USB 2.0 external drive transfer speeds - confused !!

  • Thread starter Thread starter Ian
  • Start date Start date
I

Ian

Is there anyone that can help me understand whether my external USB 2.0
drive is transferring at the correct speed. At first I thought that it
was only transferring at 1.1 speeds but I think I mixed up Mbit and
Mbyte speeds.

Anyway, using SiSoft Sandra reports a transfer speed of:

11,036 kB/s

At first I thought this must only be operating at USB 1.1 speed but then
I notcied that the Sandra program had a reference benchmark of 11,610
KB/s for a Hi-Speed USB ATA 100 drive. I am using a Maxtor 200Gb ATA
133 drive so now I am confused as to whether this is operating at USB
2.0 which I thought was 480 Mbit/s which = 60 MB/s ??

Help please !
 
At first I thought this must only be operating at USB 1.1 speed but then
I notcied that the Sandra program had a reference benchmark of 11,610
KB/s for a Hi-Speed USB ATA 100 drive. I am using a Maxtor 200Gb ATA
133 drive so now I am confused as to whether this is operating at USB
2.0 which I thought was 480 Mbit/s which = 60 MB/s ??
Click to expand...

Tht sounds about right. USB speed are measured in Mbit, which is 8
times Mbytes. So 480 Mbit is 60M byte, 12 Mbit (USB 1.1) = 1.5 Mbyte
and the original USB specs: 1.5 (IIRC) Mbit which is 187.5 Kbyte

ATA speed are measured in Mbyte so ATA66 are about 66 Mbyte/sec.
Confusing? Consider unless you have hard drive capable of 10K RPM,
most hard drive can't read or write fast enough to take full advantage
of ATA100/133 and generally maxes out at 50Mbyte/sec and that's just
the burst rate. Sustained rate is a lot lower.

PS as long as we're talking about USB drives, I'd still suggest
firewire drive. Even though Firewire is slightly slower than USB2
(400 Mb vs 480 MB), Firewire can handle more traffic on the system
while USB is more of one-at-a-time thing. If you have USB drives, USB
modem, USB ethernet, USB mouse, USB game controller, etc, the USB
system would be very busy and the the speed of USB drive would
degrade.
 
Tht sounds about right. USB speed are measured in Mbit, which is 8
times Mbytes. So 480 Mbit is 60M byte, 12 Mbit (USB 1.1) = 1.5 Mbyte
and the original USB specs: 1.5 (IIRC) Mbit which is 187.5 Kbyte
Click to expand...


Thanks for replying to my message but I'm still unclear about whether my
external USB drive is performing as expected for a USB 2.0 connection.
The reported speed of the drive is 11,036 kB/s which doesn't seem to
match up with any of the documented USB standards ???
 
I believe max through put for USB 2.0 is 12 MBs (or 12,000 kBs)
and USB 1.1 max's around 1.5MBs
where as ATA100 and ATA133 is around 50-60MBs.
so it sound like your system is normal.
 
Now why should a mere 33% increase in ATA bus speed lead to a 500%
increase in benchmark result? Do you have all your marbles in a row?

No, they are not.

Nope.
First there is serial protocol overhead and next there is command overhead.
So 480 Mbit is 60M byte, 12 Mbit (USB 1.1) = 1.5 Mbyte
Click to expand...

So all false.
Thanks for replying to my message but I'm still unclear about whether my
external USB drive is performing as expected for a USB 2.0 connection.
The reported speed of the drive is 11,036 kB/s which doesn't seem to
match up with any of the documented USB standards ???
Click to expand...

That is because you snipped the part of his post that tried to deal with that
but you didn't bother reading it first.

And since when do IDE drive benchmarks ever
"match up with any of the documented IDE standards"?
 
I believe max through put for USB 2.0 is 12 MBs (or 12,000 kBs)
and USB 1.1 max's around 1.5MBs
where as ATA100 and ATA133 is around 50-60MBs.
so it sound like your system is normal.
Click to expand...

Thanks Tod. At least I know it's working as it's supposed to. Although
it seems a long way off 480Mbit/s.
 
Thanks for replying to my message but I'm still unclear about whether my
external USB drive is performing as expected for a USB 2.0 connection.
The reported speed of the drive is 11,036 kB/s which doesn't seem to
match up with any of the documented USB standards ???
Click to expand...

Not all hard drive can operate at full speed. Some of the higher
speed is usually only in burst speed and sustained speed is usually
lower.

Another possibility is you have other USB devices (modem, network,
etc) that is also communicating with the PC at the same time. The USB
can only handle so much traffic.
 
Impmon said:
Not all hard drive can operate at full speed.
Click to expand...

*No* drive will operate (sustained) at bus-speed.
In theory burst speed should be bus-speed but the benchmarks measure
the cachebuffer to interface speed and that excludes command overhead.
 
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