>> To my dissappointment, dual channel SCSI TURBOchannel option card
>> PMAZB-A (TCDS) could not achieve better performance than IOASIC SCSI
>> of my Personal DECstation builtin.  Probably, the limiting factor is
>> its artificially lowerd 12.5MHz TC clock rate.  I'm day-dreaming to
>> have a memory-rich DECstation 5000/260 with the regretful loss of
>> DECsystem 5900s two years ago... 
>
> It seems to me the issue is quite probably not just that the TCDS card is
> on a 12.5MHz TurboChannel bus, it's also that, as mentioned above, it
> can't DMA directly to/from host memory -- everything has to be copied to
> a buffer on the card first.

I compared PMAZ-A and PMAZB-A TC option cards side by side, and wow,
found PMAZB-A has no SRAM memory like chips on board.  It seems to
work unlike PMAZ-A which has little intelligence on board.

Tohru Nishimura
Information Technology Centre
Nara Institute of Science and Technology