Hard Drive Overhead
While constantly reviewing ATA/100 hard drives we saw interface speeds of up to87 MBytes/s. These speeds can only be achieved when the drive transfers data to and from its fast buffers, but also affect real world performance. This is especially true if you copy large files within one drive, as we will see a little later in this story.
For our storage reviews we normally use Tyans Trinity motherboard, it comes with VIAs MVP3 chipset.
You can't really expect ATA/100 to deliver more than these 87 MBytes/s. On the one hand, taking 1024 as a factor, the interface only gives you maximum speeds of 95,4 MBytes/s. On top of that, apart from the actual data commands and status information has to be transferred, which narrows the bandwidth even more.
With Ultra-ATA/133 cycles have shortened from 40 ns (ATA/100) to 30 ns. Data is transferred the rise and fall of the signal. The interface has a theoretical maximum of 127,2 MBytes/s. Not taking the overhead into account, Ultra-ATA/133-drives should be able to transfer about 100 MBytes/s in burst mode.
The speed while doing sequential transfers from the hard drive media itself is actually much lower than that. High end IDE drives max out at about 40 MBytes/s currently. If you consider the overhead, these drives can only push older Ultra-ATA/66-controllers to their limits.