Help with USB speeds
in [Home Built PC]
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From: david on 3 Jan 2010 08:34 On Sun, 03 Jan 2010 00:58:32 +0000, usbProblems rearranged some electrons to say: > USBproblems(a)hotmail.com wrote: >>> When I transfer files to flash drive, I am only seeing speeds of about >>> 8-10 MB/second. >>> >>> If USB 2 is capable of 60MB/second why the am I only getting 8-10. >>> When the copy first starts, I have seen 60 MB/second for 5-10 >>> seconds, but then it gradually slows down to 8-10. Seems the larger >>> the file the slower the transfer. >>> >>> WIN 7 Pro x64... fwiw. >>> >>> Thanks in advance. >>> >>> >>The interface rate on the cable is 480 megabits/sec. Dividing by 8, that >>is 60MB/sec. > >>USB protocol uses packets. The packets have headers. That wastes some of >>the bandwidth. Now your usable rate is 57MB/sec. > >>Next, comes the packet protocol. There isn't a 100% stream of data >>packets in one direction. The protocol is more complicated than that. >>USB uses a polled protocol. > >>The end result, is you see things like hard drives in external USB >>enclosures, do stuff at about 30MB/sec. Performance tops out, somewhere >>in that vicinity. > >>This is an example of a dual channel USB stick. There are two flash >>chips and a controller chip. It is a way of combining the bandwidth of >>two chips. The numbers stated here are peak values. After a while, you >>may see the average rate being somewhat lower than the manufacturer's >>stated values. The peak rates are most likely to be evident when >>transferring a single big file. Small file transfers will be >>considerably slower. > >>http://www.ocztechnology.com/products/flash_drives/ ocz_rally2_turbo_usb_2_0_flash_drive > >>Try a dual channel stick, and see if you get double what you're >>currently seeing. More than one manufacturer should make them. It is >>pretty hard to fit more channels than that, without making the device >>bulky. > >> Paul > > Hi Paul, as luck would have it I had a Super Talent dual channel stick > and yes it does acheive twice the speed. Accourding to the profram > USBDeview: > > Data traveler write speed is 6.26 while the Super talent is 13.2. When I > plugged it into the motherboard USB port it actually slowed to 12.6. > > I guess I don't get where they can say USB 2.0 has a rate of > 480mbs/second. I mean.. under what circumstance does it even acheive 90% > of that? > > ANy way thanks for your help. That is the maximum transfer rate of the physical interface. It does not take into account the protocols involved. FWIW we designed a custom USB interface to capture high speed serial data from a large number of devices. Because it was custom, we were able to optimize the transfer rate by using mostly high speed isochronous block transfers.
From: Sam Yosemite on 3 Jan 2010 11:29 david <none(a)nospam.com> wrote in news:hhq6cb$211$1(a)news.eternal-september.org: > On Sun, 03 Jan 2010 00:58:32 +0000, usbProblems rearranged some > electrons to say: > >> USBproblems(a)hotmail.com wrote: >>>> When I transfer files to flash drive, I am only seeing speeds of >>>> about 8-10 MB/second. >>>> >>>> If USB 2 is capable of 60MB/second why the am I only getting 8-10. >>>> When the copy first starts, I have seen 60 MB/second for 5-10 >>>> seconds, but then it gradually slows down to 8-10. Seems the larger >>>> the file the slower the transfer. >>>> >>>> WIN 7 Pro x64... fwiw. >>>> >>>> Thanks in advance. >>>> >>>> >>>The interface rate on the cable is 480 megabits/sec. Dividing by 8, >>>that is 60MB/sec. >> >>>USB protocol uses packets. The packets have headers. That wastes some >>>of the bandwidth. Now your usable rate is 57MB/sec. >> >>>Next, comes the packet protocol. There isn't a 100% stream of data >>>packets in one direction. The protocol is more complicated than that. >>>USB uses a polled protocol. >> >>>The end result, is you see things like hard drives in external USB >>>enclosures, do stuff at about 30MB/sec. Performance tops out, >>>somewhere in that vicinity. >> >>>This is an example of a dual channel USB stick. There are two flash >>>chips and a controller chip. It is a way of combining the bandwidth >>>of two chips. The numbers stated here are peak values. After a while, >>>you may see the average rate being somewhat lower than the >>>manufacturer's stated values. The peak rates are most likely to be >>>evident when transferring a single big file. Small file transfers >>>will be considerably