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IRQ refers to an "interupt" which is a technical term for something going on in all DOS, Windows, and NT systems (not Macintosh). The IRQ system is the last piece of technology that actually goes back to IBM's original 1980 design for a computer. Essentially, everything attached to the system must have an interrupt, everything. So there is an interrupt needed for the mouse, another for the keyboard, another for the monitor, and so on. Even things that you would not think of as "attached" to the computer, such as the system clock timer and the math-coprocessor, also each need a unique IRQ. They are numbered, and there are only 16 of them.
When IBM originally designed this system (and remember not to blame them too much since they thought at the time they would sell at best some 9,000 systems (not the current 80,000,000)) they introduced an "expandable" system, since they used up 12 of the IRQs leaving 4 for "future devices". The problem is, since then we now have 1) high resolution graphics, 2) graphics AGP accellerators, 3) a mouse, 4) a modem, 5) network, 6) second or large capacity hard drives, 7) scanner, 8) zip drives, 9) CD-ROMS, 10) plotters, 11) second printers, 12) SCSI devices (don't ask), and so on, all of which did not exist in 1981 when this system came out with room for 4 devices. You probably noticed that there are more than 4 devices.
The band-aid approach used for more than a decade to kludge (a pejoritive computer term meening to fake or cobble) these things things together is to "share" interupts. Techies found that they could match certain combinations of devices and put them on the same interupt. Even though this is not supposed to work, as the system will, 60 times a second, send a signal through to check those 16 devices in order, sometimes you can hit on something that won't (immediatly) crash the system. For various technical reasons all such microcomputers must crash eventually, which is why you should re-start them each day, but let's not go into that part of this right now. Combinations that worked in the past were they would put the mouse (which only sends signals IN to the processor) on the same interupt as a serial plotter (which only recieved signals OUT from the processor). This system doesn't work now because plotters are obsolete (another story) and what we use now are actually large format printer/plotters through the parallel port (which is bi-directional, which means of course it cannot share an interupt with anything). Other devices which are bi-directional, and thus don't like sharing an IRQ are modems, network cards, hard disks, and zip disks.
However, because the public has continually demanded that systems have more and more, and, particularly, keep up with the Macintosh (which has never had any of these problems) the technical engineers have, in recent years, gotten even more creative. Particularly troublesome nowadays is that all systems are expected to have a fully operational CD-ROM in addition to a modem (at least one), plus you have to be able to print out, and you now must have a mouse. Thus, the engineers are doubling (or even trippling up on devices on the same IRQs) essentially crossing their fingers and hoping that people do not notice stuttering or intermittant operation of certain devices and that it doesn't crash. In the meantime, the engineers are frantically trying to design and release the next generation of computers which will, hopefully avoid all this. Most really high end WindowsNT systems make use of the same SCSI system that was invented for the Macintosh 10 years earlier, albeit only partially, and they still do have to allocate IRQs. Better yet, hopefully, is the USB or Universal Serial Bus, system, which, theoretically, will solve this mess. An irony right now is that if you want to add USB to your current system, you need another IRQ.
Some real exchanges on internet forums :
<< When working in DataCad with the CD Player running the cusrsor
tends to move with sudden jerks across the screen. The system that I'm
using is a P2 350MHz 128MB RAM and 4MB AGP Graphics Card. What could cause
this to happen and is there a solution for this behaviour? >>
Langdon responds :
I was installing software at an office last week on a new P2 450 by Gateway. In the process of checking all systems, I noticed with great surprise that they had TRIPPLED up on one of the IRQs (potentially creating even greater nightmares from the "usual" doubling up that manufacturers do). The one that was sharing three devices on one IRQ was - the AGP video accellerator, the DVD CD-ROM, and something else (I forget what). I remember I must have made a noise of surprise because the new owner of the system came over and asked what was wrong. I said "nothing wrong, as Gateway must know what they are doing, but that such an arrangement could potentially cause interesting problems" (not wanting to get into explaining the technical nuances of IRQ interupts) "and, it would DEFINITELY cause problems if you want to change just about anything later on - i.e. switch video cards, add a scanner or network, yada yada."
