On Oct 24, 2011 7:21 PM, "walt" <w41...@gmail.com> wrote: > > On 10/24/2011 10:28 AM, walt wrote: > > ... > > Over at least six trials on each docking station I consistently > > get 105 seconds for USB and 84 seconds for e-sata, a 5:4 ratio > > in favor of e-sata/sata over USB3/sata... > > Wow, lots of great answers, guys, thanks. Enough material to give > me lots more questions to ask you :) > > Like, for example, in theory the raw bit-rate for USB3 is more than > enough to keep up with any existing consumer hard drive, right? The > speed of usb/sata protocol translation should be very fast compared > to the speed of a spinning mechanical disk (I think?) > > Now, lack of DMA is another story for hard disks, certainly. Here's > where my ignorance of hardware limits my thinking: > > AFAIK the device driver *always* sits between the disk drive and the > DMA hardware, doesn't it?
DMA means a device is told where in the system's address space it may write to, and it writes directly to that place without further CPU involvement. Since drivers run on the CPU, the drivr isn't a go-between. When the CPU *is* involved in the passing of bits around, things slow down. IIRC, that's called PIO--programmed IO.
