performance of async interfaces

[wnj]

the able dmax works just fine.
others are too new for final word on them, although many have had problems
with early cs11s; emulex has fixed most of these problems.

on vax, we see following overheads for output at 9600 baud with reasonably
long lines (i.e. not all characters require special processing):
	dz-11	5%
	dh-11	3%
this of a 11/780 processor.  the dz-11 uses pseudo-dma.  on 32/v pre
pseudo-dma one 9600 baud line was > 100%, i.e. you couldn't drive one
line at full 9600.

	bill joy