Data transfer rate USB 2.0 vs PCI card

[rijir2001]

Maybe a dumb question. But what is the max data transfer rate of a USB 2.0 connection compared to a PCI slot? So, if I was comparing a USB capture device to a PCI capture card I want to get the specs.

[junkmalle]

USB2 theoretical max transfer rate is 480 Mbit/sec = 60 MByte/sec. Real world max data throughput rate is about half that.

PCI theoretical max transfer rate is 128 MByte/sec. Real world data transfers max out around 90 MByte/sec.

I don't know that any of this really matters for video capture though.

[rijir2001]

I always had the feeling that USB 2.0 couldn't handle the data transfer of USB capture devices. That they would result it too many frame drops. And that a capture card in a PCI slot would be better.

But maybe that is just me assuming.

[ROF]

Maybe a dumb question. But what is the max data transfer rate of a USB 2.0 connection compared to a PCI slot? So, if I was comparing a USB capture device to a PCI capture card I want to get the specs.

USB2.0 = 480Mbps
PCI = 133Mbps / 266Mbps or 533Mbps

For PCI transfer rates it depends on your motherboard specs. USB2 is the same no matter which board you have.

[junkmalle]

Maybe a dumb question. But what is the max data transfer rate of a USB 2.0 connection compared to a PCI slot? So, if I was comparing a USB capture device to a PCI capture card I want to get the specs.

USB2.0 = 480Mbps
PCI = 133Mbps / 266Mbps or 533Mbps

For PCI transfer rates it depends on your motherboard specs. USB2 is the same no matter which board you have.

Very few people have PCI-X on their motherboards unless they're running servers or specialized workstations. And those PCI speed are MegaBYTES per second, whereas USB is MegaBITS per second.

[edDV]

So what is the problem we are trying to apply this to?

SDTV rates

MPeg4 (H.264, VC-1, WMV-HD, DivX, etc.) 1-5 Mb/s = ~0.4MB/s
DVD MPeg2 2-9 Mb/s = ~1 MB/s
DV format 25Mb/s video (34Mb/s total) = ~ 4MB/s
SMPTE 259M-C (4:3 SDI) uncompressed serial 4:2:2 = 270Mb/s = 34MB/s
SMPTE 259M-D (16:9 SDI) uncompressed serial 4:2:2 = 360Mb/s = 45MB/s

HDTV rates

MPeg4 (H.264, VC-1, WMV-HD, DivX, etc.) 4-8 Mb/s = ~0.7MB/s
HDV format 25Mb/s (34Mb/s total) = ~ 4MB/s
DVCAM-HD 100Mb/s = 12.5 MB/s
HDCAM 144 Mb/s (video) Video and Audio up to 450 Mb/s = ~56MB/s
HDCAM SR 440Mbps Video and Audio equals approximately 600Mbps = 75 MB/s

Note that all of these are sustained rates. USB and PCI devices are are often spec'd in burst rates.

[ROF]

Maybe a dumb question. But what is the max data transfer rate of a USB 2.0 connection compared to a PCI slot? So, if I was comparing a USB capture device to a PCI capture card I want to get the specs.

USB2.0 = 480Mbps
PCI = 133Mbps / 266Mbps or 533Mbps

For PCI transfer rates it depends on your motherboard specs. USB2 is the same no matter which board you have.

Very few people have PCI-X on their motherboards unless they're running servers or specialized workstations. And those PCI speed are MegaBYTES per second, whereas USB is MegaBITS per second.

Thanks for the correction on the Mbps Vs. MB/s. The above should have been MB/s instead of Mbps. I didn't list current PCI-x transfer rates because the OP didn't ask for them. I would hope most people have PCI-x of some flavor by now. The bus has been available for quite sometime and the selection of graphics options for those cards run from $49 up to and beyond $500. It's an affordable option now which shouldn't be overlooked when you decide to replace your motherboard.

[edDV]

I would hope most people have PCI-x of some flavor by now. The bus has been available for quite sometime and the selection of graphics options for those cards run from $49 up to and beyond $500. It's an affordable option now which shouldn't be overlooked when you decide to replace your motherboard.

PCI-X is nice to have but hardly needed for most video tasks. I still fail to see the problem we are trying to solve.

If it is uncompressed capture, normal PCI can handle it fine (assuming a very fast HDD subsystem). USB2 is not adequate for uncompressed capture due to various system issues. SMPTE-259 (SDI) still requires dedicated hardware cards.

[ROF]

I didn't bring up the PCI-x discussion but was just responding to it. I agree it's not necessary and could be overkill if your only purpose is video capture. Like the rest here, in my opinion USB2 will achieve dropped frames for raw footage captures. I've always wondered why since it shouldn't be like this. Does it have something to do with USB2 not achieving it's 480 in a constant stream?

[junkmalle]

I didn't bring up the PCI-x discussion but was just responding to it.

You are confusing PCIe and PCI-X. PCI-X is the (non-Intel) extension to PCI which took it 66 and 132 MHz. The original PCI was 133 MB/s. PCI-X enables 266 and 533 MB/s. PCIe (e for Express) is Intel's latest bus. Many (most?) motherboards and graphics cards now support PCIe.

Like the rest here, in my opinion USB2 will achieve dropped frames for raw footage captures. I've always wondered why since it shouldn't be like this. Does it have something to do with USB2 not achieving it's 480 in a constant stream?

USB is a packetized multipoint serial protocol with start bits, stop bits, ECC bits, and a lot of CPU overhead. 480 Mb/s represents the timing of individual bits moving through the wire. Real world throughput is roughly half that, 240 Mb/s or 30 MB/s. Uncompressed 720x480, 30 fps, 4:2:2 video is close to that so USB2 is likely have problems with it.

[edDV]

[quote="junkmalle"]

Like the rest here, in my opinion USB2 will achieve dropped frames for raw footage captures. I've always wondered why since it shouldn't be like this. Does it have something to do with USB2 not achieving it's 480 in a constant stream?

USB is a packetized multipoint serial protocol with start bits, stop bits, ECC bits, and a lot of CPU overhead. 480 Mb/s represents the timing of individual bits moving through the wire. Real world throughput is roughly half that, 240 Mb/s or 30 MB/s. Uncompressed 720x480, 30 fps, 4:2:2 video is close to that so USB2 is likely have problems with it.

Conservative design requires 2-4x safety margin for reliability. USB data throughput is influenced by so many external factors that 4-8x safety margin seems appropriate.

[rijir2001]

Thanks. I learned quite a bit from my question. I really appreciate it guys!!

[junkmalle]

Thanks. I learned quite a bit from my question. I really appreciate it guys!!

So what capture devices are you considering?