I believe the 32-bit bus speed is 133MB/s, and each slot shares that bandwidth limitation.

Ok so now my next question is why do people use ide or sata pci cards if it consumes the entire bandwidth and isn't the on board ide use the same bandwidth as the pci as well?

1) Working around compatibility problems and limitations such as disk size, early Triton problems, etc.
2) Hardware RAID support.
3) Some people prefer parallel SCSI.

Server boards are often configured with multiple PCI buses. PCI-X was also introduced to lift the bandwidth limitation (66mhz-133mhz depending on revision, 32 and 64 bit). 64 bit, 133mhz PCI-X could pump data at 1066MB/s.

Oldskoolmaniac wrote:

Ok so now my next question is why do people use ide or sata pci cards if it consumes the entire bandwidth and isn't the on board ide use the same bandwidth as the pci as well?

You're looking at it from today's perspective. Think back when PCI was first introduced. There were no devices or even combination of devices that could saturate that bus. And even when devices started to approach the limit years later, it was only in *bursts* where the likelihood of multiple devices peaking in any moment at the same time was unnoticeable. But you'll notice that as soon as devices started to come close to threatening pegging the PCI bandwidth, along comes AGP to offload the video from that bus, then later on PCI-e. PCI slots are hard to even find on modern motherboards now.

clueless1 wrote:

You're looking at it from today's perspective. Think back when PCI was first introduced. There were no devices or even combination of devices that could saturate that bus.

Indeed. To put that in perspective, PCI was the successor to ISA (and in a way to the short-lived VLB, which had very similar performance characteristics). ISA also shared the bandwidth between all devices, but it was just a 16-bit bus at 8 MHz instead of a 32-bit bus at 33 MHz.
This gave you only 16 MB/s as opposed to 133 MB/s.
(For professional grade systems there was EISA, but even that was only twice as fast as ISA).
So when PCI came along, it was a huge leap forward in terms of performance (back then, harddisks delivered nowhere near 133 MB/s, the burst speed was only interesting for small cached transfers. You'd be lucky to get 20-30 MB/s sustained. Likewise, network cards were commonly 10 mbit or 100 mbit tops, so only capable of about 1.25 MB/s or 12.5 MB/s respectively).

The reason im asking is cuz i have a asus p3v4x with a power leap 1.4ghz p3-s, 2gb of ram 2x 120gb HDDs, asus xonar dg pci audio card, 10/100 ehernet card, usb 2.0 card and i was going to throw in a promise ata133 card cuz the onboard is only ata66. Do high end audio cards consume that much bandwidth tho?
My HDDs might not even consume the whole ata66 anyways, but on the other hand if i did raid.
Also do onboard devices use the PCI lane as well?

HDtune says my average is 53MB/p so if i do raid on the promise card it should be roughly 100MB/p so i still have 33MB left over.

Keep in mind it's rare for all PCI devices to be pegging their respective bandwidths *at the same time*. They tend to be bursty, so the bus will rarely be saturated for more than a moment at a time.

realistically speaking, pci caps at ~100MB/s. new sata2 hard drives have NO problem saturating this. There really isnt a problem here. pci was created because video took up SO MUCH of the isa bandwidth. Then AGP did the same for ISA. It took a relatively long time before all the other parts caught up. pci express fixed all this. There is no more bandwidth sharing, practically everything is connected directly to the cpu now.

There is no problem here, in old games they dont need large data transfers. Sure the hard drive can give 100+ MB/s, but the game only needs 1MB. The hard drive isn't going to keep sending data 100% of the time. So it ends up being a non-issue. In reality, fast hard drives only make for short loading times.

Makes since plus i can only play older games so that 53MB/p is probably more then plenty it all ready seams snappy as it is so i might just continue using the onboard at66 then.
Thanks everyone for clarifying this better and im sure it will help out others as well.

Sound cards don't take much bandwidth by the way.
If you take CD quality audio streaming, that is 16-bit stereo at 44.1 KHz. Which comes down to 2*2*44100 = 176100 bytes per second. So roughly 172 KB/s bandwidth required.
Sound cards mainly moved to PCI for convenience. Better plug&play, and ISA slots started to disappear from motherboards.