PDA

View Full Version : New MacBook Pro: Performance Level of USB2.0 vs. Firewire


MacBytes
Oct 28, 2008, 07:56 AM
http://www.macbytes.com/images/bytessig.gif (http://www.macbytes.com)

Category: Apple Hardware
Link: New MacBook Pro: Performance Level of USB2.0 vs. Firewire (http://www.macbytes.com/link.php?sid=20081028085631)
Description:: none

Posted on MacBytes.com (http://www.macbytes.com)
Approved by Mudbug

mcnicks
Oct 28, 2008, 08:44 AM
Its not just about transfer speed. Isochronous mode is important for audio and video streaming, and that is something FireWire 400 does very well.

Dudeman486
Oct 28, 2008, 08:54 AM
the question is whether usb can consistently maintain constant read/write speeds, which is one of the main reasons why firewire is preferable over usb.

oticon6
Oct 28, 2008, 08:58 AM
Its not just about transfer speed. Isochronous mode is important for audio and video streaming, and that is something FireWire 400 does very well.

USB has isochronous mode. Blame the chipsets, not the protocol.

tshort
Oct 28, 2008, 09:01 AM
USB 2.0 is rated at 480 Mbps, FW400 is rated at 400 Mbps. That means that USB 2.0 is supposedly 20% better than FW400...

Yet, the results that are shown in this article show that FW400 (at ~39 MBps) is about 10% faster than USB 2.0 (at ~35.5 Mbps). Write speeds are similar, FW400 at ~32 MBps and USB 2.0 at ~30.

Those are almost 10% differences, which can be significant.

dogcowx
Oct 28, 2008, 09:16 AM
USB 2.0 is rated at 480 Mbps, FW400 is rated at 400 Mbps. That means that USB 2.0 is supposedly 20% better than FW400...

Yet, the results that are shown in this article show that FW400 (at ~39 MBps) is about 10% faster than USB 2.0 (at ~35.5 Mbps). Write speeds are similar, FW400 at ~32 MBps and USB 2.0 at ~30.

Those are almost 10% differences, which can be significant.

You need to factor packet overhead (header, chunk rate, etc.) and any latencies into that calculation.

The 400Mbps and 480Mbps are almost like speed limit signs. They don't represent the trucks that drive on the highway and how many trucks can get through when things get busy (considering that each truck varies a bit in size).

john-c
Oct 28, 2008, 09:38 AM
USB 2.0 is rated at 480 Mbps, FW400 is rated at 400 Mbps. That means that USB 2.0 is supposedly 20% better than FW400...

Forgive me, but this is not correct. 480Mbps is the clock speed. It is not the data rate. The same is true for processor speeds: a 2.8GHz processor might be faster than a (different) 3.0GHz processor. The clock speed is not the full story.

I have read the USB specification and in my opinion it was not designed for fast data transfer. Although it does have a "burst mode" (I think that is what it is called) which allows fast data transfer, this mode blocks every other device from using the bus, for the duration. Hence burst mode should only be used for short durations. This is why USB 2 is consistently slower than FireWire in every test I've seen reported.

humera
Oct 28, 2008, 09:58 AM
The 400Mbps and 480Mbps are almost like speed limit signs. They don't represent the trucks that drive on the highway and how many trucks can get through when things get busy (considering that each truck varies a bit in size).

USB isn't unlimited bandwidth like trucks rolling down a highway, its more of a series of tubes.....

shamino
Oct 28, 2008, 10:59 AM
USB has isochronous mode. Blame the chipsets, not the protocol.
Yes, but if you try and attach two isochronous devices to a single USB bus, they step all over each other, and neither ends up working reliably.

FireWire doesn't have this problem (assuming sufficient bandwidth exists to satisfy both devices, of course.)
I have read the USB specification and in my opinion it was not designed for fast data transfer. Although it does have a "burst mode" (I think that is what it is called) which allows fast data transfer, this mode blocks every other device from using the bus, for the duration. Hence burst mode should only be used for short durations. This is why USB 2 is consistently slower than FireWire in every test I've seen reported.
It's very similar (in concept) to ATA. One device at a time may use the bus, and only in response to requests from the host computer.

FireWire behaves like SCSI (which isn't surprising, because FW's protocols are based on SCSI) where any device may interact with any other device on the bus, without the host getting involved, using protocols designed to keep this from becoming a tangled mess.

It is a credit to the USB chipset makers that performance for a single hard drive is as good as reported, but that's just one test. Watch when happens if you attach two or three drives to a single bus and try to create a RAID solution. Faced with large amounts of simultaneous access, USB will choke. FW will attempt to divide the bandwidth among the devices and will provide better overall throughput. And if there is enough FW bandwidth (e.g. on a FW800 bus with only two drives), both devices may actually run at full speed.

nagromme
Oct 28, 2008, 02:01 PM
Firewire's better for sure--and that's a reason to go Pro, but generally not the biggest reason.

For the majority of low-end consumer users, massive high-speed data transfers with external devices are rare, and a few % of speed difference isn't relevant. For that segment who use Firewire camcorders, want a new laptop now, but can't afford the new Pro... I feel bad for them but they still have good options: the new $999 Firewire-equipped white MacBook, or the previous Pros which have gotten cheap (see Amazon). What they can't do is get the new metal MacBook, which is a great machine for most other people.

It's almost as though Apple is providing SOME options for the minority, and MORE options for the majority. It makes a crazy kind of sense! :p

Full disclosure: I am a pro user with a bunch of Macs. I use wireless most often, USB next, and occasionally FW800. Never 400. My main machine is a MacBook Air and I've never wished for Firewire. Its main use for me is backups--and wireless, although slower, is far more convenient. Even my Firewire Macs do their backups wirelessly.

shamino
Oct 28, 2008, 03:44 PM
Full disclosure: I am a pro user with a bunch of Macs. I use wireless most often, USB next, and occasionally FW800. Never 400. My main machine is a MacBook Air and I've never wished for Firewire. Its main use for me is backups--and wireless, although slower, is far more convenient. Even my Firewire Macs do their backups wirelessly.
Since we're on the subject of full disclosure.

My desktop Mac at home is a PowerMac G4 (QuickSilver 2002). I have a USB 2.0 card installed. I use a lot of different devices, both FW and USB. On my FW bus, I have a scanner, an iSight camera, a tape drive and three hard drives (two of which are switched off except when I'm running a backup.) On the USB bus is my keyboard, mouse, game controller, printer, camera dock, flash card reader, iPod cable, and Palm cradle.

My laptop, on the other hand, is different. It is an iBook G4. On it, I have only used the FW port for two things: my iSight camera (when traveling) and Target Disk mode. The iSight is moot for modern Mac laptops, because they have built-in cameras. And with the new MacBook, the hard drive is easily removable, so Target Disk mode isn't nearly as necessary for maintenance as it is with my iBook.

Still, on those occasions when I want to run Disk Warrior on my laptop's drive, it is really convenient to run it on my desktop Mac, mounting the iBook via Target Disk mode. Removing the drive or booting from a CD/DVD just isn't nearly as convenient.