[Simon]

I have been using a LaCie external FireWire disk for a while and everything seems OK apart from the fact that the 20GB are getting a bit small and I was thinking of getting a larger disk.

When looking at web sites about external FireWire cases containing IDE disks I don't understand the terminology. There's talk about first and second generation bridges and so on. But nobody says what this means in terms of speed.

My own experience puzzles me a bit. FireWire is 400Mb/s or about 50MB/s theoretically, so I'd expect more than 10MB/s possible. The IDE disk inside my LaCie external case is surely capable of 10MB/s but in everyday use I never get more than a couple of MB/s - definitely not near the 10MB/s I'd expect.

Is this just because I have a "first generation" FW-IDE-Bridge? What does first and second generation mean in terms of through-put and how can I find out what generation I have or what generation the case I see at a store has? Is there any software which shows this info? Apple System Profiler?

Does buying a fast IDE disk for my external case have any influence on the transfer speeds or is the additional speed lost because of a "slow" bridge? Do I have to get a new disk AND a new case for more speed?

BTW, is there any nice tool (that runs under OS X) that measures the read/write speeds of a drive - possibly freeware? I'd like to compare the internal IDE and the external FW drive.

It would be nice if somebody with some insight could shed light on these questions. I haven't been able to find a web site explaining this stuff.

Thanks,
Simon

[Macola]

[quote]Originally posted by Simon C. Leemann:
<STRONG>

It would be nice if somebody with some insight could shed light on these questions. I haven't been able to find a web site explaining this stuff.
</STRONG>

For a good overview and real-life performance comparisons, take a look at OWC's Tech Page. Look for the Firewire article.

[Camelot]

The short answer is that the FireWire BUS has a limit of 400mpbs (or 50 MB/sec), but that's the limit for all devices on the bus communicating at the same time. Not all devices can (or will) generate that much data.

If each device maxxed out at, say, 10MB/sec, you could theoretically have 5 of them running at the same time without any degradation in throughput.

As for bridges, most external 'FireWire' drives are actually regular IDE drives with a 'bridge' chip which interfaces between the FireWire bus and the ATA bus that the drive sits on. Most IDE drives have a maximum throughput of 20 to 30 MB/sec. In addition, the early incarnations of these bridge chips were slower, and introduced delays in data transfer resulting in a real-world transfer rate well below the FireWire limit.

Newer FireWire bridges (Oxford 911 is one of the better known) reduce the latency between the FireWire and ATA busses resulting in better throughput - closer to the drive's limit but still under the FireWire limit.

[Simon]

Thanks for the help guys.

<STRONG>In addition, the early incarnations of these bridge chips were slower, and introduced delays in data transfer resulting in a real-world transfer rate well below the FireWire limit.</STRONG>

And how do I know if my LaCie has this bridge or not? I would like to know, because if my bridge sucks, I'll get a new disk and case, but if the bridge is OK I'll just get a new disk...

Simon