I strongly advised him to quit listening to CD's while using CADD (which he didn't like 'cause this new DVD thing was better than his stereo) because it would definitely cause blips while using real video intensive applications (like CADD). Also, get one of thos blips at just the wrong time, and, well, you do make heirarchial-backups right ?
The upshot is, no, don't use that CD for music while using DataCAD.
Appropriate technology - yse the right tool for the job. Use your stereo for music.
>> You've got to be kidding! My new Dell pII 450 has 23 devices hooked to 16
>> interrupts, some are tripled. Where are you going to fix them?
>Sounds like tough cookies .... or get another computer (oldie or
>something) for the proliferation of devices
Langdon Responds :
You cannot fix them, or move them. I frequently go into offices to add network cards, better modems, and so on and will find that even moving to an "unused" IRQ can suddenly cause the mouse to stop working (sometimes just with one particular program) and so on. The issue is that the oxymoronly named "plug and play" will (try to) automatically allocate IRQs on the fly each time the computer is turned on - the symptom in non-computerspeak is sometimes certain things will work and other times they won't.
This IRQ nightmare is the last (and only) part of our systems that actually goes back to IBM's original 1980 design based on an 8 bit computer. Even Compaq's later improvements, EISA, PCI, and AGP did nothing to improve this.
The only solution in the long run is to use the (Apple inspired) SCSI connection system (which takes another IRQ but gains 6 more devices) as most high end WindowsNT systems now do (mostly for the speed advantage of SCSI hard drives), or, to pin hopes on the upcoming USB (universal serial bus) which should be standard on all the 600 mhz systems later this year.
Now you might be saying to yourself, oh great, another new system, who needs it when I can run DataCAD just fine now on my (semi-)new Pentium xxx.
However, you need to look at what is different about a PentiumIII as opposed to a PentiumII.
The answer is 3D CADD.
The PIII chip has special 3D CADD abilities and internet Web abilities burned into it as an integral part. This means that very soon the various CADD software developers will take advantage of those new abilities to help give us part of what we have been directly or indirectly asking for. Things such as dynamic walk arounds of fully texture rendered interiors with lights, and drag and drop of such models across the web will be commonplace within the next two years - and architectural firms that can do this first will win more clients (which will be more important as this current boom eventually and inevitably slows down). To put it all concisely, virtually everyone on this forum had better budget for a PIII system exactly a year from now.
Maybe THEN, you can run DataCAD with your music CDs.
The following exchange is a real exchange between two architects, one who just tried to add a printer to his system. If you can truely understand what they are talking about, or want to, then go ahead and delve into the nightmare of IRQ interupts in adding devices to a Windows system.
Date: Sun, 28 Feb 1999 11:34:14 +1100
From: "Gary Finn" <gfinn@fs-architecture.com.au>
Subject: Re: DBUG> IRQueuing
We are always grappling with IRQ settings. Your Zip drive will be using one
for its virtual "Scuzzie" and another one for the port it is attached to.
I stumbled my way around this recently by purchasing an Intel Print Server
and connecting to it to my computer using 10baseT LAN cabling. (10Base2
would be just fine if you dont have a network setup). Note that the LAN card
on your computer also needs a dedicated IRQ. I therefore have managed to put
all my printing/plotting and copying in another area where layout space is
available. Consequently there is no need to use valuable window space for
all that hardware as now they can operate remote from the computer's LPT. I
now have all printer ports free for other peripherals such as dongles, zip
drives and laplink cables.
