Hello All
  Thanks to Robert and David for the clarification which I found
surprising.  It has been many years since I had an all scsi box and even
then it was built from used (affordable to me) parts which were old enough
to barely feel the scsi advantage compared to my much more modern ATA box. 
I ended up back around Warp3 days using a 150Meg SCSI drive as a dedicated
swap file in an otherwise IDE box and that was pretty darn nice but
obviously kept me ignorant of multiple scsi devices on one bus.  I'm not
sure now where I got the idea of individual drive autonomy on a scsi bus
but apparently that was unwarranted and incorrect.  It is possible that I
jumped to a conclusion based on OS/2 and scsi's ability to read and write
to multiple devices simoultaneously.  In any case sorry for the negative
comment on LSI's tech support quality since it was I that was wrong.  I now
wonder if this will still be true in serial scsi.  This is idle curiosity
since the division between performance to cost rati

o has only tipped more in favor of IDE of late but it would be interesting to know.
Thanks
Jimmy


> 
> 
> >The issuse is that the CDROM device will limit the MAX speed of the SCSI 
> >buss. When the buss powers up, the host adapter asks each device on the 
> >chain to respond at the the fastest data rate that the adapter can 
> >support. As each device respnds, the host adapter rackets down the max 
> >data rate to match the slowest devices on the buss.
> >  
> >
> 
> Actually no, that's not exactly how SCSI works, not quite.
> 
> The main problem with SCSI is the newer HDD uses LVD signalling, which
> is an absolute must when running high speed and with cable long enough
> to be useful. However, SCSI CDROM with LVD signalling is far and few in
> between, if you connect a SE signal CDROM, the whole bus will drop to SE
> signals and your HDD will either work slowly, or not work at all.
> 
> If all of your devices runs at 40MB/s or slower, then it is not going to
> be such a big deal, as the effect will not be as big or as bad as it is
> with LVD... running an LVD drive in SE mode was a pain that I hope no
> one needs to endure, PITA...
> 
> >What the LSI tech rep was saying is TRUE. Putting a 5-10MBS CD-ROM on a 
> >SCSI buss with a 40MBS HDD makes the 40MBS HDD have the SAME thruput as 
> >the CD-ROM, Hence the suggestion to put the CD on a separate SCSI chain 
> >so that the data rate from the HDD speeds up.
> >  
> >
> if it is all running at 40MB/s or slower, it won't make a very big
> difference, the CD rom running at slower speed will take a bit more bus
> time, but when it is HDD's turn, the bus will run at 40MB/s again...
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
> 


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