minix wrote:I'm not sure what you mean with your final explanation.
My last statement was just a theory of what might be involved if there are marginally slower copy times on the same channel compared to separate channels. The idea is that command processing might be less efficient on the same channel, operating in consecutive cycles rather than simultaneous cycles. In any event, under most circumstances the effect (if noticed) would be minimal.
Back to the main question: Can data transfers between two devices on the same channel be done efficiently. Evidence indicates that the answer is yes for most newer computers. There is no significant throughput constraint between intrachannel
transfers. I think this thread has gotten off track because the quoted statements regarding "blocks" and constraints were taken to mean intrachannel transfers. The warnings about not being able to use one device until the other is released is meaningless for same channel transfers, which by definition use both devices simultaneously . I contend that these cautions about ATA behavior are concerned with multitasking interchannel
For example, consider tests just run using a primary channel with a 12x Plextor as master and DVD-ROM as slave, and a secondary channel with another 12x Plextor as master and a 52x Liteon as slave. Four 7200 RPM hard drives are on a mainboard IDE controller. Tests were run with Stomp RecordNow Max copying 700 MB AVI files. All times include initialization and finalization.
12x Plextor alone: 6:54
52x Liteon alone: 2:33
Copying two different files simultaneously from separate hard drives on the same channel to two burners on the same channel:
12x Plextor: 8:37
52x Liteon: 8:10
Copying three different files simultaneously from three separate hard drives, two drives on the same channel and the third from a separate networked computer. The first two burners below are on the same channel and the third on a separate channel.
12x Plextor: 8:29
52x Liteon: 8:10
12x Plextor copying from network: 7:33
Interestingly, in the simultaneous separate source tests above, CPU utilization for RecordNow Max was from 8-10%. Next, I ran some tests copying the same (one) 700 MB file simulaneously to multiple burners.
Plextor, Liteon, Plextor: copied to all three burners simultaneously: 8:41
Plextor, Plextor on separate channels: 6:54 (same as single Plextor).
Plextor, Liteon on the same channel: 8:29
When copying one file with multiple burners, CPU utilization was 3%. In summary, it appears that when data is copied to two burners on the same channel, only one burner at a time can be accessed and the other burner on that channel will not be simultaneously available. This is due to to the constraints of the ATA protocol when not using command queuing.
I don't consider these tests to be definitive, because the 52x Liteon burner is obviously a mismatch for a 12x Plextor in dual (triple) burning. Even so, the RecordNow Max program handled it well and I tend to think that similar results would have been obtained even if another Plextor were substituted for the Liteon. It was easy to tell when burners on the same channel were operating together, as the lights indicated that buffer underrun protection was being used.
If anyone else would care to run some tests to corroborate my results or find a different result, please do so in order to help clear up this subject.