just wondering, I have a 2.5" external hard drive connected on a usb 2 port

does anyone know(or know how to find out) which is the limiting part with respect to data transfer rate, the 5400 rpm drive or the usb 2 port?





[Edited on 31/10/06 by liam.mccaffrey]

Raw speed for USB 2.0 is 480 Mb/s, so I'm guessing it'd be the drive that is slower. I'm just checking for rough transfer speeds on drives now.

Uhh usb2.0 specs cant be that hard to find!

But i guess it will be the 5400rpm drive but marginal only.

Also it will depend on the brand of the interface (IDE 2 USB)

upgrade it to a high rpm drive 7200 with the lowest seek rate you can find. that will be the best performing drive. always.

480MBiT i guess usb2.0 is sow 48Mbytes / sec.. but when you need that you are doing other things then normal pc use.


Guess its the drive! also think about the fact that those drives aren't designed for External use!!

Tks

Think thats 480Mb across the whole bus, so if you have any other devices on USB they will share that.

Scott.

the more devices on the bus the slower because

USB works with polling..

sow ever known device occupies the bus for a split second... every time again.

the bus isn't used continously by everyone.

Tks

i don't want to get the rate faster, i was just wondering,

i have a laptop hard drive in an external enclosure which is bus powered. anything bigger would need an externa power supply. I'm happy with what I've got

not actualy true..

there are drives that donīt need external supplies i use a Fujitsu handy drive its 60Gb and weight less then a mobile phone! its 10mm high and 110mm x 70mm big

TKs

I would have though the limiting factor would be the Circuit board that converts USB to IDE!

Open it up theres a small chip that has to take all the data from 33 wires and get the data down 6 wires in USB.

If you want a fast data transfer try Flash drives or Flash cards, the ones designed for Cameras have the best access times.

John

at a guess it would be the USB, USB transfer rate barring overheads and other devices is about 40MB/s whereas a 5400rpm drive sustained trasfer rate is about 40-60MB/s

its not the 'chips' problem it just down the the USB2 spec.

although it would all depend on exactly what you were doing, if you want massive throughput then USB Harddrives are not the way, but since you are happy with what you've got then all is good!

its not the USB that slows it down. If u boot windows of a USB thumb drive then its about 40% faster apparently, then again there no real seek time with a flash drive

works with 2 wires its serial data.

Clock en data line.

Memory does has acces time altough its in the nano second range.

en not in the mili second range.


Tks

its certanly the parallel to serial conversion with its protocol wich slows down the bus

USB is actually 1 data signal with the clock embedded in it, which is then encoded differentially down two lines.

Its sod all to do with the serial to parallel conversion, it is just the limit of the spefication. PCI express is a serial protocol and that runs in the hundreds of megabytes per second per channel, ditto for firewire

it totally depends what you want to do if it lots of random accesses to data all over the disk then it is the seek time of the disk slowing it down, if its sustained sequential data access then its the usb thats the bottleneck.

Defrag the disk!!

and the high seek time will have less effect!

Tks