martyjs :
I trust these people. We have been buying off them for years and have no reason to tell me stories. The SATA and IDE Optical drives we buy are the same buy price and the same sell prices.
As I said in my previous post they do a lot of testing of there own, with both burn in's and testing to make sure products work together.
Their not a mass producing company but they do build lots of custom built units from base model system through to high end servers.
They might think they are telling you the truth when in fact they are wrong. Nobody knows everything. Heck, what i'm about to write below is my thoughts, and they could be wrong too! The important thing is to be smart enough to know when it really will matter and when it won't.
I can't imagine how sharing a SATA DVD and SATA HDD matters. SATA is serial connections. Point to point transfers, IE NOT parallel! SATA DVD should not run in 'parallel' with a SATA HDD so it shouldn't matter. If someone does show benchmarks proving that when they hook up their DVD it goes slower, then the bottleneck is something else. Maybe a crappy SATA chipset design. BUT, as consumers we should expect that reguardless of the device it should not effect the performance of the other devices. This was one of the reasons SATA was superior. Serial connections are independent of each other.
Yes, back in the day IDE was limited if you hooked up a DVD ROM and HDD on the same channel. But with SATA the very definition of 'channel' is obscured. SATA0 and SATA1 is a separate channel. They no longer put 2 devices on the same bus. Each is individial and it's own. Even calling it a 'bus' is technically invalid as far as I know because it's point to point, only 2 devices are connected(card and device).
Overall however, there's 3 possibilities:
1. Connecting DVD and HDD slows down the HDD.
2. Connecting DVD and HDD doesn't freakin' matter.
3. There's a few special cases that this happens(IE crappy SATA chipsets, compatibility problems, etc).
If it's #1 I'd think that ALOT, and I mean ALOT of people would have realized something is terribly wrong with their brand spankin new build and they are VERY unhappy that their hard drive is running at snail speed.
If it's #2 then who cares? If you are truely concerned that this is happening, hook them up separately. Most motherboards have 4 plugs, so use 2 for hard drives, and 1 for DVD-ROM leaving the 4th one empty.
If it's #3 then the reason this problem hasn't creeped up is probably because the 'performance nazis' don't buy the $5 SATA cards, they buy the $200 RAID controllers. These same people also benchmark their systems like crazy and the $5 card buyers just care that their hard drive works. In the end nobody really notices because of the distinction between the consumer that doesn't care about performance, and the people that want to see every ounce of it.
Overall, make your own judgment. I use the above quite often to determine the likelyhood of someone's post having validity in terms with how likely it is. I'm voting #2 - no damn difference.