iMac network speed

[philipz]

Has anyone done some tests already to measure the gig-port speed you can achieve with the new iMac?
I did some tests on my old fast-ethernet eMac, and only get 40 MBs instead of the theoretical limit of 100MBs.
I want to buy a new iMac and a NAS for storage of video and pictures, but am not sure if I should go for a gigabit ethernet NAS or a 10/100.
If somebody with an imac could test the port speed limit with iperf that would be great...

tx,

Phil

 

[Queso]

Firstly, remember that network speeds are always quoted in gigabits, not gigaBytes, so a 100Mbps network port only has a theoretical maximum of 12.5MBps (note that capital B and lower-case b mean different things). All types of Ethernet also have a packet overhead, where source, destination and type information are added to each packet of data just before transmission so that receiving devices can identify what they are reading. The buffer on the Network Interface is also going to have an effect on performance, as is the type of device you are connecting to and whether the connection is at full or half-duplex.

So Gigabit Ethernet as on an iMac has a theoretical maximum of 125MBps, but you'll never get anywhere close to that. 85MBps is probably the absolute best you can hope for.

 

[philipz]

Firstly, remember that network speeds are always quoted in gigabits, not gigaBytes, so a 100Mbps network port only has a theoretical maximum of 12.5MBps (note that capital B and lower-case b mean different things).

Thanks, but I'm talking about bitrate indeed. I know you won't get close to port speed for any application, but on my iMac I don't even get half of the port speed when measuring the throughput between my iMac and my router. When I do the same Iperf exercise with a PC, I get close to 90Mbits/s. I don't know what the bottleneck is (IP stack, NIC, ...) but it's definitely not the cabling or my router (hence the PC example) so I was wondering what the REAL network performance is of an iMac compared to the port speed.

 

[Queso]

Could it be duplexing which is the issue? Is the router's ethernet port set to autonegotiate or locked to a duplex setting? It has to be set the same on the other end of the connection or you'll get a mismatch and everything will slow right down.

 

[ParishM]

also if it's a 10/100 router you will never get 1000 speeds between computers.





P....

 

[Tracer]

Can your hard drive move data that fast?

Not even newer drives can achieve that sort of throughput unless they are raided.

Tracer

 

[philipz]

also if it's a 10/100 router you will never get 1000 speeds between computers.
P....

True but I should get more than 40 on a 100 Mbits connection. My PC gets 90Mbits.

Can your hard drive move data that fast?

Iperf just generates bulk network data, doesn't use the HD.