jmsellens@watmath.UUCP (John M Sellens) (10/19/84)
In PCWeek September 25, 1984, page 5 there is mention of a board that allows you to add COM3: to COM18: to your PC or AT (and requires DOS 3.0?). This will get around the three user restriction in Xenix for the PC/AT. Quoted prices start around $570US for four more ports. This includes the $75 for HostBOIS software. It's called "The Hostess Multiuser Host Adapter". From: Control Systems, 2855 Minneapolis, MN, 55418, (612) 781-5043. John
lauren@vortex.UUCP (Lauren Weinstein) (10/19/84)
Note that unless very specialized software is going to be used, the practical limit on PC serial ports will usually be 3. This is accomplished by buying a 2 port serial add-on board (like the AST cards) to provide COM1 and COM2. Then, a third port may be added as COM3, *if* you are willing to steal one of the (few) interrupts from some other device. In my case, I have a modified standard PC async port that is addressed at an unusual location. I use the printer interrupt for this third async line, and let the printer run busy wait instead of interrupt driven (no big deal -- it all works fine). However, the critical point is that as soon as you go beyond 3 ports (unless you are willing to steal yet another interrupt from the system) you start getting into complex interrupt-sharing techniques that will be by definition completely non-standard and incompatible with much (or most) software that uses the async lines. --Lauren--