Archived from groups: alt.comp.periphs.mainboard.tyan (
More info?)
Dan Irwin wrote:
> But then why does my 133mhz PCI scsi card fit into my regular PCI slot
> and work, with just the back hanging out and i take it a slow speed.
Because
1.) The card is voltage compatible with the legacy slot or you
wouldn't be able to fit it in.
2.) The card is *not* a 133 MHz card - it is a card CAPABLE of running
at 133 MHz. It has no clock on it that gives it any specific speed.
Instead it gets it clock signal from the PCI bus. Hence if the PCI
bus is feeding it a 33 MHz signal, it uses at 33 MHz clock.
Not all chips can run at 1/4 of their designed speed, but the ones on
your SCSI card apparently can. Its a little more complicated than
that - cards can have clock multipliers on them, for example - but
that is the general idea.
3.) The contacts on the part of the PCI-X card that extend past the
end of a legacy PCI slot are the ones that extend the width of
the card's data bus from 32 bits to 64 bits. Between the card
and its drivers/software there is either hardware or software
logic to detect the available bus width and to take advantage of
the 64 bit bus width if a 64 bit bus is detected.
There is a PCI specifications consortium that decides how it
is all supposed to work. They have both highly technical
documents on there web site, as well as more basic info/FAQs
for people like you and me. Its been a couple of years since
I've looked at that site, but it is undoubtedly still around.
Google should find it quickly for you.
> If that can happen why can't my regular pci card go in the 133mhz slot
> and just not fill in the back?
>
Because your legacy 33 MHz card undoubtedly cannot handle the
clock speed that it would be getting from a 133 MHz slot.
A few motherboards, the Tyan S2885 for example, have a jumper
on them that will let you slow some or all of the PCI-X slots
down so that they can be used with slower 32 bit cards.
>
> Rob Stow <rob.stow@sasktel.net> wrote in message news:<107iv8lcbig7v94@corp.supernews.com>...
>
>>Dan Irwin wrote:
>>
>>>How is it that PCI-X cards fit fine into legacy pci slots, with just
>>>the end hanging out, but legacy PCI cards dont fit into pci-x slots,
>>>without just filling up the back end?
>>>
>>
>>It depends on the voltage that the PCI-X card is designed for.
>>
>>
>>The slots look like this:
>>
>>+-------------------------------+
>>| 32bit/33MHz 5 Volts | | (Legacy 32 bit PCI)
>>+-------------------------------+
>>
>>+-------------------------------+
>>| | 32bit/33+MHz 3.3 Volts |
>>+-------------------------------+
>>
>>
>>+-------------------------------+-----------------+
>>| 64bit/66 MHz 5 Volts | |(Legacy 64 bit) |
>>+-------------------------------+-----------------+
>>
>>+-------------------------------+-----------------+
>>| | 64bit/66+MHz 3.3Volts | |
>>+-------------------------------+-----------------+
>>
>>
>>The "|" characters indicate either the ends of the slot
>>or dividers/barriers in the middle of the slot. Those
>>dividers are intended to stop you from using a 3.3 Volt card
>>in a 5 volt slot and vice versa.
>>
>>Each card will have notches in it that match up with the
>>dividers for the type of slots it is compatible with. If
>>a card is compatible with both 3.3 V and 5 V slots, it will
>>have notches for both.
>>
>>Hence a PCI-X card can be used in a legacy 32bit/33MHz slot
>>if it is either of the following is true
>>- it is a 5 Volt card going into a 5 Volt slot
>>- it is a 3.3 Volt card going into a 3.3 Volt slot
>>- The card can use either 3.3 Volts or 5 Volts.
>>
>>
>>All of the PCI-X slots on the Tyan S2885 are 3.3 volts.
>>
>>
>>
>>
>>
>>
>>>Rob Stow <rob.stow@sasktel.net> wrote in message news:<107h90pe2a65041@corp.supernews.com>...
>>>
>>>
>>>>Rob Stow wrote:
>>>>
>>>>
>>>>
>>>>>Dan Irwin wrote:
>>>>>
>>>>>
>>>>>
>>>>>>because the k8w olny has 1 33mhz slot, but i still need to use 3 cards
>>>>>>
>>>>>>"nut cracker" <nutcracker@internationalhacker.org> wrote in message
>>>>>>news:<PZednT0ksY_iq-rdRVn-sA@speakeasy.net>...
>>>>>>
>>>>>>
>>>>>>
>>>>>>>ewwww, why would you want to do that ?
>>>>>>>
>>>>>>>64bit 33Mhz slots typically are. not sure about the others.
>>>>>>>
>>>>>>>NuTs
>>>>>>>
>>>>>>>"Dan Irwin" <harryguy082589@aol.com> wrote in message
>>>>>>>news:2a779348.0404091346.156bd005@posting.google.com...
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>hi,
>>>>>>>>
>>>>>>>>I was wondering, are 133 and 100 mhz pci-x slots backwards compatable
>>>>>>>>with regular pci cards
>>>>>
>>>>>
>>>>>There are 4 PCI-X slots and one 5 Volt 32bit/33Mhz legacy PCI slot.
>>>>>
>>>>>For the two PCI-X slots closest to the legacy slot, there is a jumper
>>>>>on the motherboard that you can set to force the those two slots
>>>>>to run in legacy mode.
>>>>>
>>>>>Note, however, that a legacy PCI card won't fit in a PCI-X slot
>>>>>unless you move the bracket to the other end so that you can turn
>>>>>the card around. For a card that is providing internal IDE or
>>>>>SATA ports, this is no big deal. However, for something like a
>>>>>sound card or a USB/FireWire card where there are external ports
>>>>>on the end bracket you are screwed.
>>>>
>>>>Forgot that I had tried that with a Promise SATA card
>>>>after a Promise techie had told me it would work. However,
>>>>after removing the end bracket and turning the card around
>>>>nothing in any of the slots on that bus worked. Thankfully
>>>>nothing seemed to have been damaged.
>>>>
>>>>
>>>>
>>>>>I can see you needing two legacy PCI cards for the S2885 - a
>>>>>sound card and a card to give you a few USB 2.0 ports. Everything
>>>>>else you should be able to get with a PCI-X compatible cards. Care
>>>>>to tell us what else you need legacy PCI for ?
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