The major PC configuration trip_up has got to be the IRQ to PCI slot assignment business. If you don't understand it then you may end up having perplexing PC configuration problems unlike the Mac RISC setup which doesn't use IRQs. I've only recently realized that only 3 IRQs are available for PCI slot assignment regardless of the amount of IRQs that are free.<P>The deal:<BR>PCI slot 1 gets one or witll share it with an AGP slot if present. Sharing will work depending on card placed into slot if AGP is occupied. I can use my sound card here but not a SCSI board.<BR>PCI slot 2 gets its own. Network or SCSI card goes here.<BR>PCI slot 3 get its own. Network or SCSI card goes here.<BR>PCI slot 4 will share the one with PCI slot 3 about as well as slot 1 and the AGP (depends on the cards). My NIC said no to this slot but I got another SCSI board working here sharing the IRQ with the NIC in slot 3. Soundcard reports SCSI noise when in this slot.<BR>PCI slot 5 don't get no IRQ although it can still DMA. No NIC, SCSI or soundcard can go here.<BR>And the ISA slots get their own IRQs.<P>It may be different for some mainboards but I'm suspicious it is the same for all PC boards with PCI slots. If the board doesn't have AGP then I'm sure that only the first 3 PCI slots get IRQs and a 4th slot, if present, is a no IRQ slot that does DMA only or shares with 3. If anyone could clarify any of this then much is to be appreciated.<P>So, anyways, I haven't heard of Macs having this problem 'cause RISC is supposed to be IRQ free, but then again, they usually don't have all the PCI slots a recent PC mainboard has.<P>Edit: I goofed. Up to 4 IRQs are available for the PCI. 4 and 5 share and not 3 and 4. If slot 4 is occupied than 5 can accept an DMA card that does not need an IRQ. Slot 4 is unacceptable to my NIC. And I ferget to mention that some devices prefer certain IRQs which further fouls the mix which might be why the NIC doesn't do slot 4.<BR><P>[This message has been edited by msearcy (edited January 26, 2000).]
IRQs Have Got to Go!
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not true. mine isn't like that. What about the MOBO's that have 6 PCI slots? what about the really small ones that only have ONE PCI slot? in my experience, <I>ANY</I> PCI slot is capable of giving an IRQ. now, wether or not that IRQ is actually free is a different question.
Can anyone explain to me why Intel hasn't made a chipset/processor that gives us more IRQs and DMA channels? Is it just a limitation of the x86 architecture? Is it for legacy compatibility? All of the above?<P>Regardless, I find it hard to believe that Intel couldn't figure out a way to fix this situation.
Wow, the Macintosh 'Risc' architecture doesn't use interrupts. It's a revelation!
<BLOCKQUOTE><font size="-1">quote:</font><HR><I>Originally posted by seandelk:</I><BR>Can anyone explain to me why Intel hasn't made a chipset/processor that gives us more IRQs and DMA channels? Is it just a limitation of the x86 architecture? Is it for legacy compatibility? All of the above?<P>Regardless, I find it hard to believe that Intel couldn't figure out a way to fix this situation. <HR></BLOCKQUOTE><P>Fisrt off, this isn't intel's doing whatsoever. It's IBM's doing when they created the AT ISA. Even then, the IRQ assignments aren't exactly the same as you described them, and can change, especially with the new i8x0 chipsets. <P>For a better way to show where PCI slots' INT comes into play (in BX/EX/LX chipset mobo's)- <P>INTA - PCI slot 1 and AGP share it<BR>INTB - PCI slot2<BR>INTC - PCI slot3<BR>INTD - PCI slot 4,5,USB<P>In order to get more IRQ's in a system, the AT ISA would have to be changed, hence it wouldn't be AT anymore. And then the industry would have to agree on it, etc. It would be a mess (O/S's would have to be re-written, and legacy stuff wouldn't work in it). So it's pretty much too late for it. But hopefully when the PC industry moves to 64-bit goodness, we'll move out of the AT ISA and move onto bigger, better things.<P>If you want to take control of your PCI IRQ assignments, you'd have to get a board that does it, such as Asus and Abit (to name the two on top of my head; there maybe more). You may also want to find out what type of PCI cards can share IRQ's, and which ones cannot. It is normally explained in the moherboard manual.
I've never had a problem with my IRQs either way... Most components that share IRQs end up communicating just fine. By the way, RISC has nothing to do with not having IRQs, it's just the way Macs are made.<P>I'm actually surprised... I thought this was gonna be a rant about running out of IRQs... I think that the problem could be solved by making USB worthwhile (i.e. making it have bandwidth of around 150Mbps or so...) so you can run NICs, Modems, sound, etc... off of that interface. Then you can just have a USB cable running to your Monitor (many already have USB hubs built in) which would have your modem and Sound built into it. Then your video (with DVD decoder, TV in and out and video capture built in) and SCSI card (that's a requirement, isn't it?) can go in your PCI slots (video in AGP) without any problems.
