A UPS gives you better coverage for a desktop. You can even cable up the
control cable, the UPS sends a shutdown signal before battery is
exhausted,
and in WinXP for example, there is a UPS agent to accept the signal
and shutdown the OS if you aren't there. I've had a UPS on this computer
for at least 11 years, and had to change out the battery after 10 years.
The new battery cost around $60-$70, and the price had dropped over time.
The battery in a laptop, is its own UPS. No need for the Supercap there.
*******
You can see some capacitor examples here. One of them appears to
be 0.09F or 90,000 uF. So they aren't the higher capacity ones.
But in the case of the single, metal jacketed one, I checked and
the capacity doesn't affect the price - the 1.0F cap costs $34
and a 0.09F one costs $34 too. The prices on the various cap types
is all over the place. Presumably one of the requirements, is
high G rating, so some of the ones that look like electrolytic
caps would be less preferred. That's so you can drop the SSD
on the floor and it doesn't immediately shatter.
http://www.anandtech.com/show/4366/computex-2011-sandforce-msata-drives-no-more-supercap
Whether they need a supercap, depends on how many outstanding operations
they can have queued inside. With AHCI, you can use tagged command
queuing. So that represents a small number of outstanding commands.
Some designs seem to have a cache RAM, but it isn't always clear
what they're caching in it. It could be a read-cache for example.
Or it could be used to hold the lookup table for blocks (remapped
for load leveling and for bad block management).
The scary part, would be the internal operations attempted, the
moving of data the drive does, when not being accessed. It's up
to the firmware to do that in a safe way, inside the device. Having
a Supercap and advanced power fail detection, just makes them
lazy.
The capacitor inside the ATX power supply, would be an excellent way
to manage a computer. It has enough energy stored in it, to last
for at least 16 milliseconds under full load. If the ATX power supply
had an advanced power fail signal to deliver to the OS, many of these
exposure cases could have been handled by other levels in the computer.
And a "flush" command could be sent by the OS, to the SSD. But modern
computers lack such a capability (there is no advanced power
fail signal on the main ATX cable).
Paul