Choice article on Plug and Play (September). However, you omitted one important part: how a trivial hardware botch in the original PC has made this all much worse than it had to be.
Many machines have fewer interrupt levels than the PC but aren't hurt nearly as badly by it. Why? Because on the other machines, I/O boards can share an interrupt line. For instance, there is no reason COM ports need distinct IRQs (interrupt requests), except that I/O cards cannot share the same one and have it work.
There are boards with multiple UARTs (universal asynchronous receiver/transmitter) on a card, all of which internally share one IRQ for the whole card, but the problem is that the original PC bus didn't arrange for IRQ sharing between cards. This only would have cost a pull-up resistor per line (and possibly an inverter), and the IRQ l
ine could have been driven low by open-collector TTL drivers, instead of the single totem-pole outputs specified. With this trivial fix, we would have been able to share the IRQs just fine. It would have all been a lot easier.
Michael O'Dell
mo@uunet.uu.net
If I had listed everything wrong with the PC system architecture, my story would have been twice as long! You're right about the PC's limited ability to share interrupts, of course, but keep in mind that those kinds of compromises were not nearly as obvious when IBM was designing the PC in 1980 and 1981. Many of the devices we plug into our computers today didn't even exist then. Also, component costs were much higher in the early 1980s, so what seems like a trivial expense now would have been more significant in those days. In fact, IBM chose the slower 8088 processor with its 8-bit bus instead of the full 16-bit 8086 just to reduce the cost of peripheral parts.--Tom Halfhill
I work on the technical-support staff for the New England Jo
urnal of Medicine, supporting PCs, Macs, and Novell servers. I actually understand IRQs (interrupt requests), cascading, memory ports, and even segmented addressing, but that did me little good when I bought a CD-ROM drive. It took me 14 hours with three different brand units before I could get one installed and working properly in my 386. During the same week, my boss bought a CD-ROM for my Mac at the office, and it honestly took me less than five minutes from opening the box to viewing a sample CD.
The PC as we know it will never be PnP (Plug and Play). The ISA bus is not intelligent and cannot be made so; the DOS/Windows combination is even more pathetic. The only hope for PnP on non-Macs is a system that uses Windows NT or OS/2 with a PCMCIA or SCSI primary bus. PnP is just another case of Bill Gates ``inventing a vision'' of something that the Macintosh has been doing for seven years. Your article seemed to lead to the conclusion that PnP is a kludge that doesn't have a snowball's chance in Hades
of success, but you never actually said so. I'd be curious to know why.
Don Leamy
New England Journal of Medicine
Waltham, MA
Yes, PnP is a kludge, and yes, it is merely a stepping stone to the real solution--and I made both points in my story. But I disagree that it doesn't have a chance for success or won't make life easier for millions of people. What's the alternative? Are PC users suddenly going to junk all their machines and buy systems based on an entirely new architecture? Or will they migrate in droves to the Macintosh? Not likely. For the vast majority of people, PnP will seem like wondrous technology. Why burst their bubble?--Tom Halfhill
Plug and Play in Hindsight
