Very Basic Data Transfer Rate Question

[X-Caliber]

Hi,

A simple question, the Ultra 160 SCSI specification states a data transfer rate of 160M/s, and the Firewire specification states a data transfer rate of 400M/s. But isn't the 32bit PCI bus standard set at 133M/s? So how are these transfer rates achieved. or are they only "theoretical?"

-V-

[albatorsk]

Yes, you're right. A 32bit 33MHz PCI bus is not fast enough to take full advantage of a U160 or FW at full speed. But also keep in mind that most U160 (and U320, I would assume) is used in 66MHz 64bit PCI systems, so that's not really a big problem.

[X-Caliber]

But there are U160 cards for 32bit PCI buses (although I don't have one). The same holds for firewire cards.

[az]

Yep, you can't use their full potential then, but that hardly matters - no single drive can saturate even 133 MB/sec, so it only matters for cached bursts, which are very small anyway.

AZ

[Gurm]

Or for RAID arrays.

But yes, you're 100% correct in assuming that it's a waste of power.

- Gurm

[spadnos]

Right - PCI is too slow.

As an aside, the FireWire rate is 400 Mbits, not 400 MBytes per second. Standard 32bit/33MHz PCI can handle FW400 and FW800 just fine.

- Steve

[VJ]

Originally posted by albatorsk
Yes, you're right. A 32bit 33MHz PCI bus is not fast enough to take full advantage of a U160 or FW at full speed. But also keep in mind that most U160 (and U320, I would assume) is used in 66MHz 64bit PCI systems, so that's not really a big problem.

Even moreso, in recent systems, PCI-X slots (not to be confused with PCI Express !) are used. They are specced at: 64 bit, and have speeds of 33 MHz, 66 MHz,
100 MHz and 133 MHz (IIRC it depends on the number of PCI-X devices present on the bus).

I've only seen U160, U320 and gigabit ethernet cards on PCI-X. Indigita is said to come out with a PCI-X Firwire 800 card within a couple of months.


Jörg

[Gurm]

Oh, I've seen plenty of standard PCI U160 and gigabit ethernet devices. No U320's though.

- Gurm

[VJ]

Originally posted by VJ
I've only seen U160, U320 and gigabit ethernet cards on PCI-X. Indigita is said to come out with a PCI-X Firwire 800 card within a couple of months.

Hmm, this could indeed be misinterpreted... I've also seen U160 and gigabit cards on regular PCI... What I've meant to say is that I haven't seen other cards with a PCI-X interface apart from the ones mentioned...

(but, euhm, don't most PCI-X card work i a PCI slot ?)


Jörg