One major difference between disk and RAM is the tradeoffs between size,
speed, and price. It's highly unlikely that any one technology will ever
beat all others in both of the usage patterns which are normal for RAM and
disk in devices considered by their users to be "computers".
CONFIG_SWAP=n
I think current ramdisk code skips it.
You still need the distinction between what's in a process's address space
and what's in the filesystem, in order to have a system that feels like a
computer.
Userspace setup stuff hugely dominates boot time. Some drivers, and it's
not known which, only successfully initialize on the assumption that some
other drivers are not initializing hardware at the same time. This has
been tried, and it (a) had some hard-to-track bugs and (b) didn't help
enough to be worth dealing with.
Writing all of RAM to disk burns more power than powering RAM for several
minutes, even assuming you don't have to spin up the hard drive. For that
matter, restarting the system will power up all of the devices on the bus
that you've shut down because you're not using them.
You have a wood-fired power plant?
In general, any time you switch drivers or kernel versions, you'll want to
have the device return all of its registers to a default state and take it
through an initialization process. For that matter, even if the memory
keeps its state, on power failure some calcuations will have been done and
some will not, so the resulting storage will be in some unknown state and
need to be reinitialized from storage that wasn't changing.
It's likely that the power cost of getting a consistant state to the
bistable memory will be more than the idle power required for a couple of
seconds.
-Daniel
*This .sig left intentionally blabk*
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