What's the difference between Maximum Speed and Connection Speed?

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Level 1

21 points

What's the difference between Maximum Speed and Connection Speed?

Hi. My system profiler lists my iSight with a Maximum Speed of up to 400 Mb/sec, but it lists Connection Speed at up to 200 Mb/sec. I guess I'm just not sorting this out in my head correctly. I get the 400 Mb/sec part, since that's my firewire port speed, but why would the connection speed be half of that? Does that refer to the maximum capable speed of an iSight when broadcasting over the web, or is that a factor that changes dependent on whether I have a faster internet connection or not? I guess my main question is, does the iSight cap out at 200 MB/sec by default? If so, how does that compare to a USB2 driven cam? I like the iSight and all, but it does seem a bit choppy and slow, and the picture, even locally, seems pretty grainy (although that might have something to do with iGlasses?). I have a G4 DA with a 1.5GHz processor and 1.5 gigs of RAM. I guess I was just expecting a little more performance and quality from the iSight than I am getting. Any ideas or hints? Any other brand of cam work and play well with the Mac that would give performance superior to what I'm getting now? Thanks!

G4 DA w_1.5 gHz under the hood, Mac OS X (10.5.2), 1.5 gHz, 1.5 GB RAM, 1TB, & many bells/whistles

Posted on Feb 25, 2008 12:45 PM

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Answer 1

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EZ Jim

Level 7

22,590 points

Feb 25, 2008 3:25 PM in response to garygg

Hello garygg

I tried looking everywhere I could think of including web and Apple Developer Connection searches. The answer to your specific question may be in there, but I couldn't find it.

Interestingly, my System Profiler also shows my external iSight's Firewire speeds at 400/200 when iSight is connected to my dual-processor G5 running 10.5.2. However, when I connect the same iSight to my G4 PowerBook running 10.4.11, the PB's System Profiler shows 400/400. The difference apparently has nothing to do with the network connection speeds or iChat System Requirements because both of my computers are connected to the same LAN and the numbers do not change whether iChat is running or not.

I formerly ran Tiger on my G5 PPC Mac, and I have not noticed any change in my iSight's performance with any app since upgrading to Leopard, different "connection speed" notwithstanding. I doubt that you would either. However, if you want to try another camera, and if you get no better response here, you might be interested in the suggestions in this post:

http://discussions.apple.com/thread.jspa?messageID=5725045&#5725045

If you don't get a better answer to your "Connection Speed" question here or in Apple's developer info, and if you want to pursue it further, you might get better help by searching or posting in the appropriate Power Mac Discussions Forum.

In the meantime, I will see if I can find someone who might be able to give you a better answer.

EZ

Jim

PowerBook 1.67 GHz w/Mac OS X (10.4.11) G5 DP 1.8 w/Mac OS X (10.5.2) External iSight

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Answer 2

EZ Jim

Level 7

22,590 points

Feb 26, 2008 8:58 AM in response to garygg

Hello again, garygg.

The following info was given to me by BDAqua:

"FireWire 400 can transfer data between devices at 100, 200, or 400 Mbit/s half-duplex data rates (the actual transfer rates are 98.304, 196.608, and 393.216 Mbit/s, i.e. 12.288, 24.576 and 49.152 megabytes per second respectively). These different transfer modes are commonly referred to as S100, S200, and S400."
http://en.wikipedia.org/wiki/FireWire

I think this answers your question about the difference between Maximum Speed and Connection Speed. Based on that info, it seems to me that the connection speeds of 200 vs 400 might merely be a difference in which number is being reported by Leopard vs Tiger.

As shown in the following image, USB cams can give a maximum speed up tp 480 Mb/sec, but 480 would only be the possible maximum if no other USB device shares the bandwidth:

I do not know whether the 480 maximum is comparable to either Firewire speed number. In my experience, Firewire cams are the best choice if you are using your USB ports for other things. USB would be a good choice if you experience hardware or software conflicts with iSight.

Do you still have unanswered questions?

EZ

Jim

PowerBook 1.67 GHz w/Mac OS X (10.4.11) G5 DP 1.8 w/Mac OS X (10.5.2) External iSight

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Answer 3

garygg Author

Level 1

21 points

Feb 28, 2008 1:31 AM in response to EZ Jim

Very interesting. That sheds quite a bit of light on things. I never really noticed what the speed was reported at when I was running Tiger, so it could be the way the different OSs report the speed. I did recently add a second 500Gb external firewire drive, in addition to the 320Gb firewire drive I already had. I have each of those coming straight out of the ports on the back of the computer, and the iSight running out of one of the ports on the back of one of the external drives. What I think I'll try is disconnecting both of the external drives and plug the iSight directly in to the computer and see if that changes anything. If not, I'll just assume it's the way Leopard goes about displaying the speed. If it does change, I may have to rethink my external drive situation. Anyway, thanks SO much for giving me a starting point and some things to ponder. If it wasn't so late I'd play around with it tonight, but I'll save the experiments for after work. Thanks for the help!

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Answer 4

EZ Jim

Level 7

22,590 points

Feb 28, 2008 8:38 AM in response to garygg

You're most welcome, garygg

I add this link in case you encounter some while doing your testing. Many of us have experienced hardware or software conflicts with iSight or iChat when using external (Firewire) iSights. However, FYI, the 200 speed reported in my Leopard Mac was independent of whether I had any Firewire devices connected.

Cheers,
EZ

Jim

PowerBook 1.67 GHz w/Mac OS X (10.4.11) G5 DP 1.8 w/Mac OS X (10.5.2) External iSight

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Answer 5

BDAqua

Level 10

238,997 points

Feb 28, 2008 11:42 AM in response to garygg

Hi, it's just like USB... plug a USB mouse into a High-Speed USB2 port, and there is no need to have the mouse use up the 480Kb/Sec! 🙂

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