<BLOCKQUOTE><font size="-1">quote:</font><HR><I>Originally posted by msearcy:</I><BR>Anyone using a NIC in slot 4 or 5 on their PC?<HR></BLOCKQUOTE><P>Uhhh... You have got to be kidding me... Maybe a 10Mbps one, but a 10/100Mbps or higher would definately choke trying to share an IRQ with the USB (not to mention fighting for bus mastering). <P>All I gotta say is, you may have problems with a NIC in slot4 or 5 (in a BX/EX/LX environment).
<BR>And this is why mac users keep saying that Windows plug and play is not up to Mac standards.<P>
Every PCI and AGP card I have can share IRQs with any other PCI card just fine.... IRQs aren't a big deal after the demise of ISA- the PCI bus can share IRQs just fine. I don't have performance problems with my 100 mbps NIC sharing with my USB AND my SCSI card- they all work great, and at full speed. That BS about PCI cards not working right when they share IRQs is just that, BS. As I said, I have an AGP graphics card, a NIC, a SCSI card, and an ISA card- my 3com NIC shares IRQ 9 with my USB controller and my SCSI card absolutely perfectly. I even have a free IRQ left.<P>Now, ISA cards trying to share completely screw things up. But since my next computer will be completely ISA free, it doesn't matter.<P>The IRQ problem is greatly overrated. If you have all PCI cards, you can simply toss anything in and it will be configured fine.
The #1 culprit that I see in PCI IRQ conflicting stuff is the user putting the BIOS setting for "PnP OS" or similar to "Yes". Generally, if you let the mobo do it's thang and assign mobo resource sharing and not allow Winblows to totally fark things up by calling the shots, you should be OK. View image: /infopop/emoticons/icon_biggrin.gif<P>edit: forgot PCI<P>[This message has been edited by GatewayTech (edited January 26, 2000).]
I personally haven't had to worry about IRQs since Win95. Since then everything has configured just fine on its own.
<BLOCKQUOTE><font size="-1">quote:</font><HR>not to mention fighting for bus mastering<HR></BLOCKQUOTE><P>One thing to mention is the bus mastering. INTA, B, C, and D each have their own bus mastering (PCI slots 4 and 5 share the busmastering with USB since all of them are INTD). If you have your SCSI card and NIC in PCI slots four and five and all sharing one IRQ with the USB (which they would), you will definately have problems (don't believe me, try it and find out). <P>That's why its best to throw any non-bus mastering cards in PCI slots 4 and five (such as sound cards, Voodoo x cards, etc).
I have a NIC in slot 2, and a SCSI card in slot 3. Nothing is in slot 4 or 1 (I only have a mobo with 4 PCI slots). My NIC, SCSI card, and USB controller all use IRQ 10. Absolutely no problems whatsoever. None in any respect. Let me repeat that: NONE.<P>I was having problems with an ISA soundcard with a built in IDE interface (what the hell were they thinking?), where the IDE's interface conflicted with a PCI card. That caused large problems. Replacing the card with one that didn't have IDE on fixed the problem perfectly. But on an all PCI system, you generally won't have problems.<P>Oh yeah, wouldn't Macs have the same problems with slots 4 & 5 on their mobo, since they use the same PCI scheme with ints A, B, C, and D? Ooooahhh, that's rights! Macs only have 3 PCI slots. I guess that's an easy, convenient way to solve that particular problem. View image: /infopop/emoticons/icon_smile.gif<P>So, Mac users, do not bash these issues PCs have with 4 PCI slots or more.
Ozguid,<P>This isn't a bash, but I just thought I'd let you know that my Mac has 6 PCI slots. Supporting an Ultra Wide SCSI card, (in addition to the 2 SCSI buses built on the MB), a USB card, a 10/100 Enet card, and 2 video cards. <P>All work wonderfully together. View image: http://forum.arstechnica.com/forum/ubb/tongue.gif <P>
StephenB: I see. It's great that your Mac has 6 PCI slots, but do any not support bus mastering, like some one PC mobos? Or do you not have that problem at all?<P>Too bad none of Apple's new computers have more then 3 slots.... with OS X installed, and enough slots, they could become kickass video editing machines!
I am not sure if Macs use the same bus mastering scheme as PC's do. They may have INT's, they may not. They may have more INT's, they may have less. <P>Any well-versed Mac person know this?
Well, they HAVE to use the PCI 4 A-B-C-D interrupt scheme, as I see it. I know Macs don't use IRQ's. Damn.... this is getting complicated. I'll leave it with that I have never had any problems over PCI cards sharing IRQs. It's a whole lot better then ISA.