As for your IRQ problems, I have never managed to free up a computer for
more than 2 LPT's as they tend to want either IRQ 5 or IRQ 7. You need to
check that the new i/o card with additional LPT doesn't have jumpers on it
restricting its IRQ allocation. I have one port with lots of flexibility IRQ
wise but couldn't fit it as a third port unless I removed the Sound Card,
which anyway, is useless for production drawings. As far as I know, you
cannot double up IRQ's for printer ports.
By instinct, it sounds like something else grabbed the IRQ you released by
disabling your com port. You should be able to go into start, settings,
control panel, system, device manager, computer properties, select ports,
delete the com port from there (as well as from your BIOS which I assumed
you already did), then computer properties, reserve resources, set to
reserve the IRQ you just released, restart your computer. When you restart,
there should be one IRQ reserved which I assume you can then allocate to the
new LPT??
Good luck,
Gazza
- -----Original Message-----
From: David Bergman <bergman@cyberg.com>
To: datacad-dbug@world.std.com <datacad-dbug@world.std.com>
Date: Sunday, 28 February 1999 11:09
Subject: DBUG> IRQueuing
>At 03:04 PM 2/25/99 -0600, you wrote:
>>You've got to be kidding! My new Dell pII 450 has 23 devices hooked to 16
>>interrupts, some are tripled. Where are you going to fix them?
>>Dick Eades - Architect
>>Jonesboro, Arkansas USA
>In the midst of this IRQ discussion, I just spent a day trying to install a
>dual parallel port card in my new PII. I ran into problems of both IRQ's
>conflicting with other devices and port addresses conflicting with the
>onboard parallel port. And when I thought I'd free'd up IRQ's (by removing
>USB in Device Mnager and disabling Comm 1 in BIOS) still no satisfaction.
>I've gotten to know both more and less about IRQ's than I'd like to. Does
>anyone know how to make this installation and doubling up of IRQ's work. My
>Micron already has some doubled (with "IRQ holders for PCI steering,"
>whatever that is). I can't wait until everything is USB.
>The parallel port business is a real pain -- I've got two printers, a Zip
>and Laplink , not to mention the dongle -- and the Zip and Laplink don't
>work with sharing devices.
>Would love to hear of miraculous solutions....
>David Bergman
>David Bergman Architects/Fire & Water Lighting
>bergman@cyberg.com
>http://cyberg.com
>
>V 212 475 3106 F 212 677 7291
From: "Phil Laing" <laingp@ozemail.com.au>
On 27 Feb 99 at 10:35, David Bergman wrote:
> onboard parallel port. And when I thought I'd free'd up IRQ's (by removing USB in Device Mnager and disabling Comm 1 in BIOS) still no satisfaction.
If you are prepared to spend more time on this ... you need to "manually" set your IRQ's then simply experiment with what Windows will let you change. Other things can be changed to suit your IRQ's e.g. Jumper settings on your devices can be checked and changed to allow a different IRQ for that device. Having said that ... Many plug and play devices usually won't let you do this .. however others are more obliging
Date: Sun, 28 Feb 1999
From: David Bergman <bergman@cyberg.com>
Thank you both Gary and Phil for the IRQ responses. Gary, you're right that LPT cards apparently only want to work on IRQ 5 or 7. This particular card has jumpers that supposedly allow it to use several additional IRQ's, but none of the settings seem to work. The onboard port uses IRQ 7, and IRQ 5 is used by a sound card which, I'm told, can't be changed to a different number.
The idea of manually changing the existing IRQ's, especially on a new machine in which most of the devices are probably plug and play, is very intimidating. I think I'll live with changing cables as needed for now.
>conflicts ... but you would have to ask yourself whether a day spent
>playing around with these gremlins is worth it.
Langdon responds :
You are right. Of course it is POSSIBLE (usually) but many a time I have spent more than a day trying to work out all the gremlins. With prices now so low for an entire new computer, it is not even worth one days work. Thus, to avoid that agravation ('cause they're still not going to be completely happy with the band-aided system) I simply no longer recommend doing any such thing. It is better to buy a whole new computer system.