What is the standard DV data transfer rate via 1394/Firewire?

[James Emory]

I have seen 1394 cables with 100, 200, 400, 800 and 1600Mbps ratings. Do 1394 ports on PC's have different ratings as well? What is the DV standard for data transfer or is it only limited to the speed of the 1394 port being used? Is there an area in my PC that I can find out what my 1394 port and USB port data rates are?

[Christopher Lefchik]

Originally Posted by James Emory

I have seen 1394 cables with 100, 200, 400, 800 and 1600Mbps ratings. Do 1394 ports on PC's have different ratings as well?

Most IEEE 1394 ports on computers to date adhere to the 1394 "a" standard of 400Mbps. An IEEE 1394 "b" standard of 800Mbps has been ratified as well; Apple has been shipping at least some of its desktop computers with 1394b connections. I don't know how 1394b acceptance is coming along in the PC realm.

However, all of this is academic when it comes to DV's 3.6Mbs per second datarate, which works out to 25Mbps (1Mb = 7Mbps). As you can see, 25Mbps is nowhere near the bandwidth of the IEEE 1394a standard, let alone IEEE 1394b.

As for USB, if your computer is at least four years old chances are it probably has USB v1.1 connections (now called USB Full Speed) that plod along at a pokey 7Mbps datarate. I believe USB v2 ("High Speed") connections started appearing on computers in 2002; USB v2 has a data transfer rate of 400Mpbs.

I don’t know what kind of computer you have, but I’d guess it is probably three years old or younger, in which case it would probably have USB 2.0 and IEEE 1394a connections (as far as I know IEEE 1394b adoption hasn’t really started in the PC area yet).

[James Emory]

Thanks Christopher. That's just what I wanted to know. That explains why I have seen supports DV 25 in some of the specs for cables and cards. My laptop is 3 years old and it has USB 1.1. I thought that it had USB 2.0 when I got it until I plugged in a 2.0 flash drive in the last year and it showed the discrepancy. Of course the drive is backwards compatible but it's still aggravating to spend $2500.00 and get USB 1.1. I guess I must have gotten the last of them because I ordered it in December of 2002 and received it in late January 2003. They probably said, get that last pallet of '02s on the plane, lucky me. Another great reason to know this is that I won't spend more money on cables and/or cards with higher data rate capacity because it won't matter.

[David Andrews]

I, too, have run into problems in the past with low USB1 data rates. For USB (don`t know about ieee 1394) the rates quoted are for burst mode not continuous transfer. These burst mode speeds are unreliable for use with video. At the time I had the problem I tested my system using the Canopus Storm test which gave a rough and ready reading of each drives transfer speed. This proved accurate for the purpose of calculating read and write speeds. I have found USB2 works OK.

[Christopher Lefchik]

Originally Posted by James Emory

My laptop is 3 years old and it has USB 1.1.

Ah, I was thinking of desktops and I forgot about laptops. They used to lag behind desktop computers when it came to adopting the latest technology, though I think that may be changing somewhat now.

[Christopher Lefchik]

EDIT: 1Mb = 8Mbps, not 7Mbps as I wrote in my first post. Also, the USB 1.1 transfer rate is 12Mbps, and the USB 2.0 transfer rate is 480Mbps. You might think that would make USB 2.0 faster than IEEE 1394a, but in reality USB 2.0 performs a little slower in the real world than IEEE 1394a does.