It would have to be a dynamic caching system from data coming from BluRay or other sources. But then the problem may well be that it wears too fast. I don't know how far they've come with that.
Also, do we think they'll go with a laptop drive again? Or is a regular size drive in order? (assuming they do go for hdd, but I assume that's an important one as more and more people will want digital only).
The whole storage thing is one of my biggest interests, for sure.
The HDD that they go for is going to have to be a compromise between power consumption, heat, performance, cost, and size.
So lets take a look.
7200 RPM versus 5400 RPM.
7200 RPM drives would allow for faster speeds. The drawback is higher heat, power consumption, and cost.
Notebook (1.8" or 2.5") versus Desktop (3.5")
A desktop drive will almost always be faster, especially on the outer edges of the drive. It will also be cheaper. The drawback is that it's larger, uses more power (more mass to spin and more distance for the read heads to move), and generates more heat (those platters and larger read head motors).
From a budget and hardware design POV, you'd want a Notebook drive running at 5400 RPM. That gains you size, cost, power, and heat advantages making the design of the console easier.
From a performance POV, you'd want a desktop drive running at 7200 RPM. That gains you speed. And uh...speed.
IMO, the most likely compromise will be a notebook drive running at 7200 RPM.
But that said, I would not be surprised if one or both decided to go with a 5400 RPM drive again or some hybrid like WD's 5900 RPM or variable RPM (highly unlikely, IMO) drives. The thinking in this case will be that it's faster than an optical drive and has significant cost savings in terms of money and heat compared to a 7200 RPM drive.
And 5400 RPM drives won't be horribly slow. Areal density has increased significantly since the X360/PS3 launched so they'll still be faster than the drives that launched in those. But they'll still be relatively slow and a major bottleneck. Then again even a 7200 RPM desktop drive will be a significant bottleneck, just less of one.
A flash cache is decent, but mostly beneficial when the workload is predictable. In a machine tailored around gaming. That's going to be hit and miss as to whether it's noticeable by someone in your target audience or not. For someone who plays COD multiplayer everyday it's an obvious win. For someone that frequently hops between multiple games, not so much. So then you have to consider whether the cost involved will bring in enough additional sales that it's a better design decision than not having one.
Regards,
SB