| Ultra is not yet supported in the ZX. That does not preclude putting
in an ultra drive and running it at Wide/Fast speeds.
Engineering is putting together a position statement on Ultra in
prioris, when it is released, I will oublish it on our internal
WEBsite akin40.ako.dec.com
Chet White
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Keep in mind that Ultra-Wide SCSI allows for maximum cable length
of 1.5meter! With the SCSI backplane, and the standard cables, you
would almost always exceed the cable lengths.
Ultra-Wide me look like a nice feature, but brings an enormous
amount of configuration headaches. Also keep in a mind that a single
disk in random access mode (and not sequential streaming) would give
a throughput in the range of 2MB/s.
The Ultra-Wide SCSI disks, are physically different not different to
their Fast-Wide brothers/sisters. Only their bus interface can run
at a higher clockrate.
Same thing for FC-AL. (Fiber Channel Arbitrated Loop. Although you
here you can hook up maximum 126 devices.)
FC-AL cables can be 30 meters long with coaxia cable, or up to
10 Kilometer for fiber-optic.
Bandwith ranges from 100MB/s to 200MB/s (200MB/s is for dual-ported
designs). However FC-AL devices and controllers are still very
expensive. As well that you need a NameServer in the FC-AL.
These are not really available yet, so you need to resolve the
world-wide unique id addressing completely in the drivers.
Something which is not simple, and current drivers are still very
buggy. Anyway I'm drifting off.
You can do a quick translation of how many drives you would have to
fit in a single SCSI chain to go beyond the Fast/Wide SCSI bandwith
of 20MB/s. At least impossible to be used in a 1.5Meter cable.
Bottom line: You don't need Ultra-Wide SCSI, and you can't even use
Ultra-Wide SCSI for most of the occasions, unless you're real time
video shop.
Pjotrr
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