> 
> so.  it'd be real nice if we could use the 64k size.
> matt thomas was concerned that not all devices could support 64k xfers.
>
The reason MAXPHYS is 63k is historical. Yes, there are devices that 
can't handle 64k transfer sizes (16-bit byte counters), but that should
be handled by the device instead. I can revisit the vax-specific 
drivers and see if something would break it it is set to 64k instead.

MAXBSIZE is set to 16k because increasing it steals too much kernel
memory (and thus physical). This is mainly a problem on small-memory
machines. I have actually increased it, it used to be 8k in old BSD.

-- Ragge