From: harris@garfield.catt.ncsu.edu (Michael Harris)
Subject: Re: Doing Multiple Simultaneous Floppy Copies
Organization: North Carolina State University
Date: Tue, 6 Oct 1992 14:12:33 GMT

>harris@garfield.catt.ncsu.edu (Michael Harris) writes:
>>SCSI-I won't even do it simultaneously.  I'm looking at a SCSI 50 pin diagram
>>right now.  There are only 8 data lines.  Each one for one bit of
>>information.  This means that only one drive can talk at a time.  They all
>>multiplex the data bus.

rdippold@qualcom.qualcomm.com (Ron Dippold) writes:
>Not necessarily - Okay, it's not possible to send data to both of them
>at exactly the same time but with floppies it shouldn't be necessary.

[... technical stuff removed ...]

I figured that some of my fellow engineers would catch me on this one.

[More info coming... keep reading.]

From: Stuart M Lichtenthal <smlg1015@uxa.cso.uiuc.edu>
To: harris@garfield.catt.ncsu.edu
>It seems a shame that identical instructions can't be given to 5 different
>floppies simultaneously.  Isn't there some way to hook them all up in
>parallel and have them do the copying as one? I feel as if this SHOULD
>be as simple as a cable and I'd like to know why I'm mistaken.

It is just a little more complicated than that.

There are two types of multitasking that we can talk about in this case.  One
is hardware multitasking and the other is simulated software multitasking.
My response was directed towards those concerned with hardware multitasking.
In other words: Both floppies (or whatever devices) working completely
independently transmitting and receiving data at the same time.  This type
of multitasking requires special hardware depending upon what you want to do.
For example, if you wanted to have both drives reading and writing to memory
at the same time, you would need to have two data busses on your motherboard
and a special memory controller.  With most of the memory out today, you still
couldn't write to the same physical chips at the same time.  (not locations...
chips.)

The other type is simulated software multitasking where the operating system
(or just software in general) alternates its time between the two devices.
In theory, if you do this fast enough, the user will perceive that both are
working simultaneously.

The problem in your case is that most likely, your floppy controller was not
designed to *quickly* receive a command and data and then let the cpu go on
about its business.  Also it probably isn't designed to work with more than
one floppy drive at the same time.  Floppy drives are much slower than the
controller cards.  If the controller card manufacturer chooses, he can make
the board such that it can process commands from/to one floppy drive while
it is waiting for the other.  All of these features add to the cost of the
hardware.  And everything comes down to cost vs. benefit when you talk about
computer hardware.

______________________________________________________________________________
     Michael Harris - harris@catt.ncsu.edu or harris@carvm3.vnet.ibm.com
 System Administrator, Computer & Technologies Theme Program, NC State Univ.
(My opinions are my own and do not represent those of NCSU or IBM Corporation)
Newsgroups: comp.os.os2.misc