Bob WIllard wrote in
message ...
Rod Speed wrote:

Even SCSI doesnt allow the use of all 4 drives simultaneously anyway.

Sure it does. SCSI allows all drives to be used simultaneously;

Wrong. You cant simultaneously transfer data from all
drives literally simultaneously, there is still only one bus.

What SCSI can do is use the bus for another drive when
one of them is seeking etc. Thats not the same thing as
simultaneous data transfer from all drives at once.

up to 7 HDs on a narrow bus and up to 15 HDs on a wide bus.
E.g., SCSI allows the initiator (the Host Adapter) to issue a
read command to each target (HD) and then disconnect from
the SCSI bus; each HD may then, concurrently, do the seek,
then read data from the platter into its buffer, and reconnect
only when it is ready to copy data into host RAM.

Yes, but that is NOT simultaneous data transfer.

This capability is one reason why it makes sense to use
a 320 MB/s (U320) version of SCSI to attach HDs which
have STRs of less than a quarter of the bus data rate.

Separate issue entirely.

Moreover, with command queuing, a bunch of read commands can
be issued to each HD, and each HD can execute them out-of-order
and briefly re-occupy the SCSI bus to do the actual data transfer.

Separate issue entirely. And command queuing
isnt just available with SCSI anyway.

And yes, it works the same way for writes
and for mixtures of reads and writes.

Sure, but you never get simultaneous data transfer from
multiple drives, they still have to do that sequentially.

IDE is actually better with the usual 2 controllers in that respect.

I am not claiming that WinWhatever takes full advantage of the
capabilities of SCSI, but there are grown-up OSs which do.

No OS can achieve simultaneous data transfer
with multiple SCSI drives on a single bus.