Originally posted by: Ken90630
I've never really fully understood what the limiting factor is in terms of 'preventing' these drives from reaching the theoretically possible speed of the interface. Is it that the drives themselves can only output data at a certain rate, and if so, why is that? Is it the rpm's, or some other aspect of the drive? Anyone care to educate me on this? (I had a great article on this subject saved or bookmarked somewhere awhile back, but I can't seem to find it.)
AFAIK, no 'regular' drives can even utilize the data transfer speed potential of the conventional IDE spec (133 theoretical max, right?), let alone specs with even greater potential like 150. Again, what prevents them from doing so?
Lastly, is there any reason whatsoever (other than rounded cables) to buy a serial HD, since they too, as I understand it, can't utilize the interface potential either? (For discussion purposes, let's exclude 10,000-rpm Raptors from the equation.)
I've posted this before, so forgive me if some of you have read this in another thread that I wrote. Basically, Ken, the transfer rate is the maximum rate an HD can move data to the CPU/Memory bus, provided that:
- The info in question is not in CPU cache; and
- it is not in RAM; and
- it
IS in the HD cache.
Now, if the first two are met, then there is no real need for the HD, as it is never accessed. If the last one of these conditions cannot be met however, then the HD has to go to what is recorded on the platters of the HD. Now unless the head of the HD happens to be at the EXACT spot the data is question is located (you'd have better chance winning the lottery -- Think about how many sectors are on a HD), it has to look for it. Now it all becomes a question of RPM -- how fast the platters rotate, and seek time -- a timing encompassing how much time it takes for a head to move to the right track on the platter, read it, and throw the info to the CPU.
HDs can only spin so fast since it it a physical movement, and 7200 RPM has pretty much been the standard speed for quite some number of years. Add to that if there was a way to reach over 10000 RPM, you start to have serious heat issues. I think the next logical step in the next 5 years or so will be flash memory HDs or some derivative thereof, as they don't require moving components.
As for your last question, people buy SATA drives merely as a consequence. It is the same price as a IDE, so why not?
It's just like PCI-E cards. People already have a hard enough time saturating the 4x AGP bus, let alone the 8x AGP, so why do we need 16x PCI?? Because all the latest cards with high GPU are on 16x PCI. Same thing with SATA.
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