Does the empeg explicitly spin down the disks?

Yes. Disks, even laptop ones, have much much better vibration tolerance when spun down. That's important in a vehicle. Also, much less heat is produced when spun down; in some installs, that's important too.

We could just have set the IDE auto-spindown timer, but seeing as we know exactly what the disk access pattern is (in the steady state, it's "cache frantically for two seconds, then do nothing for five minutes, then repeat") we can control the spin explicitly so it's only up for those two seconds, and is spun down the moment it's not needed rather than waiting for a timeout.

or is it just that mounting them read-only does so fairly well? I guess I'm asking if there's a difference between a disk-spun-down db and a regular db that's running on a readonly disk...

The player software needs to be able to get at the data instantly. It can take up to five seconds to wake up a spun-down disk. Imagine how much it would annoy you if going into the Playlists menu or the search screen waited for five seconds before it could show you anything!

(Yes, the disk always spins up when you go into the Playlists menu or the search screen. But that's because it's hopefully going to take you at least five seconds to choose what you want to listen to, so it can start getting music off the disk instantly once you've chosen, rather than waiting five seconds then. The menu appears and is usable long before the spin-up completes. It's attention to details like that which is why you bought an Empeg in the first place.)

The tension is between on the one hand needing to keep all that data in a limited amount of RAM, and on the other being able to access it flexibly and efficiently. The database on the Rio Central is indexed up the wazoo and can (and does) soup to its heart's content, but the data ends up about 30Mb in size on a fullish player, and the thing ships with a 128Mb swap partition which at times (e.g. database rebuild) it's pretty glad of.

But as Rob implies, I have a Cunning Plan(TM), which would be nice to get onto the car-player sooner or later. But that would be waaaay in post-2.0-land.

Peter