tube Audio
> From: lee davison <leeedavison at yahoo.co.uk>
> Date: Thu, 20 Oct 2005 17:02:33 +0100 (BST)
> To: cctalk <cctalk at classiccmp.org>
>
>> I didn't say nonexistant, only rare. Dynaco was amoung the best
>> then. The alternate was a filiment that was balanced to ground to
>> minimize the amplitude of AC heater to cathode coupling, also only
>> seen on quality gear.
>
>Another, rarer, alternate used with directly heated cathodes is to
>have two cathodes heated by a Scott wound transformer that gives
>two phase AC current with a 90 degree phase difference. This
>reduced heater generated noise because the noise is a function of
>the square of the heater voltage and sin^2 + cos^2 = 1, effectively
>a DC component.
>
>I have only ever seen this arrangement used on broadcast equipment.
>
>Lee.
The other technique is far simpler. Balance, do the same thing only
in mirror image. The reduction in hum and some types of noise is
substantial and tube engineers understood it well. The common
examples were 3A5s, 810s or maybe 813s in push pull pairs (both
have directly heated cathodes).
Allison
On Oct 18 2005, 8:29, John Foust wrote:
> At 01:39 PM 10/17/2005, Bob Bradlee wrote:
> >With the aid of a paperclip and a prybar, I opened up the drive to
fine a
> >shattered CD inside.
> But I've seen this happen *twice* to a client who wasn't
> dunking them in LOX. CDs are spinning quite quickly.
I've never actually seen it happen, but a couple of years ago one of
the manufacturers who supplies the University issued a warning about
fast drives, and IIRC some were recalled. The explanation was that the
faster "52x" drives run at a speed which is very close to that at which
centrifugal force can make a polycarbonate disk break up, so a defect
in the disk can have a profound effect.
--
Pete Peter Turnbull
Network Manager
University of York
Regarding the drive termination, I distinctly remember pulling terminators
on the middle drive in a two-drive setup...just like a SCSI chain. I don't
know about new drives (because I don't usually have multiple drives in my
machines now), but some more modern Teac drives have a termination jumper
rather than a resistor DIP pack.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Chuck Guzis
Sent: Thursday, October 20, 2005 1:19 PM
To: cctalk at classiccmp.org
Subject: Re: PC floppy cable twists...
On 10/20/2005 at 5:48 PM Jules Richardson wrote:
>... 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?
It's actually pretty simple--there's only a single "motor on" line for the
standard floppy pinout. IBM wanted to control drive motors individually.
The only ways to do that are with individual drive cables or using the
"twist" (or some modification of it) so that the individual drive motor
enables are given different conductors in the cable.
Other systems using "straight through" cables switched all drive motors on
and off--and many consequently used drives with head-load solenoids. IBM's
solution let them economize a bit on power-supply design and use a cheaper
(and quieter) drive without the head-load mechanism. FWIW, IBM makes no
mention of terminator removal or addition and I don't even recall if the
standard 5.25" drive allowed one to play with termination.
On one of the ISA floppy/hard controllers--I think it was DTC--you could
add a third drive to the string using a special cable and a drive jumpered
for DS0. (I'd have to check my doc files to get the rest of the details on
the cable construction).
Cheers,
Chuck
All:
There's a listing on eBay for ASCII art TTY printouts (#8707360741)
and it raised an interesting question. I remember as a kid going to my
father's office (he worked for New York Telephone in New York City) at
Christmas and they had various computer systems that they let the kids play
on. One of them (I don't remember which) had a program to print calendars.
In the eBay listing, there's a Snoopy Red Barron calendar, which I
distinctly remember printing out.
What program would have made this calendar and is one still
available, somewhere, that I could run on Windows or through something like
SIMH?
Rich
Rich Cini
Collector of classic computers
Build Master for the Altair32 Emulation Project
Web site: http://highgate.comm.sfu.ca/~rcini/classiccmp/
/************************************************************/
>I was reminiscing to someone about an old GE mainframe
> with an analog meter that registered Kops/sec.
... made by Keystone Electronics perhaps? :)
-Charles
>In a message dated 10/19/2005 6:56:33 PM Eastern Daylight Time,
>julesrichardsonuk at yahoo.co.uk writes:
>We've just been offered one of these - I'm assuming (awaiting further
>details) that it's a rebadged Apple II Plus, as in:
>http://oldcomputers.net/bellandhowell.html
>... but that doesn't mention the "Digital Video Presentation" side of
>it, or even any video extras over and above what the II Plus has.
>Anyone know any more details? Did Bell and Howell ever do any other
>computer-based systems?
>I will get some more info from the owner (and they have the full doc set
>apparently), but I'm being impatient :-)
That's interesting, I work at B+H (now Bowe Bell and Howell) and I've never
heard of any of the old stuff at work. BBH is primarily know for mail
processing systems and technologies, neat stuff!
> I didn't say nonexistant, only rare. Dynaco was amoung the best
> then. The alternate was a filiment that was balanced to ground to
> minimize the amplitude of AC heater to cathode coupling, also only
> seen on quality gear.
Another, rarer, alternate used with directly heated cathodes is to
have two cathodes heated by a Scott wound transformer that gives
two phase AC current with a 90 degree phase difference. This
reduced heater generated noise because the noise is a function of
the square of the heater voltage and sin^2 + cos^2 = 1, effectively
a DC component.
I have only ever seen this arrangement used on broadcast equipment.
Lee.
.
___________________________________________________________
To help you stay safe and secure online, we've developed the all new Yahoo! Security Centre. http://uk.security.yahoo.com
Gordon recently mentioned that he had a dwindling supply of absolute filters for his RL02 drive. They are still readily available from several sources including Air Filtration Products (airfiltrationprod.com) and isesurplus.com. I just ordered one from The Filter Factory (www.thefilterfactory.com) for $28.95 plus UPS.
-Charles
