🚀 go-pugleaf

On Sat, 6 Dec 2003 16:30:46 +1000, "Cristian Croitoru" <c_croitoru@hotmail.com>
wrote:

>> Me
>> >Speaking of speed and not being particularly familiar with the SCSI
>> >protocol, my common sense tells me that having a stripe on a IDE
>> >multichannel controller can push the speed quite some way..
>> >Again my common sense tells me that a SCSI controller can not stream data
>> >from more than one drive at a time, as only one drive can put data on the
>> >bus at the same time
>"derek:
>> Your common sense failed this time.
>> With a SCSI ALL disks can read or write at the same time.
>> That is one of the strengths of scsi
>>
>> Of course, at home you will have trouble using this strength.
>
>Well, I have tried to understand HOW, how is posibile for multiple devices
>to send electrical signals on the same wire in the same time.. How is this
>possible form the electrical point of view?
>
>With separate channels you have separate buses, separate electrical paths;
>the data of the stripe is rebuilt in the controller's logic but essentialy
>the logical path is 6 times wider.
>
>I am not trying my skills in retorics, I am just trying to understand..

Yes, I understand, and I did not explain myself very well at all.

Let me say that all drives on a controller can be reading and writing at the
same time, this does not mean that they are holding onto the buss at that time.

Buss speed 160Mb/s, drive speed 20Mb/s  therefore 8 devices r/w at the same
time.

All drives have buffers (double buffers actually), when a buffer is full, the
drive raises a flag (data available) to say he wants to transfer some data, when
the buss is free there will be a buss available signal.

In effect we have a multiplexed system happening here, unlike an IDE device
which holds the buss for the complete transfer.

I hope that sounds better.

Derek