(note: I think you mean 5.25-inch drives, not 5.5-inch, since that has never been a standard size for PC expansion bays.)
Originally posted by: Imp
God I hope they don't. The 3.5" is loud enough....5 1/2...*shudders*.
There's not really a direct correlation between noise and platter size. Although larger platters would probably tend to be heavier and thus require more powerful motors (generating somewhat more noise and heat). A single-platter 5.25" drive could easily be quieter than a multi-platter 3.5" model.
At the same RPM, bigger drives will have a higher STR (overall). This is because at the outer part of the disk, the drive surface will be moving more quickly underneath the read/write heads. So... why not make bigger drives?
1) Centripetal acceleration (ie, "centrifugal force"). The bigger the disk, the more it tries to pull itself apart when you spin it (see: cheap/flawed CDs breaking apart in 52X drives on occasion). To make a bigger disk at the same RPMs, you have to use stronger materials for the platters -- usually meaning they are thicker and heavier, making it harder to spin them fast, so then you need more powerful motors and your heat and noise go up. Or else you would need to reduce the number of platters -- but that kills your per-drive density advantage. And they already use pretty exotic materials (such as tempered glass and ceramics) for high-speed 3.5" drive platters... 5.25" drives at the same speeds would need some incredibly strong (read: expensive) platters.
2) Size. 3.5" drives are a nicer form factor for compact computers. Not that it couldn't be worked around... but since it's so popular, and manufacturers would rather not make two sizes, 3.5" drives have become the standard.
3) Seek times will also be worse on bigger drives (the actuators literally have to move further), although it's not *that* much of a factor between 3.5" and 5.25" drives.
As noted, Quantum (now defunct... I think Seagate bought what was left) marketed a line of "Bigfoot" 5.25" drives a while back. They didn't exactly take off.
But, basically... I think you could probably make 5400RPM 5.25" drives that at least gave you a 100% improvement over the data density of 3.5" drives -- but probably at higher $/GB due to needing new designs and parts. Most people just don't need that kind of storage space -- 500GB holds a lot of stuff. Fewer still would pay a premium for it, especially when it doesn't perform the same and you could just buy two 3.5" drives instead. And when you start talking enterprise-class storage (where they
do need that kind of space, and GB/square foot starts to come into play), they generally also want it to be fast.