An IRQing situation.

JANUARY 1997

I agree with PC Magazine's columnist Jim Seymour - these new PC's are coming loaded with every accessory one could want or wish for, and some the future owner probably didn't wish for. Because of this, many brand new PCs will probably be unable to accept additional hardware.

The problem? There are a limited number of very important resources the PC can assign to high-performance accessories. These are called interrupts or IRQs and there are only 15 of them. In my Pentium-133 clone PC, 13 of the 15 IRQs are dedicated to indispensable motherboard functions such as the 2 hard drive controllers, the floppy drive controller, the 2 serial ports and the 1 printer port. The other two IRQs are assigned to my sound card and SCSI card. That maxes out my PC - I can put in no more accessories requiring an IRQ.

I see this situation frequently in customer's new machines. Usually occurring when I am asked to install a 2nd or 3rd printer port, a frequent upgrade today in small offices with more than one printer. I am then in the position of telling the customer that his PC has no ability to accept this additional hardware. Since the customer recently spent $2000-$5000 for his new PC and now can't get it to do what he needs - he is understandably upset!

How can you prevent this from happening to you? It's not easy. When looking to buy a new PC keep in mind that the flashy accessories such as high end sound cards and TV cards consume an extra IRQ (or two) from your system. Finding a PC with a basic sound card or without those it's-nice-to-have-but-I'll-probably-never-use toys might be a difficult search - but a worthwhile one.

Somewhere down the road you'll want to add something to your PC. You'll either have to replace the factory installed whiz-bang cards with simpler functioning accessories, or forgo the desired addition. Hopefully later this the promise of the Universal Serial Bus presently installed on new PCs will come true and external devices will be on the market. These accessories will require no IRQs other the one already assigned to the existing USB port. Perhaps then the problem of the IRQs will go away.