Re: Can I mix a CD drive and an HDD on the same IDE cable?

jameshanley39@xxxxxxxxxxx wrote:
On 5 Mar, 21:40, Philip Herlihy <thiswillbounceb...@xxxxxxx> wrote:
Showing my ignorance, undoubtedly, but is there any reason I can't use
the same IDE cable for a CD-Drive and a hard disk? I have a PC with a
SATA HDD, and a handy IDE disk I'd like to bolt in. The only ribbon
cable is the CD one, which has an unused connector in the middle.

Phil, London

My main point is just that if using an IDE cable that came with a
CDROM drive.. it is likely that the cable is 40 wire. Well, if
connecting a hard drive to it, then it is recommended to use an 80
wire. (may be related to data corruption more likely to occur on 40
wire.. I cannot remember!)

I recall once reading that sometimes you have to put the CDROM at the
end of the cable(as oppose to the middle).. something about it having
a "terminator", and the hard drive not being accessible.. That may
be bull, or may be old, or may be rare. You`d know anyhow if you tried
it and it didn`t work. minimal experimentation..

The possible issue with putting 2 on te same IDE, is one of speed. I
am not that familiar with the speed issues.. But it seems you should
be ok.

note- Saying ATA instead of IDE..
from googling, it seems it`s ok if they are both DMA- which I guess is
likely.. Apparently there was an issue with original IDE.. It would
drop to the slower speed. EIDE solved that one. But leaves or has a
different problem of mixing earlier ATA drives (they used PIO). With
newer ones, ones that use DMA. In that instance, the faster waits for
the slower when there is an "interleaving IO operation". That is what
posts seem to suggest....

Anyhow.. since most devices now are prob DMA. PIO is prob not used.
And you are no doubt using EIDE(which has been out for many many years
already, people just call it IDE) I guess you should be ok.

If you`er suspicious you can always check your speeds.


Here is a dump on a few sources that discuss it
"
Now I will explain why most vendors will recommend not mixing devices
of
different speeds on the same IDE channel. Part of it is habit since
the
original IDE controllers would drop the channel speed to that of the
slowest
device. With EIDE however, that constraint no longer exists. The
problem
however is with interleaved IO operations. If you have a ATA-100
device on
the same channel as a PIO-4 device, both doing bulk data transfer,
then the
faster device will have to wait for the slower device to give up the
channel
before it can process another IO request. This will effectively
throttle the
faster device, but the device will run full speed when it has control
of the
channel.


--
Walter Clayton - MS MVP(DTS)
(on usenet)
"



dansdata
http://www.dansdata.com/onstream.htm
The DI30(tape drive) seems perfectly happy to sit on the same IDE
cable as any reasonably recent IDE CD-ROM drive. .....
Putting the DI30 on the same cable as a hard drive will work, too, but
it's probably not a great idea to do it. Modern motherboards can
handle two IDE devices that use different IDE transfer modes connected
to one IDE channel on the motherboard - most motherboards have two IDE
channels, each with its own connector. You can put a device whose best
mode is Programmed Input/Output (PIO) 3, for instance, on the same
cable as a PIO 4 device, and if the drives and the motherboard are all
pretty recent then both drives should be able to run as fast as they
can; the PIO 4 device won't have to use PIO 3.

But if you put a PIO device on the same cable as an Ultra DMA (UDMA)
device - pretty much all current hard drives can use at least UDMA/33,
and maybe UDMA/66 - you choke back the hard drive to the old PIO mode.
The DI30 is a PIO device, so it should go on the same cable as your CD-
ROM, or on a cable by itself, if you want to keep your system
performance at its best. UDMA isn't just faster - it also loads up the
CPU less. So letting your hard drives use UDMA can do your computer
more good than you might think.



"techimo.com" forum (thread found via google)
You can run different speed DMA drives off the same cable without
affecting each other's speed. New controllers (not only intel) are
capable of doing this.

However there is a catch:

You cannot mix PIO and DMA drives. The controller can only switch
speed, not transfer mode. If a PIO device is connected on the cable,
all the bus is taken to PIO and there's nothing you can do but remove
the offending drive. Even newer CD/RW's (the 16x Plextor most notably)
are PIO only drives which is bad if you are running many drives off
your IDE controllers.

Also, immature drivers, poor OS implementation and bad configuration
can cause the controller to stick to the lower speed. Many older
controllers that claimed to support ATA66 were incapable of switching
speeds (these were actually ATA33 controllers masquerading as ATA66).

Thanks - really useful and interesting!

Phil
.

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