IT> Is there anybody, who could explain me, whether I do 
 IT> really need an I/O card
 IT> with UART 16550 to work better with external ZyXELL 1496E?
If you are multitasking or doing bi-directional transfers, probably yes.
 IT> A was said several times, that the fast computers (as 
 IT> 486 dx2-66) do not need
 IT> that special I/O card. Is that true?
Yes/No. Depends on _your_ application. In general, I'd say most people do 
require a 16550 for satisfactory performance, but if your running OS/2 or 
plain DOS, you _may_ not need one, although it would still be desirable.
--- Maximus/2 2.02
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