Ultra DMA (80-Conductor) IDE/ATA Cables, Why is Illegal...?

  • Thread starter Thread starter The Beyonder
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T

The Beyonder

Hello

"It is not a good idea to connect a single drive to the middle connector on
a ribbon cable, because the "STUB" of left-over, unconnected cable causes
signaling problems

With Ultra DMA this "STUB" connection is not just "not recommended", it is
ILLEGAL (a single device must be at the end of the cable)"


What means STUB?

Why is ILLEGAL to connect a single drive to the middle connector on a ribbon
cable?


Ref: http://www.pcguide.com/ref/hdd/if/ide/confCable80-c.html

Thanks
 
"illegal" only in that it violates the "specification". Not that police
will arrest you.
 
Yes, but the question is

Why is ILLEGAL to connect a single drive to the middle connector on a ribbon
cable?

Malfunctions? will the CPU burn in flames? Errors in DVD burning?

Thanks
 
The said:
Yes, but the question is

Why is ILLEGAL to connect a single drive to the middle connector on a
ribbon cable?

Malfunctions? will the CPU burn in flames? Errors in DVD burning?

The drive may not work. You may get errors using the drive if it does work.
In most cases if the drive is specifically jumpered as a master it will work
but there is a chance that file corruption may occur.
 
The article was trying to explain all that with the remark about a stub.
It's analogous to sound waves in tubes--the 'stub' end of the cable, if you
place a single drive in the center, is like a closed-end tube, and causes
signal reflections from the 'hard' end--i.e., no absorbing of the signal at
the end, either by terminating resistors, as in SCSI cables, or by a device
at the end to absorb the signal. This has been a potential problem in older
IDE busses, but the timing wasn't tight enough to make it difficult for a
device (in the middle) to discriminate between the signal and reflections,
but now it is.

Hth,
Joe
 
Specifications are written to ensure the system works properly. CPU
would not burst into flames, but data may be corrupted, drive errors may
result etc.
 
Can set up what's called standing waves. In the old ethernet which used
co-ax any unused ends had had to be properly terminated to avoid this.
Similar thing can happen in incorrect TV aerial installations.
 
You're wrong!

The stub police will be knocking on your door, right after the mattress
police - because you removed the "do not remove under penalty of law" label.

--
Regards,

Richard Urban
Microsoft MVP Windows Shell/User
(For email, remove the obvious from my address)

Quote from George Ankner:
If you knew as much as you think you know,
You would realize that you don't know what you thought you knew!
 
Hello

"It is not a good idea to connect a single drive to the middle connector on
a ribbon cable, because the "STUB" of left-over, unconnected cable causes
signaling problems

With Ultra DMA this "STUB" connection is not just "not recommended", it is
ILLEGAL (a single device must be at the end of the cable)"


What means STUB?

A stub is a short length of something that goes nowhere. In this case
it's the piece of cable going from the second connector to the end
connector. At the frequencies being used such things tend to cause
signal reflections. Controlling such stray signals is a big part of
making fast computers. After all, note that it's an 80-pin cable.
Examine the plugs--you'll find there's only 40 holes. In other words,
two wires per hole. That's all about electrical noise control.
Why is ILLEGAL to connect a single drive to the middle connector on a ribbon
cable?

Illegal in the electrical context--an unacceptable configuration. No
cop will bust you for it but it probably won't work.
 
Can set up what's called standing waves. In the old ethernet which used
co-ax any unused ends had had to be properly terminated to avoid this.
Similar thing can happen in incorrect TV aerial installations.

And in the really old days you *HAD* to have the standing
waves--cables had to be some multiple of the wavelength and taps could
only occur at certain points in the wave.
 
The Beyonder said:
Hello

"It is not a good idea to connect a single drive to the middle connector
on a ribbon cable, because the "STUB" of left-over, unconnected cable
causes signaling problems

With Ultra DMA this "STUB" connection is not just "not recommended", it is
ILLEGAL (a single device must be at the end of the cable)"


What means STUB?

That's the end connector with no ide device attached.
Why is ILLEGAL to connect a single drive to the middle connector on a
ribbon cable?

For choice of words, illegal is as good as any. Signal reflections from the
stub cause low level communication problems for an ide device connected in
the middle. In a nutshell, whether jumpered master (alone for WD), slave,
or cable select, such a lone device needs to be connected to the end of the
ide cable. Has nothing to do with XP.
 
Signal reflections from the stub cause low level communication problems
for an ide device connected in the middle.

It's a historical thing.

When the earth cooled and IBM XTs strode the planet, it was considered
preferable to carry data bits in parallel for greater speed. That's
why DOS-era Lap Link users preferred using the parallel printer port
to serial ports, even the latter were designed for those sort of tasks

The original 40-pin IDE cable was fine at a time when data flowed over
the cable at a relatively slow rate, under processor control. It was
still fine when hardware took over data transmission from the
processor, in the original UDMA mode at PCI's baseline 32MHz.

Then it was discovered you could transfer data on both edges of a
clock pulse - so although the PCI was still clocking at 32MHz, it
would be possible to transfer data from controller to hard drive at
66MHz (UDMA66). This later became UDMA100 and finally UDMA133, which
maxed out the speed of the PCI.

However, data flowing at that rate starts to create capacitance
between the parallel conductors in the cable, so the 80-pin cable was
born - it was the same cable pinouts, except now there were ground
lines between each active signal to help screen them.

At the same time it was noticed that there were signal reflection
issues, and designing to minimize these may have required adjustments
according to where on the cable the device was attached. So these new
80-pin cables have each plug marked for a particulat purpose; the
controller at the "long" end, then slave in the middle, and the master
at the end. This used to be required in using Cable Select jumpering,
but now it's required for Master and Slave for these other reasons.

Since then, ways have been found to send data very fast, one bit at a
time, in serial. So we have USB, Firewire and S-ATA that are all
serial transmission systems, and these outperform what used to be the
faster parallel methods. If one attempted the same speed on parallel
cables, the interference would make it impossible to sustain over any
sort of realistic cable length.

The other reason why serial is preferred today, is to reduce the pin
count of the various chips, and the interconnects on the circuit
boards between these,


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