<BLOCKQUOTE><font size="-1">quote:</font><HR><I>Originally posted by GatewayTech:</I><BR>The #1 culprit that I see in PCI IRQ conflicting stuff is the user putting the BIOS setting for "PnP OS" or similar to "Yes". Generally, if you let the mobo do it's thang and assign mobo resource sharing and not allow Winblows to totally fark things up by calling the shots, you should be OK. View image: /infopop/emoticons/icon_biggrin.gif<HR></BLOCKQUOTE><P>Not neccesarily. I have discovered a weird OEM Adaptec SCSI card that causes problems with any card in slot 5 on my BE6 board if it is inserted in any slot. It absolutely won't work in slot 3. It makes Windows 98 lock up on boot. I guess I could try putting it in slot two with it's own IRQ if my SB Live card is happy sharing with someone else. It might really be a screwy board though. Placing it in slot 1 shares fine with my V3 3000 but messes up anything in slot 5 even though it's IRQ isn't shared with slot 5.<P>Even setting PnP OS to NO still gives the same results.<P>Taddeusz
Inserting a malfunctioning card into any slot will cause malfunctions- PC or Mac. I have an old ISA nic that fried a mobo.... goddamn NIC. I, too, had a PCI SCSI card that just plain wouldn't work in both computers I tried it in- it caused instability and pissant-ness. I'm sure it would do the same in a Mac. Returning it and getting another one worked- that card was defective.
Macs with 6 slots simply used a PCI bridge. I'm not sure about the Bus Mastering though. I do know that all the slots weren't equal. You could put say a Targa2000 in the upper slot and it would work fine but move it to a different slot and there could be problems. Noone had the definitive answer as to why this was the case. It's probably the reason why Apple doesn't want to make 6 slot machines as the cost is not prohibitive.
<BLOCKQUOTE><font size="-1">quote:</font><HR>Macs with 6 slots simply used a PCI bridge<HR></BLOCKQUOTE><P>The PCI technology was invented by intel. If you have PCI, you have a PCI bridge. So, this isn't a "Mac only" thing. It's a "PCI only" thing.
See? I said you can just slap them in. Here's why.<P>PCI is geared at 33Mhz. Yer average processor in a PC these days is 300Mhz. This means that a processor has an average of TEN MILLION clock cycles to context switch, service the interrupt, stick it into a DPC (or whatever) and switch back. You would have to have over a thousand cards in to monkey the processor up at that rate.<P>Hence, it doesn't matter, and you can just slap them in any old order. See? View image: /infopop/emoticons/icon_smile.gif<P>[This message has been edited by Paul Hill (edited January 27, 2000).]
Ozguid, you are correct that modern Macs only have 3 PCI slots, but They also have AGP for video, and ethernet, modem, USB, Firewire, sound, are all built into the mother board. This limits the amount that macs rely on PCI needs. And I am pretty sure that the AGP is all by itself, and not 'sharing' with PCI 1.<P>It is still a problem when you are doing very high end stuff, in which you want two video cards, or a better sound card, or more than one SCSI card. But I don't think these situations crop up a lot.<P><BR>Also, the PCI slots in Macs are all 64 bit, and I believe there are expansion chassis that will allow you to piggyback more.<P>And the point was that even with the boxes carrying 6 (or more?) slots, Macs never had IRQ problems to worry about.<P>[This message has been edited by resteves (edited January 27, 2000).]<P>[This message has been edited by resteves (edited January 27, 2000).]
<BLOCKQUOTE><font size="-1">quote:</font><HR>Also, the PCI slots in Macs are all 64 bit, and I believe there are expansion chassis that will allow you to piggyback more.<HR></BLOCKQUOTE><BR>OK, how many 64-bit devices are there available for the Mac? I'm genuinely curious.<P>And how does it solve the fundamental problem -- that there aren't enough slots. There were expansion chassis available for older Macs, but I don't know about the new ones. Should you really have to buy an add-on to get a reasonable amount of storage, though? It seems a bit silly to me.<P>Is the modem built-int? I can't find anything to say if it is or it isn't; the fact that it's optional makes the idea seem a bit suspect, but I suppose it might be (especially if it's a soft-modem).<P>USB is built onto any PC motherboard, too. But that doesn't reduce the INT requirements -- it just reduces the slot requirements.<P>But if you want a Mac with decent sound, SCSI, and decent video capture (which means, not FireWire DV cameras), it looks like you're gonna be pushing the number of slots you have available.
One thing I'd like to know about the 64-bit PCI slots in the Macs is: Does this conform to a PCI specification? Next, what cards for the Mac are truly 64-bit? Since there are a number of PCI cards that are used in both the Mac and x86 systems, these would have to be 32-bit as there are few x86 boxen with 64-bit slots that I am aware of (mostly servers, I've seen).<P>And I guess my last question is: How much of a benefit is it to use 64-bit PCI slots with a 32-bit CPU?
One thing I will throw into this debate is that the new i840 boards from intel have at least two 64-bit PCI slots. <P>Some real good 64-bit PCI boards would be SCSI cards, Gigabit Ethernet (fiber optic), and only a few (E&S) video cards (check the Alpha platform; they've had 64-bit PCI slots for years now). Heck, even Sun ULTRASparc's only have 32-bit PCI slots in them for some odd reason.<P>The only Macs to show up with 64-bit PCI slots is the new G4 ones with the Sawtooth motherboards (it memry serves me right). Anything before that only has the standard 32-bit PCI slots and the NuBus slots.
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