Hi

On an Ultra 10, up to 4 cards can be attached on to the PCI-A bus. The
PCI-A bus is specified as being 32-bits wide and working at 33MHz. My
question is: Does the speed of the bus (33MHz) vary with the number of
cards on the PCI slots? I don't know anything about hardware so,
intuitively, I would have guessed that the more devices you have on the
bus, the slower the speed of the bus. Because you have more than one
device contending for the same amount of bandwidth on the bus.

Thanks

Troy

Troy Fiddler <tfiddler@calendar.com> writes:

>On an Ultra 10, up to 4 cards can be attached on to the PCI-A bus. The
>PCI-A bus is specified as being 32-bits wide and working at 33MHz. My
>question is: Does the speed of the bus (33MHz) vary with the number of
>cards on the PCI slots? I don't know anything about hardware so,
>intuitively, I would have guessed that the more devices you have on the
>bus, the slower the speed of the bus. Because you have more than one
>device contending for the same amount of bandwidth on the bus.


No, the PCI bus always runs at the same speed; more devices would
be competing for cycles on the bus, though.

Casper
--
Expressed in this posting are my opinions. They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.

Troy Fiddler <tfiddler@calendar.com> wrote:
> Hi
>
> On an Ultra 10, up to 4 cards can be attached on to the PCI-A bus. The
> PCI-A bus is specified as being 32-bits wide and working at 33MHz. My
> question is: Does the speed of the bus (33MHz) vary with the number of
> cards on the PCI slots? I don't know anything about hardware so,
> intuitively, I would have guessed that the more devices you have on the
> bus, the slower the speed of the bus. Because you have more than one
> device contending for the same amount of bandwidth on the bus.

Whether one card or four, the bus speed will always be the same. The
speed hit comes when 4 devices want to push data across the bus at
the same time -- someone's gets to win, and the rest lose -- you're
competing for the available cycles, but, the *practical effect" is
to slow it down for the losers.

Kurt
--
A closed mouth gathers no foot.

Thanks for the answers guys!

I've got one more small query. Recently, one of the cards that sits in
one of the PCI slots was broken. Other cards on other PCI slots were OK.
We have some way of 'pinging' a card to check to see if it's healthy and
working. It seemed that the broken card was stopping us pinging the
other good cards: If the broken card is in place, we can't ping the
other good cards. Take out the broken card, and we can ping the other
good cards. Does the broken card screw up the PCI bus to such an extent
that it can't transfer information for other cards? Does anyone have any
explanations?

Thanks

Troy

Kurt Wall wrote:

>Troy Fiddler <tfiddler@calendar.com> wrote:
>
>
>>Hi
>>
>>On an Ultra 10, up to 4 cards can be attached on to the PCI-A bus. The
>>PCI-A bus is specified as being 32-bits wide and working at 33MHz. My
>>question is: Does the speed of the bus (33MHz) vary with the number of
>>cards on the PCI slots? I don't know anything about hardware so,
>>intuitively, I would have guessed that the more devices you have on the
>>bus, the slower the speed of the bus. Because you have more than one
>>device contending for the same amount of bandwidth on the bus.
>>
>>
>
>Whether one card or four, the bus speed will always be the same. The
>speed hit comes when 4 devices want to push data across the bus at
>the same time -- someone's gets to win, and the rest lose -- you're
>competing for the available cycles, but, the *practical effect" is
>to slow it down for the losers.
>
>Kurt
>
>