How does an add-on IDE controller card work?

[DJFuji]

Exactly how does an add-on IDE controller card work? i.e. the Maxtor/Promise controllers. Does the card actually create two new IDE channels or does it somehow "borrow" resources from the original two channels. In other words, are the new channels as efficient and good as if they were built in like the primary and secondary? And what limitations do the channels have? For example, the IDE controller can only access one device on the channel at a time. So therefore your fastest performance between IDE devices comes from cross-controller data transfers. If you have IDE3 and IDE4 controllers, does that mean IDE2 to IDE4 is just as fast as IDE1 to IDE2? Or is IDE4 kind of a "virtual" controller that pulls from the IDE2?

 

[natto fire]

I would imagine that they are independent because they are on the PCI bus which connects to the Memory Controller Hub. They probably get DMA and an IrQ as if any other PCI device is connected.
As for it being faster to transfer from an integrated IDE to add-on it might be faster because eventually the integrate IDE interfaces with the MCH which might making it faster because it can access the drive on the add-on and the one on the integrated at the same time and transfer the data along a fairly speedy bus.

Just my $.02

 

[PHATJACK]

The new channels are just like the ones on your mobo. They each have two channels. It would be like the mobo having four IDE channels. The card is just adding two more independent channels. Hope this helps

 

[jonnyGURU]

Fact is, that even your on board IDE controllers are "PCI". Think back to when controller cards for PCs were what you plugged your IDE, floppy and even Serial and Parallel connectors into. Once upon a time, a motehrboard was JUST a board with only slots. That on board PCI controller is STILL a PCI device.

Think of your onboard IDE as taking the components off of a PCI IDE controller card and soldering them down to the motherboard. Sure, the functionality of the IDE controller is now integrated into the Southbridge, but so is onboard sound, so that shouldn't come as a big surprise.

When you add a PCI controller card, you're only doing just that... ADDING AN INDEPENDENT PCI CARD. It is forced to take a different resource (I/O and IRQ) of course, because the standard IRQ 14 and 15 are already taken, but it's not taking anything AWAY from the board... it's just YET ANOTHER PCI controller card.

As for the effect of the two different IDE controllers: There's no effect... They are merely two seperate PCI "cards".

 

[Recneps]

Not all add-on IDE controllers go over the PCI bus. My neibhor has on the ISA bus and it only has a primary channel.

 

[jonnyGURU]

<< My neibhor has on the ISA bus and it only has a primary channel. >>



Well... if you want to split hairs over old school interfaces; My 386 had an ISA IDE controller, my 486 had a VLB IDE controller and I've worked on some older 486s that had EISA IDE controllers. But we're not talking about THAT far back.

 

[Mday]

yah, back in the 486 days, there was only one channel. 2 channel mobos did not appear until the pentium days.

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most ide controller cards are treated as scsi cards by the bios and the operating system. it's a mislabeled piece of hardware though. scsi cards are merely storage controller cards (that can also control scanners, etc). the same can be said of those ata controller cards (asside from the scanner thing ;-))

just like scsi controllers, the cards need a bios on them in order for them to be bootable.

as for transfer speeds, the addon cards suffer from the same limitations of ATA in that only one device per channel can be used at any given time (thus 2 drives communicating on the same channel is slower than 2 different channels). this &quot;flaw&quot; in design is a fault of the ata specifications, not the controller which is restricted by said specifications.

performance between drives on different controllers is as fast as the slowest drive\controller combination. obviously controller performance depend on how the controller was designed. whether they are faster than the onboard (non extra) controller depends on the controller. a benefit of an addon card is that they only require 1 irq for both channels, while the onboard (non extra) ones require an irq for each channel (a remnance of the 486 days). of course it is also true that both types of controllers are limited to the slowness of the pci bus in general.

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there is no BORROWING of any resources at all, it's an INDEPENDENT controller.