I need some clarification on USB drives...

[fretman]

There are 2 USB drives that I'm looking at. Both are 8 gigs and both are rated USB 2.0 High Speed.

One of them is a the Kingston Data Traveller. The specs are as follows for Maximum Data Transfer Rate...5Mbps (Read); 1.5Mbps (Write). This one is selling for about $60.

The other one is a Hewlett Packard and sells for about $25 but does not list the Maximum Data Transfer Rate.

My question is this. I know that there are 3 types of speeds...low speed, full speed, and high speed.

Looking at the specs for the Kingston it looks like it's at best low speed. But I don't understand why it's listed as USB2.0 High Speed. I thought that if a USB drive shows USB2.0 High Speed then it should be possible to get up to 480Mbps.

Anyways, if someone here could explain all this to me it would be great. I kind of remember seeing 480Mbps listed for the Hewlett Packard which is why I'm leaning towards that one.

Thanks for the help and clarification.

 

[taltamir]

"low speed, full speed, and high speed. " - that is USB speeds, not the speed of your drive.

It uses a USB2 interface, just like most HDD today use SATA2, but there platter drive on the market that comes close to maxing out the speed of SATA1.
They have to support USB2 or nobody will buy them, that and USB1 is so slow that it will limit the drive.

The kingstone drive is... average, there are better, cheaper ones... high end drives go much faster... low end drives can go at under 1mbps.

ps, if i am not mistaken USB2 is 480mbps, megabit... aka 480 / 8 = 60 megabytes/second (the space is measured in mega bytes, and the speed windows shows is in megabytes, and I think USB flash drives also report speeds in megabytes/second)

this site offers good reviews for USB flash media:
http://www.everythingusb.com/
here is a specific link
http://www.everythingusb.com/h...e/USB_Flash_Drives.htm

 

[fretman]

Thanks for the help. I'm still a bit confused though. Maybe I should just get the HP and hope for the best.

 

[tcsenter]

Performance of the USB2.0 interface is 12Mbps for full-speed and 480Mbps for high-speed. Performance of the device located on the other side of the USB interface is defined by the device itself, up to the point where the interface becomes the limiting factor.

e.g. maximum throughput over the conventional 32-bit 33MHz PCI bus is 133MBps. If you plug a 56Kbps PCI modem into a PCI slot, it doesn't turn the modem into a 133MBps modem. Its still 56Kbps even though the interface it is plugged into can support plenty more than that.

 

[fretman]

I think I'm beginning to understand a bit more. However, I'm using an old USB2.0 High Speed USB drive right now just to do some testing. It's rated at High Speed and is a 1 gig USB drive.

I'm using it on Vista and a fairly new machine with somewhat up to date specs.

It takes 90 seconds to read 1 gig and 4 minutes to write 1 gig.

By MBPS calculations, I think that works out to a read rate of 11.38/mbps and a write rate of 4.26/mbps.

That's well short of the 480/mbps I was expecting.

Am I still missing something here?

Thanks.

 

[BlueAcolyte]

No drive has even come close to 480. Your drive does ok, pretty average. I think the fastest ones get around 40.

 

[fretman]

Thanks for the help. I ordered the HP. I guess I won't be too disappointed since 480mbps now seems out of reach.

 

[tcsenter]

Originally posted by: fretman
By MBPS calculations, I think that works out to a read rate of 11.38/mbps and a write rate of 4.26/mbps.

That's well short of the 480/mbps I was expecting.

MB = Megabyte
Mb = Megabit

There are eight bits in one byte:

480 Megabits = 60 Megabytes

 

[fretman]

Originally posted by: tcsenter

Originally posted by: fretman
By MBPS calculations, I think that works out to a read rate of 11.38/mbps and a write rate of 4.26/mbps.

That's well short of the 480/mbps I was expecting.

MB = Megabyte
Mb = Megabit

There are eight bits in one byte:

480 Megabits = 60 Megabytes

So the transfer rate on USB drives is measured in Megabits and NOT Megabytes...correct?

Based on that I have recalculated so correct me if I'm wrong again...

It took 90 seconds to read 1 gig
It took 240 seconds to write 1 gig

Therefore read rate is 8192/90 = 91
Therefore write rate is 8192/240 = 34

Since 1 gig = 8192 Megabits

So is it correct to compare 91 and 34 to the 480 number?

 

[tcsenter]

Maximum USB interface transfer rates are expressed in megabits. Actual USB device transfer rates are usually expressed in megabytes if they are over 1MB/sec.

480Mbps is the maximum theoretical data rate of USB2.0 high-speed. Maximum achievable data rates are limited to ~425Mbps due to overheads.

So is it correct to compare 91 and 34 to the 480 number?

Yes (or 425Mbps as noted above, whichever you prefer).