slower. >> >>>http://www.ocztechnology.com/products/flash_drives/ > ocz_rally2_turbo_usb_2_0_flash_drive >> >>>Try a dual channel stick, and see if you get double what you're >>>currently seeing. More than one manufacturer should make them. It is >>>pretty hard to fit more channels than that, without making the device >>>bulky. >> >>> Paul >> >> Hi Paul, as luck would have it I had a Super Talent dual channel >> stick and yes it does acheive twice the speed. Accourding to the >> profram USBDeview: >> >> Data traveler write speed is 6.26 while the Super talent is 13.2. >> When I plugged it into the motherboard USB port it actually slowed to >> 12.6. >> >> I guess I don't get where they can say USB 2.0 has a rate of >> 480mbs/second. I mean.. under what circumstance does it even acheive >> 90% of that? >> >> ANy way thanks for your help. > > That is the maximum transfer rate of the physical interface. It does > not take into account the protocols involved. FWIW we designed a > custom USB interface to capture high speed serial data from a large > number of devices. Because it was custom, we were able to optimize > the transfer rate by using mostly high speed isochronous block > transfers. > May I ask who "we" is and what rates you acheived? Thanks, Sam
From: david on 3 Jan 2010 13:54 On Sun, 03 Jan 2010 16:29:03 +0000, Sam Yosemite rearranged some electrons to say: > david <none(a)nospam.com> wrote in > news:hhq6cb$211$1(a)news.eternal-september.org: > >> On Sun, 03 Jan 2010 00:58:32 +0000, usbProblems rearranged some >> electrons to say: >> >>> USBproblems(a)hotmail.com wrote: >>>>> When I transfer files to flash drive, I am only seeing speeds of >>>>> about 8-10 MB/second. >>>>> >>>>> If USB 2 is capable of 60MB/second why the am I only getting 8-10. >>>>> When the copy first starts, I have seen 60 MB/second for 5-10 >>>>> seconds, but then it gradually slows down to 8-10. Seems the larger >>>>> the file the slower the transfer. >>>>> >>>>> WIN 7 Pro x64... fwiw. >>>>> >>>>> Thanks in advance. >>>>> >>>>> >>>>The interface rate on the cable is 480 megabits/sec. Dividing by 8, >>>>that is 60MB/sec. >>> >>>>USB protocol uses packets. The packets have headers. That wastes some >>>>of the bandwidth. Now your usable rate is 57MB/sec. >>> >>>>Next, comes the packet protocol. There isn't a 100% stream of data >>>>packets in one direction. The protocol is more complicated than that. >>>>USB uses a polled protocol. >>> >>>>The end result, is you see things like hard drives in external USB >>>>enclosures, do stuff at about 30MB/sec. Performance tops out, >>>>somewhere in that vicinity. >>> >>>>This is an example of a dual channel USB stick. There are two flash >>>>chips and a controller chip. It is a way of combining the bandwidth of >>>>two chips. The numbers stated here are peak values. After a while, you >>>>may see the average rate being somewhat lower than the manufacturer's >>>>stated values. The peak rates are most likely to be evident when >>>>transferring a single big file. Small file transfers will be >>>>considerably slower. >>> >>>>http://www.ocztechnology.com/products/flash_drives/ >> ocz_rally2_turbo_usb_2_0_flash_drive >>> >>>>Try a dual channel stick, and see if you get double what you're >>>>currently seeing. More than one manufacturer should make them. It is >>>>pretty hard to fit more channels than that, without making the device >>>>bulky. >>> >>>> Paul >>> >>> Hi Paul, as luck would have it I had a Super Talent dual channel stick >>> and yes it does acheive twice the speed. Accourding to the profram >>> USBDeview: >>> >>> Data traveler write speed is 6.26 while the Super talent is 13.2. When >>> I plugged it into the motherboard USB port it actually slowed to 12.6. >>> >>> I guess I don't get where they can say USB 2.0 has a rate of >>> 480mbs/second. I mean.. under what circumstance does it even acheive >>> 90% of that? >>> >>> ANy way thanks for your help. >> >> That is the maximum transfer rate of the physical interface. It does >> not take into account the protocols involved. FWIW we designed a >> custom USB interface to capture high speed serial data from a large >> number of devices. Because it was custom, we were able to optimize the >> transfer rate by using mostly high speed isochronous block transfers. >> >> > May I ask who "we" is and what rates you acheived? > > Thanks, > > Sam Sorry, I can't divulge that info. It was done by my company for a restricted project.
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